Jonathan Urbach, via Facebook asked:
I read once that airplane contrails may cool the climate and that this effect was observed following the grounding of planes after the September 11 attacks. Could this effect be the basis for climate change mitigation?
Dave - I think there have been some studies done on this - there's one 3 or 4 years back - and I think they can either increase the temperature or decrease it, depending on where they are. If you're somewhere very, very sunny then they can actually reflect more heat out, than they reflect back in. I think on average, they reckon, especially in places like the UK, they tend to actually heat up the Earth more because they are acting as an insulating blanket, as cloud does, and so they actually, if anything, increase the temperature.
The actual Nature article
I think the idea is this.
Perhaps there is scope to modify the path of a landbound hurricane. Environmental conditions permitting multiple contrails could be arranged to divert an oncoming hurricane a little like the opposite of the role played by a sweeper in curling. The idea is that all things being equal (such as prevailing wind conditions,) a hurricane may tend to move toward warmer water (or away from cooler water). Contrails can cast enormous shadows which is just as well given the size of weather systems such as hurricanes. I'm aware of several hurricane modification programmes but have never seen anything like this tried. When hurricanes do land fall the insurance bill can be enormous so as wacky as it sounds it might be worth a try? Mootle, Sun, 16th Oct 2011