Written evidence submitted by Corinne Le Quéré and Andrew Watkinson (IPC0050)

 

Andrew Watkinson, Professor in Environmental Sciences, University of East Anglia.

IPCC involvement: Review editor 4th Assessment Report

 

Corinne Le Quéré, Professor of Climate Change Science and Policy and Director of the Tyndall Centre for Climate Change Research, University of East Anglia.

IPCC involvement: author (Lead Author) of the 3rd, 4th, and 5th Assessment reports, including the Summary for Policy Makers of the 3rd report (as Draft Author) and of the 5th report (as Contributing Author).

 

Key points:

 

 

 

Questions

How robust are the conclusions in the AR5 Physical Science Basis report? Have the IPCC adequately addressed criticisms of previous reports? How much scope is there to question of the report’s conclusions?

  1. The overall conclusions of the report are robust and little changed from previous reports. Each IPCC assessment has strengthened the results of the previous report, in line with the increasing evidence. The general conclusions that the Earth is warming, and that the emissions of greenhouse gases are causing the observed warming are stated clearly with a level of uncertainty that represents the overall body of evidence. The climate projections and associated compatible emissions are based on fundamental and reliable knowledge of the physical processes that control the dynamics of the climate, and the uncertainty provided reflects the available knowledge, including from observations. The coordination of the model experiments by the World Climate Research Programme (the Coupled Model Intercomparison Project – CMIP5) means that the results are comparable and thorough, and provide a large number of results from many groups around the world. Results from 47 models developed by 21 research groups were used in the report, representing all the main climate research groups across the world. The design of these experiments is very thorough, from all aspects of the forcing and analysis. The report itself is prepared by a large number of authors (259) covering all components of the physical climate research. In no other areas of science is there such an organised and thorough assessment of the available evidence.
  2. The details of the report however remain open to criticism as a result of its reliance on review by a small group of experts who do not necessarily carry out formal systematic reviews of the literature, and because of the difficulty to keep up to date with a rapidly evolving research field as the report gets written. Although the report gets reviewed twice by experts and governments, the body of evidence to review is large and exceeds in cases the capacity of the experts in charge, whose contribution to the IPCC is done in addition to their normal workload. This is exemplified by the case of glacial melt in the Himalayas, statements about which, were strongly criticised in the AR4 report. You might, therefore, have expected this issue to have been dealt with thoroughly in the latest report but a number of key references were missed that have been identified in a parallel systematic review (Miller, J., Rees, G., Warnaars, T., Young, G., Collins D. & Shrestha, A. 2013. What is the evidence for glacial shrinkage across the Himalayas? CEE review10-008. Collaboration for Environmental Evidence: www.environmentalevidence.org/ SR10008.html).

To what extent does AR5 reflect the range of views among climate scientists?

  1. This question is difficult to answer without a formal assessment, which has not been done. However, our contacts with a wide range of climate scientists indicate that AR5 does largely reflect their views. This was certainly not the case in AR4 for the issue of sea level rise where there was considerable unease over the way in which the future projections of sea level rise were handled.

Can any of the areas of the science now be considered settled as a result of AR5’s publication, if so which?  What areas need further effort to reduce the levels of uncertainty?

  1. The key conclusion that the emission of anthropogenic greenhouse gases is resulting in climate warming and ocean acidification remains robust and can be considered as settled, unless new evidence to the contrary is forthcoming. The greatest areas of uncertainty lie in the projection of regional climate change, the contribution of climate change to hurricane intensity and tropical storms, whether or not we approaching any significant climate tipping points for glaciers melting and ocean circulation, and the size of the carbon cycle feedbacks particularly with respect to permafrost melting in the high warming scenarios.

How effective is AR5 and the summary for policymakers in conveying what is meant by uncertainty in scientific terms? Would a focus on risk rather than uncertainty be useful?

  1. No, a focus on risk would not be useful. IPCC has a well documented and appraised approach to conveying uncertainty in our knowledge, whether that relates to past historical climates or future climate projections. It would not make sense to talk about the risk associated with past historical climates; it is rather our knowledge that is uncertain. Moreover risk is generally interpreted in terms of the likelihood of an event occurring and its consequences. This only relates to a subset of the findings in AR5. For these elements (e.g. the risk of exceeding global warming of 4 degrees), an analysis of risks would be appropriate, but this should come in addition to the current assessment of uncertainty.

Does the AR5 address the reliability of climate models?

  1. Yes. The AR5 includes a full chapter on the evaluation of climate models. It explains how the models have evolved since the AR4 and what aspects of the climate system the models can accurately reproduce. The models are evaluated compared to the metrics of climate change (the climate sensitivity and transient climate response). This can be done because of the coordination and availability of the appropriate model simulations requested by the CMIP5 experiments. Results presented usually represent 5-95% of the model range for each scenario projection, which implicitly removes outliers from the analysis.
  2. The IPCC process provides a major incentive to co-ordinate modelling activities, without which it would be more difficult to make intermodal comparisons and assess the reliability of climate models.

Has AR5 sufficiently explained the reasons behind the widely reported hiatus in the global surface temperature record?

