Summer heat waves ‘likely to become the norm’

Severe heat waves lasting five or more days are likely to become an annual occurrence in Britain as the climate warms, with peak temperatures increasing by up to 10 degrees C - more than previously forecast.

When atmospheric CO2 concentration doubles compared to pre-industrial levels, European countries including Britain will face soaring temperatures like those experienced last July several times each summer, according to a new modeling study from the Met Office.

At present prolonged heat waves lasting five days and more only occur once in every 20 years. In a double CO2 world, more frequent and severe heat waves are also expected across North and South America, researchers from the Met Office’s Hadley Centre said.

Scientists predict a doubling of atmospheric carbon dioxide concentration over the course of this century, but how average and peak temperatures will rise in response to this change are two distinct although connected issues.

CO2 concentrations have already increased from the pre-industrial level of 280 parts per million (ppm) to 367 in 1990 – more than they had ever reached over the previous 420,000 years and most likely also the past 20 million years.

The modelling study, which involved several simulations of the future evolution of the climate, also looked at the way that rising temperatures were affecting the frequency and strength of heat waves.

It found that soils which would normally buffer some of the heat became drier as climate heated up, losing some of their ability to absorb atmospheric heat during the night.

The results are published in the paper Modeling Northern Hemisphere Summer Heat Extreme Changes and Their Uncertainties Using a Physics Ensemble of Climate Sensitivity Experiments, by Robin Clark, Simon Brown & James Murphy, in the current issue of the Journal of Climate.

Goska Romanowicz

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