Going to the Extremes

Abstract

Projections of changes in climate extremes are critical to assessing the potential impacts of climate change on human and natural systems. Modeling advances now provide the opportunity of utilizing global general circulation models (GCMs) for projections of extreme temperature and precipitation indicators. We analyze historical and future simulations of ten such indicators as derived from an ensemble of 9 GCMs contributing to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC-AR4), under a range of emissions scenarios. Our focus is on the consensus from the GCM ensemble, in terms of direction and significance of the changes, at the global average and geographical scale. The climate extremes described by the ten indices range from heat-wave frequency to frost-day occurrence, from dry-spell length to heavy rainfall amounts. Historical trends generally agree with previous observational studies, providing a basic sense of reliability for the GCM simulations. Individual model projections for the 21st century across the three scenarios examined are in agreement in showing greater temperature extremes consistent with a warmer climate. For any specific temperature index, minor differences appear in the spatial distribution of the changes across models and across scenarios, while substantial differences appear in the relative magnitude of the trends under different emissions rates. Depictions of a wetter world and greater precipitation intensity emerge unequivocally in the global averages of most of the precipitation indices. However, consensus and significance are less strong when regional patterns are considered. This analysis provides a first overview of projected changes in climate extremes from the IPCC-AR4 model ensemble, and has significant implications with regard to climate projections for impact assessments.

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“…In addition, future climate simulations generally project increases in the greatest precipitation events over northwestern and northeastern US (Meehl et al 2005). However, there are large uncertainties related to GCMs, RCMs and statistical downscaling methods, and by natural variability of the climate (Tebaldi et al 2006;Kharin et al 2007;Kyselỳ and Beranová 2009;Kenyon and Hegerl 2010;Orlowsky and Seneviratne 2012).…”

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“…Modelling groups have also now taken a similar approach through the Joint Scientific Committee (JSC)/CLIVAR Working Group on Coupled Models so that observations and model output can be compared consistently. The study by Tebaldi et al (2006) was the first to use the multi-model approach to assess potential future changes in climate extremes showing that the twenty-first century would bring global changes in temperature extremes consistent with a warming climate. While that study also showed that global changes in precipitation extremes were consistent with a wetter world with greater precipitation intensity, the consensus and significance amongst the models were weaker when regional patterns were considered.…”