Detecting and Quantifying the Anthropogenic Influence on Extremes

Abstract:

The body of evidence indicating a human contribution to observed climate change has continued to strengthen as indicated by the 5^th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). This includes an accumulating body of evidence suggesting that temperature and precipitation extremes have both changed in response to human influences on the climate. The research on temperature extremes is well established, with recent work indicating that temperature extremes have continued to warm over land despite the global warming “hiatus”, and that anthropogenic forcing has substantially increased the odds of extreme warm years and summers, both globally and regionally. The evidence on precipitation extremes is less well established, although there is increasingly strong evidence that human influence is detectable in observations at the largest scales that are resolvable in available international compilations of daily precipitation records. In contrast, assessments of historical and projected changes in the terrestrial branch of the hydrological cycle and storminess remain cautious, due to data limitations, uncertainty in process understanding, modelling, and in the case of terrestrial hydrological impacts, the highly heterogeneous nature of the impacted systems. Despite uncertainties and limitations in knowledge, observed and projected changes in the simple temperature and precipitation indicators in which we have greatest confidence provide strong evidence that adaptation is required now, and that further adaptation will be required in the future.