How Do Jet Contrails Affect Local Climates?

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Do jet contrails have an effect on local temperatures?  Andrew M. Carleton, a professor of geography at Penn State believes the answer to that question is “yes”.  Contrails are lines or trails of condensed water formed around small particles from airplane and rocket exhaust.  In order to understand how contrails affect sun penetration and temperature, Carleton and  Jase Bernhardt, a graduate student in geography at the same university took at look climate conditions for two locations in the United States: one in the South and one in the Midwest.

Carleton and Bernhardt’s research expanded on a 2002 study that looked at changes in temperature during the three days that airplane traffic was halted as a result of the terrorist attacks on September 11, 2001.  “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“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.”

Numerous contrails captured by Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite on November 25, 2006. Source: NASA.
Numerous contrails captured by Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite on November 25, 2006. Source: NASA.

To look at the effect of contrails on local climate, the researchers located areas with sustained contrails (lasting longer than four hours) using satellite imagery.  Temperature data was then pulled for that location and paired with weather data from a similar non-contrail site that broadly matched in terms of  land use-land cover, soil moisture, and synoptic air mass conditions.  Minimum and maximum daily temperatures were then compared for each paired site.  The researchers found that the contrails reduced the maximum daily temperature and raised the minimum daily temperature, reducing the total temperature range for the day.  Carleton and Bernhardt found this resulted in a six degree Fahrenheit reduction in temperature ranges in the South and a five degree reduction in range for the Midwest.

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