Was the 2003 European summer heat wave unusual in a global context?

Abstract

We place the European summer heat wave of 2003 in the context of other extreme summer tropospheric temperature events from 22°N to 80°N since 1979, as well as globally using annual averages. The analysis is performed in terms of standard deviations (SD) exceeded and correlations between regional extremes and temperatures at larger spatial scales. As has been pointed out previously the heat wave was statistically unusual and was a deep tropospheric phenomenon. In this analysis we also find the following. (1) Extreme warm anomalies equally, or more, unusual than the 2003 heat wave occur regularly. (2) Extreme cold anomalies also occur regularly and occasionally exceed the magnitude of the 2003 warm anomaly in terms of the value of SD. (3) There is a correlation between global and hemispheric average temperature and the presence of warm or cold regional anomalies of the same sign (i.e., warmer than average years have more regional heat waves and colder than average years have more cold waves). (4) Natural variability in the form of El Niño and volcanic eruptions appear to be of much greater importance in causing extreme regional temperature anomalies than a simple upward trend in time. Extreme temperature anomalies in the wake of the 1997–98 El Niño were larger than the anomalies seen in summer 2003 both in area affected and SD extremes exceeded. (5) Regression analyses do not provide strong support for the idea that regional heat waves are increasing with time.