Contrails Force Temperatures to Rise

(Plum Pine via Flickr)

(CN) – A study released Thursday finds that clouds formed by condensation trails from airplanes contribute most of the global warming caused by air traffic and predicts that by 2050 the contrails’ effects on climate will triple from those in the year studied.

The study, published Thursday in scientific journal Atmospheric Chemistry and Physics, calls for changes to reduce the ice crystals the contrails produce, which would ease overall effects.

“This would enable international aviation to effectively support measures to achieve the Paris climate goals,” said study co-author Lisa Bock, of the German Aerospace Center DLR, in a statement.

Though often ignored as contributors to gradual rise of the average temperature across the planet, contrails have added more warmth to the lower atmosphere than all the CO2 airplanes have ever emitted.

Contrails that last more than 10 minutes in the upper troposphere form icy cirrus clouds. The icy clouds interfere with radiation that shines down from the sun and radiation that rises from Earth’s surface.

The difference between energy absorbed by Earth and energy sent back upward is a measure called radiative forcing. With a positive net gain, there is warming.

In 2005, air traffic was responsible for about 5% of human-caused radiative forcing. The contrails contributed to most of that.

While projecting a fourfold increase in airplane traffic from 2006 to 2050, and allowing for expected decreases in CO2 emissions, researchers find that the contrail contribution will rise faster than that of CO2.

Carbon dioxide, water vapor, methane and nitrous oxides in the atmosphere create a blanket that warms Earth’s surface and changes global weather patterns. The Paris Agreement and related endeavors, such as the UN Corsia plan to offset carbon emissions from aviation, do not deal much with contributors other than carbon, as carbon is the major culprit. But the study suggests more can be done.

A reduction of soot in airplane emissions would lead to a decrease in ice crystals, which would lessen the overall impact of the contrail increase. Yet, soot is projected to decrease by 50%, and researchers say more like 90% is needed.

“It is important to recognize the significant impact of non-CO2 emissions, such as contrail cirrus, on climate and to take those effects into consideration when setting up emission trading systems or schemes like the Corsia agreement” Bock said.

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