Contrails warm the world more than aviation emissions
 Updated 17:50 12 August 2011 by Michael Marshall
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Using satellite observations of spreading contrails as a guide, Burkhardt built a model that simulated how they form, spread out and dissipate. Then she embedded it in a global climate model and watched what happened. She found that contrail cirrus ended up covering 0.6 per cent of Earth's surface an area nine times as great as that covered by line contrails.
Burkhardt then used this figure to produce a more accurate estimate of the total energy trapped by contrails. Her calculations suggest a global figure of 31 mW/m2 higher than that attributable to aviation CO2.
There is a catch, though. "[The measurement] says nothing about what will happen tomorrow," says David Lee of Manchester Metropolitan University in the UK. While a contrail lasts a day, the CO2 released from a plane lingers in the atmosphere for hundreds of years. For example, while contrails and their warming potential disappeared from European skies last April when an Icelandic volcanic ash cloud grounded flights, atmospheric CO2 continued to warm the world.
The flip side is that cutting contrails would make an immediate difference to atmospheric warming, whereas emissions cuts take years to have an effect, says Robert Noland of Rutgers University in New Brunswick, New Jersey.