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    • New evidence confirms warming by contrails

    A new study from Germany adds weight to growing evidence that, as far as aircraft are concerned, contrails have contributed more to global warming than greenhouse gas emissions.

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    The white vapour trails, which some people find quite pretty, have always been known to trap heat, and thus contribute to global warming, but until recently it has been thought to be a relatively small amount. In 2005, the Intergovernmental Panel on Climate Change estimated the effect of contrails to be about a third of all the carbon dioxide released by aircraft since the start of aviation.

    But research in the last few years suggests the effect of contrails may be much greater. The line of thought is that the IPCC has only studied a small part of the problem, as its estimate leaves out the effect of contrails that have spread out and join normal cirrus clouds.

    Now two scientists from the Institute for Atmospheric Physics in Oberpfaffenhofen, Germany, have confirmed other estimates of the contribution of aircraft contrails to global warming by process modelling. The two, Ulrike Burkhardt and Bernd Kärcher, put the impact of contrails at around 10% more than the impact of CO2.

    ‘The significance of this study,’ said T&E programme officer Bill Hemmings, ‘is that it lends a robustness to the estimates that have been made up to now. What is clear is that cutting contrails would have an instant effect on reducing aviation’s contribution to global warming. One solution is for aircraft to fly at lower altitudes when atmospheric conditions favour contrail formation.’