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Climate Hot Spot

Cleaner Air Means a Warmer Europe

By Volker Mrasek

Europe is heating up much faster than climate researchers expected, and now they think they know why: air made dramatically cleaner by anti-pollution programs. With less particle pollution clouding the air, more sunlight is coming through and the continent is getting warmer.

The 1970s were a hazy time: Cars ran on sulfur-rich gasoline, power plants and heavy industry burned sulfur-rich coal. Europe lay under a blanket of fumes filled with sulphate particles. Acid rain brought the particles back to earth, ravaging the continent's forests.

That was then. The situation today is considerably different. Auto emissions are low in sulfur, power plants only run with smoke filters and acid rain is no longer an issue. But the success of efforts to restore Europe's air quality have had an unintended side effect that is just now coming to light. Because the atmosphere over Europe is increasingly clean, global warming is impacting the continent more quickly than other regions of the world.

The dwindling clouds of pollution are apparently the reason that Europe is heating faster than other mid-latitude regions. Since 1980, the average surface air temperature between the Bosporus and the Bay of Biscay has risen by almost an entire degree Celsius -- twice as much as expected. The reasons for this were until recently a matter of heated dispute. Greenhouse gases could explain half that increase, at best. But now climate researchers in Germany, Switzerland and the United States, using data and computer simulations, claim that the rise in temperatures has been caused most directly by a decline in sulfate aerosols in the atmosphere.

Sulfates work like a filter on sunlight: They reflect short-wave solar radiation back into space, thereby letting less energy pass into the layer of air closest to the ground. But because the concentration of sulfur particles is declining so rapidly, this unintended cooling effect no longer works the way it once did -- and Europe is getting hotter. To Martin Wild of the Swiss Federal Institute of Technology Zurich (ETH Zurich), it makes perfect sense: "We have less aerosol in the atmosphere, more radiation reaching the surface of the Earth and an exorbitant increase in temperature."

At the annual conference of the European Geosciences Union (EGU), which begins on Tuesday in Vienna, climatologists and atmospheric researchers will discuss whether the trend will continue. As the air in developing regions like India and Central Africa get ever dirtier and the light penetrating the cloud of pollution dims, Europe is rapidly getting brighter.

Together with Joel Norris, an atmospheric scientist at the Scripps Institute of Oceanography in San Diego, Wild has been calculating fluctuations in European radiation levels. In the middle of the 1980s, there appears to have been a major shift. Until then, as the air became its most sulfur-laden, radiation near the surface reached all time lows of around three watts per square meter. Beginning in 1986, when efforts to clean the air began to pay off and the atmosphere became more transparent to sunlight, radiation started to increase about 2 watts per square meter in each year over the next decade.

Wild based his work on an aerosol-tracking computer simulation developed by researchers at the Max Planck Institute for Meteorology in Hamburg. "Extensive air pollution temporarily compensated for the global warming in Europe," said Johann Feichter, leader of the institute's Aerosol, Clouds and Climate working group.