Importance of new study on the sensitivity of the Earth’s climate

Posted on 9 Mar 2014 in Press releases

Policy-makers should now treat with caution recent studies that suggest that the short-term sensitivity of the Earth’s climate to increases in carbon dioxide levels may have a low value, according to an article by a researcher at the ESRC Centre for Climate Change Economics and Policy and the Grantham Research Institute on Climate Change and the Environment at the London School of Economics and Political Science, which is published today (9 March 2014) in the journal ‘Nature Climate Change’.

In a ‘News and Views’ article, Dr David Stainforth highlights the importance of a new paper by Drew Shindell of the NASA Goddard Institute for Space Studies, also published today in ‘Nature Climate Change’.

Dr Shindell’s paper on ‘Inhomogeneous forcing and transient climate sensitivity’ warns that some influential recent studies have failed to take account of the evidence that the Earth’s climate is more sensitive to levels of aerosol particles and ozone emitted into the atmosphere from human activities than it is to concentrations of greenhouse gases.

As a result, some studies that have used recent observed trends in global surface temperature to estimate the transient climate response (defined as the change in global surface mean temperature after a doubling of the atmospheric concentration of carbon dioxide, at a rate of increase of 1 per cent a year over 70 years) have produced values that are too low.

Dr Shindell was a co-author on a paper by Alexander Otto and others, published in the journal ‘Nature Geoscience’ last year, which suggested that the value of the transient climate response lies between 0.9 and 2.0 centigrade degrees, with a median value of 1.3 centigrade degrees. However, Dr Shindell’s new paper shows that if a correction is made to the assumptions about aerosols and ozone, the transient climate response would be estimated to be higher, lying within the range of 1.3 to 3.2 centigrade degrees, with a median value of 1.7 centigrade degrees.

The paper by Otto and others helped to persuade the Intergovernmental Panel on Climate Change to reduce its estimate of the value of the transient climate response from a likely range of 1.0 to 3.0 centigrade degrees in its Fourth Assessment Report in 2007 to a likely range of 1.0 to 2.5 centigrade degrees in its Fifth Assessment Report, published in September 2013.

Dr Stainforth points out that Dr Shindell’s paper shows that “removing a key simplifying assumption would have led some recent studies to conclude that climate is more sensitive than they did.”

Dr Stainforth draws attention to new range suggested by Dr Shindell, writing: “Of particular relevance for economic assessments and risk-centred perspectives of climate change is that the upper temperature bound has increased more than the central value”.

Dr Stainforth’s article states: “It is worth reflecting, however, that this new estimate for TCR [transient climate response] comes about by questioning a widely-made implicit assumption in the application of simple climate models. Climate predictions would generally benefit from increased efforts to understand, rather than reduce, their uncertainties – something that can be in conflict with the remit provided by funders. Greater emphasis on the inherent assumptions could aid both policy interpretation and the advancement of science.”

The article adds: “The robust physical basis for confidence in some results, such as the reality and seriousness of anthropogenic climate change, could then be separated from more speculative, cutting-edge research. This would be valuable for public discourse on the subject and help science focus on those issues most likely to increase understanding, if not necessarily reduce uncertainty.”

To obtain an electronic copy of the article on ‘Testing climate assumptions’, or to arrange interviews with Dr David Stainforth, please contact Bob Ward on +44 (0) 7811 320346 or r.e.ward@lse.ac.uk.

 NOTES FOR EDITORS

1. The ESRC Centre for Climate Change Economics and Policy (http://www.cccep.ac.uk/) is hosted by the University of Leeds and the London School of Economics and Political Science. It is funded by the UK Economic and Social Research Council (http://www.esrc.ac.uk/). The Centre’s mission is to advance public and private action on climate change through rigorous, innovative research.
2. The Grantham Research Institute on Climate Change and the Environment (http://www.lse.ac.uk/grantham) 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 (http://www.granthamfoundation.org/).