All the rich, earthy smells of the farm fill the air. It’s morning on May 11, 1944, and the bloodshed on the continent seems far away from this quiet field in south east England.

A distant buzz builds into a roar as suddenly it is not the bucolic scent of the soil that fills the air but hundreds of airplanes from the United States Army Air Force. The gigantic B-17 Flying Fortress bombers paint the blue sky white with their contrails. The morning ends up to be chillier than expected, as the bombers soar off to rain death on Germany.

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World War Two changed everything about life in Britain, even the weather.

Allied bombing raids leaving from Britain seem to have affected the local climatic conditions. Rob MacKenzie, now at the University of Birmingham, and Roger Timmis of the British Environment Agency looked at weather records from 1943 to 1945 and found that after massive air raids the areas the planes flew over were cooler than similar areas nearby.

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The white vapor trail left by an airplane, called a contrail, can cause weather changes. The contrails form when hot, particulate-filled airplane exhaust blasts into the cold air of the upper atmosphere, in a layer called the troposphere. Sometimes the contrails simply fade away, but they can also become seeds for larger cirrus clouds. The thin, wispy cirrus clouds block some of the sun’s rays, causing the shaded area underneath to be cooler.

“Witnesses to the huge bombing formations recall that the sky was turned white by aircraft contrails,” said MacKenzie in a Wiley-Blackwell press release.

“It was apparent to us that the Allied bombing of WW2 represented an inadvertent environmental experiment on the ability of aircraft contrails to affect the energy coming into and out of the Earth at that location,” MacKenzie said.

By looking at World War Two records, the researchers were able to look at a time when commercial and civilian air traffic was rare. In East Anglia, the Midlands and the West Country, where many of the bombing raids were launched, there were almost no other airplanes.

In 1943 the United States began basing bombing raids out of England, and there was a tremendous increase in the amount of air traffic in specific and well recorded areas. That made distinguishing airplane-influenced climate data more clearly discernible from unaffected nearby climatic conditions.

For example, on May 11, 1944, a massive number of planes flew through an otherwise clear sky in south east England. A total of 1444 aircraft were recorded. The area they flew over stayed an average .8 degrees Celsius (1.44 degrees F) cooler than surrounding areas from about 7 a.m. to 1 p.m.

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“This is tantalising evidence that Second World War bombing raids can be used to help us understand processes affecting contemporary climate,” concluded MacKenzie. “By looking back at a time when aviation took place almost entirely in concentrated batches for military purposes, it is easier to separate the aircraft-induced factors from all the other things that affect climate.”

The research was published in the International Journal of Climatology.


IMAGE 1: Fighters protected bomber formations at high altitudes where thin, freezing air made vapor trails like these left by P-47s. (Wikimedia Commons)

IMAGE 2: This is a formation of B-17F Flying Fortress bombers of USAAF 92nd Bomb Group over Europe, circa 1943. (COURTESY: United States Air Force)

IMAGE 3: These are vapor trails as a flight of B-17′s joins another flight for a long-range mission. (COURTESY: United States Air Force)