Climate scientists are afraid of using expert opinion in assessing uncertainty of future impacts

The risks of climate change are being understated in official assessments because scientists have become afraid of using their expert opinion in assessing the uncertainty of future impacts, a leading researcher will warn today (24 May 2012).

Arthur Petersen, Chief Scientist at the PBL Netherlands Environmental Assessment Agency and a Visiting Professor at the Grantham Research Institute on Climate Change and the Environment at London School of Economics and Political Science, will reveal that policy-makers and the public are not being fully informed of the worst potential consequences of climate change, such as a large rise in sea level from melting ice sheets or a rapid increase in warming due to the release of methane from thawing permafrost, because scientists are reluctant to overrule conservative estimates by computer models.

Speaking at the UK launch of the new edition of his book on the use of climate models, Professor Petersen will say: “Although recent controversies about the Intergovernmental Panel on Climate Change have highlighted that its last assessment in 2007, for instance, overstated the rate of melting of the Himalayan glaciers and overemphasised in its summary the most negative projected regional impacts of global warming, it is less well appreciated that the report also provided estimates of some of the most important future risks that many scientists think were too conservative.

“For example, the IPCC’s estimates of possible rises in global sea level by the end of the century excluded the possibility of a rapid destabilisation of the land-based ice sheets in West Antarctica and Greenland, which could cause a much bigger increase. The report openly acknowledges that this impact was excluded because current models of ice sheets cannot produce reliable estimates. Yet it would have been far more helpful to policy-makers if the scientists had made an expert judgment about how much more sea levels might rise than the 59 centimetres presented in the worst case scenario in the report.”

Professor Petersen’s book, ‘Simulating Nature: A Philosophical Study of Computer-Simulation Uncertainties and Their Role in Climate Science and Policy Advice’, examines the importance of uncertainties in climate models and how it affects the expert guidance being offered to governments. He says that scientists have become so worried about attacks on climate research that they are reluctant to point out the shortcomings of models that are unable to estimate the full range of uncertainties, including the possibility of the most dangerous potential impacts.

Professor Petersen says: “In the past, the IPCC has not provided the authors of assessments with good enough guidance about how they should convey uncertainties in estimates of future impacts. The next assessment report, the first volume of which will be published next year, needs to give clearer explanations of the different sources of uncertainty, as well as estimates of their importance. For instance, it needs to distinguish between uncertainty that can be quantified statistically, uncertainty that can be expressed by a range based on ‘what if’ assumptions, and recognised ignorance. All three dimensions of uncertainty should be addressed when assessing scientific knowledge about climate processes, such as the effect of clouds on surface temperatures.”

Notes for Editors

1. The Grantham Research Institute on Climate Change and the Environment was launched at the London School of Economics and Political Science in October 2008. It is funded by The Grantham Foundation for the Protection of the Environment.
2. Professor Petersen is also a Visiting Professor at the Centre for the Analysis of Time Series at the London School of economics and Political Science, and at the Centre for Climate Change Economics and Policy, which is hosted by the University of Leeds and the London School of Economics and Political Science, and funded by the UK Economic and Social Research Council and Munich Re. He is also Professor of Science and Environmental Public Policy at the VU University Amsterdam, and is active within the Intergovernmental Panel on Climate Change (IPCC), on behalf of the Dutch government. Professor Petersen received graduate training as a theoretical physicist (MSc), atmospheric scientist (PhD) and philosopher of science (MA and PhD). Since 2001, he has gained considerable experience in shaping the science-policy interface at Dutch, European and global levels on issues of climate change and sustainable development. He has become a world-leading expert on assessing and communicating uncertainties.