Rice Paddies in China: This image shows Chinese farmers transplanting rice in paddy fields in Yunnan Province, China, July 1999. Fossil fuels, cattle, landfills and rice paddies are the main human-related sources. Previous studies have shown that new rice harvesting techniques can significantly reduce methane emissions and increase yields. Credit: Changsheng Li
Scientists face difficult challenges in predicting and understanding how much our climate is changing. When it comes to gases that trap heat in our atmosphere, called greenhouse gases (GHGs), scientists typically look at how much of the gases exist in the atmosphere.
However, Drew Shindell, a climatologist at NASA’s Goddard Institute for Space Studies, New York, NY, believes we need to look at the GHGs when they are emitted at Earth’s surface, instead of looking at the GHGs themselves after they have been mixed into the atmosphere. "The gas molecules undergo chemical changes and once they do, looking at them after they’ve mixed and changed in the atmosphere doesn’t give an accurate picture of their effect," Shindell said. "For example, the amount of methane in the atmosphere is affected by pollutants that change methane’s chemistry, and it doesn’t reflect the effects of methane on other greenhouse gases," said Shindell, "so it’s not directly related to emissions, which are what we set policies for."
Chemically reactive GHGs include methane and ozone (carbon dioxide, the most important GHG, is largely unreactive). Once methane and the molecules that create ozone are released into the air by both natural and human-induced sources, these gases mix and react together, which transforms their compositions. When gases are altered, their contribution to the greenhouse warming effect also shifts. So, the true effect of a single GHG emission on climate becomes very hard to single out.
Rob Gutro | EurekAlert!
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