Methane on the rise


Wetland input: A waterfall on Siberia's Kutamarakan River. One explanation is that unusually warm conditions over Siberia throughout 2007, led to an increase in methane from bacteria in thawed wetlands.

Credit: iStockphoto

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One surprising feature of this recent growth in methane, said the researchers, is that it appears the rise was the same at locations across the globe. However, the majority of methane is pumped into the Northern Hemisphere, which means that emissions are likely not the sole cause.

Warmer wetlands

According to the researchers, a rise in Northern Hemispheric emissions may be a result of very warm conditions 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.

An alternative explanation for the rise may lie, at least in part, with a drop in the concentrations of methane-destroying free radicals in the atmosphere.

Theoretical studies show that if this has happened, the required global methane emissions rise would have been smaller and more strongly biased to the Northern Hemisphere. More data is needed, though, to test if there was a drop in the level of hydroxyl concentrations.

Trend or anomaly?

"The key is to determine more precisely the relative roles of increased methane emission versus a decrease in the rate of removal. Apparently we have a mix of the two, but we want to know how much of each is responsible for the overall increase," Prinn said.

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 Rigby and Prinn.

Given that methane is about 25 times stronger as a greenhouse gas per metric ton of emissions than carbon dioxide, the situation will require careful monitoring in the near future to better understand methane's impact on future climate change.

With NASA and MIT

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