Oregon Public Empowerment News, OregonPEN, regrets to announce that, having published weekly for just shy of three years, the publication must go on hiatus for the indefinite future.

The hope is that OregonPEN can someday be reorganized and return to publication and fulfill the original vision:

  • Offering readers news and information for making Oregon a better, more just, more informed, and more environmentally sustainable place, with Oregonians enjoying better health and prospects for the future;


  • Offering all Oregonians and the over 1400 state and local governments and special districts that serve them with a new all-digital-format newspaper of general circulation;


  • Making public and legal notices publishing much faster, and much, much cheaper, all while offering richer notices in a medium far more suitable — both for those required to  publish the notices and for those seeking the content they contain — to the task than the existing paper-based newspapers of general circulation in print today.


  • Using the net OregonPEN revenue from publishing public and legal notices to fund organizations that support public empowerment in Oregon, starting with such vital services as Legal Aid Services of Oregon (LASO) and growing to help fund other groups that provide the many essential services for the betterment of Oregon that the market struggles to provide.

Farewell for now.


In our last issue, OregonPEN printed the first part of an adaptation of a telling report by Royal Society, its November 27, 2017 Climate change update report (available at royalsociety.org/climate-change).

In the report titled, Climate Update: What have we learned since the IPCC’s 5th Assessment Report?, the scientists at the Royal Society examined data that has been collected since the 2013 and 2014 5th annual assessment (AR5) by the Intergovernmental Panel on Climate Change (IPCC) of the evidence about climate change and its impacts.

Each “Question” of this report can be read and understood individually, but Royal Society has crafted the whole as a broad thematic progression, with the inclusion of new studies that will clarify understanding over time. As the original introduction states, “In some cases, new work suggests changes in the probability of certain outcomes occurring, but in most cases the broad statements made by IPCC still appear valid.”

With the next IPCC assessment report (AR6) not due until 2022, while the pace of palpable effects appears to be quickening, reports such as the Royal Society’s update lets us assess whether the evidence presented since the publication of AR5 affects the assessments made then.

The last OregonPEN presented the first eight sections from the Royal Society update, including such fundamental questions as

  • How sensitive is global temperature to increasing greenhouse gases?
  • How are methane concentrations changing and what does this mean for the climate?
  • Was there a ‘pause’ in global warming?

In this issue, OregonPEN proudly provides the rest of the text from this important survey of where we are, and where our fossil fuel emissions are taking us:

  • Question 8 Is the land taking up carbon dioxide because of faster plant growth?
  • Question 9 How do increasing carbon dioxide concentrations impact ocean life and fisheries?
  • Question 10 How will climate change affect food production on land?
  • Question 11 What is the influence of climate change on water availability across the globe?
  • Question 12 What is the influence of climate change on species extinction?
  • Question 13 How will human health be affected by climate change

An Appendix follows

Adapted from Royal Society’s November 27, 2017 Climate change update report; original viewable at royalsociety.org/climate-change.

Abbreviations used throughout this report:
IPCC Intergovernmental Panel on Climate Change
AR4/AR5/AR6 Fourth/Fifth/Sixth Assessment Report of the IPCC
RPC Representative Concentration Pathway

QUESTION EIGHT – Is the land taking up carbon dioxide because of faster plant growth?


Increasing atmospheric carbon dioxide increases plant growth, in turn removing carbon dioxide from the atmosphere, but this increased removal is counteracted by the challenge of continued climate change for terrestrial ecosystems.

In AR5 IPCC said:

With high confidence, the carbon dioxide fertilisation effect will lead to enhanced NPP [net primary production], but significant uncertainties remain on the magnitude of this effect, given the lack of experiments outside of temperate climates.

What is this about?

Plants use the energy of sunlight to convert carbon dioxide into sugars, through photosynthesis. The total amount of carbon taken up by an area of land each year is gross primary production. About half of this carbon is used to create new plant material, called net primary production, the other half being released to the atmosphere by plant respiration.

Plant material eventually decays with most of the dead carbon being consumed or broken down by fungi, bacteria, animals or by fire, and carbon being released back to the atmosphere as a result. The net carbon balance of an ecosystem is the balance between these processes of carbon uptake and release.

Increasing atmospheric carbon dioxide concentration increases photosynthesis and reduces transpiration, generally leading to increased plant growth and water use efficiency. The processes of plant death and carbon release lag behind, resulting in net carbon uptake by the ecosystem. According to terrestrial ecosystem models, this ‘carbon dioxide fertilisation’ is the main cause of the net uptake of carbon dioxide emissions by the land (the land carbon sink).

It is also thought to be the main cause of the observed increase in vegetation leaf cover (the ‘greening’ of the biosphere) as more carbon is being allocated to leaves.

What was the basis for the statement in AR5?

IPCC concluded that co2 “fertilization” leads to enhanced primary production, with net primary production increasing by 20 to 25% for a doubling of carbon dioxide over pre- industrial levels.

However, nitrogen and phosphorus availability were considered very likely to limit that increase, with nitrogen limitation prevalent in temperate and boreal ecosystems and phosphorus limitation in the tropics.

What do we know now?

Global observations
Several lines of evidence point to an increase in primary production over the industrial period. Observed changes in global atmospheric co2 and oxygen concentrations indicate, with a high degree of confidence, that the terrestrial biosphere is absorbing about one third of anthrpogenic co2 emissions, thereby acting as a brake on the rate of atmospheric co2 increase.

Satellite observations of vegetation cover show widespread “greening”. Models suggest that this greening is predominantly due to co2 fertilisation because of increased water-use efficiency as atmospheric co2 rises, although climate and land use change have also contributed. The large increase observed in the amplitude of the atmospheric carbon dioxide seasonal cycle (especially at high latitudes) has been predominantly caused by increasing photosynthesis, as a response to co2 fertilisation (and potentially also climate change at high latitudes). Independent atmospheric observations of carbonyl sulphide – which is taken up with co2 during photosynthesis, but not released again – indicate that gross primary production increased by circa 30% during the 20th century. Long-term field inventories also support a long-term carbon sink in the world’s forests.

Global models

In AR5 only two of the Earth System models used included a coupled carbon-nitrogen cycle which accounted for nitrogen availability effects. Both models used the same land model, which showed greatly reduced co2 and a greatly reduced climate- carbon cycle feedback. Although carbon-only models are expected to overestimate land carbon sinks, recent analyses have shown that the extremely low responses found with the two carbon-nitrogen models in AR5 are probably unrealistic.

Limits to carbon dioxide fertilisation

Current understanding shows that reality is more complex than was indicated in AR5. In some ecosystems the effect of co2 on plant growth is independent of nitrogen availability; other ecosystems have shown little or no co2 effect under low nitrogen availability. Much less is known about the influence of phosphorus availability, which may be particularly constraining in tropical ecosystems.

First experimental results from a forest experiencing phosphorus limitation have suggested no response of plant growth to increasing co2, but there are still no experiments in mature tropical forests. Another factor that may limit co2 fertilisation is forest demography, with tree mortality accelerating as a result of enhanced tree growth.

Fertilisation versus climate feedbacks

The positive effect of increasing co2 on the land carbon cycle currently dominates over the negative effect of climate change (primarily the warming induced increase in soil carbon decomposition rate).

Further climate change will affect this balance and reduce land carbon sinks efficiency, with regional droughts reducing productivity and higher temperatures accelerating rates of decomposition.

Conversely, between 2002 and 2014 the growth rate of atmospheric co2 stayed relatively constant despite a continued increased of anthropogenic emissions, indicating an increase in the size of carbon sinks. Recent studies suggest that the reduced level of surface warming in that period led to a slowdown in temperature-driven ecosystem respiration. How long land carbon dioxide uptake will continue to dominate over release is unknown.

How might this affect the IPCC statement?

The statement in AR5 remains true. Increasing atmospheric carbon dioxide continues to increase net primary production and so leads to a proportion of that extra carbon dioxide being removed from the atmosphere. However, there are still large uncertainties about the geographic distribution, and the future, of the land carbon sink. The benefit of increased plant growth (including of crops, which are discussed later) will be reduced if rising temperatures and change in precipitation cause heat stress or water stress and reduce plant productivity.


QUESTION NINE – How do increasing carbon dioxide concentrations impact ocean life and fisheries?


Carbon dioxide emissions are redulting in warming, deoxygenation and acidification of the ocean and this poses significant risk to ocean ecosystems including those relied on for food and livelihoods.

In AR5 IPCC said:

Marine organisms will face progressively lower oxygen levels and high rates and magnitudes of ocean acidification, with associated risks exacerbated by rising ocean temperature extremes.

Climate change adds to the threats of over-fishing and other non-climatic stressors.

What is this about?

The ocean plays a key role in regulating climate. It has absorbed about 25% of anthropogenic carbon dioxide emissions since 1750. This has had the effect of causing the oceans to become more acidic. The ocean has also absorbed about 90% of Earth’s additional heat since the 1970s, but this has led to ocean warming and decreasing oxygen content (due to reduced oxygen solubility caused by warming and decreased supply to the ocean interior due to less mixing).

These changes have important consequences not only for marine biodiversity and ecosystems but also for the goods and services they provide, including protein and other nutrients from fin fish and shellfish, coastal protection, and livelihoods for hundreds of millions of people. The ocean’s content of carbon, oxygen, acidity and heat would continue to change long after atmospheric carbon dioxide emissions cease, as the changes only spread slowly into deeper waters, but the extent and rate of carbon dioxide emissions will affect the magnitude of the changes.

What was the basis for the statement in AR5?

AR5 concluded that increasing carbon dioxide and temperature will cause changes in global marine species’ distributions and reduction of marine biodiversity in sensitive regions. Evidence for these changes came from model projections of ocean warming and acidification under different emission scenarios, numerous laboratory and field studies, and meta-analyses.

Whilst global ocean warming is expected to cause the number of species and fisheries catch potential to increase (on average) at mid and high latitudes, decreases are projected in the tropics and in semi-enclosed seas. IPCC also assessed that progressive expansion of ocean minimum zones and anoxic ‘dead zones’ will further constrain fish habitats. Such changes would challenge the sustained productivity of fisheries and the provision of other ecosystem services, especially in tropical regions.

What do we know now?

Many new studies have further documented effects attributed to acidification. It also appears that deoxygenation is happening faster than was projected by models. Effects, including coral bleaching, have been attributed to warming which continues to occur in all oceans. There have been new studies on the complex effects of multiple stressors on biodiversity, ecosystems and fisheries.

Other studies have shown that local variability in conditions and the response of different species can result in complex food-web interactions. There is potential for a shift or reduction in the ranges of some species, or even loss of some ecosystems, such as those supported by corals, with reduced functioning of the food web. Whilst some species may be able to acclimate, many will not.

There is increasing evidence that a high emissions scenario will significantly alter many ecosystems and food webs through increased warming, acidification and deoxygenation and the spread of oxygen minimum zones or their combination. Not all of the impacts would necessarily be negative but these stressors can threaten fin fisheries and shellfish aquaculture in vulnerable regions.

A low emissions scenario reduces the overall risk, but even in this case the risk to current coral reef ecosystems, for example, remains high. The potential loss of tropical coral reefs would not just reduce local biodiversity but would also have major consequences for coastal protection, tourism, income, livelihoods
and fisheries.

The nutrition (protein and micro-nutrient supply) of about 1.4 billion people is at risk as fish make up a significant proportion of their animal-based food. Climate change under a high emission scenario is projected to reduce fish catch by about 5% globally and 30% in tropical regions. The communities that live there are the most vulnerable, due to their dependency on wild fish, their poor current adaptive capacity, and projected increases in food demand (related to population growth).

How might this affect the IPCC statement?

On this basis we expect the IPCC statements to stand. Climate change will place multiple stresses on many marine organisms, potentially resulting in decreases of biodiversity, changes to species distribution and altering marine food webs and ecosystems.

The evidence base is now stronger and more complex and diverse. The combined impacts of warming, deoxygenation and acidification on marine ecosystems and fisheries may lead to a more adverse risk assessment, but studying and attributing their combined impacts is difficult.

QUESTION TEN – How will climate change affect food production on land?


Increasing carbon dioxide can increase crop yields while high temperature and drought in some regions can decrease them. The aggregate impact at the global level is for climate change above 2 degrees Celsius to reduce yields.

In AR5 IPCC said:

For wheat, rice, and maize in tropical and temperate regions, climate change without adaptation is projected to negatively impact production for local temperature increases of 2°C or more above late-20th-century levels, although individual locations may benefit.

What is this about?

Wheat, rice and maize are staple crops and feeding the growing human population depends on their continued success. Climate change poses a range of effects: the increased concentration of carbon dioxide can increase crop yields, while changes in temperature and rainfall will have a variety of effects, with very high temperatures and drought both adversely affecting yield.

Taking all factors into account, AR5 concluded that a change of 2°C or more above late-20th-century levels will adversely affect yields and food production.

What was the basis for the statement in AR5?

The statements were based on a global analysis of studies up to 2013 reporting climate impacts on crop yields. While climate change impacts were variable across crop types and by region, the global impacts on food production for these crops were negative.

What do we know now?

Some studies since 2013 project somewhat lower impacts than those estimated in the analysis on which the IPCC statement is based, and more regional nuance has emerged, with some regions expected to see increasing yields for some crops. The conclusions in the original statement are not altered (see figure), though new studies point strongly to the importance of accounting for how land use and cropping intensity might change.

Since 2013, there has been more emphasis on nutrition, and not only on yield change. Higher-yielding wheat crops adapted to higher temperatures, or growing under increased atmospheric carbon dioxide concentrations, may produce grain of poorer nutritional quality under climate change.

AR5 considered productivity changes in yields for the three major cereals, but since 2013, we can also say more about the impact of climate change on other crops and rangelands (open lands used for grazing).

Subsequent analyses have examined potential changes in food production as a result of changes in the area suitable for agriculture, though greater confidence in the conclusions of such studies requires the further inclusion of other criteria for crop growth and development, soil nutrient availability and the incorporation of uncertainty and sensitivity analyses. Rangelands will be impacted by climate change, but this may not necessarily translate to large impacts in animal production because of the capacity to intensify livestock production through production systems transitions, dietary supplementation and other means.

The need for transformative adaptation in agriculture might be large, and different depending on the climate scenario and socio-technical development pathways. Since 2013, the costs of adaptation for agriculture have been estimated at 3% of total agricultural production costs in 2045 ($145 billion), somewhat higher than reflected in the literature available in 2013.

Since grass yields are less affected by climate change than arable crop yields, production system shifts towards mixed livestock-cropping systems appear to be a cost effective adaptation option.

How might this affect the IPCC statement?

On this basis we expect the conclusions to stand, though the evidence base is now stronger and more nuanced.


QUESTION ELEVEN – What is the influence of climate change on water availability across the globe?


Climate change will lead to reductions in water resources in many water-stressed regions, particularly in the dry subtropics, but the changes will vary between regions and there remains considerable uncertainty in the magnitude of change.

