Clearer skies in Europe added to warming

Yahoo News 18 Jan 09;

PARIS (AFP) – Fog, mist and haze in Europe have declined over the last three decades, a trend that may have stoked regional warming and ironically could be linked to better air quality, a study published on Sunday says.

From 1978-2006, temperatures in parts of Europe rose above the global land average, with prominent increases in the north, centre and eastern parts of the continent.

As much as 20 percent of Europe's warming during this time, according to the study, can be pinned on a reduction in fog, mist and haze, which -- because they are white -- reflect solar radiation and thus keep the ground cool.

In eastern Europe, the decline in fog, mist and haze could account for 50 percent, the paper believes.

The authors, led by Robert Vautard of France's Atomic Energy Commission (CEA), pored over data from 342 weather stations around Europe.

They found that over nearly 30 years, the number of days categorised as having restricted visibility fell by half. These categories were determined by ranges of visibility at two kilometres (1.2 miles), five kms (three miles) and eight kms (five miles).

The phenomenon is closely linked to falling levels of atmospheric sulphur dioxide (S02), a byproduct of burning oil and coal that causes notorious "acid rain" that damages forests and lakes.

The temperature rise has been especially perceptible in Eastern Europe, where the end of the Communist system closed down innumerable sources of coal pollution.

However, the SO2 cleanup is now largely tapering off.

This means the fog reduction will probably stop and "the warming trend in Europe will not be so large in the coming years," Vautard told AFP.

According to the Intergovernmental Panel on Climate Change (IPCC) -- the UN's paramount authority on global warming -- the global average temperature rose 0.74 degrees Celsius (1.33 degrees Fahrenheit) from 1906-2005, and the pace in the last 50 years was double that of the first half-century.

A blanket of fog can reduce local temperatures by some 2 C (3.6 F), according to figures quoted in the new study.

Europe's lost mist 'boosts heat'
BBC News 19 Jan 09;

Quite what Keats would have made of it is anyone's guess, but "mist and mellow fruitfulness" appears to be on the decline in Europe.

The number of foggy, misty and hazy days is diminishing across the continent, say scientists who have analysed the meteorological data.

The researchers found this clearing of the air in the past 30 years may have amplified the warming of Europe.

They report their findings in the journal Nature Geoscience.

The research was led by Robert Vautard at the Atomic Energy Commission, Gif sur Yvette, France.

Since the 1970s, European temperatures have risen by about half-a-degree Celsius per decade.

This warming rate is faster than the global mean change (roughly equal to 0.18C per decade) and the trend averaged over all the Earth's land (roughly equal to 0.27C per decade) during the same period.

The regional climate models used by scientists have failed to simulate the European experience, say Vautard and colleagues; and they point to legislation that has cleaned up Europe's air as the probable cause.

This has limited the presence of the tiny particles, or aerosols, in the atmosphere which help trigger the low-visibility phenomena.

All seasons

With fewer fogs, mists and haze, more of the Sun's energy has been reaching the surface, leading to a rise a rise in temperatures, they tell Nature Geoscience.

The team's analysis suggests the clearer air's contribution to the background warming trend may have been about 10-20% across Europe as a whole; and in Eastern Europe specifically, it may have been as much as 50%.

The team looked at horizontal visibility data from 342 meteorological stations across Europe. The changes recorded affect all seasons and all distances from zero to eight km.

However, the team says the data also indicates that the decline in the low-visibility phenomena has slowed since 2000.

"We conclude that the large improvements in air quality and visibility achieved in Europe over the past decades may mean that future reductions in visibility will be limited, possibly leading to less rapid regional warming," the team write.

The group says its findings emphasise the importance of ground-level atmospheric processes in understanding the differences in regional climates.