Climatologists have found that the bomber planes used in World War II may have changed the temperature of the ground below with the contrails they left in their wake. Contrails are air vapor trails left by certain aircraft, and they affect climate by trapping heat below like a thermal barrier while reflecting incoming solar heat back up into the atmosphere. Research has shown that, by measuring the contrail information which was tracked by pilots, climatologists can measure the effect they had on global climate.
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There may, however, actually be a link between contrails and megachryometeors. We don't know for sure, but they have something to do with condensation building up in the upper layers of atmosphere, they form large balls of ice which are held up by air pressure until they reach a weight enough to fall through the pressure barrier, then they come screaming down to earth and blow up someone's house.
photo of the B-17. Those mega thingies sound like some nasty stuff! Can aircraft reach the altitudes were they form? Hitting one at 600 knots could ruin your whole day.
(guess I best add another layer to my tin foil hat)