In AR5 IPCC said:

Freshwater-related risks of climate change increase significantly with increasing greenhouse gas concentrations.

Climate change over the 21st century is projected to reduce renewable surface water and groundwater resources significantly in most dry subtropical regions, intensifying competition for water among sectors.

What is this about?

The availability and reliability of water supplies have a major influence on societies and economies. Where resources are limited or unreliable, societies have tended to develop infrastructure and institutional arrangements to reduce risks. Areas with limited or unreliable resources are found in dry subtropical regions, but resources can also be placed under pressure where demands are high. Future river flows and groundwater recharge will be affected by climate change, and impacts vary between catchments. Globally, changes are predominantly determined by changes in precipitation and at this global scale, wet regions are projected generally to get wetter, and dry regions to get drier. Increases in evaporation exaggerate the effects of reductions in precipitation and can offset small increases. In some places (for example downstream of parts of the Himalayas) future river flows will be affected by changes in the volume of meltwater from glaciers.

Future water availability and reliability are also affected by other changes in the catchment (such as land use change) and by changes in demands for water resources. These depend on future population change and patterns of exploitation of water resources. At the local scale, these other drivers may be more significant for future reliability of water supply than climate change.

What was the basis for the statement in AR5?

The AR5 conclusions were based on a small number of global-scale assessments of change in river flows and recharge, a larger number of local-scale studies and on changes in runoff as simulated by climate models.

What do we know now?

The strong relationship between changes in precipitation and changes in river runoff has been confirmed by more global and local-scale studies. Projected reductions in runoff and groundwater resources are large in dry subtropical regions. Research using the current generation of climate models has shown that the ‘wet gets wetter and dry gets drier’ paradigm does not necessarily hold at the local scale and in all seasons.

Studies published since the AR5 have used multiple hydrological models as well as scenarios constructed from an ensemble of climate models to estimate hydrological changes. This wider range of evidence has resulted in larger assessed uncertainty ranges. Differences between hydrological models’ representation of evaporation and, to a lesser extent, processes during the cold season (the simulation of snow cover and the effect of soil freezing and thawing on runoff generation) have been shown to result in different magnitudes of response to the same change in climate.

A small number of studies have shown that vegetation changes stimulated by increasing carbon dioxide can influence the water cycle at the catchment scale. The effects vary with catchment vegetation and current climate (specifically whether the amount of evaporation that occurs is limited by the amount of water available rather than the energy available), but there is increasing evidence that the effects of carbon dioxide may be substantial in forested catchments and also in semi-arid environments where increased carbon dioxide leads to increased vegetation cover and therefore greater evaporation and less runoff or recharge. The effect at the regional and global scale is currently uncertain.

How might this affect the IPCC statement?

The IPCC statement was very qualitative and remains valid. Climate change is still projected to lead to reductions in water resources in many regions, particularly in the dry subtropics.


QUESTION TWELVE – What is the influence of climate change on species extinction?


Extinction rates are expected to rise, particularly at higher rates of climate change, and most seriously for those species unable to adapt in response.

In AR5 IPCC said:

A large fraction of both terrestrial and freshwater species faces increased extinction risk under projected climate change during and beyond the 21st century, especially as climate change interacts with other stressors, such as habitat modification, overexploitation, pollution, and invasive species.

What is this about?

Species depend upon local climates for suitable conditions, in a predictable seasonal cycle. Both conditions, such as food and pollinators, and abiotic conditions, such as water and shelter, can be disrupted by climate change. This can in turn cause alterations to the abundance and distribution of species, and lead to local extinctions and/or geographical range shifts.

The consequences will be more serious if new climate conditions cause species to go extinct globally or if resulting changes to biological communities have effects on key ecosystem functions including, for example, the carbon cycle.

What was the basis for the statement in AR5?

There was high confidence that species extinction rates would increase with the magnitude and rate of climate change, but low confidence in the fraction of species at increased risk, the regional and taxonomic focus, and the time frame over which extinctions could occur. Different mechanisms by which species might adapt to climate change, including dispersal, behavioural, genetic and evolutionary plasticity were all noted as significant but poorly understood.
What do we know now?

A synthesis of 131 species extinction studies concluded that 1 in 6 (16%) species might go extinct under high emission pathways compared to less than 3% under current levels of warming. This reduces to 1 in 20 (5.2%) under the international policy target of 2°C (see Figure); but with considerable variation depending on geographical region, type of species, and model assumptions. When global biodiversity was modelled under alternative socioeconomic growth pathways, mean species abundance was found to decline by 18 – 35% and extinction risk to increase for 8 – 23% of species under the high emissions pathway.

Local extinctions have been shown to vary spatially as well as with the extent of climate change: in marine areas local extinctions are expected to be concentrated near the equator and local invasions to be more common in temperate regions.

All these estimates have high uncertainty because many other biotic and abiotic factors determine species persistence and interact with climate changes. A common mismatch in spatial scale between climate models and species biology means models may have particularly poor predictive power for small-bodied and small-range species, which is especially significant given recent evidence of the important role of microclimates in providing refuges.

Species vary widely in their responses to climate changes. Empirical studies have identified certain demographic, ecological and genetic factors that explain variation in species vulnerability, as well as significant interactions between these, and with other stressors. Those species with poor dispersal ability, small ranges, facing physical barriers, with ecological specialisations and without a resting or dormancy period have been shown to be especially vulnerable.

The capacity for adaptation and the limits to the rate of adaptive responses, through genetic, behavioural or ecological mechanisms remains a critical gap in understanding. Recent theoretical and empirical studies are starting to reveal those factors that will limit the rate and effectiveness of adaptation, but an overall predictive framework remains elusive and the complexities are unlikely to be resolved soon.

How might this affect the IPCC statement?

There is very strong evidence that changes in population abundance and local extinctions are common responses to a changing climate and that these increase with greater rates and intensities of climate change (see Figure). New findings do not change the IPCC message. Increasingly detailed understanding highlights yet more uncertainty about the rate of extinction and about the most strongly affected species and ecological communities.

Robust risk assessment and modelling methods, to guide conservation decisions being taken now, remain a research priority. Traditional conservation actions, such as species conservation planning and protected areas, have been shown to continue to be effective, even in a rapidly changing environment.

QUESTION THIRTEEN – How will aspects of human health be affected by climate change?


Human health will be affected by climate change in multiple ways, with imacts including those from extreme heat, food availability and changes in the geographical occurrence of infectious diseases.

In AR5 IPCC said:

Throughout the 21st century, climate change is expected to lead to increases in ill-health in many regions and especially in developing countries with low income, as compared to a baseline without climate change.

What is this about?

The human health effects of climate change are an important concern in seeking to keep warming below 2°C (or 1.5°C). These occur through several mechanisms with a variety of impacts. This section considers some new research on a limited subset of these mechanisms: the impacts of changes in exposure to heat stress, increased infectious disease risk, and effects on nutrition.

These are clearer now than before AR5. Other impacts, including potentially far-reaching effects mediated through social and economic disruption such as increasing poverty, conflict, and migration are not considered here.

What was the basis for the statement in AR5?

AR5 considered that climate change will act initially by exacerbating existing health problems. It is likely that rising temperatures have already increased the risk of heat-related death and illness. Particularly under high emissions scenarios, impacts on health were expected to increase substantially and to be greatest where other stressors, promoted by low economic and social development, inhibit adaptation and resilience.

What do we know now?

Since the IPCC AR5 report there have been a number of new estimates of the extent to which populations will be exposed to extreme levels of heat. For example recent work shows that, even with global warming of only 1.5°C and midrange population growth, over 350 million more people could be exposed to hazardous levels of heat by 2050 in cities such as Lagos and Shanghai.

Another new study identified a threshold in air temperature and relative humidity beyond which increased deaths occur. Around 30% of the world’s population is currently exposed, for at least 20 days a year, to conditions exceeding this threshold. By 2100, this percentage is projected to increase to around 48% under an intermediate emission pathway (RCP 4.5) and around 74% under high emissions pathway (RCP8.5) (see Figure).

Social adaptation could reduce exposure to these conditions, but would not affect their occurrence.

High income regions will also experience serious consequences and a study of ten large metropolitan areas in the USA showed that under a high emissions scenario towards the end of the century eight of them would experience increases in heat related deaths exceeding projected reductions in cold related deaths, in some cases by a large amount. Furthermore substantially fewer deaths are projected under a lower emissions scenario.

Results of large multi-country analyses indicates that increased heat-related deaths will greatly exceed reductions in cold-related mortality in some regions particularly under high emission scenarios, in particular warmer and poorer areas that are projected to include a substantial proportion of the global population. Most studies on the effects of temperature have focused on adults but a recent study of seven cities in Korea shows substantial increases in infant mortality, both total and from sudden infant death syndrome (SIDS), with high temperatures in the period before death.

Dengue accounts for about 390 million infections annually. The two main mosquito vector species are affected by multiple drivers including climate change. Several modelling studies since 2013 have confirmed that climate change would cause dengue to expand into areas at the edge of current distribution ranges. One study suggests that the population exposure to the main vector (as well as other diseases spread by mosquitoes) would increase by 8 – 12% due to climate change alone, amplifying the larger increase in exposure caused by population growth.

The complex influence of climate change on health via nutrition is illustrated by a modelling study which projected that by 2050, climate change will lead to per- person reductions of about 3% in global food availability compared to a reference scenario, together with an important reduction in fruit and vegetable consumption. These declines are estimated to lead to a net increase of about 500,000 deaths annually.

How might this affect the IPCC statement?

The new evidence discussed above provides a basis for replacing qualitative statements with more quantitative ones, and for targeting specific adaptation and mitigation strategies that can reduce the excess fatalities incurred.

This section explains some of the methodology and terminology used in the remainder of the report.


This report touches on a limited list of topics, considered by the working group to be areas of particular interest or progress in recent years. They are by no means a comprehensive list of issues that are discussed in the scientific literature or in popular articles. For example, quantifying the role of aerosols (small particles in
the atmosphere) in climate is important, but is not covered here.

For each topic, the most relevant conclusion from the AR5 was chosen, and a lead author and critical reviewer were appointed from within the working group authorship.

Authors surveyed recent literature to examine work (including review articles) that addressed the chosen IPCC quotation and other relevant conclusions. They used this, contributions from other researchers and their expert judgement to produce the final sections, which were discussed and agreed by the whole group.

Peer review was then undertaken by a small review group (consisting of people not involved in the drafting), and final revisions were made on the basis of their comments.

This process is far below the level of scrutiny that is carried out over several years by writing teams in producing the IPCC statements. However we believe that we have captured the main advances, confirmations, and new issues that have arisen, allowing us to assess whether the IPCC statements remain valid.

IPCC and terminology

The IPCC Fifth Assessment Report (AR5) was produced in stages. The Working Group (WG) 1 report was published in 2013, WG2 and 3 in 2014, and the synthesis report in 2015. However for inclusion in the report, findings had to have been submitted into the literature at different dates in 2013 for all 3 WG reports. For this reason, we assess here findings that have appeared in the literature since the cutoff dates in 2013, and this is what we mean when we refer to advances “since AR5” or “since the last IPCC report”.

The next full IPCC report is due to be finalised in 2022, with WG reports ready in 2021. There will also be three special reports:

  1. The Special Report on Global Warming of 1.5°C (SR15) will be finalised in September 2018;
  2. Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC),
  3. Special Report on Climate Change and Land (SRCCL) will be finalised in September 2019.

These will provide a more authoritative conclusion on some of the issues we consider.

In making projections about future change AR5 used 4 different ‘representative concentration pathways’ (RCPs). These are time series of future greenhouse gas and aerosol concentrations intended to represent the results of different scenarios, in particular for socioeconomics and energy use. These RCPs were used as the input to climate models in many cases.

The pathway with the lowest concentrations of greenhouse gases, RCP2.6 represents scenarios with extreme mitigation measures, much beyond those currently agreed between nations. The highest concentration scenario, RCP8.5, represents a highly industrialised, low mitigation scenario.

In the report we sometimes refer to a high or low emissions scenario. Most often in such cases we are referring to model studies using RCP8.5 or RCP2.6 respectively, although occasionally this refers to studies using a previous generation of scenarios. The supplementary information will, where appropriate, use the technical terminology that the main text avoids.

Throughout IPCC publications, levels of confidence and uncertainty in statements are described using calibrated language. Confidence is described as from ‘very low’ to ‘very high’ based upon the level of evidence and agreement between sources, and likelihood is described from ‘exceptionally unlikely’ (≤ 1% probability) to ‘virtually certain’ (≥ 99% probability).

Such terms have been retained in the IPCC quotations, but elsewhere in this report they are not used with these calibrated meanings.

Working Group members

The members of the Working Group involved in producing this report are listed below. The Working Group members acted in an individual and not organisational capacity and declared any conflicts of interest. They contributed on the basis of their own expertise and good judgement. The Royal Society gratefully acknowledges their contribution.

Working Group

Professor Eric Wol FRS (Chair) University of Cambridge
Professor Nigel Arnell University of Reading
Professor Pierre Friedlingstein University of Exeter
Professor Jonathan Gregory FRS University of Reading / Met Office Hadley Centre
Professor Joanna Haigh CBE FRS Imperial College London
Sir Andy Haines FMedSci London School of Hygiene and Tropical Medicine
Professor Ed Hawkins University of Reading
Professor Gabriele Hegerl FRS University of Edinburgh
Sir Brian Hoskins CBE FRS Imperial College London
Dame Georgina Mace DBE FRS University College London
Professor Iain Colin Prentice Imperial College London
Professor Keith Shine FRS University of Reading
Professor Peter Smith FRS University of Aberdeen
Professor Rowan Sutton University of Reading
Dr Carol Turley OBE Plymouth Marine Laboratory

Royal Society staff

Many staff at the Royal Society contributed to the production of this report. The project team are listed below.

Royal Society staff

Helene Margue Policy Adviser
Elizabeth Surkovic Head of Policy, Resilience and Emerging Technologies
Dr Richard Walker Senior Policy Adviser

Review panel
This report has been reviewed by a number of independent experts. The Review Panel members were not asked to endorse the conclusions of the report, but to act as independent referees of its technical content and presentation.

Panel members acted in a personal and not an organisational capacity and were asked to declare any potential conflicts of interest. The Royal Society gratefully acknowledges the contribution of the reviewers.

