Jet contrails affect surface temperatures

Space Daily: High in the sky where the cirrus ice crystal clouds form, jet contrails draw their crisscross patterns. Now researchers have found that these elevated ice cloud trails can influence temperatures on the ground and affect local climate, according to a team of Penn State geographers.

"Research done regarding September 2001, during the three days following 9-11 when no commercial jets were in the sky, suggested that contrails had an effect," said Andrew M. Carleton, professor of geography. "But that was only three days. We needed to look longer, while jets were in the air, to determine the real impact of contrails on temperature and in terms of climate." "Certain regions of the U.S. have more favorable atmospheric conditions for contrails than others, " said Jase Bernhardt, graduate student in geography.

For contrails to form, the atmosphere at the level the jet is flying must be cold enough that the moisture from the jet exhaust freezes into ice crystals. There also must be enough moisture in the air that the clouds that form remain in the sky for at least a few hours as persisting contrails.

Bernhardt and Carleton looked at temperature observations made at weather station sites in two areas of the U.S., one in the South in January and the other in the Midwest in April. They paired daily temperature data at each contrail site with a non-contrail site that broadly matched in land use-land cover, soil moisture and air mass conditions. The contrail data, derived from satellite imagery, were of persisting contrail outbreaks. The researchers reported their results in a recent issue of the International Journal of Climatology.

They found that contrails depress the difference between daytime and nighttime temperatures, typically decreasing the maximum temperature and raising the minimum temperature. In this respect, the contrail clouds mimic the effect of ordinary clouds....

US Air Force photo

Re-routing flights could reduce climate impact, research suggests

EurekAlert via the Institute of Physics: Aircraft can become more environmentally friendly by choosing flight paths that reduce the formation of their distinctive condensation trails, new research suggests.

In a study published today, 19 June 2014, in IOP Publishing's journal Environmental Research Letters, researchers from the University of Reading have shown that aircraft contribute less to global warming by avoiding the places where the thinly shaped clouds, called contrails, are produced – even if that means flying further and emitting more carbon dioxide.

Contrails only form in regions of the sky where the air is very cold and moist, which is often in the ascending air around high pressure systems. They can sometimes stay in the air for many hours, eventually spreading out to resemble natural, wispy clouds.

The findings suggest that policymakers need to consider more than carbon emissions in discussions about how to make aviation less environmentally damaging. Recent research has shown that the amount of global warming caused by contrails could be as large, or even larger, that the contribution from aviation CO2 emissions.

The work was carried out by Dr Emma Irvine, Professor Keith Shine, and Professor Sir Brian Hoskins, at the Department of Meteorology at the University of Reading. Dr Irvine said: "If we can predict the regions where contrails will form, it may be possible to mitigate their effect by routing aircraft to avoid them. Our work shows that for a rounded assessment of the environmental impact of aviation, more needs to be considered than just the carbon emissions of aircraft."...

An Airbus in flight, shot by greg Yablin, Wikimedia Commons via Flickr, under the Creative Commons 2.0 licemse