Wednesday, March 30, 2011
How is the Air up There?
With respect to the environment, climatologists have long wondered whether contrails (e.g., condensation or vapor trails) from the thousands of jetliners airborne over the United States each day cool or heat the atmosphere.
Climatologists had an unprecedented opportunity to study that issue when all airline activity in the nation was grounded on September 11, 2001. Several studies now suggest that “contrails can suppress both daytime highs (by reflecting sunlight back to space) and nighttime lows (by trapping radiated heat). That is, they can be both cooling and warming clouds.”
Indeed, it is popular news that aviation emissions now account for about three percent of annual CO2 emissions from fossil fuels.
In a paper published this week by two researchers of the DLR German Aerospace Center in the journal Nature Climate Change, it appears
[a]viation makes a significant contribution to anthropogenic climate forcing. The impacts arise from emissions of greenhouse gases, aerosols and nitrogen oxides, and from changes in cloudiness in the upper troposphere. An important but poorly understood component of this forcing is caused by ‘contrail cirrus’—a type of cloud that consist of young line-shaped contrails and the older irregularly shaped contrails that arise from them. Here we use a global climate model that captures the whole life cycle of these man-made clouds to simulate their global coverage, as well as the changes in natural cloudiness that they induce. We show that the radiative forcing associated with contrail cirrus as a whole is about nine times larger than that from line-shaped contrails alone. We also find that contrail cirrus cause a significant decrease in natural cloudiness, which partly offsets their warming effect. Nevertheless, net radiative forcing due to contrail cirrus remains the largest single radiative-forcing component associated with aviation. Our findings regarding global radiative forcing by contrail cirrus will allow their effects to be included in studies assessing the impacts of aviation on climate and appropriate mitigation options
Meanwhile, many passengers will remember when, in April 2010, all commercial aviation to-and-from Europe was shut down for six days as the Eyjafjallajokull volcano in Iceland erupted, throwing volcanic ash several kilometers into the atmosphere, creating a humongous ash cloud over Europe, and causing the biggest closure of airspace in peacetime. Once operations normalized, airlines and passengers alike demanded compensation for the extensive delay and disruption caused by the air space ban (estimated to have cost the industry more than £1 billion).
Where weather is a contributing factor to an aviation accidents, litigation frequently centers on issues of weather reporting, air traffic control, and responsibility for weather forecasting. See, e.g., United States Aviation Underwriters, Inc. v. United States, 569 F.3d 1296 (11th Cir. 2009).
While technological changes, including new jet engine technology, and air traffic control procedures are in the works and may help to alleviate aviation environment concerns, it will be interesting to see how the law responds -- traditionally, it has favored the expansion of air travel on grounds of commerce and practicality.