The Review Panel

Professor Stephen Belcher Met Office Hadley Centre
Professor Alex Halliday FRS Vice-President, Royal Society
Professor Gideon Henderson FRS University of Oxford
The Lord Krebs Kt FMedSci FRS University of Oxford
Professor Yadvinder Malhi FRS University of Oxford
Professor John Mitchell FRS Met Office Hadley Centre
The Lord Oxburgh KBE HonFREng FRS House of Lords
Professor Tim Palmer CBE FRS University of Oxford
Professor John Shepherd CBE FRS University of Southampton
Professor Theodore Shepherd FRS University of Reading
Dr Emily Shuckburgh British Antarctic Survey
Dame Julia Slingo DBE FRS Former Chief Scientic Adviser, Met Office Hadley Centre

This project would also not have been possible without contributions from a range of individuals. In particular we wish to thank:


Professor Andrew Challinor, University of Leeds
Dr Ed Dlugokencky, US National Oceanic and Atmospheric Administration
Natalya Gallo, Scripps Institution of Oceanography
Dr Mario Herrero, The Commonwealth Scientific and Industrial Research Organisation
Chris Jones, Met Office Hadley Centre
Professor John Roy Porter, Supagro Montpellier
Professor Corinne Le Quere FRS, University of East Anglia
Dr Richard Pearson, University College London
Dr Doug Smith, Met Office Hadley Centre
Dr Peter Stott, Met Office Hadley Centre
Professor Chris Thomas FRS, University of York
Professor Mark Urban, University of Connecticut
Dr Phillip Williamson, University of East Anglia
Dr Richard Wood, Met Office Hadley Centre
Dr Tim Woollings, University of Oxford

The Royal Society

The Royal Society is a self-governing Fellowship of many of the world’s most distinguished scientists drawn from all areas of science, engineering and medicine. The Society’s fundamental purpose, as it has been since its foundation in 1660, is to recognize, promote and support excellence in science and to encourage the development and use of science for the benefit of humanity.

The Society’s strategic priorities emphasize its commitment to the highest quality science, to curiosity-driven research, and to the development and use of science for the benefit of society. These priorities are:

* Promoting excellence in science
* Supporting international collaboration
* Demonstrating the importance of science to everyone

Rising ocean acidity, caused by increasing levels of dissolved CO2 in seawater, affects every part of the ocean food chain. When atmospheric CO2 levels rise, the ocean begins to absorb some of the excess, a process which has created a 30% increase in acidity of surface ocean waters since around 1800. We are just now starting to understand how this affects marine life throughout the seas, including the species at the base of the entire global food web, from deep sea corals and plankton. What affects these tiny species affects the health of the oceans, all the way up to the capstone species such as whales and sharks.

OregonPEN is pleased to present this article from Hakai Magazine, which explores the affect rising acidity has on the mussels that inhabit coastal Pacific Northwest waters.


Mussels on Acid

Variability in ocean acidity may be a bigger deal than scientists thought

By Ashley Braun, Hakai Magazine

Imagine sitting in a pool of water that seesaws between too hot and too cold and being unable to control your body temperature. Now substitute temperature with acidity. Congratulations, you’re a mussel—and you’re stressed out.

The acidity of ocean water can vary due to tides, location, and the time of day or year. But the shallow water along the coast is more susceptible to ups and downs in acidity than the open ocean. And recently, scientists, including marine biologist Ceri Lewis at the University of Exeter, in the United Kingdom, have been paying more attention to how this variability in acidity may affect marine life now and in the increasingly acidic ocean of the future.

In recent experiments, Stephanie Mangan, who was a master’s candidate working with Lewis, examined how blue mussels responded to seawater at current acidity levels (at pH 8.1), and water with an acidity 150% higher, around pH 7.7. This more acidic water is expected by century’s end because of anthropogenic climate change.

But unlike most ocean acidification studies, which plop marine life into seawater with steady acidity, Mangan’s experiments also tested how mussels fare when the acidity fluctuates.

First, Mangan looked at how the mussels responded to a kind of shock treatment: the water started at pH 8.1, and over six hours dropped to 7.1, before climbing back up to 8.1 over another six hours. She and her colleagues found the mussels had very little ability to cope with the fluctuations by regulating their own internal acidity levels.

“What happens inside the mussel almost parallels what the seawater is doing,” Lewis says.

In contrast, humans have a complex system that maintains blood acidity at a relatively steady level around pH 7.4. A change in blood acidity of just 0.1 pH, however, is incredibly dangerous and potentially fatal. A change in internal acidity isn’t as serious for mussels, but it’s not good for them either.

Mangan also ran a version of this experiment over two weeks. In some cases, the mussels lived in seawater that was locked at current acidity levels. In other cases, they were in water fixed at levels representative of the future. In a subset of each of these tests, Mangan also set the acidity to fluctuate twice daily, rising and falling by about 0.5 pH, like an acidic rollercoaster ride. The experiment was meant to expose the mussels to fluctuating acidity similar to what they might experience in shallow tidal estuaries.

The researchers had expected the more acidic water to be more stressful to the mussels than the present-day conditions. But, after evaluating several stress markers, they determined that was generally not the case.

“What our data showed was that actually the variability mattered more than the total change,” Lewis says. Mussels living in seawater where the acidity yo-yoed worked harder and burned more energy to keep running basic metabolic processes, even under present acidity. But when the acidity level remained steady—whether at present or future conditions—mussels responded similarly.

“What our data showed was that actually the variability mattered more than the total change.”

Jon Havenhand, a marine scientist who has studied the effects of fluctuating acidity on barnacles, welcomed the contribution to an underrepresented corner of ocean acidification research. Still, he emphasizes that the few studies looking at the variability in acidity, rather than just the net change, have yielded mixed results. “This [variability] might be really important, and we don’t have enough data to know,” Havenhand says.

Lewis acknowledges the pressing need for more data. In particular, she says, scientists need better measurements of the ocean’s actual short-term fluctuations in acidity, which this study lacked. She’s looking for funding to put in place sensors to remotely and continuously monitor coastal conditions. “I think it’s really important that we get a good sense of how variable are coastal environments,” she says, especially for aquaculture species like mussels.

About the author

Based in the urban wilds of Seattle, Washington, Ashley Braun is a freelance science and environmental journalist who likes to think a lot about topics such as ecology, climate change, and conservation. She is a deputy editor for the fossil fuel industry watchdog site DeSmogBlog.com and is a contributing science writer for Natural History Magazine. She has written for publications including Discover Magazine, Popular Science, Hakai Magazine, Earth Touch News, Grist.org, and OnEarth.org.

Read more stories like this at hakaimagazine.com.

The Royal Society – which authored What have we learned since the IPCC’s 5th Assessment Report?, the second part of which appears this edition of OregonPEN – is far from the only international scientific organization that takes an active fact-based interest in climate issues.

In 2018, California’s Governor’s Office of Planning and Research (OPR) posted a list of some 207 international science organizations that “hold the position that climate change has been caused by human action.”

To allow for further exploration, the California OPR list itself allows readers to click on the name of nearly every organization. This means readers can instantly connect with the web site of the Uganda National Academy of Sciences or the Royal Swedish Academy of Sciences and view the unique publications, positions and research of each. Work on climate change is being conducted in every part of the globe. Among the organizations listed are:

* Union of German Academies of Sciences and Humanities
* Pakistan Academy of Sciences
* Russian Academy of Sciences
* Science and Technology, Australia
* Science Council of Japan

Many of these non-western websites are written in English.

Created by statue in 1970, OPR serves California’s Governor and his Cabinet as staff for long-range planning and research and constitutes the comprehensive state planning agency.

In a sane world, serious and growing threats to the survival of human civilization would take top priority in the press, government, and business, and such threats would prompt political and business leaders to band together urgently to overcome nationalism and its juvenile racist thinking and the urge to denigrate others for the color of their skin or the poverty of their country of origin.

Besides, not so very long ago, the “huddled masses yearning to breathe free, The wretched refuse of your teeming shore” were fleeing the grinding poverty and feudal misery of places like Ireland, Scotland, Wales, Italy, and Germany and more.

And when those “homeless, tempest-tost” souls passed through the golden door by the light of Lady Liberty’s lamp, they often found grinding poverty and feudal misery in America as well, in her brutal mines and logging camps, in sweatshops, and spinning mills that killed and maimed child workers relentlessly. And throughout the Jim Crow South, Slavery by Another Name ensured that the systematic and savage theft of the lives and bodies of African-Americans to produce wealth for white-owned corporate masters would continue, which had the effect of crippling unions throughout the South. With the rule of the Dixiecrats — the Congressional barons with essentially lifetime tenure so long as they supported segregation — the South’s poisonous politics infected all of America, as they do to this day.

But we don’t just need to have an accounting and confront and change our racist structures for moral reasons. Another reason is that, until we do, we seem entirely unable to comprehend treating most of the worlds’ billions of peoples as full human beings, with a shared stake in the global commons and a livable future.

In 1984, the malevolent O’Brien tells Winston Smith “If you want a picture of the future, imagine a boot stamping on a human face — forever.” But as it turns out, thanks to our monkey-brain inability to muster the discipline to defer immediate gratification in the face of well-known suffering that immediate pleasure is causing others, the new picture of our future could be a young brown child struggling to keep from drowning while floodwaters rise ever higher.

So, because those rising waters and the forces driving them are what would be the real top story in a sane world,  OregonPEN presents the first part of the Royal Society’s 2017 Climate Update Report, with the second part to follow. 

Climate Update

What have we learned since the IPCC’s 5th Assessment Report?

Adapted from Royal Society’s November 27, 2017 Climate change update report
Abbreviations used throughout:

  • IPCC – Intergovernmental Panel on Climate Change
  • AR4/AR5/AR6 – Fourth/Fifth/Sixth Assessment Report of the IPCC
  • RPC – Representative Concentration Pathway


  1. Question 1  – How sensitive is global temperature to increasing greenhouse gases?
  2. Question 2 – How are methane concentrations changing and what does this mean for the climate?
  3. Question 3  – Was there a ‘pause’ in global warming?
  4. Question 4 – How high could sea level rise because of anthropogenic climate change?
  5. Question 5 – Decreasing Arctic sea ice – is there any influence on the weather in middle latitudes?
  6. Question 6 – Have temperature and rainfall extremes changed, and how will they change in the future?
  7. Question 7 – Are there thresholds beyond which particularly dangerous or irreversible changes may occur?


“Climate change is one of the defining issues of our time.” – Dr. Ralph J Cicerone and Sir Paul Nurse, in the foreword to ‘Climate Change: Evidence and Causes. An overview from the Royal Society and the US National Academy of Sciences’ 2014

Climate has a huge influence on the way we live. For example, it affects the crops we can grow and the diseases we might encounter in particular locations. It also determines the physical infrastructure we need to build to survive comfortably in the face of extremes of heat, cold, drought and flood.

Human emissions of carbon dioxide and other greenhouse gases have changed the composition of the atmosphere over the last two centuries. This is expected to take Earth’s climate out of the relatively stable range that has characterized the last few thousand years, during which human society has emerged.

Measurements of ice cores and sea-floor sediments show that the current concentration of carbon dioxide, at just over 400 parts per million, has not been experienced for at least three million years. This causes more of the heat from the Sun to be retained on Earth, warming the atmosphere and ocean.

The global average of atmospheric temperature has so far risen by about 1 ̊C compared to the late 19th century, with further increases expected dependent on the trajectory of carbon dioxide emissions in the next few decades.

In 2013 and 2014 the Intergovernmental Panel on Climate Change (IPCC) published its fifth assessment report (AR5) assessing the evidence about climate change and its impacts. This assessment considered data from observations and records of the past. It then assessed future changes and impacts based on various scenarios for emissions of greenhouse gases and other anthropogenic factors. In 2015, almost every nation in the world agreed (in the so-called Paris Agreement) to the challenging goal of keeping global average warming to well below 2°C above pre-industrial temperatures while pursuing efforts to limit it to 1.5°C.

With the next assessment report (AR6) not due until 2022, it is timely to consider how evidence presented since the publication of AR5 affects the assessments made then.

The Earth’s climate is a complex system. To understand it, and the impact that climate change will have, requires many different kinds of study. Climate science consists of theory, observation and modelling.

Theory begins with well-established scientific principles, seeks to understand processes occurring over a range of spatial and temporal scales and provides the basis for models. Observation includes long time series of careful measurements, recent data from satellites, and studies of past climate using archives such as tree rings, ice cores and marine sediments. It also encompasses laboratory and field experiments designed to test and enhance understanding of processes. Computer models of the Earth climate system use theory calibrated and validated by the observations, to calculate the result of future changes.

There are nevertheless uncertainties in estimating future climate. Firstly the course of climate change is dependent on what socioeconomic, political and energy paths society takes. Secondly there remain inevitable uncertainties induced for example by variability in the interactions between different parts of the Earth system and by processes, such as cloud formation, that occur at too small a scale to incorporate precisely in global models.

Assessments such as those of the IPCC describe the state of knowledge at a particular time, and also highlight areas where more research is needed. We are still exploring and improving our understanding of many of the processes within the climate system, but, on the whole, new research confirms the main ideas underpinning climate research, while refining knowledge, so as to reduce the uncertainty in the magnitude and extent of crucial impacts.


Figure 1 – Historic atmospheric carbon dioxide levels (NOAA)


This report considers a number of topics that have been a focus of recent attention or where there is significant new evidence. This is by no means a comprehensive review such as that being carried out for the AR6 or in IPCC special reports that are underway. It instead tries to answer, in an authoritative but accessible way, some of the questions that are asked of climate scientists by policymakers and the public. The answers start from the evidence in AR5, updated by expert knowledge and by a necessarily limited assessment of work published since then.

A full description of the process used is discussed in the appendix. The information here is supported by supplementary evidence available on the Royal Society webpages (royalsociety.org/climatechange) that describes the evidence base and literature sources used. This report does not attempt to cover every topic, and does not address more distant socioeconomic impacts of climate change such as its possible impact on migration and conflict. In particular, it does not discuss policy questions about how the aims of the Paris climate agreement might be achieved.

Each section of this report is designed to be read on its own, but the document as a whole follows a broad thematic progression, starting with aspects relating to the physical basis of climate change, and progressing through physical impacts towards those related to ecosystems and human wellbeing. The report shows where new studies are starting to fill identified gaps in knowledge. In some cases, new work suggests changes in the probability of certain outcomes occurring, but in most cases the broad statements made by IPCC still appear valid.

QUESTION ONE – How sensitive is global temperature to increasing greenhouse gases?


In 2013 the IPCC report stated that a doubling of pre-industrial carbon dioxide concentrations would likely produce a long-term warming effect of 1.5 – 4.5 degree Celsius; the lowest end of that range now seems less likely.

In AR5 IPCC said:

Equilibrium climate sensitivity is likely in the range 1.5°C to 4.5°C.

Transient climate response is likely in the range 1.0°C to 2.5°C.

What is this about?

Climate sensitivity is a measure of how global surface temperature rises in response to increasing atmospheric concentrations of greenhouse gases. Understanding this measure provides insight into the amount of carbon that can be emitted for a given amount of future warming.

A higher value of sensitivity implies a lower remaining budget of greenhouse gas emissions to stay below a given warming threshold, and vice versa.

Equilibrium climate sensitivity is the increase in global surface temperature that would arise from the Earth fully adjusting to a doubling of atmospheric carbon dioxide (generally calculated from its preindustrial level). Temperature adjustment is slow, and surface temperatures will continue to rise well after the date of the doubling (even if the concentration of carbon dioxide has then stabilised).

