Researchers: Contrails Add More To Global Warming Than Airplane Emissions

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A woman looks up to the mass of contrails left by jet aircraft crossing the sky in England.

Matt Cardy/Getty Images

A woman looks up to the mass of contrails left by jet aircraft crossing the sky in England.

Whenever you hear someone talk about the ecological cost of flying, they're almost invariably referring to the sizable amount of fuel a plane burns and the amount of carbon dioxide it emits during flight.

Well, in a new paper in the first edition of the Nature Climate Change journal, scientists found that condensation trails or contrails left in the sky by jets "may be causing more climate warming today than all the carbon dioxide emitted by aircraft since the start of aviation."

How can this be? Wired explains:

What the authors do consider is the fact that carbon emissions are only one of the impacts of aviation. Others include the emissions of particulates high in the atmosphere, the production of nitrogen oxides, and the direct production of clouds through contrail water vapor. Over time, these thin lines of water evolve into "contrail cirrus" clouds that lose their linear features and become indistinguishable from the real thing. Although low-altitude clouds tend to cool the plant by reflecting sunlight, high altitude clouds like cirrus have an insulating effect and actually enhance warming.

In short, contrails and the cirrus clouds that emerge create a net warming effect of 31 milliwatts per square meter. Compare that to the 28 milliwatts that accumulated CO2 is responsible for.

The New Scientist provides some analysis and a caveat:

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.

Reuters adds that the findings could help governments better access penalties on planes for greenhouse emissions and it could help build smarter planes — ones that put out ice or water drops instead of vapor.