More intense, more frequent, and longer lasting heat waves in the 21st century.

Gerald A Meehl,Claudia Tebaldi

doi:10.1126/science.1098704

Abstract

A global coupled climate model shows that there is a distinct geographic pattern to future changes in heat waves. Model results for areas of Europe and North America, associated with the severe heat waves in Chicago in 1995 and Paris in 2003, show that future heat waves in these areas will become more intense, more frequent, and longer lasting in the second half of the 21st century. Observations and the model show that present-day heat waves over Europe and North America coincide with a specific atmospheric circulation pattern that is intensified by ongoing increases in greenhouse gases, indicating that it will produce more severe heat waves in those regions in the future.

Highlights

A global coupled climate model shows that there is a distinct geographic pattern to future changes in heat waves
Observations and the model show that present-day heat waves over Europe and North America coincide with a specific atmospheric circulation pattern that is intensified by ongoing increases in greenhouse gases, indicating that it will produce more severe heat waves in those regions in the future
There is no universal definition of a heat wave, but such extreme events associated with hot sustained temperatures have been known to produce notable impacts on human mortality, regional economies, and ecosystems (1–3)

Summary

Simulated Composite Heat Wave

Heat waves are generally associated with specific atmospheric circulation patterns represented by semistationary 500-hPa positive height anomalies that dynamically produce subsidence, clear skies, light winds, warm-air advection, and prolonged hot conditions at the surface (15, 19). This was the case for the 1995 Chicago heat wave and 2003 Paris heat wave (Fig. 3, A and B), for which 500-hPa height anomalies of over ϩ120 geopotential meters (gpm) over Lake Michigan for 13 to 14 July 1995 and ϩ180 gpm over northern France for 1 to 13 August 2003 are significant at greater than the 5% level according to a Student’s t test. This corresponds to a similar pattern for increased standard deviations of both summertime nighttime minimum and daytime

Height Anomalies Future minus Present

Findings

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