In contrast, transient climate response is the increase in global surface temperature at the time when doubling of carbon dioxide occurs and relates more directly to the temperature increases we might expect to see in the coming century. The transient response represents a situation in which the climate has not yet fully adjusted and so is smaller than the equilibrium sensitivity.

The heat-trapping properties of carbon dioxide have been known since the 1860s and, if the only thing to change was the carbon dioxide level, it would be straightforward to calculate the warming resulting from a given concentration.

However, physical processes, known as climate change feedbacks (due, for example, to changes in humidity, cloud or ice cover) modify the direct impact of carbon dioxide substantially.

Climate sensitivity can be estimated by several different methods. Direct measurements of temperature have been made since 1850, and, prior to that, records can be deduced indirectly from, for example, ice cores formed over 100,000s of years.

One method uses this record together with energy-balance models and estimations of the effect of natural and anthropogenic processes to relate historical changes in carbon dioxide concentration to records of surface temperature change. Energy-balance models estimate the global average climate based solely on considerations of heat transfer (to the Earth from the Sun, and from the Earth via infrared radiation). These models make a number of assumptions, including how much heat is taken up by the oceans, and generally do not consider the geographical distribution of warming.

Another method to estimate equilibrium climate sensitivity uses computer simulations with complex global climate models. These models attempt to represent detailed physical processes, such as ocean heat uptake and climate feedbacks, and calculate a resulting sensitivity value. Each method is subject to its own approximations and uncertainties resulting in a range of estimates of sensitivity.

What was the basis for the statement in AR5?

Studies using different data sources and methodologies had produced a range of estimates of equilibrium climate sensitivity. In 2007 AR4 concluded that doubling of carbon dioxide concentration would lead to an equilibrium sensitivity in the range 2.0 to 4.5°C. In 2013, AR5 expanded the range to 1.5 to 4.5°C, to reflect some more recent studies based on past observations, but with no best estimate given. The range of transient climate response given in AR5 was 1.0 to 2.5°C.


Figure 2 – Global mean surface temperature projections (ICMP5, Coupled Model Intercomparison Project)


What do we know now?

Publications since AR5 continue to show equilibrium sensitivity estimates across the IPCC range. Those based on past observations and energy-balance models generally produce lower values than those derived from the more complex global climate models, including some suggesting ranges extending to values lower than those of AR5. There have, however, been advances in understanding of the reasons for this disparity.

One important advance is that it is now known that as the climate warms it becomes less effective at emitting heat to space, mainly as a result of regional variations in surface warming. This means that climate sensitivity derived from historical data (which typically fails to fully represent regional areas that may be warmer or cooler than the average) gives an underestimate of the value for high carbon dioxide atmospheres. It is also now clear that the very slow changes in patterns of ocean surface warming are inadequately represented in time varying global climate models resulting in an underestimate of climate sensitivity.

Insight has been evolving into the impact of localized processes on warming, for example volcanic eruptions or emission of industrial sulphate particles. The individual impact of these varies from type to type, but models ignoring such regional variations tend to give lower values for sensitivity. Another approach, in which global climate models that have been assessed on the basis of their ability to reproduce observed changes in cloud cover and properties, such as ice content and reflectivity, shows that the best performers generally have higher sensitivities.

Surface temperatures continue to be imperfectly observed. Gaps in the observation network and differences between measurement techniques for land and ocean mean that blending procedures are required to produce a global dataset. It has been demonstrated that incomplete geographical sampling of temperature can impact estimates of sensitivity. For example, the use of data with less coverage over the Arctic, where warming has been larger, has biased some climate sensitivity estimates to be too low.

How might this affect the IPCC statement?

Growing understanding of the complex, non-linear factors determining climate sensitivity is leading to improvements in methodologies for estimating it. A value below 2°C for the lower end of the likely range of equilibrium climate sensitivity now seems less plausible.

QUESTION TWO – How are methane concentrations changing and what does this mean for the climate?


After an apparent slow-down between 1999 and 2006, atmospheric methane concentrations have entered a period of sustained growth, increasing their contribution to surface warming.

In AR5, IPCC said:

Methane [concentrations] began increasing in 2007 after remaining nearly constant from 1999 to 2006

The exact drivers of this renewed growth are still debated.

What is this about?

Human activity results in a number of drivers of climate change. Carbon dioxide emissions have the largest overall effect, but, for example, increased concentrations of greenhouse gases such as methane and nitrous oxide add to carbon dioxide’s warming effect. The non- carbon dioxide drivers of climate change are a continuing research priority, in part because many influence local air quality as well as climate. Methane is the major greenhouse-gas driver of climate change after carbon dioxide, and there have been notable increases in its atmospheric concentration in recent years (and since AR5) that are not yet understood.

What was the basis for the statement in AR5?

Methane concentrations had increased markedly since the beginning of the industrial era, more than doubling from 770 parts per billion (ppb) approaching 1800 ppb in 2011. This increase was mostly attributed to human activity, including agriculture, waste, landfills, biomass burning and fossil fuel extraction. As for co2, evidence from air enclosed in polar ice cores demonstrated that present-day methane concentrations exceed any seen over the past 800,000 years. The growth rate of methane concentrations had not been steady; there was a slow-down in growth from 1990, which was particularly marked between 1999 and 2006.

At the time of writing of AR5, there was an indication that this period of slowdown had ended.

The total warming effect of methane emissions for the period 1750 – 2011 was assessed to be about 55% of the size of the warming effect of carbon dioxide emissions over the same period. This value includes methane’s direct warming effect and the impact of a number of indirect effects, notably the increase in ozone concentrations that results, via a sequence of atmospheric chemical reactions, from methane emissions.


Figure 3 – Global monthly mean methane (NOAA)

What do we know now?

The end of the slowdown in the growth of methane concentrations has been confirmed by continued global measurements. Annual-average concentrations increased from 1800 ppb in 2011, exceeded 1840 ppb in 2016 and may exceed 1850 ppb in 2017. Average growth rates now approach those seen in the 1980s prior to the slow-down.

Methane concentration is impacted by the rates of both emission and destruction, and the contributors to the recent changes remain debated. Evidence from the geographical distribution of changes, and from isotopic measurements, indicates that increased emissions have been strongest from biological sources, most likely associated with tropical agriculture and tropical wetlands, but increased emissions from fossil-fuels, due to their extraction and use, may also play a role.

There is little evidence of a significant increase in emissions from the Arctic. There is also further evidence that the rate of atmospheric destruction through chemical processes has slowed compared to what it was during the 1999 to 2006 period; the destruction rate is affected by human activity (including emissions of pollutants and concentrations of ozone), but the exact drivers of variations are not yet known.

How might this affect the IPCC statement?

There is no doubt that a period of renewed and sustained growth rate in methane concentrations has occurred since AR5. As a result, estimates of methane’s contribution to climate change have increased above those in AR5. Significant debate surrounds the factors that influence these trends, and projections of future emissions will need to focus on both emissions of methane and the rate at which chemical reactions destroy it.

QUESTION THREE – Was there a ‘pause’ in global warming?


In the 2000s the rate of surface warming was slower than in some previous decades, but the ocean continued to accumulate heat. Globally, 2015 and 2016 were the warmest years on record, and seen in this context the multi-decadal warming trend overwhelms shorter-term variability.

In AR5 IPCC said:

In addition to robust multi-decadal warming, global mean surface temperature exhibits substantial decadal and interannual variability. Due to natural variability, trends based on short records are very sensitive to the beginning and end dates and do not in general reflect long-term climate trends.

What is this about?

Earth’s surface temperature, averaged globally over ocean and land areas, is one important measure of climate change. Since pre-industrial times, it has increased by around 1°C. However, the rate of increase has not been constant, and observational data assessed by the IPCC in AR5 suggested only a small increase between 1998 and 2012.

This period was referred to as a ‘hiatus’ or ‘pause’ in global warming, and raised questions in the media and elsewhere about whether it was evidence of problems with the models used to project future climate. Since then (and since AR5) global temperature has significantly increased.

What was the basis for the statement in AR5?

More than 90% of the heat energy associated with global warming accumulates in the ocean rather than in the atmosphere. Observations of ocean heat content and sea level rise suggested that over the period of slow surface temperature rise Earth’s climate system had continued to accumulate heat, particularly in the ocean beneath the surface.

It was understood that natural processes cause variability in surface temperatures from year-to-year and decade- to-decade, and hence in the rate of surface warming. Interactions within and between different parts of the climate system (known as ‘internal variability’), volcanic eruptions and fluctuations in the Sun’s energy output all contribute to the overall variability.

There were unresolved questions about the specific processes that had contributed to the slower surface warming seen between 1998 and 2012. The IPCC concluded that both internal variability and reduced heating of the Earth “due to volcanic eruptions and the timing of the downward phase of the 11-year solar cycle” were important factors. With regard to the comparison between models and observations, the IPCC again highlighted the importance of internal variability but acknowledged that weaknesses in some of the models and inaccurate estimates of some forcing agents (such as volcanic eruptions) might be an additional factor.

What do we know now?

Globally 2015 and 2016 were the warmest years in the surface temperature record, even allowing for the effects of the strong El Nino that affected both years. Seen in the context of the most recent years, the multi-decadal warming trend overwhelms shorter-term variability

The ‘pause’ apparent in the data used in AR5 can be attributed to two main factors: observational biases and the variability caused by natural processes. There is some evidence that changes in atmospheric aerosols (small particles in the atmosphere) caused by human activities may have been an additional factor.

Figure 4 – Global temperatures relative to 1850 – 1900 (Met/NASA/NOAA)


Improved understanding of observational biases has shown that the rate of surface warming between 1998 and 2012 was greater than the evidence available at the time of AR5 suggested.

There is now more evidence that the handling of observational gaps over the Arctic, a region of rapid warming, is important. When these biases are taken into account, a temporary slowdown in the rate of surface warming can still be seen in the data, albeit less prominently. Research since AR5 has strengthened the conclusion that this slowdown was primarily caused by natural variability, associated partly with variations in the surface temperatures of the Pacific Ocean.

The apparent differences in the rate of global surface temperature rise between models and observations have now been largely reconciled by taking proper account of internal variability, volcanic eruptions, and solar variability, in addition to the biases in the observational records. There are outstanding questions about the mechanisms that shaped the regional pattern of surface temperature change during the ‘pause’ – this is an area of ongoing research.

How might this affect the IPCC statement?

New evidence since AR5 supports the IPCC assessment that the period of slower surface warming that was observed between 1998 and 2012 was a short- term phenomenon not representative of long-term climate change. Despite the ‘pause’ in surface temperature rise, climate change carried on: the Earth continued to accumulate energy, particularly in the ocean, at a rate consistent with warming caused by human activities. In future the rate of surface warming is expected to continue to exhibit year-to-year and decade-to-decade variability in addition to the longer-term trend.

QUESTION FOUR – How high could sea level rise because of anthropogenic climate change?


Global mean sea level will likely rise by no more than a metre by 2100, but if warming is not limited, then its effects on the ocean and ice sheets could make a rise of several metres inevitable over centuries to millennia.

In AR5 IPCC said:

Global mean sea level rise for 2081 – 2100 relative to 1986 – 2005 will likely be in the ranges of 0.26 to 0.55 m for RCP2.6 … and 0.45 to 0.82 m for RCP8.5. Only the collapse of marine-based sectors of the Antarctic ice sheet, if initiated, could cause global mean sea level to rise substantially above the likely range during the 21st century.

What is this about?

The majority of large cities and 10% of the global population are located in low-lying coastal areas. Coastal floods are, generally, most likely to occur when storms drive the sea onto the land, but their increasing incidence during the 20th century was caused mainly by the rise in sea level (global mean of about 0.2 m since 1901), rather than greater storminess. Assessing the amount and rate of sea level rise into the future is therefore essential for assessing the risks and frequency of such flooding.

What was the basis for the statement in AR5?

Global mean sea level rise is caused by both expansion of the ocean as it gets warmer and addition of water to the ocean due to loss of ice from glaciers and the ice sheets of Greenland and Antarctica. During the 21st century, the largest projected contribution was from thermal expansion. However, the greatest uncertainty related to the contribution from ice sheets, which could become significantly greater after 2100. Surface temperature warming passing an estimated threshold in the range 2 to 4°C above pre-industrial temperatures could lead to the complete loss of the Greenland ice sheet over a millennium or more, with a 7 m rise in global mean sea level.

Warming of sea water which is in contact with those parts of the West Antarctic ice sheet resting on land below sea-level could cause partial disintegration of the ice sheet, through a process called ‘marine ice sheet instability’, and lead eventually to several additional metres of global mean sea level rise.

What do we know now?

Recent work has confirmed that observed warming of the ocean, contraction of glaciers and sea level change in the last few decades is due mainly to anthropogenic climate warming. An acceleration in the rate of sea level rise since the 1990s is consistent with increasing ice mass loss particularly from the Greenland Ice Sheet. There has recently been more attention paid to the West Antarctic Ice Sheet. Some glaciers there are currently retreating, and this has been suggested to be a sign that marine ice sheet instability is underway.

For 2100, under high emissions scenarios, most recently published estimates for the Antarctic contribution (mainly West Antarctica) to sea level rise do not exceed 0.4m. Global sea level rise from ice loss in both Greenland and Antarctica could however increase in rate beyond 2100, and will continue for centuries under all scenarios.

Concern about the likely long-term sea level rise is heightened by evidence that sea level was 6 – 9 m higher than today during the last interglacial period (125,000 years ago) when new climate reconstructions confirm that polar temperatures were comparable to those expected in 2100.

How might this affect the IPCC statement?

With the exception of one prominent study that projects the loss of most West Antarctic ice by 2500 under even moderate warming scenarios, other recent research is still broadly consistent with the AR5 assessment that marine ice sheet instability contribution to sea level rise will “not exceed several tenths of a meter” by 2100. Thus the AR5 projections still represent current understanding, although suggestions that the contribution could be greater than was previously assessed need further evaluation.

Quantitative uncertainties, reflected in the spread of results from recent studies, reinforce the need for better understanding of the processes leading to ice shelf and ice sheet retreat. It is moreover virtually certain that sea level rise will continue for many centuries. In a climate as warm as those projected in many models for 2100 and beyond under high emissions scenarios, large parts of both ice sheets would be lost over millennia, leaving sea level many metres higher than present.

QUESTION FIVE – Decreasing Arctic sea ice – is there any influence on the weather in middle latitudes?


The long-term decrease in Arctic sea ice extent continues and the effect of ice loss on weather at mid-latitudes has become a subject of active scientific research and debate.

In AR5 IPCC said:

The annual mean Arctic sea ice extent decreased over the period 1979 to 2012 with a rate that was very likely in the range 3.5 to 4.1% per decade (range of 0.45 to 0.51 million km2 per decade), and very likely in the range 9.4 to 13.6% per decade (range of 0.73 to 1.07 million km2 per decade) for the summer sea ice minimum (perennial sea ice).

