Beyond mean climate change: What climate models tell us about future climate extremes

Condensed summary: Atmosphere–ocean general circulation models (AOGCMs) necessarily have a limited ability to simulate extreme phenomena, due to their finite – and currently still relatively coarse – resolution. Nevertheless, recent studies have analyzed output from AOGCMs in order to assess their ability to simulate current extremes, mostly temperature-related, in order to infer what the future may bring, under scenarios of continuing and increasing greenhouse gas emissions. We present results of analyzing heat wave changes as projected by the Parallel Climate Model (PCM; National Center for Atmospheric Research/US Department of Energy [NCAR/DOE]) under a “business as usual” emission scenario, pointing at future increases in frequency, duration, and intensity of heat waves. We also describe a broader study of extreme indicators from multiple AOGCMs that contributed their output as part of the activities Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). We looked at ten different indicators, describing aspects of extreme temperature and precipitation events, for current climate and for the rest of the twenty-first century, under a range of emissions scenarios. We find strong and consistent signals of changes towards warmer temperature extremes, and an overall agreement of the different models on the intensification of precipitation, particularly in the high latitudes of the Northern Hemisphere. Introduction: Atmosphere–ocean general circulation models (AOGCMs) are the principal tools at our disposal when we seek to characterize projections of future climate. Many studies in the past decade have addressed projected changes in global average temperature and precipitation, and other general climate indicators.