Airplanes and Climate Change

contrails.gifFirst Richard Branson offered to use the profits from his airline and railway businesses to combat global warming. Now he suggests cutting airplane emission when planes are on the runway by towing them instead of using their own engines on the ground. Arnold Schwartzenegger, the governor of California, has offered Los Angeles airport as a test site.

This is all about CO2 emission.

Airplanes have another interesting effect on the climate. The condensation that trails airplanes has an effect like cirrus clouds, high altitude clouds that work like a thin, white blanket, trapping heat below at night and reflecting the sun’s rays during the day.

Condensation trails should therefore dampen natural temperature swings between day and night.

We have a natural experiment. After 9/11 all airplanes in the U.S. were grounded, and from the 11th til the 14th of September 2001 there was an anomalous increase in diurnal temperature ranges, that is, the difference between the daytime maximum and night-time minimum temperatures (Nature paper here, pdf).

The authors argue “that the absence of contrails was responsible for the difference between a period of above normal but unremarkable DTR [diurnal temperature range] and the anomalous conditions that were recorded…

Moreover, the 11–14 September increase in DTR was more than twice the national average for regions of the United States where contrail coverage has previously been reported to be most abundant.”

Condensation trails cover some 0.1 percent of the Earth’s overall surface, with regional concentrations as high as 20 percent.

CNN covered the story here,

“Contrails are denser and block sunlight much more than natural cirrus clouds,” said Travis, who conducted the study with Andrew Carleton of Penn State University in University Park, Pennsylvania. They reported the findings this week in the journal Nature.

“And contrails are much more prevalent when the sun is out,” he said. “When this is factored in, there is a possibility that they offset global warming, and this is what we are trying to determine now.”

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