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Fog clears, Europe warms [updated]

londonfog.jpgAh, January in London. It’s gray. It’s clammy and damp. As I write, it’s begun to bucket rain unreservedly and, in my view, rather un-Britishly. Where’s the fog?

Heading here from the US last winter, I vaguely expected Dickensian mists to greet me. It was only after expatriation that I learned the old ‘pea-soupers’ were laden with noxious coal smoke, dispelled by environmental laws after a particularly deadly fog in 1952. Now a new paper in Nature Geoscience (subscription) quantifies similar trends across Europe – and the warming that has resulted.

Averaging visibility data from 342 weather stations across Europe, Robert Vautard at the Atomic Energy Commission in France and colleagues found what they call a “massive decline” – of roughly 50% – in foggy, misty and hazy days when visibility fell below 8 kilometres, 5 kilometres or 2 kilometres. [Update: That decline was over the last 30 years.]

The trend is particularly pronounced in eastern Europe. Tellingly, three available long time series show that visibility in Potsdam, in the former East Germany, didn’t start improving until sulphur dioxide emissions dropped off with the decline of the communist economy – noticeably later than the turnaround in the Netherlands and Switzerland. When Vautard et al. compare their visibility records to an inventory of SO2 emissions, they find that places with greater reductions in the pollutant from 1990-2000 also had greater increases in visibility.

Fog forms around airborne particles, including pollutants, Dave Britton of the UK Met Office explains to the Guardian: “Go back to the 1950s and the big pea-soupers in London came from the amount of crap that people were putting out of their chimneys from coal fires.” Since then measures like London’s Clean Air Acts have played a role in clearing things up.

But they also may have inadvertently warmed the continent, the authors say. A standing problem in climate science is to account for the 0.5 C average temperature rise in Europe in the last three decades, which models don’t reproduce. Correlations between visibility and temperature suggest that lifting the fog could have contributed 10-20% of daytime temperature rises in Europe overall, and about half in central and eastern Europe.

The authors add that more sophisticated regional modelling is needed to understand the link between pollution, fog and temperature. But their correlations play into the idea that “global dimming” (Nature News, subscpription) from aerosol pollutants has suppressed global warming until recent cleanups. The visibility trend has slowed in Europe since 2000, Vautard et al. note, as anti-smog regulations have done their work. But there’s no word from this team on how dealing with pollution in developing countries might affect regional temperature trends to come.

Anna Barnett

Photo: Flickr user King Coyote, Creative Commons


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