Hmm, hadn't thought of that.Care to eyeball how much jet fuel that would burn, and thus the heating that it would produce? I wouldn't be surprised if that completely nullified the cooling.
Even the takeoff phase of a 747 flight uses about 5,000 gallons of fuel. One gallon weighs about 3kg, so that's 15,000kg.
The specific energy of jet fuel is about 43,000 kilojoules per kilogram.
So just the heat produced from the fuel required for 200,000 747s to take off would be 200,000 x 15,000 x 43,000 = 1.29 x 10^14 kilojoules.
We had 7 trillion tons of air, which is 7 x 10^15kg. So in fact the energy from the fuel would only be enough to raise the temperature of the air by 0.018ºC, or about 54 times less than the cooling from the urea.
Hey, maybe it is a plausible technique after all