Might Future Heatwaves be Underestimated?

Abstract:

In this presentation, the case study of the Dustbowl heatwaves across the US is briefly introduced as a historical event that was triggered by climate variability yet strongly enhanced by local feedbacks. It highlights the importance of water availability in moderating the strength of heatwaves, and the value of observed events to investigate mechanisms.

For prediction of changing strength of heatwaves and their impact, we depend on climate models. However, the magnitude of the change in heatwaves varies greatly among different models, an uncertainty that has been linked to differences in land-atmosphere feedbacks across models. Models that show stronger present day variability in hot days tend to simulate less change in the future than models that are realistic at present time. An emergent constraint locally based on maximum temperature variability performs well predicting future change in extremes in tests across a large multi-model ensemble comprised of CMIP5 and CMIP6 models. Applied to observations, it indicates that the best estimate increase in hot extremes could be worse than previously estimated. Related constraints can be determined based on mechanisms of latent heat flux change, and the regions where the emergent constraint is most robust across mechanisms include tropical regions and South-East Asia. This presentation will end with a discussion of how focus on feedbacks and high impact events drawing on realistic predictions of future extremes will be important to determine future ‘safe’ climates.