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Even though there are an estimated 35 million commercial airline flights per year little research has been done on the effects of aircraft emissions on global warming. Now, scientists at Stanford University have released the results of the first such study conducted in the United States to be based on actual emissions data.
Their results are unsettling but also provide new insight into the delicate physics of the atmosphere.Using emissions data from 2004 and 2006, the research team was able to determine that commercial aircraft emissions were responsible for between four and eight percent of total surface warming since records began in 1850. This, they explained, is the equivalent of 0.03-0.06 degree Celsius increase.
The situation in the Arctic is more extreme. Research showed that between 15 to 20 percent of warming in this region was caused by the vapor trails of commercial aircraft.
To reach these conclusions, Mark Jacobson, a Stanford engineer, and his team, built a model that considered "atmospheric composition, cloudiness and the physical properties of emissions, particularly of black carbon." These variables were then applied to a grid and aligned with historical data.
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The picture that emerged shows how and why emissions have a different effect on different parts of the atmosphere. Emissions, they discovered, increased the fraction of cirrus clouds where vapor trails were most prevalent but decreased the fraction in some areas by increasing the temperature and consequently decreasing the relative humidity in the lower atmosphere.
Black carbon, too, plays a key role in this process. Jacobson explained that a 20-fold decrease in black carbon emissions would completely mitigate the warming effects of aircraft emissions, and could even result in a slight cooling effect.
Politicians in Europe are already pushing for taxes and emissions limits on the commercial airline industry but, researchers explain, a more precise understanding of the effects of aircraft emissions on the atmosphere are necessary if such plans are to be effective.
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