Anthropogenically-driven increases in the risks of summertime compound hot extremes

Jun Wang,Jinming Feng,Panmao Zhai,Simon F B Tett,Zhongwei Yan,Jiangjiang Xia,Yang Chen

doi:10.1038/s41467-019-14233-8

Abstract

Compared to individual hot days/nights, compound hot extremes that combine daytime and nighttime heat are more impactful. However, past and future changes in compound hot extremes as well as their underlying drivers and societal impacts remain poorly understood. Here we show that during 1960–2012, significant increases in Northern Hemisphere average frequency (~1.03 days decade−1) and intensity (~0.28 °C decade−1) of summertime compound hot extremes arise primarily from summer-mean warming. The forcing of rising greenhouse gases (GHGs) is robustly detected and largely accounts for observed trends. Observationally-constrained projections suggest an approximate eightfold increase in hemispheric-average frequency and a threefold growth in intensity of summertime compound hot extremes by 2100 (relative to 2012), given uncurbed GHG emissions. Accordingly, end-of-century population exposure to compound hot extremes is projected to be four to eight times the 2010s level, dependent on demographic and climate scenarios.

Highlights

Compared to individual hot days/nights, compound hot extremes that combine daytime and nighttime heat are more impactful
Severe damage comes from sequential occurrences of hot day and hot night within 24 h, which accumulate and aggravate adverse impacts of daytime and nighttime heat on various sectors[9,10]
Combined daytime–nighttime hot extremes might differ from individual hot days/nights in meteorological and climatological aspects[15,16,17] but more importantly in impacts on human and natural systems[18]

Summary

Introduction

Compared to individual hot days/nights, compound hot extremes that combine daytime and nighttime heat are more impactful. It is worthwhile to revisit observation, detection–attribution and projection of hot extremes based on a bivariate definitional framework, to refine and further advance our understandings about their past changes and underlying drivers as well as future impacts and risks[21] To this end, we first define three nonoverlapping types of summertime hot extremes, i.e., independent hot days (daytime events, hot day–mild night), independent hot nights (nighttime events, mild day–hot night), and compound hot extremes (hot day–hot night, see the Methods section). We first define three nonoverlapping types of summertime hot extremes, i.e., independent hot days (daytime events, hot day–mild night), independent hot nights (nighttime events, mild day–hot night), and compound hot extremes (hot day–hot night, see the Methods section) With respect to these bivariate-classified hot extremes, we conduct a series of analyses on their historical changes, mechanism explanations, quantitative detection and attribution, constrained projections, and future population exposure. At the end of the 21st century, uncurbed greenhouse gases emissions would make three-quarters of summer days typical of today’s compound hot extremes, leading to several-fold growth in population exposure to them

Methods

Results

Conclusion