Contrail effect greater than CO2: study
Trailing effect A new study has found clouds left behind by aeroplanes are causing more global warming than the carbon dioxide they release.
Condensation trails, also known as contrails, are the white clouds that slowly spread behind an aeroplane at high altitude.
"Aircraft vapour trails form behind aircraft engines when the hot, moist air of the plume is mixing with environmental air that's colder and drier," says Dr Ulrike Burkhardt, a climate scientist at the Institute for Atmospheric Physics at the German Aerospace Centre.
That hot, moist air then freezes, and the result is a thin cirrus cloud that spreads out over time. When you consider there are tens of thousands of aircraft flights around the world every day the effect of these clouds can be cumulative.
"They trap the long-wave radiation from the Earth and therefore they warm the atmosphere," says Burkhardt.
In a study that appears today in the journal Nature Climate Change , Burkhardt and colleague Dr Bernd Kärcher, used satellite observations of spreading contrails to develop a computer model that estimates their affect on temperature.
"We've found that contrail cirrus are really a major part of the aviation climate impact," she says.
"We find that contrail cirrus are warming today the climate more than the accumulated CO2 from the past flights until now."
In other words, all the carbon dioxide emissions throughout the 108-year history of aviation is having less of an effect on global warming that the condensation trails produced by aeroplanes each day. Aviation emissions account for approximately three per cent of annual CO2 emissions from fossil fuels.
"The aviation CO2 is estimated to change the radiation by 28 milliwatts per square metre whereas contrail cirrus is about 31 milliwatts per square metre," says Burkhardt.
But there's a catch - contrails may only hang around for a few hours.
"Carbon dioxide lives longer and therefore will exert a warming even in 50 years," she says.
"But for the warming today, contrail cirrus is really the most important aviation climate change agent."
Burkhardt believes more should be done on reducing CO2 emissions from aeroplanes, as well as cutting back on condensation trails, which could be done by avoiding moist air.