permaculture

["Lawrence F. London, Jr." <lflj@intrex.net>]

<http://news.bbc.co.uk/2/hi/science/nature/6929668.stm>
Last Updated: Saturday, 4 August 2007, 13:40 GMT 14:40 UK
European heatwaves 'have doubled'
By Paul Rincon
Science reporter, BBC News

Aftermath of wildfires in Greece, AP
Wildfires during heat waves can ravage countryside
The duration of heatwaves in Western Europe has doubled since 1880, a study 
has shown.

The authors of the research also discovered that the frequency of extremely 
hot days has nearly tripled in the past century.

The study shows that many previous assessments of daily summer temperature change underestimated heatwaves in Western 
Europe by about 30%.

The research appears in the Journal of Geophysical Research - Atmospheres.

The team found that heatwaves lasted an average of three days now, with some lasting up to 13 days. This compares with 
an average of about 1.5 days in 1880.

Paul Della-Marta, from MeteoSwiss in Zurich, Switzerland, and colleagues analysed daily maximum temperature data from 54 
recording stations across Europe.

        
We're getting stronger heat waves or perhaps summers that are not so strong in terms of heat - this is a major cause for 
concern
Paul Della-Marta, MeteoSwiss

Forty-six hold records dating back to the 19th Century; others go back to the early 1900s. The data sets come from as 
far north as Finland, as far south as Spain and as far east as Croatia.

In the past, however, thermometers were not kept in modern Stevenson screens.

These wooden shelters protect thermometers from direct sunlight and indirect radiation coming from the ground, both of 
which distort temperature readings.

Once the researchers had corrected for these effects, they found a "warm bias" in observations made prior to the 
introduction of these screens. In other words, temperatures were recorded as being hotter than they really were.

This in turn meant the increase in temperature over time appeared to be 
smaller than it actually was.

Hot zone

The authors of the latest study also corrected for other biases in the 
variability of summer temperatures.

Temperature in Budapest, Hungary, this year, AP
We can expect more extremes of temperature in future
"After looking at the records more closely, we believe... heat waves have been underestimated by about 30% over the 
entire Western European region," Dr Della-Marta told the BBC News website.

"We see a doubling of the length of heatwaves and we also see a tripling in the 
frequency of one-off events."

The results support the idea that the western European climate in summer is becoming more variable - that the range of 
temperatures had increased. "That means we're getting stronger heatwaves or perhaps summers that are not so strong in 
terms of heat," Dr Della-Marta explained, "this is a major cause for concern."

The heatwave experienced by Europe in 2003 had major adverse socio-economic 
and environmental effects.

Thousands of elderly people died. Forests were devastated by fire, water ecosystems were strained, and the total mass of 
Alpine glaciers shrank by 10%.

The authors say we can expect extreme weather events like this to occur more 
frequently in future.

The paper's other authors were Malcolm Haylock of the Climate Research Unit at the University of East Anglia, UK, Jurg 
Luterbacher and Heinz Wanner, both of the University of Bern, Switzerland.

Paul.Rincon-INTERNET@bbc.co.uk

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RELATED INTERNET LINKS
Journal of Geophysical Research - Atmospheres
Impacts of 2003 Summer Heatwave, Unep
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