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Aircraft contrails have unusual impacts on global warming

Of the varied conspiracy theories regarding contrails – you know, chemtrails – one stands out for being especially wrong: the belief that the plane-made clouds are chemicals the government is secretly spraying to battle climate change, to the peril of those on the ground.

First, contrails are nothing but the incidental result of mixing hot, water-vapor-filled jet engine exhaust with cold air. Second, the government has nothing to do with them. Most important, they’re not battling climate change. They’re accelerating it.

New experiments have shown that contrails (a condensation portmanteau and trails) will add as much or more to the warming up of the earth as all flights do.

You may think of contrails across a massive sky as tiny dots, but they can be a ton more in some circumstances. They can span tens of kilometres. They can be propagated by wind. They will last for hours. And as plane after plane follows the same path through the clouds, fresh and old contrails combine and collect, creating ice cloud airborne mosh pits. This are named “contrail cirrus” by scientists – high-altitude clouds that can extend across hundreds of square miles. And they’ll definitely become more of an issue: one analysis showed that the heat-trapping impact of contrail cirrus in 2050 may be three times higher than it was in 2006 when the air traffic rises. According to Nasa, clouds trap heat coming off the earth that would otherwise head for space, making them the largest temperature and climate variable on the planet.

Recent British work has found two bright linings of the gloomy conundrum. The first is that just 2.2 per cent of flights produce 80 per cent of the warmth correlated with the contrail.

According to a January paper in the journal Environmental Science & Technology, the troublemakers are mainly flights that take off in the late afternoon and early evening, the contrails of which live more throughout the night – when they still catch some heat but can’t block some sunlight (which can offset their impact). “The effects at night are purely warming,” says Marc Stettler, the paper’s lead author, Mitigating the Climate Forcing of Aircraft Contrails by Small-Scale Diversions and Technology Adoption. The better news, reports Stettler and his coauthors, is that with minor altitude changes, these planes can avoid making most of the contrails.

And when the air becomes highly filled with water molecules that can bind to the soot particles from the exhaust and condense of the vehicle, expand into ice crystals and enter in clouds, can contrails shape. However, often this saturation is confined to a narrow band of altitude, and by moving up or down, aircraft can find drier areas.

The mathematics of the researchers could minimize the overall environment effect of contrails by 59 percent by diverting fewer than two percent of flights either up or down by 2,000 feet or less. So compared to the CO2 that already lives the high life, contrails only do harm during their short lifespan. “It’s a really, really quick way that the aviation industry could address its impact on the climate,” says Stettler, an engineering professor at Imperial College London’s Centre for Transport Studies.

Stettler and his fellow authors focused their observations on flights over Japan in 2012 which provided the strongest details on the exact locations of individual flights that they could reach. They compared this to weather data and used a computer model this forecasts when airplanes produce contrails to see which flights will have caused the most harm.

The next move is to check that such findings are held up in certain areas of the world and to know whether modifying their flight patterns is fair for airlines. One challenge might be finding out whether a plane leaves a cloud in their path.

“There’s no mirror,” the professor of aeronautical science and airline operations at Embry-Riddle Aeronautical University, Les Westbrooks says. Stettler thinks some sort of indicator on the aircraft, that when they see the white material, pilots warn each other.

Westbrooks often suspects that airlines are able to change flight routes planned to reduce fuel usage – which accounts for nearly one-third of the costs of an airline. They ‘re impossible to sprint up and down across the world in pursuit of a perfect place.

Katherine Estep, communications director for the industry trade group Airlines for America, says airlines are working with Nasa and the FAA “to address potential contrail effects through more efficient aircraft, air traffic management strategies, and the substitution of traditional jet fuel with sustainable aviation fuel.”

Stettler’s research suggests that the recommended altitude changes will just boost fuel usage – and carbon pollution – by 0.27 per cent on such flights. Tettler calls the study a proof of concept, a reason for examining more deeply how the effects of contrails can be mitigated. Airlines are more mindful of their climate change picture than ever – see JetBlue and Delta ‘s latest carbon-neutral proclamations – and that may be an convenient opportunity to reassure the public and support the world. Only the people on the ground could steal a catchphrase: leaving no trace.

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