Sunday, December 5
Jet Contrails: Artificial Clouds Affect the Climate
NASA has a good web page called "Astronomy Picture of the Day" with various pictures of Earth, space, and natural astronomical phenomena like aurorae, each image accompanied by a scholarly explanation.
I was digging through the archives to find some nice picture to put on my computer desktop background, and I came across this, an image of "contrail clutter" above the southeastern United States. According to the explanation, this is not just a view of benign human activity but of a potential threat to our climate. From an April NASA press release linked by the explanation:
NASA scientists have found that cirrus clouds, formed by contrails from aircraft engine exhaust, are capable of increasing average surface temperatures enough to account for a warming trend in the United States that occurred between 1975 and 1994.
"This result shows the increased cirrus coverage, attributable to air traffic, could account for nearly all of the warming observed over the United States for nearly 20 years starting in 1975, but it is important to acknowledge contrails would add to and not replace any greenhouse gas effect," said Patrick Minnis, senior research scientist at NASA's Langley Research Center in Hampton, Va. The study was published April 15 in the Journal of Climate. "During the same period, warming occurred in many other areas where cirrus coverage decreased or remained steady," he added.[. . . . . . . .]
"This study indicates that contrails already have substantial regional effects where air traffic is heavy, such as over the United States. As air travel continues growing in other areas, the impact could become globally significant," Minnis said.
Of course, reflective contrails are not air travel's only environmental impact. If you visit the AirHead emissions calculator (provided by the Center for Neighborhood Technology), compare the results of entering the default values (representing the average American) with the results of taking a single round-trip airplane flight. All other variables remaining the same, the plane trip adds a month's worth of the average American's automobile emissions to the calculated total, according to AirHead.
The very amount of energy an airliner requires to defy gravity as it does is, by the way, a large argument in favor of California's proposed high-speed rail system--that the system would satisfy the bulk of north-south travel demand by replacing most short-distance, intra-California flights with a fast transportation mode that remains on the earth's surface.