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2010 Literature Review Archives - Policy/Mitigation

Anderegg, W.R., J.W. Prall, J. Harold, and S.H. Schneider. 2010. Expert credibility in climate change. Proceedings of the National Academies of Science Early Edition. Published on-line before print on June 21, 2010, doi: 10.1073/pnas.1003187107.

Study demonstrates that, as a group, scientists who accept the basic tenets of anthropogenic climate change have substantially more climate-related expertise than do a group of scientists who are unconvinced of the evidence.

In the public debate about climate change, there is a vocal contingent who contest the main findings of the assessment report(s) of the Intergovernmental Panel on Climate Change (IPCC) and who frequently claim that there are a large number of scientists who share this view. There is therefore value in assessing the credentials of scientists on both sides of the issue. A paper published in the early on-line edition of the Proceedings of the National Academies of Science reports on work characterizing the relative scientific credibility of two groups of specialists: those convinced of the evidence of human-induced climate change and those unconvinced of the evidence. The group of individuals assumed to be convinced of the evidence (CE researchers) included all contributors to the Working Group 1 report of the IPCC Fourth Assessment, as well as individuals who had signed public statements affirming their acceptance of the evidence for anthropogenic climate change (eliminating duplicate names). The list of those assumed to be unconvinced of the evidence (UE researchers) was compiled from signatories to a number of prominent statements expressing strong dissent with the views of the IPCC. This set of 1372 individuals was then reduced to 908 by counting only those who had a minimum of 20 climate publications, using Google Scholar (Search term author:fi-lastname climate) to retrieve the publications. 80% of the UE group did not meet this minimum criterion for expert credibility, while less than 10% of the CE group were similarly affected.  The scientific credibility of the remaining researchers (>800 CE; <100 UE) was then evaluated using metrics of scientific expertise (# of climate-related publications) and of prominence (# citations for top cited papers). When the individuals were ranked on the basis of number of publications, the authors found that only 3% of the top 100 researchers were from the UE group. Taking the top ranked 50 in each of the two groups, they found that those in the CE group had significantly more climate related publications (median of 344) than those in the UE group (median of 68). Examining the citation record for the top 4 cited papers by each researcher also revealed that CE researchers were far more ‘prominent’ than UE researchers. This study does provide strong evidence that the relative climate expertise and scientific prominence of a large sample of experts deemed to be convinced of anthropogenic climate change is substantially higher than that of those deemed unconvinced. The authors acknowledge that alternative ways of sampling these communities and evaluating credentials could have been chosen but defend their methods as reasonable and conservative and suggest the results are unlikely to change qualitatively under different assumptions in these respects.


Bernie, D., J. Lowe, T. Tyrell, and O. Legge. 2010. Influence of mitigation policy on ocean acidification. GRL Vol 37, L15704, doi:10.1029/2010GL043181.

Study shows that in the long-term, the level of ocean acidification is largely determined by the extent to which annual carbon emissions can be reduced though stronger and more immediate action can limit the magnitude of acidification this century.

Evidence indicates that human emissions of carbon dioxide are causing ocean acidification as well as global warming. A mean decline in ocean surface pH of about 0.1 units (from 8.16 to 8.07) since the pre-industrial era has been observed. This paper by Bernie et al. examines how three different aspects of mitigation policy would impact ocean acidification: 1) peak year of emissions, 2) post-peak rate of decline in emissions, and 3) the level of the eventual ‘emissions floor’ (GtCO2e/yr). They conducted simulations with over 100 different emission mitigation scenarios, developed as part of the U.K. AVOID programme, using a simple ocean carbon cycle model that they show projects similar declines in ocean pH with increasing atmospheric CO2 as does a complex climate model coupled to ocean and terrestrial carbon cycle models (HadCM3LC). Under the most aggressive mitigation scenario considered, where global emissions peak in 2016 and are reduced at a rate of 5% per year thereafter down to a low long-term emissions floor, global mean surface ocean pH is projected to decline to 8.02 by 2100 [8.04-7.96 (10-90th percentile range)]. In comparison, surface ocean pH is projected to decline to 7.67 [7.74-7.57] by 2100 under the non-mitigation IPCC SRES A1FI emission scenario (a high emission scenario). The authors demonstrate that stronger emission reductions at a later date can allow for a delay in peak emissions while still reaching the same pH minimum this century. Over longer timescales (out to 2500), minimum pH is dominated by the emissions floor (annual emission rate) which reflects the close association between this metric and the cumulative emissions amount.


Moss, R.H., J. A. Edmonds, K.A. Hibbard et al.2010. The next generation of scenarios for climate change research and assessment. Nature(Perspectives) Vol 463 February 11, 2010 pp747-756.

