Scientists have long suspected that airplane condensation trails — the wispy, white tails found in the wake of high-flying jets — form larger cloud banks that substantially alter the atmosphere’s heat balance.

These jet-generated clouds, called contrails, may in turn play an important role in shaping our weather.

For three days starting last Sept. 11, meteorological researchers were presented with just such an opportunity when the FAA grounded commercial flights nationwide for three days following the terrorist air attacks.

And now it has emerged that the American climate was indeed noticeably different during those three days without air travel. More here.