There’s an interesting article over at Nature on the effect of aircraft contrails on climate. As you may remember, the lack of air travel in the days immediately following 9/11 coincided with a significant rise in average temperatures in the US. This led one group of scientists to speculate that perhaps contrails had a significant effect. No one should have concluded that this proved anything either way, because coincidence does not prove causality, and to be fair to the scientists involved they never said that it did. The media, however, latched onto the story with its customary enthusiasm and lack of rigor.

The right thing to do is, of course, to investigate possible mechanisms, and so another group of scientists has looked at the effect of clouds on climate to try to see if the type of clouds created by aircraft have significant effects. Their conclusion, as Nature reports, is that they don’t.

Note that this does not prove that air travel has no effect on climate. It simply casts doubt on one possible mechanism. But I can see where this will go. Sections of the environmental movement are already convinced that contrails are “Destroying the Planet!!!” and will assume that any evidence to the contrary is simply lies paid for by the airline industry. Meanwhile the PR flacks in that industry will be preparing material explaining how the effect of aircraft on climate has been “proven to be false”. And the people who will suffer most will be the scientists trying to make sense of all this.