Allied bombing raids during the second world war inadvertently experimented on the weather by producing huge contrails over south-east England. A study of one 1944 raid offers a rare opportunity to check our models of how contrails change temperatures.
After listening to a radio programme in which an elderly woman recalled seeing a wartime sky "turn white with clouds" as fleets of bombers took off, Roger Timmis of Lancaster Environment Centre in the UK realised that the planes could have affected the weather.
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