What is this about?

The Arctic has warmed more rapidly than elsewhere. There are a number of reasons for this. Warming leads to a reduction in Arctic sea ice area, which leads to less of the Sun’s energy being reflected from the surface, and therefore additional warming during the summer, which is mainly absorbed by the ocean. During the winter the reduced Arctic sea ice area allows heat to escape from the ocean to the atmosphere above it.

Since 1979, when satellites first enabled a complete picture to be obtained, the reduction of sea ice is striking, particularly in the late summer minimum ice period, when the decrease is at a rate of more than 10% per decade.

Despite the long-term average increase in surface temperature at high-latitudes, there has been a wintertime cooling trend both in eastern North America and in central Eurasia over the last 25 years including a number of extremely cold winters (e.g. 2009/10 in northern Eurasia and 2014 in eastern North America). This period coincides with the period of pronounced Arctic sea ice decline. Some research has suggested that warming in regions of reduced sea ice leads to a weakening westerly polar jet stream that is more likely to meander. In such meanders very cold air may reach deep into middle latitudes.

What was the basis for the statement in AR5?

Increased levels of warming in the Arctic and the associated decrease in sea ice had been observed and were in general understood. However, at the time there was no indication of any particular link with changed patterns in extremes of mid-latitude weather and the lack of comment by IPCC reflected this.

What do we know now?

In the last five years, changes in the extent of Arctic sea ice has been consistent with a general decline and large natural variability from year to year. 2012 had a record September minimum, some 40% below typical values seen in the early 1980s. 2016 and 2017 have seen the smallest March maxima in sea ice area. There is no particular basis for making significant changes to the IPCC projections for future amounts of sea ice.

It is challenging to attribute observed changes in mid-latitude weather to Arctic sea ice loss, but there are indications from observations that sea ice loss may be causally linked to changes in wintertime atmospheric circulation over Eurasia that are consistent with the cooling seen there.


Figure 6 – Arctic sea ice area in September from 1979 to 2017 (National Snow and Ice Data Center)


There has been considerable use of computer models to investigate possible influences of Arctic warming on regional mid-latitude weather, and some theoretical, but conflicting, mechanisms have been proposed. If the weather systems stayed the same, enhanced Arctic warming would mean that the cold air blowing into middle latitudes from Arctic regions would be less cold.

However, there is some evidence from models that regional decreases in sea ice, such as in the Barents- Kara Sea (north of Finland and western Russia), can interact with the regional weather systems to increase the likelihood of very cold winter weather in Central Asia, as has been more prevalent since 1990. The nature and strength of linkages between Arctic sea ice loss and mid-latitude weather is a focus of considerable current research.

How might this affect the IPCC statement?

Arctic sea ice extent observed in the past five years is consistent with the statements made in AR5 on its general rate of reduction. It is likely that the next IPCC report will include more discussion on linkages between Arctic sea ice loss and midlatitude weather, particularly in Central Asia.

QUESTION SIX – Have temperature and rainfall extremes changed and how will they change in the future?


Climate change has increased the frequency of heatwaves. The effect on rainfall and tropical storms is more complex and harder to detect, but there is strengthening evidence that warming may increase the intensity of the strongest tropical storms.

In AR5 IPCC said:

It is now very likely that human influence has contributed to observed global scale changes in the frequency and intensity of daily temperature extremes since the mid-20th century, and likely that human influence has more than doubled the probability of occurrence of heat waves in some locations.

There are likely more land regions where the number of heavy precipitation events has increased than where it has decreased.

It is very likely that heat waves will occur with a higher frequency and duration.

Extreme precipitation events over most of the mid-latitude land masses and over wet tropical regions will very likely become more intense and more frequent by the end of this century, as global mean surface temperature increases.

What is this about?

Extreme events such as unusual heat, heavy rainfall, month- long droughts, or hourly very intense rainfall can have important impacts, for example on health, food production and infrastructure, especially if they happen infrequently which makes it difficult to adapt. As climate warms, some events that used to be rare, or even unprecedented in the context of today’s climate, will become more common, such as summer heat waves, while others will become less common, such as winter cold spells.

The warmer atmosphere increases the potential for heavy rainfall in general, even while some regions will receive less rainfall due to changes in atmospheric circulation. As temperature rises evaporation increases and will add to the potential for drought in some regions.

As well as these more direct effects, extreme events can also be affected indirectly by the impacts of changes in vegetation or ecosystems.

What was the basis for the statement in AR5?

The statements in AR5 were based on research considering observed trends in extremes on a globally widespread scale. Observed large-scale changes were compared with changes simulated over the 20th century in climate models, and with changes that are expected from natural climate variability only, attributing them to human influences. Confidence was higher for daily temperature extremes than rainfall extremes. There was also an emerging scientific literature determining to what extent climate change has influenced the likelihood of individual events, such as a particular observed heat wave event for example the European heatwave of 2003.

What do we know now?

Observations show that many extremes have continued to become more frequent and intense. Heat waves continued to increase in frequency even between 1998 and 2012, and research indicates an important interaction between dry conditions and heat waves.

Since AR5, analysis of specific extreme events has continued to indicate that human influences have made many individual heat waves much more likely, and cold spells less likely. Methods to quantify this change have improved, and different methods and approaches tend to lead to the same conclusions. Nevertheless some uncertainty remains as changes in atmospheric weather patterns can locally have a strong impact.

It is much more difficult to determine if humans have influenced other types of events, such as drought, or heavy rainfall events. Generally a warmer atmosphere is more conducive to heavy rainfall just because it can hold more water. However, natural climate variability in precipitation is very large, and changes in atmospheric circulation patterns have a substantial influence.

Therefore, results of attribution studies for precipitation- related events tend to depend on the type of event that is considered, and what assumptions are used. For example, results will often differ depending on whether a study considers how extreme the rainfall would have been without greenhouse gas increases for the exact same atmospheric conditions, or if it considers how extreme rainfall overall has changed in a region.

2017 was (at least until early October) a very active tropical cyclone season where severe damage was caused. IPCC AR5 indicated low confidence in observed long-term changes of intense tropical cyclone activity, and low confidence in the causes of those changes, but predicted more likely than not increases in intensity by the end of the century in the Western North Pacific and North Atlantic.

There is evidence from physical understanding and modelling that warming may increase the intensity of the strongest tropical cyclones. Also, analysis of model simulations and physical understanding suggest that heavy rainfall associated with tropical cyclones and other extreme storms should increase in a warmer atmosphere, all else being equal. Sea level rise exacerbates the impact of storm surges.

How might this affect the IPCC statement?

Further evidence supports the existing IPCC statements. Temperature extremes have become more frequent globally and rainfall extremes have increased in some regions and these trends are likely to continue in the future. More specific statements about the role that human influence has played in changing the frequency of specific types of events, particularly heat waves, are becoming possible.

Improved model simulations and physical understanding may strengthen confidence in projected changes in extreme daily and sub-daily rainfall, and in tropical cyclones and the heavy rainfall and the coastal inundation associated with them.

QUESTION SEVEN – Are there thresholds beyond which particularly dangerous or irreversible changes may occur?


There are a number of possible thresholds, but unless warming significantly exceeds expectations it is not expected that the most dangerous ones discussed here will be crossed this century.

In AR5 IPCC said:

It is unlikely that the AMOC [Atlantic Meridional Overturning Circulation] will collapse beyond the end of the 21st century for the scenarios considered but a collapse… for large sustained warming cannot be excluded.

It is very unlikely that methane from clathrates will undergo catastrophic release during the 21st century.

There is low confidence in projections of the collapse of large areas of tropical and/or boreal forests.

What is this about?

Several components of the Earth system might have thresholds or “tipping points”. If climate change passes certain levels, abrupt transitions could occur and parts of the climate system could be significantly altered. In some cases, these changes may be irreversible and in others it may take much longer to return to the original state even when the underlying drivers of climate change have ceased. Among the phenomena of concern are:

  • Collapse of the Atlantic Meridional Overturning Circulation, which transports ocean heat to North Atlantic surface waters, with widespread consequences for the climate.
  • Rapid release of methane from organic carbon
    in permafrost on land, or from methane hydrates (clathrates) below the ocean or causing significant further warming.
  • Large-scale dieback of the Amazon forest and consequential loss of ecosystem and carbon sink.

Potential thresholds for loss of large ice sheets leading to sea level rise, are discussed under the topic of sea level.

What was the basis for the statement in AR5?

AR5 concluded that collapse of the overturning circulation would cause significant global-scale climate disruption, including abrupt cooling around the North Atlantic. Weakening was expected in the 21st century, but an abrupt collapse was not, unless models seriously underestimate sensitivity to heat or freshwater, or the input of meltwater from Greenland is much faster than expected.

Warming at high latitudes will reduce the area of permafrost, and this will cause carbon dioxide and methane to be released to the atmosphere. However there was a wide range of estimates for the magnitude of these emissions. Ocean warming can destabilize clathrates below the sea floor, releasing methane to the ocean.

If large volumes reached the atmosphere, this would have a massive warming effect. However, AR5 concluded that oxidation would convert most of the methane to carbon dioxide before it reached the ocean surface, and the slow rate of heat penetration through the sediment meant that the destabilization of hydrates would be small on century scales.

AR5 recognized that the Amazon rainforest might have a critical threshold; particularly in relation to a rainfall volume below which large-scale dieback might be expected. However considering likely scenarios and the combined effects of carbon fertilization, warming, and changes in rainfall, fire and land use, they gave the cautious statement above.

What do we know now?

New palaeoclimatic measurements have strengthened the evidence linking changes in overturning circulation in the last glacial period to abrupt climate change, indicating that destabilization of overturning circulation can occur and is associated with climate disruption. However, these occurrences are not direct analogues for today’s interglacial period, because they were associated with inputs of meltwater from ice sheets much larger than the one that remains in Greenland.

Modern measurements confirm the variability of the Atlantic Meridional Overturning Circulation on daily, seasonal and interannual timescales, which makes detecting current trends challenging. Recent work suggests that climate models have biases favouring stability. This could imply that the likelihood of circulation collapse has been underestimated, but much more research is needed to reach firm conclusions.

Many new measurements have led to revised estimates of the amounts of carbon stored in permafrost, and the amounts of greenhouse gases released when permafrost thaws. These show that release of permafrost carbon will be a significant positive feedback for climate change; however, release is still expected to be prolonged and gradual rather than abrupt on decadal scales.

Several new measurements have suggested a limited influence of current clathrate releases (and indeed from permafrost on land) on the atmosphere. Assuming that the whole ocean does warm significantly, heat will reach larger volumes of clathrates, but this is expected to be gradual, implying a commitment to slow rather than catastrophic release to the ocean.

Many of the factors that influence the nature and health of forest ecosystems have been reported on, but recent modelling studies considering all the interactions and the ecosystem complexity show that there remains much uncertainty about the possibility of substantial spatially- coherent forest loss.

How might this affect the IPCC statement?

Based on current models, significant but gradual reductions in strength of the overturning circulation are expected if warming continues. However, sudden ocean circulation collapse remains unlikely, while still not being excluded, especially beyond 2100. Ocean warming implies a long-term commitment to some clathrate destabilisation with timescales up to millennia, but not necessarily to significant methane release into the atmosphere. The cautious IPCC statement about the Amazon as a whole is still valid.

In summary, gradual climate change could trigger abrupt changes – with large regional and potentially global impacts – associated with thresholds in the Earth system. The possibility of crossing any of these thresholds increases with each increment of warming. However, although surprises cannot be excluded, there is no compelling evidence that the thresholds discussed here will be crossed this century, or that the IPCC statements need significant amendment.

The text of this work is licensed under the terms of the Creative Commons Attribution License. License is available at creativecommons.org/licenses/by/4.0

To be continue: the final five questions of the Royal Society Climate Update and a further look at rising ocean acidity and its effect on mussels.

Greenhouse gas emissions don’t just disrupt the climate. The same emissions also pump billions of tons of acid into the oceans, year after year.

Result: Greater ocean acidity.

And disruption of the entire planetary food web, starting at the base. 

Oh, and … a massive economic toll.

Dissolved CO2 is called “carbonic acid” — which you probably recognize as that sharp bite when you taste soft drinks. When oceans absorb massive amounts of the excess CO2 humans have been emitting for 250 years, the ocean pH drops.

We use pH to report how far from neutral (pH = 7.0) — that is, how acid (pH below 7) or how basic (pH above 7) — a mixture has become.

The pH scale is based on powers of 10. So acidic coffee with a pH of 5.0 is 100 times (2 factors of 10) more acid than neutral water. In the other direction, the highly alkaline Great Salt Lake at pH = 10.0 is 1,000 times (three factors of 10) less acid (called “basic”) than neutral water with pH = 7.0.

Since the Industrial Revolution began, the pH of surface ocean waters has fallen by 0.1 pH units – which represents about a 30% increase in acidity.  

The greater acidity of the sea surface has wide-ranging implications for life on the planet: risk of the loss of marine species such as oysters, clams, shallow water corals, deep-sea corals and plankton. Jeopardize these organisms and the entire food web of the planet that arises from them is in jeopardy as well.

As we emit ever more CO2 each year, the rising ocean acidity speeds up. NOAA – the National Oceanic and Atmospheric Administration – part of the US Department of Commerce, tacit recognition that our economy rests on our ability to understand our environment – estimates suggest by the year 2100, ocean surface waters could be nearly 150 percent more acidic, a pH last present more than 20 million years ago.

While capturing acidic CO2, the oceans are the ultimate heat sink, absorbing as much as half of the excess heat we are trapping on Earth with our greenhouse gas emissions. So oceans are growing more acid and warmer too. Greater ocean warmth means increasing tropical storm severity, rising sea levels, “dead zones,” and the foreseeable loss of marine life such as large tuna and keystone species like sharks and whales. 

Oregon has 363 miles of coastline, connecting us to the great World Sea that covers 71% of the planetary surface and that formed the cradle for all life around the globe. 

The scale of these slow-moving (to human eyes — they are abrupt in geologic time) sibling catastrophes, rising ocean acidity and temperatures, both children of our addiction to fossil fuels – is massive. So massive that people struggle to accept that they are even possible; it is difficult to accept that a colorless, odorless gas can force changes in something as massive as the oceans.

And it seems impossible to quantify the costs these changed conditions will impose on us.

Luckily, the Center for Sustainable Economy (CSE), a 25-year old environmental think tank located in Oregon, has has begun the effort to put into dollars and cents what our thoughtlessness will cost us.

For decades SCE has investigated the obstacles to a truly sustainable economy by rigorously examining both science and economics in relation to issues as diverse as fossil fuels, timber and biodiversity. The Center utilizes the work of distinguished fellows with expertise in the fields of ecological economics, conservation biology, sustainability analysis and public interest law to analyze public policy and current practices.

