From: Winfield Winter, ENN
Published June 26, 2014 10:40 AM

Choosing the Right Path: How Air Travel Affects Climate Change

It has been well documented that one negative of air travel — besides the food — is the emission of CO2 from jet engines. But what about contrails?

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Dr. Emma Irvine, Professor Keith Shine, and Professor Sir Brian Hoskins, at the Department of Meteorology at the University of Reading have linked contrails to global climate change in a study published in IOP Publishing's journal Environmental Research Letters.

According to their report, contrails may have a greater radiative forcing (the capacity for an agent to enact climate change via warming) than CO­2.

Contrails are the visible trails of condensed water vapor that form from aircraft at high altitudes, making their effects on the atmosphere similar to those of clouds. Contrails work to increase Earth's albedo, reflecting incoming short-wave radiation from the sun and cooling the earth. However, contrails also act as a greenhouse gas to trap outgoing long-wave radiation and heat the earth. Measurements have been made in support of the latter outweighing the former, making contrails an agent of global warming.

Therefore, Dr. Irvine et al. discuss the possible trade-off between contrails and CO2, suggesting that there is a way to minimize radiative forcing by re-routing planes. Their argument is laid out as follows:

Contrails form predominantly near high-pressure systems with cold, moist air. Specifically, these are ice-supersaturated regions (ISSRs) — many of which coincide with the heavily-trafficked North Atlantic. Research predicts that if a plane leaving from New York City were to deviate slightly from its flight path to London in order to avoid a region where contrails form, the plane could reduce its effect on global warming at the cost of a little more fuel.

Still, the relative impact on climate change from contrails and CO2 is challenging to predict. There are too many variables lost in the clouds.

For example, smaller planes can travel farther out of their way to avoid ISSRs than larger planes and use the same amount of fuel. Also, planes could avoid fuel-efficient cruising altitudes where contrails form in favor of lower altitudes where they don't. This multiplicity makes it difficult for a practical model to be put in place.

Another concern is uncertainty. The world does not have the infrastructure to monitor the formation of contrails — which have less-than-one-day lifespans. Neither does the world have precision to map flight-by-flight weather patterns for the potential of contrail-formation associated with ascending air in high-pressure systems.

What we do have, courtesy of Dr. Irvine et al., is a basic model to further look into the conundrum that is contrails. 

Read more at Environmental Research Letters.

Contrails image via Shutterstock.

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