The new process of developing standardized scenarios for use in climate change research is described in a special report in the journal Nature.
The climate change research community has, for some time, been using a suite of baseline emission scenarios developed by the Intergovernmental Panel on Climate Change (IPCC) and published in the IPCC Special Report on Emission Scenarios. These scenarios were referred to as the IPCC SRES scenarios. Partly in response to the availability of more recent data on economic trends, technology developments, and environmental factors, and partly due to a decision by the IPCC not to commission a new set of emission scenarios, the expert community instituted a new process for developing scenarios. This process, and the resulting set of standard scenarios, are described in the Perspectives section of a recent issue of the journal Nature. Of note is that whereas the previous approach was sequential, the current approach is described as being parallel. In the sequential approach, development of emission scenarios based on socio-economic factors occurs at the beginning of the process, providing the necessary input to models producing climate change scenarios which in turn are used to investigate climate change impacts on human and natural environments. In contrast, the starting point in the new process was selection from the published literature of representative scenarios for changes in radiative forcing referred to as Representative Concentration Pathways (RCPs). These are not associated with specific emission trajectories but rather could be consistent with any number of socio-economic scenarios and emissions pathways. Development of climate scenarios based on the RCPs will occur in parallel with development of a range of new socio-economic scenarios consistent with the RCPs. The expectation is that research integrating the new climate change and socio-economic scenarios will enable a more comprehensive exploration of issues related to impacts, adaptation and mitigation.


O’Neill, B.C., K. Riahi and I. Keppo. 2010. Mitigation implications of midcentury targets that preserve long-term climate policy options. PNAS Vol 107:3:1011-1016.

Study finds that mid-century conditions are crucial determinants of the likelihood of achieving longer term climate change outcomes.


A number of recent studies have found that cumulative CO2 emissions budgets are robust indicators of eventual global temperature increase and have provided estimates of emissions budgets compatible with limiting global warming to different amounts. One implication of this result is that the timing of CO2 emission reductions is less critical than the total amount emitted, since different emission pathways are compatible with similar cumulative emissions totals. However, in this paper, O’Neill and colleagues use an integrated assessment model with detailed representation of the energy sector to examine to what extent emission paths for the first half of the 21st century might render some emissions paths in the second half of the century technically infeasible. They define ‘infeasibility’ as “not possible to achieve with technologies currently at least in early demonstration or commercialization phase” which excludes geoengineering technologies for example. There are two key features of their results. The first is that for each long-term stabilization goal (from <450 ppm to >1000 ppm CO2-eq) there is a range of mid-century emissions that minimize total costs over the century, with costs increasing for emissions below and above this range (i.e. the cost curves for the century as a whole are U-shaped). This range is small for more stringent long-term targets. The result held true for both baseline development scenarios (variations on IPCC SRES B2 and A2r scenarios) and all long term targets. The authors suggest this finding could help inform climate policy. The second is that critical thresholds in 2050 do exist for each long-term goal, demarking mid-century conditions beyond which achieving the 2100 target becomes infeasible. For example, the study shows that to preserve the technical feasibility of keeping global warming below 2° C above pre-industrial with a 50% likelihood, global emissions must be reduced by at least 20% below 2000 levels by 2050 under the B2 scenario, and by at least 50% with the A2r scenario.


Patt, A.G., P. D.P. van Vuuren, F. Berkhout, A. Aaheim, A.F. Hof, M. Isaac, R. Mechler. 2010. Adaptation in integrated assessment modeling: where do we stand? Climatic Change Vol 99, pp 383-402. doi: 10.1007/s10584-009-9687-y.

Recent paper suggests that integrated assessment models are too optimistic about the net benefits adaptation can provide leading to potential underestimates of the amount of mitigation required to reach socially optimal targets.

Integrated Assessment Models (IAM) are tools for evaluating the costs and benefits of climate change policies over time.  IAMs incorporate the cause and effect chain of climate change (from emissions to impacts) and are increasingly including assessments of the costs, benefits and uncertainties of adaptation policies. Adaptation policies are essentially those designed to reduce climate change damage costs through adjustments to ecological, social or economic systems to either moderate damages or benefit from opportunities.  A recent paper by Patt et al examines how modelers have included adaptation within existing IAMs and how well these approaches represent the true costs and benefits of adaptation.  The authors suggest that the approaches tend to underestimate the difficulty of implementing adaptation measures and therefore overestimate the amount of adaptation that is likely to occur and the associated net benefits.  The authors discuss ways of improving the representation of the costs and benefits of adaptation in IAMs which focus on improving the representation of its bottom-up characteristics.


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