From The New Scentist

[Andre Kesteloot]

New Scientist Environment <http://environment.newscientist.com/>


  Cleaner skies explain surprise rate of warming

    * 09 July 2008
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GOODBYE air pollution and smoky chimneys, hello brighter days. That's 
been the trend in Europe for the past three decades - but unfortunately 
cleaning up the skies has allowed more of the sun's rays to pierce the 
atmosphere, contributing to at least half the warming that has occurred.

Since 1980, average air temperatures in Europe have risen 1 °C: much 
more than expected from greenhouse-gas warming alone. Christian 
Ruckstuhl of the Institute for Atmospheric and Climate Science in 
Switzerland and colleagues took aerosol concentrations from six 
locations in northern Europe, measured between 1986 and 2005, and 
compared them with solar-radiation measurements over the same period. 
Aerosol concentrations dropped by up to 60 per cent over the 29-year 
period, while solar radiation rose by around 1 watt per square metre 
(/Geophysical Research Letters/, DOI: 10.1029/2008GL034228 
<http://dx.doi.org/10.1029/2008GL034228>). "The decrease in aerosols 
probably accounts for at least half of the warming over Europe in the 
last 30 years," says Rolf Philipona, a co-author of the study at 
MeteoSwiss, Switzerland's national weather service.

The latest climate models are built on the assumption that aerosols have 
their biggest influence by seeding natural clouds, which reflect 
sunlight. However, the team found that radiation dropped only slightly 
on cloudy days, suggesting that the main impact of aerosols is to block 
sunlight directly.

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