Increasing Temperature Extremes during the Recent Global Warming Hiatus

Abstract:

Although the recent global warming hiatus has featured a slowdown in the annual, global mean surface air temperature trend, temperature extremes have exhibited contrasting changes, as both wintertime cold and summertime hot extremes have increased over Northern Hemisphere (NH) land from 2002-2014. To investigate the sources of NH temperature extreme variability, we use multiple linear regression analysis that includes as predictors the typical drivers of global-scale climate variability – tropical Pacific sea surface temperatures (SST), volcanic aerosols, solar variability, and the linear time trend. This analysis suggests that natural forcings, including tropical SSTs and solar variations, have contributed to the recent increase in NH winter cold extremes. The magnitude of the recent increase in summer hot extremes is only captured after including an additional SST predictor for a pattern that resembles the Atlantic Multidecadal Oscillation, which suggests the importance of Atlantic Ocean SSTs for recent increases in hot extremes. When the regression models are applied to local, grid point scales, they indicate the promise for substantial skill in seasonal predictions of extreme temperature over some NH regions. Overall, this work reveals important sources of natural variability in extreme temperature trends superimposed upon the long-term increase of hot extremes and decrease of cold extremes.