The Trends and Causes of Midlatitude Heat Extremes

March 3, 2021 3:00pm to 4:00pm
270 Seminar


Speaker: Karen McKinnon

Institution: UCLA 


A clear consequence of climate change is increasing global temperatures, with greater warming over land than ocean. The greatest impacts from continental warming occur due to extreme events; however, we do not have a good understanding of how to map from this large-scale picture to regional extremes. In this talk, I will apply three different lenses to help us better understand the physics and statistics of heat extremes. First, we will explore how daily summer temperature distributions have changed over the historical record in order to assess how the tails of the distribution are changing with respect to the middle. Across the Northern Hemisphere, we find that changes in summer temperatures can primarily be described by a simple shift, but that some regions such as eastern Europe show greater warming for hot extremes. Given the likely role of the land surface in amplifying heat extremes, I will next present a framework using dynamical adjustment to parse the circulation contributions to heat extremes from those due to other causes, and demonstrate how the central US, uniquely among the contiguous US, shows a large sensitivity to preceding soil moisture that can lead to heat extremes 50% larger than if the soil was not dry. While evaporation of soil moisture can provide a buffer to the temperature associated with heat extremes, it also leads to increased humidity, which can exacerbate the impacts of high temperatures. This highlights the importance of jointly modeling changes in temperature and humidity extremes, which is challenging given their underlying covariance. Using a newly developed semiparametric quantile smoothing splines model, we identify important dependencies between changes in temperature and humidity extremes, including large increases in humidity on already hot and humid days in the Midwest.