Today’s OregonPEN is devoted to presenting the work of CSE President and Senior Economist John Talberth who, jointly with Ernie Niemi of Natural Resource Economics of Eugene, explores the economic costs of rising ocean acidity and warming. Talbearth and Niemi outline ways we might quantify (assign a dollar cost to) what happens — including to fisheries, to coral reefs, to other species, and to us — if we so saturate the oceans with CO2 that they will not accept more.

This is denser than the usual OregonPEN but, with the rate of ocean warming and acidification predicted to accelerate, we think all Oregonians need to know.

The punch line is that even as the 2018 Oregon Legislature discusses putting a price on carbon emissions in Salem, the best science suggests that the true cost of carbon emissions — the amount it would be worth paying to avoid them, once you recognize the costs of ocean acidity and warming (OAW) — is much, much greater than we currently accept. The sooner we understand the high “social cost of carbon” (SCC), the more likely we are to respond wisely to it by raising what we’re “willing to pay” (WTP) to avoid emissions.

Ocean Acidification and Warming: The Economic Toll

by Center for Sustainable Economy (sustainable-economy.org/)
Used with permission.

In a new study authored by Dr. John Talberth and Ernie Niemi of Natural Resource Economics, CSE reviewed the economic consequences of ocean acidification and warming – the two most prominent effects of climate change on our oceans – and estimated what increment to the existing social cost of carbon (SCC) needs to be made to account for these damages.

Preliminary results suggest that proper accounting of an economic risk that could approach $20 trillion per year by 2100 would raise SCC 1.5 to 4.7 times higher than the current federal rate, to $60–$200 per metric ton CO2-e. The study has been published online by Elsevier as part of their Reference Module in Earth Systems and Environmental Sciences.

Climate change has the potential to disrupt ocean and coastal ecosystems on a scale that is difficult to grasp. There are two interrelated processes at work: ocean acidification and ocean warming (OAW). Oceans have absorbed roughly half of all anthropogenic emissions of carbon dioxide. Acidification occurs as the absorption of CO2 triggers a series of chemical reactions that increase the acidity and decrease the concentration of carbonate ions in the water. So far, absorption of CO2 has increased acidity of surface waters by about 30% and, if current trends in atmospheric CO2 continue, by 2100 these waters could be nearly 150 percent more acidic, resulting in a pH that the oceans haven’t experienced for more than 20 million years.

Among the dire predictions associated with acidification include dramatic reductions in populations of some calcifying species, including oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton – the latter effect putting the entire marine food chain at risk. Some models suggest that ocean carbonate saturation levels could drop below those required to sustain coral reef accretion by 2050.

The second process is ocean warming. The mechanisms of ocean warming are complex, and include heat transfer from the atmosphere, downwelling infrared radiation, stratification, reductions in mixing, changes in ocean currents, and changes in cloud cover patterns. Already, the global average sea surface temperature (SST) has risen by over 2.0 °F since the post-industrial revolution low point in 1909. Sea level rise is one of the most conspicuous effects with potentially catastrophic consequences.

Models that account for collapse of Antarctic ice sheets from processes driven by both atmospheric and ocean warming indicate sea level rise may top one meter by 2100 and put vast areas of coastal infrastructure at risk.

Obviously, all these physical effects have enormous economic consequences, yet relatively little research has been completed to date on their expected magnitude, timing, and distribution. Indeed, as late as 2012, several prominent climate researchers concluded that economic assessments of the effects of ocean acidification “are currently almost absent.” To help fill in this information gap, we combed through all published research on OAW economic consequences, updated figures where needed, and made some original calculations of our own to estimate some plausible worst-case scenarios. These scenarios appear in Table 4, below.

Alarmingly, they suggest that OAW costs could near $20 trillion per year by 2100 in association with a variety of dramatic impacts, such as loss of all charismatic marine species.

Table 4: Plausible worst-case scenarios and values at risk from OAW

Resource or service at risk Scenario Values at risk
2016 dollars)
Net primary productivity Ocean net primary productivity reduced by 16% $9,232.00
Coral reefs Loss of at least 50% of current coral reef area $5,661.70
Coastal infrastructure Additional SLR of 3 meters via WAIS collapse $3,561.69
Charismatic species 25% of charismatic marine species go extinct $1,104.08
Carbon sequestration 50% loss of ocean CO2 uptake $641.16
Mangroves Loss of at least 15% of current mangrove area $287.42
Fisheries 400 million at significantly increased risk of hunger $245.74
Coastal ecosystems Marine dead zones expand in area by 50% $126.82

The relative lack of understanding about economic consequences has, in turn, translated into a lack of policy mechanisms and research focused on OAW. One of the policy mechanisms where OAW costs are notably absent is the social cost of carbon (SCC) – an increasingly popular regulatory tool for assessing both the costs of greenhouse gas emissions and the benefits of actions to limit emissions.

Ostensibly, the SCC includes all known market and non-market costs, yet there are many categories missing or incomplete.  One of the bigger holes is OAW and one of the justifications for its absence is the relative dearth of methods or data to quantify economic consequences and the assumption that such impacts are minor enough that society will be able to adapt.

In the paper, we argue that such barriers need not restrain the government agencies participating in the SCC’s development and application from incorporating estimates for OAW based on the best available information and inclusive of high-impact but low probability scenarios – two factors that are baked into the regulatory framework for the SCC.

We do so by demonstrating three basic approaches rooted in standard microeconomic models of externalities, capital investment, and risk aversion. The first is based on federal agencies’ current approach for quantifying externalities from GHG emissions using the Dynamic Integrated Climate-Economy (DICE) integrated assessment model and economic damage functions suggested by existing literature. The second is a replacement or adaptation cost approach, which views SCC as a current capital investment liability that can be amortized over the adaptation time horizon. The third is an averted-risk approach based on willingness to pay to eliminate the risk of catastrophic changes, an approach that seems most compatible with worst-case scenario requirements under existing law.

In the next phase of this work, the study will be presented to the Interagency Working Group on the Social Cost of Carbon and the National Academy of Sciences, who is conducting a review of SCC methods and accepting recommendations for changes in approaches and sources of information. If the SCC is to be an effective regulatory tool and send the right market signal to polluters it must be as complete as possible. By engaging with the IWG on how to best incorporate the enormous toll associated with ocean acidification and warming, we hope to help fill one of SCC’s most serious omissions. The author’s manuscript follows:

Ocean Acidification and Warming

The economic toll and implications for the social cost of carbon

by John Talberth
President and Senior Economist Center for Sustainable Economy 16869 SW 65th Avenue, Suite 493 Lake Oswego, Oregon 97035-7865 jtalberth@sustainable-economy.org

(Corresponding author) Ernie Niemi

Natural Resource Economics 1430 Willamette St., Suite 553 Eugene, Oregon 97401-4049 ernie.niemi@nreconomics.com

Mounting evidence indicates ocean acidification and warming (OAW) pose significant risks of systemic collapse of many critical ocean and coastal ecosystem services. Attention has focused on drastic reductions, if not extinction, of coral reefs, inundation of coastlines, massive ocean dead zones, collapse of both capture and subsistence fisheries in highly dependent regions and significant disruption of the ocean’s carbon sequestration capacity.

The economic costs of OAW have yet to be adequately researched or included in estimates of the social cost of carbon (SCC). This paper summarizes current knowledge about the economic costs of OAW and suggests alternative approaches for incorporating these costs into the federal government’s SCC. Preliminary results suggest that accounting for OAW would raise SCC 1.5 to 4.7 times higher than the current federal rate, to $60–$200 per metric ton CO2-e.


Ocean acidification, Ocean warming, Sea level rise, Social cost of carbon, Risk aversion


Among the most startling manifestations of the Anthropocene is the widespread degradation and collapse of ocean and coastal ecosystems already underway as a result of symbiotic interactions between climate change, pollution, habitat destruction and overexploitation of fisheries. Over 90% of large game fish species have disappeared as a result of factory trawling and other industrial fishing methods (Myers and Worm 2003). Roughly 20-25% percent of all marine species are at risk of extinction (Webb and Mindel 2015). One fifth of all mangrove forests have been destroyed since 1980, primarily from aquaculture, agriculture and urban land uses (Spalding et al. 2010). Marine dead zones caused by nutrient runoff have spread exponentially since the 1960s and now encompass over 245,000 km2 (Diaz and Rosenberg 2008). Enormous quantities of marine debris, mostly plastic, are found floating in all the world’s oceans and litter both the seabed and coastlines. At least 267 different species are known to have suffered from entanglement or ingestion of this debris (Allsopp et al. 2006). Alarming as these effects are, they are likely to be eclipsed by climate change.

Climate change has the potential to disrupt ocean and coastal ecosystems on a scale that is difficult to grasp. There are two interrelated processes at work: ocean acidification and ocean warming (OAW). Oceans have absorbed roughly half of all anthropogenic emissions of carbon dioxide (Sabine et al. 2004). Acidification occurs as the absorption of CO2 triggers a series of chemical reactions that increase the acidity and decrease the concentration of carbonate ions in the water. So far, absorption of CO2 has increased acidity of surface waters by about 30% and, if current trends in atmospheric CO2 continue, by 2100 these waters could be “nearly 150 percent more acidic, resulting in a pH that the oceans haven’t experienced for more than 20 million years” (PMEL). Among the dire predictions associated with acidification include dramatic reductions in populations of some calcifying species, including oysters, clams, sea urchins, shallow water corals, deep sea corals, and calcareous plankton – the latter effect putting the entire marine food chain at risk. Some models suggest that ocean carbonate saturation levels could drop below those required to sustain coral reef accretion by 2050 (Hoegh-Guldberg, et al. 2007).

The second process is ocean warming. The mechanisms of ocean warming are complex, and include heat transfer from the atmosphere, downwelling infrared radiation, stratification, reductions in mixing, changes in ocean currents, and changes in cloud cover patterns (Hoegh- Guldberg 2014). Already, the global average sea surface temperature (SST) has risen by over 2.0 °F since the post-industrial revolution low point in 1909 (EPA). Sea level rise is one of the most conspicuous effects with potentially catastrophic consequences. Models that account for collapse of Antarctic ice sheets from processes driven by both atmospheric and ocean warming indicate sea level rise may top one meter by 2100 and put vast areas of coastal infrastructure at risk (DeConto and Pollard 2016).

Obviously, all these physical effects have enormous economic consequences, yet relatively little research has been completed to date on their expected magnitude, timing, and distribution. Indeed, as late as 2012, several prominent climate researchers concluded that economic assessments of the effects of ocean acidification “are currently almost absent” (Narita et al. 2012). This relative lack of understanding has, in turn, translated into a lack of policy mechanisms and research focused on OAW (Billé et al. 2013). One of the policy mechanisms where OAW costs are notably absent is the social cost of carbon (SCC) – an increasingly popular regulatory tool for assessing both the costs of greenhouse gas emissions and the benefits of actions to limit emissions.

Ostensibly, the SCC includes all known market and non-market costs, yet there are many categories missing or incomplete (Howard 2014). One of the bigger holes is OAW and one of the two justifications for its absence is the relative dearth of methods or data to quantify economic consequences and the assumption that such impacts are minor enough that society will be able to adapt (Howard 2014).

Here, we argue that such barriers need not restrain the government agencies participating in the SCC’s development and application from incorporating estimates for OAW based on the best available information and inclusive of high-impact but low probability scenarios – two factors that are baked into the regulatory framework for the SCC.

We do so by demonstrating three basic approaches rooted in standard microeconomic models of externalities, capital investment, and risk aversion. The first is based on federal agencies’ current approach for quantifying externalities from GHG emissions using the Dynamic Integrated Climate-Economy (DICE) integrated assessment model and economic damage functions suggested by existing literature. The second is a replacement or adaptation cost approach, which views SCC as a current capital investment liability that can be amortized over the adaptation time horizon. The third is an averted-risk approach based on willingness to pay to eliminate the risk of catastrophic changes, an approach that seems most compatible with worst- case scenario requirements under existing law.

In Section 2, we review the recent literature on the valuation of ocean and coastal ecosystems. In Section 3, we discuss what portion of this value is at risk from OAW including a set of plausible high-impact scenarios. In Section 4, we discuss the current regulatory approach and methods for estimating the SCC, and demonstrate three alternative models for incorporating the effects of OAW. In Section 5, we offer concluding thoughts and recommendations for further research and data gathering.

2.0 The value of ocean and coastal ecosystem services

Ocean and coastal ecosystems provide goods and services worth many trillions of dollars each year to the global economy. The concept of ecosystem services provides a comprehensive framework for valuation that incorporates both market and non-market benefits. Table 1 provides a partial list of important ecosystem services using the standard four-tier typology for these services including provisioning, regulating, cultural and supporting.

Table 1: Typology of ocean and coastal ecosystem services

Provisioning goods and services Regulating goods and services
•  Human food
(calories, protein, essential micronutrients)•  Livestock food•  Pharmaceutical and cosmetic compounds•  Fertilizer•  Water for desalination and industrial cooling•  Construction materials•  Commercial products (jewelry, curios, ornamental fish)
•  Energy storage

•  Carbon sequestration and storage

•  Oxygen production

•  Filtration of runoff by sea grasses

•  Bioremediation of waste

•  Biological control of harmful algal blooms

•  Shoreline protection

Cultural goods and services Supporting goods and services
•  Subsistence

•  Cultural and scientific education

•  Recreation opportunities

•  Tourism opportunities

•  Intrinsic values for threatened and endangered species

•  Sense of place for coastal communities

•  Cultural identity for coastal communities

•  Research opportunities

•  Biological primary and secondary production

•  Biological diversity

•  Habitat/refugia

•  Nutrient cycling

Many of these services generate multidimensional economic benefits. Fish and shellfish for human consumption, for example, typically provide high-value protein with essential micronutrients (vitamins, minerals, polyunsaturated omega-3 fatty acids) but low levels of saturated fats, carbohydrates, and cholesterol (World Bank 2013). The oceans play key roles in limiting the multiple costs of climate change by absorbing more than 90% of the thermal energy accumulated because of GHGs in the atmosphere, and about 30% of the emitted anthropogenic CO2 (IPCC 2014). Subsistence fish can embody many benefits besides nutrition: aesthetic, place/heritage, activity, spiritual, inspiration, knowledge, existence/bequest, option, social capital/cohesion, identity, and employment (Chan et al. 2012).

Costanza et al. (2014) updated their groundbreaking 1997 study on the value of the world’s natural capital and ecosystem services to account for changes in both the area of marine and terrestrial ecosystems and their unit values. The total estimated value for marine ecosystems was found to be over $57.4 trillion per year in 2016 dollars. This stream of benefits was further subdivided into those provided by open oceans ($25.3 trillion/yr), estuaries ($6.0 trillion/yr), seagrass and algae beds ($7.9 trillion/yr), coral reefs ($11.4 trillion/yr) and continental shelves ($6.8 trillion/yr). The total value of all marine and terrestrial ecosystem services was estimated to exceed $144.2 trillion/yr. Of particular note is that this aggregate global value is roughly twice that of gross world product ($75 trillion in 2015), and encompasses valuable functions – like maintenance of the atmospheric gas balance that enables us to breathe – that cannot be captured in market-based transactions.

