Contrails 'stop temperature rises'
Huge formations of allied Second World War bombers did more than inflict devastation on Dresden and other German cities - they had an impact on the climate, scientists have learned.
Experts turned to the wartime bombing raids to study the effect of thousands of aircraft on the English weather.
The missions took place at a time when skies were much less crowded than they are today, providing an opportunity to observe what difference they made to local climate.
Analysis of Met Office and military records showed a measurable impact on May 11, 1944, when 1,444 aircraft took off from airfields across south-east England into a clear sky.
Contrails from the bombers significantly suppressed morning temperature increases in areas which were heavily over-flown.
Professor Rob MacKenzie, from the University of Birmingham, who co-led the study, said: "Witnesses to the huge bombing formations recall that the sky was turned white by aircraft contrails.
"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."
The research is published in the International Journal of Climatology.
Aircraft contrails are formed when hot, aerosol-laden air from a plane's engines mix with cold air in the upper troposphere.
While some contrails swiftly disappear, others form widespread cirrus clouds which block both the sun's rays and heat energy from the ground. The effect is known as air induced cloudiness (AIC). Today's congested airways make it difficult to research AIC by comparing empty skies with those filled by aircraft.