The amount of methane in Earth's atmosphere shot up in 2007, bringing to an end a period of about a decade in which atmospheric levels of the potent greenhouse gas were essentially stable, according to a team led by researchers from Massachusetts Institute of Technology.
Methane levels in the atmosphere have more than doubled since pre-industrial times. Until recently, the leveling off of methane levels had suggested that the rate of its emission from the Earth's surface was approximately balanced by the rate of its destruction in the atmosphere.
However, since early 2007 the balance has been upset, according to a paper on the new findings being published this week in Geophysical Review Letters. This imbalance has resulted in several million metric tons of additional methane in the atmosphere, the authors reported.
Methane is produced by wetlands, rice paddies, cattle, and the gas and coal industries, and is destroyed by reaction with the hydroxyl free radical (OH), often referred to as the atmosphere's "cleanser".
One surprising feature of this recent growth is that it occurred almost simultaneously at all measurement locations across the globe.
A rise in Northern Hemispheric emissions may be due to the very warm conditions that were observed over Siberia throughout 2007, potentially leading to increased bacterial emissions from wetland areas. However, a potential cause for an increase in Southern Hemispheric emissions is less clear.
To help pin down the cause of the methane increase, lead researcher Ronald Prinn said, "the next step will be to study this using a very high-resolution atmospheric circulation model and additional measurements from other networks." But doing that could take another year, he said, and because the detection of increased methane has important consequences for global warming the team wanted to get these initial results out as quickly as possible.
"The key thing is to better determine the relative roles of increased methane emission versus an increase in the rate of removal," Prinn said. "Apparently we have a mix of the two, but we want to know how much of each" is responsible for the overall increase.
It is too early to tell whether this increase represents a return to sustained methane growth, or the beginning of a relatively short-lived anomaly, according to the report. Given that, pound for pound, methane is 25 times more powerful as a greenhouse gas than carbon dioxide, the situation will require careful monitoring in the near future. |
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