3.0 Values at risk from OAW and plausible scenarios

OAW presents a significant threat to ocean and coastal ecosystem services. The literature paints an alarming portrait of large-scale adverse changes to ocean processes and marine habitats and organisms (Table 2). Key processes at risk include carbon sequestration and storage, production of atmospheric oxygen, nutrient cycling, heat transfer, regulation of acidity, and regulation of weather patterns. Among the most disconcerting risks is to the ocean’s capacity to produce atmospheric oxygen. If the oceans were to warm by more than 6 °C, disruption of oxygen production by phytoplankton could cause the atmospheric oxygen concentration to fall below the level most organisms require for respiration (Sekerci and Petrovskii 2015).

Table 2: Risks associated with ecological and biogeochemical systems

Keyprocesses at risk Keyrisks to marine habitats and organisms
•  Increase in acidity of sea water

•  Increase in sea temperature down to 1km

•  Changes in ocean currents

•  Release of seafloor methane to atmosphere

•  Intensification of extremes in El Nino/Southern Oscillation and weather events

•  Poleward movement of storm tracks and changes in monsoons

•  Decline in phytoplankton’s production of atmospheric oxygen

•  Changes in nutrient cycling

•  Slowdown of the Biological Pump (transfer of atmospheric CO2 to the ocean floor)

•  Discharge into the atmosphere of heat and CO2 previously absorbed by the oceans

•  Intensification of global hydrological cycle

•  Rising sea levels from heat expansion of sea water

•  Melting of Arctic summer sea ice

•  Increased incidence of harmful species and toxic compounds

•  Negative effects on growth, survival, fitness, calcification, and development of marine organisms

•  Changes in metabolic pathways and biological processes

•  Global redistribution of marine biodiversity

•  Evolution of some organisms towards smaller size

•  Reduction in primary production of some marine ecosystems

•  Expanding deoxygenation, with shift away from species not adapted to hypoxia

•  Spreading anoxic dead zones and toxic blooms

•  Changes in food-web dynamics

•  Contraction of metabolically viable habitats of marine animals

•  Synergistic interactions with other stressors (pollution, etc.) of marine ecosystems

Key biological impacts include loss of habitat, increase in marine hypoxic dead zones, reduced primary production, extinction of sea-ice dependent species and declining abundance and distribution of species with thresholds for acidity or temperature. The disappearance of all the world’s coral reefs is one particularly worrisome scenario that may already be manifesting in places. A somewhat sensational article declared that the Great Barrier Reef was dead for all practical purposes from warming-related bleaching and acidification after a 25 million year reign as one of the world’s most concentrated hotspots of biological diversity (Jacobsen 2016).

A few studies predict economic losses from OAW, but mostly for just one ecosystem good or service and for either warming or acidification but not for the two effects together (Table 3). Most of these studies concentrate on impacts to one or more region, with a focus on commercial seafood production. Notable exceptions, though, address widespread global ecosystem service costs. For example, Brander et al. (2012) shows the global costs from lost recreational opportunities associated with coral reef loss could top $1.2 trillion/yr by 2100. By 2200, costs associated with warming-induced release of stored methane from methane clathrate, or hydrate, gas (CH4) trapped in ice under the East Siberian Arctic Sea could reach $60 trillion as flooding, drought, severe heat stress and other climate disasters worsen (Whiteman et al. 2013). Most global losses of ecosystem services remain unaddressed, however, largely because the economic valuation literature has not yet caught up with the relatively fast proliferation of research on the physical dimension of OAW.

Table 3: Potential economic cost of lost ecosystem servicesdue to ocean warming (OW) and/or acidification (OA)


Lost ecosystem service Source Estimated Cost Location, Year Estimate
Coral reef recreational value (OA) Brander et al. (2012) Global, 2100 $1.2T/yr
Shellfish landings (OA) Turley et al. (2009) UK, 2006 $52–131M/yr
Mollusk catch and aquaculture (OA) Narita et al. (2012) Global, 2100 $7-101B/yr
Mollusk catch and aquaculture (OA) Narita et al. (2012) USA, 2100 $436M/yr
Fish, mollusks/bivalves, crustaceans, aquaculture (OA) Armstrong et al. (2012) Norway, 2010-2110 $360M
Carbon sequestration (OA) Armstrong et al. (2012) Norway, 2010-2110 $114B
Shellfish production (OA) Hilmi et al. (2015) Global, 2100 $2.3B/yr
Sardine catch (OW) Garza-Gil et al. (2015) Spain, 2036 $17M/yr
Fish catch (OW) Jones et al. (2014) UK, 2005-2050 $0.44B
Methane storage East Siberian Sea (OW) Whiteman et al. (2013) Global, thru 2200 $60T

Practically all of the physical effects can nonetheless be quantified, at least in a preliminary sense, with standard valuation methods applicable to both market and nonmarket dimensions of economic welfare. Here, we demonstrate by discussing seven distinct high- impact/low probability outcomes of OAW by 2100 or earlier and making preliminary estimates of economic values at risk suggested by existing research and relevant methods (Table 4). Existing values at risk do not represent the cost of losing a key good or service in the year of the loss, but only what is at risk on today’s terms.

Resource or service at risk Scenario Values at risk
2016 dollars)
Net primary productivity Ocean net primary productivity reduced by 16% $9,232.00
Coral reefs Loss of at least 50% of current coral reef area $5,661.70
Coastal infrastructure Additional SLR of 3 meters via WAIS collapse $3,561.69
Charismatic species 25% of charismatic marine species go extinct $1,104.08
Carbon sequestration 50% loss of ocean CO2 uptake $641.16
Mangroves Loss of at least 15% of current mangrove area $287.42
Fisheries 400 million at significantly increased risk of hunger $245.74
Coastal ecosystems Marine dead zones expand in area by 50% $126.82

3.1 Decrease in net primary production by 16%

Primary production is the production of chemical energy in organic compounds by living organisms, or more simply the rate of accumulation of biomass. Some of this biomass is used in respiration, and so net primary production measures what is left over. Contributing roughly half of the biosphere’s net primary production (NPP), photosynthesis by oceanic phytoplankton contributes roughly half of the biosphere’s net primary production (NPP) and, as such, is a vital link in the cycling of carbon between living and inorganic stocks.

In many climate models, NPP will fall dramatically because of the effects of OAW on phytoplankton productivity. Worst-case scenarios predict a global average decline in NPP of 41% by 2100, although a range of 2% to 16% is regarded as more plausible (Randerson and Moore 2015). A preliminary valuation of the top of this range (16%) is relatively straightforward, since NPP is a widely accepted proxy for the total ecosystem service value of marine ecosystems – something valued by Costanza et al. (2014) at $57.4 trillion/yr through calibration of 14 separate studies. A 16% decline in ocean NPP translates into a values-at-risk estimate of over $9.2 trillion.

3.2 Loss of half of all coral reefs

The bleaching and death of coral reef ecosystems from OAW is already underway. As previously noted, the Great Barrier Reef has lost extensive areas due to the combined effects of warming and acidity and some models predict that the process of coral reef accretion may entirely halt by 2050 for many reefs.

In particular, models show that increases in atmospheric CO2 above 500 parts per million and a sea surface temperature rise of over 2°C relative to today will push carbonate-ion concentrations well below levels needed to sustain the accretion process and “reduce coral reef ecosystems to crumbling frameworks with few calcareous corals” (Hoegh- Guldberg et al. 2007). Less pessimistically, but only addressing the acidification effect, Brander et al. (2012) predict losses in 2100 to range between 16% and 27%. Given this, we split the difference and adopt a plausible scenario of a 50% loss of current coral reef ecosystem extent (14 million hectares) by 2100. Applying the mean value of ecosystem services from coral reefs, $404,407 per hectare, Costanza et al. (2014) suggests a current values-at-risk estimate of roughly $5.7 trillion/yr.

3.3 Additional sea level rise of one meter due to Antarctic ice sheet collapse

Current climate models used in calculating SCC depict a sea level rise of roughly 0.55 meters by 2100. But new research suggests a much more dire situation due to the effects of ocean warming on Antarctic ice sheets. Through a process known as basal melting from below, the collapse of marine-terminating ice cliffs in Antarctica could contribute more than a meter to sea level rise by 2100 (Deconto and Pollard 2016).

To translate this into an economic loss estimate, we first calculated the additional land area inundated by sea level rise of 1.55 meters (vs. 0.55 meters) for various regions including the US, southeast Asia and north Australia, the Mediterranean, northwest Europe, the Amazon Delta, east Asia, and south Asia primarily using figures published by Rowley et al. (2007). The research also reported population affected in these newly inundated areas.

We use gross domestic product (GDP) per capita to develop an initial estimate of potential economic losses without adaptation from these areas– at least for market-based transactions. (Below, we show an alternative approach, based on adaptation cost.) Using region- specific GDP per capita figures, we estimate a global values-at-risk from newly inundated areas of about $3.6 trillion/yr should the additional meter of sea level rise occur.

3.4 At least 25% of all charismatic marine species go extinct

People of all nationalities and income groups place a value on sustaining the existence of whales, dolphins, polar bears, salmon and other charismatic marine species. The loss of this “existence value” is thus an important category of OAW costs to consider. OAW is likely to cause many treasured species – like the polar bear – to slip into extinction as sea ice, coral reefs, and mangroves are reduced and food chains disrupted. One model predicts that 37% of all marine mammals are at risk of extinction from climate change and other synergistic effects (Davidson et al. 2012). Others predict that the extinction risk is in the 20% to 25% range.

We can derive a ballpark estimate of worst-case global costs by making different assumptions about the share of global income people are willing to pay (WTP) to prevent these outcomes. The range of WTP reported in the literature generally varies from <1% to about 5% for conservation and humanitarian causes. Using the upper bound figure suggests a values-at-risk of >$1.1 trillion/yr as marine species people value for their existence decline or go extinct from OAW.

3.5 Carbon sequestration capacity of the oceans declines by 50%

Currently the oceans absorb 25–30% of anthropogenic carbon dioxide emissions, and they have taken up almost half of accumulated emissions since the industrial revolution. Basic physics and standard climate models suggest this capacity will increase in the future simply as a result of the differences between the partial pressure of CO2 in the atmosphere (higher) relative to the ocean surface (lower) and the resulting diffusion into water that results.

But OAW will compromise the oceans’ future ability to capture and store emissions through a complex set of factors, including warming sea surface temperatures, changing wind patterns, changes in ocean currents, and reduction of ventilation or mixing of surface and deep ocean layers. In the North Atlantic, researchers have noted an absolute 50% reduction of CO2 uptake from the mid-1990s to 2002–2005, at least partially in response to these climate change dynamics (Schuster and Watson 2007). Other research has predicted a reduction in cumulative CO2 uptake of 38% and 49% for a doubling and quadrupling of atmospheric CO2 concentrations relative to 1996 levels, respectively (Sarmiento and Le Quéré 1996).

Society’s WTP for carbon sequestration provides the basis for valuing this loss. Kotchen et al. (2013) found that that households are, on average, willing to pay between $79 and $89 per year in support of reducing domestic greenhouse gas (GHG) emissions 17% by 2020 – the current US target. This translates into a mean WTP of $134.56 per metric ton CO2, and we use this amount to represent the global value of sequestration. We then apply this amount within a plausible scenario that assumes the ocean’s annual sequestration will decline by 4.8 billion metric tons CO2 (about half of the current annual sequestration) by 2100 to arrive at a values-at-risk of roughly $641 billion/yr.

3.6 Loss of at least 15% of current mangrove area

The World Bank has recently modeled the expected loss of mangrove habitat as climate change unfolds. Inundation from sea level rise and an increase in storm intensity are the key drivers. Modeled losses include 100% of coastal mangroves in Mexico, 85% in the Philippines, 59% in Venezuela, 31% in Papua New Guinea and 27% in Myanmar (Blankespoor et al. 2016). These and other regional estimates support a global loss range of 10%–15%, the upper bound being equivalent to a loss of 2.2 million hectares. The mean value of lost ecosystem services, $130,736 per hectare (Costanza et al. 2014), indicates a global values-at-risk of about $287 billion per year.

3.7 400 million people suffer increased risk of food insecurity

Observations and forecasts suggest that OAW will disrupt the supply of food from the sea in many regions and increase the number of food insecurities. The combination of water surface warming, the spread of low oxygen zones and increasing acidity due to decreasing pH values is altering the body size of individual animals. This is shifting the habitat ranges of whole stocks and influencing species abundance and composition, food chain linkages and the dynamics of interactions between individuals within and among species. Potential losses in the ocean’s’ yield of shellfish, mollusks, and fish for both commercial and subsistence uses have been relatively well studied in the literature (Table 3).

According to the IPCC, climate change puts the 400 million people who depend heavily on fish for food at risk, especially small-scale fishermen in the tropics (Holmyard 2014). That’s because yields are expected to fall by 40% to 60% in that region. Widespread increases in starvation and malnutrition will materialize unless food distribution systems are expanded to bring replacement food to affected communities without delay when seafood catches decline. And while seafood yields may increase in the high latitudes, it will not solve the food security issue unless there is a way for fishing infrastructure and associated distribution systems to migrate to those areas as well and unless the subsistence catch in seafood-dependent regions is replaced with other sources of nutrition.

The welfare loss associated with putting 400 million at increased risk of food security can also be evaluated from a WTP standpoint. People care about starvation, and regularly donate to organizations feeding the hungry. Globally, studies have consistently documented willingness to pay values of 1% or more of income to cut hunger in half. Globally, there are about 800 million affected by hunger, and so the 1% figure is a good proxy for the welfare loss associated with having 400 million people more at risk from OAW. This translates into a global annual values-at- risk of about $246 billion/yr should the scenario unfold.

3.8 Marine dead zones expand in area by 50%

The term “dead zone’ is a common term for hypoxic (low oxygen) areas in the world’s oceans and lakes caused mainly by nitrogen and phosphorous pollution from human agricultural lands and settlements and the burning of fossil fuels. Within these dead zones, the oxygen consumed by algae that thrive in polluted waters depletes that required to sustain most other forms of marine life. Diaz and Rosenberg (2008) estimated the global extent at 245,000 square kilometers.

Continued growth of these marine dead zones undermines global biodiversity conservation goals and poses a significant challenge to meeting the world’s increasing demands for capture fisheries and aquaculture.

CO2 emissions have the potential to increase the extent of oxygen-depleted water by 50%, or 12,250,000 ha by 2100 (Oschlies et al. 2008). This depletion would occur independent of, but compounded by the impacts of other pollutants. So the 50% figure seems reasonable as a basis for assessing the risk. The mean value of services derived from marine ecosystems is $10,271/ha/yr (Costanza et al. 2014). Assuming that this value would fall to zero in the new dead zones, the resulting values-at-risk would be about $127 billion per year.