  1. AR5 provided a partial explanation of the hiatus available by March 2013 (the cut-off date for publications to be considered by the authors), but new information is emerging (e.g. Cowtan, K. and Way, R.G. 2013. Coverage bias in the HadCRUT4 temperature series and its impact on recent temperature trends. doi: 10.1002/qj.2297). The indications are that climate warming continues and that the hiatus in the global surface temperature record is a result of more heat than expected finding its way into the deep ocean and an under recording of surface temperature in the Arctic.

Do the AR5 Physical Science Basis report’s conclusions strengthen or weaken the economic case for action to prevent dangerous climate change?

  1. The economic case for action to reduce greenhouse gas emissions and for adaptation is strengthened by AR5. The evidence for the potentially destructive effects of climate change is greater. In particular there is better evidence of an increase frequency and/or intensity of some extreme events (heat waves, heavy precipitation events, and extreme high sea level), and of the contribution of climate change to these events. The increase in the emissions of GHGs is also higher than anticipated in the previous report. There consequently remains an overwhelming economic case for immediate action as originally outlined by Lord Stern in the Stern review on the economics of climate change in 2006.

What implications do the IPCC’s conclusions in the AR5 Physical Science Basis report have for policy making both nationally and internationally?

  1. The IPCC report reaffirms that anthropogenic greenhouse gas emissions are having a significant impact on the climate system and that significant action is required both nationally and internationally to reduce greenhouse gas emissions. The efforts required to limit global climate change to 2 degrees above pre-industrial levels are larger than at the time AR4 was published (in 2007) because the emissions of greenhouse gas have continued to rise between 2007 and 2013. CO2 emissions from fossil fuel combustion (the largest single contributor to global warming) are now 61% above their 1990 levels. Yet in the only IPCC scenario that limits warming to 2 degrees the global emissions need to fall 50% below 1990 levels by 2050, and require technological means for removing CO2 from the atmosphere post 2070 which are difficult to envisage. It is therefore clear that to minimise the extent of climate warming international policy action needs to be taken now.

Is the IPCC process an effective mechanism for assessing scientific knowledge? Or has it focussed on providing a justification for political commitment?

  1. The overarching aim of the scientists involved in the IPCC is to provide an assessment of our scientific knowledge on climate change and not to provide a justification for political commitment, although others undoubtedly use it for that purpose. Whether it remains the most effective mechanism for assessing that knowledge is however unclear.
  2. After AR4 there was debate over whether a periodic review was the appropriate mechanism, moving forward, or whether the focus should now turn to shorter reports that reviewed areas where there had been substantial progress or where there was considerable uncertainty. One of the major advantages of the current system is that it provides a focus for modelling activities in WG1, which are essential to review the projections of climate change. Furthermore, the assessment process provides the only forum where all the components of the climate system can be looked at (e.g. the atmosphere, ocean, ice, land, biogeochemical cycles), and consistency across different streams of research can be analysed. This is very powerful in terms of assessing the main conclusions of the report. It is not clear however that the current process provides the most effective method for reviewing impacts or addressing mitigation and adaptation issues, where specialist reports or some sort of environmental wiki might be more appropriate. Finally, the IPCC Assessment process exerts demands on researchers which are difficult to manage as the body of research and the expectations grow. A development of web-based tools would be necessary to assist in the process and engage a larger proportion of the expert researchers, particularly for the review of the literature and for improving the transparency of the assessment.

To what extent did political intervention influence the final conclusions of the AR5 Physical Science Basis summary?

  1. The consensus from our own experience and from talking to a number of the IPCC authors is that the challenge from policy makers during the review process and during the approval by the UN in Stockholm clarified the various points that were being drawn out in the Summary for Policymakers and did not alter them. The guidance from the IPCC co-Chairs during Stockholm and throughout the process was very clear: the results presented in the Summary for Policymakers must reflect the body of evidence presented in the main report. The 10 figures shown in the Summary for Policymakers were selected by the authors and have all been approved. Importantly, all of the key statements proposed by the authors have been clarified and shortened, without a loss of substance. Thus the report and key results are understandable to a larger audience, while still containing the evidence put forward by the authors.

Is the rate at which the UK Government intends to cut CO2 emissions appropriate in light of the findings of the IPCC AR5 Physical Science Basis report?

  1. The rate at which the UK Government intends to cut emissions remains appropriate with a 34% reduction of emissions by 2020 in comparison with the 1990 baseline and an 80% reduction by 2050. There is an urgent need for global emissions to peak (they continue to rise) in the next few years and for them then to fall rapidly.

What relevance do the IPCC’s conclusions have in respect of the review of the fourth Carbon Budget?

  1. They strongly reinforce the necessity of working nationally and internationally to reduce greenhouse gas emissions by 80% by 2050 so that the amount of carbon dioxide released into the atmosphere is limited. The fourth carbon budget recommendation that emissions should be limited to 1,950 MTCO2e for the period 2023-2027, leading to a 60% emissions cut by 2030 in the UK, remains robust, but his will require commitment to Electricity Market Reform, alongside appropriate policies to reduce energy demand in buildings, agriculture, transport and industry sectors.

December 2013