Fingerprinting Heatwaves and Cold Spells and Assessing Their Response to Climate Change using Large Deviation Theory

TL;DR

This paper applies large deviation theory to climate models to quantify and analyze the increasing hazard of persistent heatwaves and cold spells due to climate change, providing new insights into their dynamics and return times.

Contribution

It introduces a novel application of large deviation theory to define the climatology of persistent temperature extremes and assesses their response to rising CO2 levels.

Findings

Heatwaves and cold spells are linked to exceptional atmospheric patterns.

The 2010 Russian heatwave and Mongolia Dzud are statistically exceptional but within natural variability.

An approximate formula for return times of temperature extremes is proposed and validated.

Abstract

Extreme events provide relevant insights into the dynamics of climate and their understanding is key for mitigating the impact of climate variability and climate change. By applying large deviation theory to a state-of-the-art Earth system model, we define the climatology of persistent heatwaves and cold spells in key target geographical regions by estimating the rate functions for the surface temperature, and we assess the impact of increasing CO$_2$ concentration on such persistent anomalies. Hence, we can better quantify the increasing hazard {\color{black}due} to heatwaves in a warmer climate. We show that two 2010 high impact events - summer Russian heatwave and winter Dzud in Mongolia - are associated with atmospheric patterns that are exceptional compared to the typical ones, but typical compared to the climatology of extremes. Their dynamics is encoded in the natural variability of the climate. Finally, we propose and test an approximate formula for the return times of large and persistent temperature fluctuations from easily accessible statistical properties.