4.0 Alternative approaches for incorporating values at risk into the SCC

The social cost of carbon (SCC) represents the increase in net global economic damage expected to result from an increase in atmospheric greenhouse gases (GHGs) equivalent to one metric ton of carbon dioxide (tCO2-e). A reliable monetary estimate of the SCC is essential for measuring, in economic terms, the potential harm from actions that would increase emissions of greenhouse gases or slow their sequestration, and the benefit of actions that would have the opposite effect. It also can broaden public understanding of the risks associated with greenhouse gas emissions by translating scientific descriptions of these risks, such as decreases in arctic ice or reductions in biodiversity, into more familiar, economic terms.

An Interagency Working Group (IWG 2016) of U.S. federal agencies has developed partial estimates of the SCC, focusing on potential costs arising from the effects of climate change on terrestrial portions of the globe: changes in agricultural production, flooding, wildfire, human health, water supply, drought, and the like. With various assumptions about discount rates and other modeling factors, IWG (2016) estimates that emissions over the next few years will have an SCC of about $42 (tCO2-e)-1. This and other efforts to quantify the SCC have not incorporated the social costs of OAW (Howard 2014). As noted in Section 3, these changes in ocean conditions are likely to have profound economic consequences for billions of people, especially the world’s poorest. As such, efforts to integrate OAW costs into the SCC will provide a much better signal of the benefits of climate action and costs of business as usual.

4.1 Regulatory mandate

Incorporating the economic costs of OAW into the SCC is of interest not just from the perspective of improving the SCC’s rigor. It also is strongly suggested by the regulatory framework governing federal agencies’ use of the SCC in decision-making. There are seven cabinet-level agencies or departments participating in the IWG that are already using or planning to incorporate the SCC into regulatory-impact analysis, including the Environmental Protection Agency and the departments of Energy, Agriculture, and Interior.

All of these agencies are bound by statutes, regulations, and rules governing economic and environmental analysis that require use of best available science, attention to all known benefits and costs of agency actions including non-market effects, treatment of uncertainty, and worst-case scenarios.

For example, Circular A-94, which provides guidance for all federal agencies conducting economic analysis, requires consideration of externalities, monetization of all benefits and costs to the extent practicable, and treatment of uncertainty through the use of expected values (OMB 1992). Executive Order (EO) 12866 as amended by EO 13563 direct agencies conducting benefit-cost analysis “to use the best available techniques to quantify anticipated present and future benefits and costs as accurately as possible.” Regulations for implementing the National Environmental Policy Act, an often-used venue for SCC, require consideration of worst-case scenarios that have “catastrophic consequences, even if their probability is low” (40 CFR §1502.22).

In the following sections, we offer three possible paths forward for meeting these mandates and present the results of some preliminary estimates of what they imply for the SCC.

4.2 Damage function approach

The IWG’s current approach to calculating the SCC relies on three integrated assessment models (IAM) known as DICE, Policy Analysis of the Greenhouse Effect (PAGE), and Framework for Uncertainty, Negotiation and Distribution (FUND) (IWG 2016). These models calculate SCC in five-year increments through 2200 based on functions that express economic costs as a fraction of gross world product in each year that would be enjoyed in the absence of climate change. In other words, the models compare gross world product with and without climate change. The IWG then divides the present (discounted) value of this difference as it unfolds in five-year increments through 2300 by the increase in cumulative emissions in the prior period to arrive at the marginal SCC estimate. The damage function itself is based on the following relationship, as reported by Ackerman and Stanton (2012):

[1] Rt = [1+(Tt 18.8-1)2]-1

In this quadratic equation, the term R represents the share of gross global product remaining at year t after accounting for damages D (so that Rt =1 – Dt) and is solely a function of temperature T expressed as an increase in degrees Celsius over pre-industrial levels. The basic function has been often criticized not only for excluding major categories of damage but also because it leads to absurd results in the long run. In particular, at an increase of 12 °C the model suggests that economic damages would only amount to 30% of gross world product, when in fact at this temperature most life on Earth, much less the human economy, may not exist. For this reason, several alternative damage functions have been proposed to account for catastrophic outcomes.

These alternatives suggest that the SCC could be almost $900 (tCO2-e)-1 for emissions in 2010, rising to $1,500 (tCO2-e)-1 by 2050 (Ackerman and Stanton 2012).

Regardless of the relevant form of the SCC damage function, incorporating OAW costs into the framework requires recalibrating damages at each point in time (Dt), re-estimating equation [1], and then running the IAMs to produce new SCC results. The full impacts on the SCC can be determined when the IWG updates its estimates. For the purposes of this paper, we use a short cut to illustrate what the effects on SCC likely would be. The short cut involves using a simple linear regression on IAM model outputs with Dt as the independent variable and SCC as the dependent variable and then using the resulting equations to solve for SCC at OAW- adjusted levels of Dt . Using 2013 public access versions of DICE, we first estimated two equations based on separate runs of the model (called the ‘Copenhagen Accords’ and ‘Limit of 2 °C’ scenarios) and then used the resulting equations – both of which fit well (R2>0.80) as linear models through 2100 – to suggest what SCC would be in various years if OAW costs were included. We based the OAW-adjusted level of damages (Dt) at 5-year increments through 2100 on the assumption that damages by 2100 would amount to $20 trillion per year, but with a relatively low probability (25%) of occurring. The $20 trillion figure is within the range suggested by Table 4. The expected value – $5 trillion/yr by 2100 on top of the IWG’s baseline estimates – was assumed to increase from zero in 2015 at a constant rate until 2100. We then plugged the resulting baseline plus OAW damage figures into the regression equations to translate them into increments to the IWG’s published SCC estimates.

The results of this simplified approach are reported in Table 5. Column one reports the IWG’s baseline SCC figures at a 3% discount rate in 2007 dollars. Column two adds modeled increments to the SCC to account for OAW using the Copenhagen scenario of DICE while column three uses the Limit2 scenario. The former suggests an SCC rising from $60 (tCO2-e)-1 in 2015 to $101 (tCO2-e)-1 in 2100. The latter suggests a range of $96 (tCO2-e)-1 to $281 (tCO2-e)-1.

Respectively, these columns suggest that adding OAW costs would yield an SCC 1.5 to 4.0 times greater than the existing federal baseline.

Table 5: Social cost of carbon – modified damage function approach

($2007, 3% discount rate, OAW damages at $20 trillion in 2100 with probability=0.25)


Year IWG baseline ($/mt CO2) OAW/DICE Limit2
($/mt CO2)
($/mt CO2)
2015 $36 $96 $60
2020 $42 $161 $75
2025 $46 $205 $84
2030 $50 $235 $91
2035 $55 $256 $96
2040 $60 $269 $98
2045 $64 $277 $100
2050 $69 $281 $101

4.2 Replacement or adaptation cost approach

An entirely different approach that may be more amenable to the damages associated with OAW is one based on the replacement or adaptation cost associated with losing key ecosystem goods and services and replacing infrastructure. Thus, as food from the sea declines there will be a replacement cost associated with providing alternative nutrition sources from the land. The tally of costs should include both the financial outlays needed as well as any additional external damages that may be associated with the substitutes.

Increasing agricultural output to make up for declining seafood consumption, for instance, may come at a steep cost to remaining native terrestrial ecosystems and the goods and services they provide if additional land needs to be put into production.

Current replacement or adaptation cost figures – and these may certainly change over time as new information permits more refined estimates – can then be used as date-certain investment targets achieved by a stream of annual investments that begins today. Dividing the necessary level of investment by emissions in a given year then represents what charge needs to be made on each ton of carbon dioxide released in order to eliminate the externalized cost burden. This approach may be better suited for costs of OAW because most of the costs are non-market in nature.

It is easier to figure out the cost of replacing these lost services than the existing economic damage their loss generates simply due to the inherent uncertainty associated with non-market valuation techniques.

As an example, consider coastal infrastructure that will need to be abandoned and replaced if sea level were to rise 1.55 meters by 2100 (See Section 3.3). As previously noted, this scenario entails a risk of losses of $3.6 trillion/yr – a figure that reflects the current value of GDP in areas that would be newly inundated above and beyond a sea level rise of 0.55 meters, the baseline IWG assumption. As a general rule of thumb, economists assume that the value of the underlying capital stock is roughly ten times the annual GDP produced by a given area. In this case, the challenge would be replacing roughly $36 trillion in infrastructure.

If we select 2100 as the date-certain when these investments need to be completed, it implies an annualized investment stream now until that date of $2.5 trillion/yr taking into account an opportunity cost of capital (OCC) of 7% – the standard now used by many public agencies when making large-scale infrastructure investment decisions. The OCC is used to reflect the opportunity of taking capital out of more productive investments elsewhere. Dividing this annual investment need by current global emissions suggests an increment of about $70 to the current SCC to account for the externalized debt obligation associated with replacing coastal infrastructure at a sea level rise of 1.55 meters rather than 0.55 meters by 2100.

Additional replacement cost increments to SCC can be made for dwindling supplies of food from the sea, lost carbon sequestration capacity (the alternative here may be reforestation), and perhaps other ecosystem services that have functional replacement that are relatively easy to identify and cost out. Adding in these other replacement cost figures would likely justify an increase of SCC by a factor of two or more.

4.2 Averted risk approach

People pay to reduce risk. Of course, this is the bread and butter of the insurance industry. But it is also one of the most basic themes in welfare economics, in particular, the branch of economics related to risk and uncertainty. Models of decision making under risk and uncertainty, including the payments of premiums to avoid or reduce risks, may be an extremely fruitful approach to the SCC since so many of the damages expected are potentially catastrophic but highly uncertain (Botzen 2013).

An averted risk approach would peg the SCC to what society is willing to pay today (WTP) to reduce the risk of future economic damages. Stated as a cost, it represents the welfare loss associated with having a large share of economic activity at risk from climate change.

Basing SCC on WTP to avert or reduce risk has advantages over damage function based approaches. For example, current damage function models are based on certainty equivalents, when in reality uncertainty over whether or not a specific damage (i.e. catastrophic sea level rise associated with the collapse of West Antarctic ice sheets) will occur as well as the magnitude of such damages is the norm. Of course this trades one complex task for another – modeling probabilities rather than damages – but nonetheless is more tractable, especially if the probabilities are based on subjective expert assessments. In this way, the averted risk approach need not be nearly as sophisticated or complex as the existing IAMs.

The standard method for determining WTP to reduce risk is based on expected utility theory. Figure 1 illustrates calculation of the risk premium an individual is willing to pay, shown as the line connecting points c and d, or Y3-Y4. It involves three key steps. First, it requires an assumption regarding the shape of an individual’s (or in our case, society’s) utility function. Utility is an economic concept that hypothetically measures the enjoyment, or wellbeing associated with a given level of income, wealth, or quantity of a good or service. For our purposes, we adopt one of the standard forms depicting the utility function of a risk-averse person or population: U = ln(W), where W is wealth (y-axis) and U the level of utility associated with that level of wealth (x- axis). The declining marginal utility of wealth is reflected by the concave shape of the curve, and is a graphical representation of the fact that as wealth increases, a given increment to wealth has less of an impact on wellbeing.

The second step depicts the loss scenario, should it unfold. The person currently enjoys a level of wealth W and utility U1, but faces a 50/50 chance that a catastrophic event will reduce her wealth by L to the point W-L with a utility of U2. Given this risk, the expected wealth and utility in the next time period is given by the points Y3 and U4. This is simply a weighted average assigning equal probability to the two outcomes of next period wealth. The third step calculates the risk premium. The risk premium reflects what society is willing to pay to have an intermediate level of wealth in the next period (Y4) for certain rather than an uncertain W. The calculations are relatively straightforward, and the results vary with the shape of the assumed utility function, probability of loss, and magnitude of loss.

Parameters Scenario1 Scenario2 Scenario 3
Existing wealth
(GWP – $trillions)
$75.80 $75.80 $75.80
Nominal loss from OAW ($trillions/yr) $20.00 $20.00 $20.00
Year of loss 2050 2100 2100
Discount rate 0% 1% $3%
Present value loss ($trillions/yr) $20.00 $8.58 $1.62
Risk of loss 0.25 0.50 0.75
Expected utility 4.25 4.27 4.31
Certainty equivalent wealth ($trillions) $70.21 $71.38 $74.58
Risk premium ($trillions) $5.59 $4.42 $1.22
SCC increment $155.66 $123.15 $33.96

Table 6 shows the result of this simplified analysis for three loss scenarios, each with OAW losses of $20 trillion (as suggested by Table 4) but with different assumptions about when that loss will occur, the social discount rate (converting future losses into present values), and the probability of the loss. The resulting risk premiums, in trillions per year, are then divided by current emissions to suggest what the SCC increment should be today to internalize the welfare loss associated with the risk of catastrophic damages associated with OAW by 2050 or 2100. The results justify an increment of $33.96 to $155.66 to the SCC, for emissions over the next few years, to account for this welfare loss. This translates into an SCC that is 1.8 to 4.7 times higher than the current federal estimate.

5.0 Conclusions

Ocean acidification and warming (OAW) has the potential to put the livelihoods of billions of people at risk, accelerate the extinction of marine species, and damage critical life support systems of the planet, including the production of adequate levels of oxygen for life on Earth to exist. Literature on the economic toll of OAW is relatively sparse compared with other aspects of climate change. As a result, past efforts to estimate SCC have excluded these costs by treating them as zero. Here, we argue that there now exists sufficient information to develop non- zero estimates of the OAW component of the SCC. Moreover, incorporating such estimates would be consistent with regulatory requirements to use best available science and take note of high-impact/low probability scenarios.

There are at least three approaches for doing so. The first is simply to fit plausible scenarios of OAW and the likely magnitude of economic costs into integrated assessment models (IAMs) used by federal agencies. The IAMs model year-by-year net economic damages as a quadratic function of temperature and then translate the present value damage stream into an estimate of the SCC for emissions today and in future years. The key conclusion we offer here is that while OAW damages are highly uncertain, they can nonetheless be input into the IAM framework as expected (probability-weighted) values.

The second is an entirely different approach that requires maintaining an ongoing inventory of necessary capital investments needed to replace or adapt to ecosystem goods, services, and infrastructure likely to be lost to OAW. Under this approach, the SCC would reflect what amount ought to be charged to emissions, beginning now, to generate an annual investment stream needed to meet long term replacement or adaptation goals. If adaptation planning is begun in earnest today, there is no reason why this approach could not supplement the SCC’s damage function basis.

The third mimics the insurance industry to estimate society’s willingness to pay to reduce or eliminate future OAW risks. We find that this approach is, perhaps, the most suitable for OAW given the fact that economic costs are potentially catastrophic in value but highly uncertain. Standard expected utility theory provides the basis for current estimates of WTP and resulting increments to SCC needed to capture the welfare losses associated with having these economic risks on the books.

Taken together, our preliminary results suggest that SCC should be 1.5 to 4.7 times the current federal rate, or in the $60 to $200 per metric ton CO2-e range, just to account for the costs of OAW.

For references cited, see the author’s manuscript, available here.