There is an interesting article in this weeks ‘New Scientist.’ The article discusses the conclusion of a study by Imperial College, London: that contrails reflect enough I.R. radiation back to earth that by 2050 (assuming current air travel growth rates), contrails will cause more global warming than the carbon dioxide produced by the engines. According to the Intergovernmental Panel on Climate Change (IPCC) currently contrails contribute a similar amount to global warming directly through I.R. reflection as the engines do through CO2 production. The upshot of this is that flying aircraft at lower altitudes (FL240-310) where contrails do not generally form will cause less global warming, even though there would be a higher fuel burn. Bizarre, eh? Here is a link to the shortened online article:
http://www.newscientist.com/news/news.jsp?id=ns99992926