Nature Geosci. 10.1038/ngeo414 (2009)

During the past 30 years, the skies of Europe have become clearer. Robert Vautard of the Laboratory for Climatic and Environmental Science (LSCE) in Gif-sur-Yvette, France, and his colleagues studied records of visibility at weather stations across the continent. They found that low-visibility conditions such as fog, mist and haze have declined by as much as 50% over the period. The pattern of improvement is correlated with local declines in sulphur dioxide emissions, suggesting a role for pollution control.

This brightening of the skies, the researchers say, could have contributed to Europe's reported daytime warming during that time by 10–20%, with a particularly marked effect in eastern Europe.