Allied bombing raids during World War II "inadvertently experimented on the weather" in England by creating massive concentrations of artificial clouds as the planes roared off toward continental Europe.
Researchers quoted by New Scientist claim that "where the aircraft circled and assembled into formation," on one particular day back in 1944 for which military, meteorological, and even anecdotal eyewitness records are available, "it was significantly cloudier and 0.8°C cooler than the area upwind of the bases."
In many ways, this is both obvious and uninteresting, as, of course, any uniquely large-scale act of artificial cloud-production-such as aircraft contrails-would have at least some effect on local weather.
But what, to me, seems most remarkable about this story is the darkly poetic idea that war brings with it its own meteorology, its own skies, storms, and atmospheres, literally altering the very firmament beneath which human affairs take place. World War II becomes an even more frightening event, as sun-obliterating cloudfronts of mechanized combat roll eastward over the ruined cities of Europe.