Climate Science for Serving Society

Abstract

Unusual or extreme weather and climate-related events are of great public concern and interest, yet there are often conflicting messages from scientists about whether such events can be linked to climate change. There is clear evidence that climate has changed as a result of human-induced greenhouse gas emissions, and that across the globe some aspects of extremes have changed as a result. But this does not imply that human influence has significantly altered the probability of occurrence or risk of every recently observed weather or climate-related event, or that such events are likely to become significantly more or less frequent in the future. Conversely, it is sometimes stated that it is impossible to attribute any individual weather or climate-related event to a particular cause. Such a statement can be interpreted to mean that human-induced climate change could never be shown to be at least partly responsible for any specific weather event, either the probability of its occurrence or its magnitude. There is clear evidence from recent case studies that individual event attribution is a feasible, if challenging, undertaking. We propose a way forward, through the development of carefully calibrated physically-based assessments of observed weather and climate-related events, to identify changed risk of such events attributable to particular factors including estimating the contributions of factors to event magnitude. Although such event-specific assessments have so far only been attempted for a relatively small number of specific cases, we describe research under way, coordinated as part of the international Attribution of Climate-related Events (ACE) initiative, to develop the science needed to better respond to the demand for timely, objective, and authoritative explanations of extreme events. The paper considers the necessary components of a prospective event attribution system, reviews some specific case studies made to date (Autumn 2000 UK floods, summer 2003 European heatwave, annual 2008 cool US temperatures, July 2010 Western Russia heatwave) and discusses the challenges involved in developing systems to provide regularly updated and reliable attribution assessments of unusual or extreme weather and climate-related events.