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Methane on the rise

Climate changeThe amount of methane in Earth's atmosphere shot up in 2007. This brings to an end a decade in which levels were relatively stable says a report in the journal Geophysical Review Letters.

Siberia

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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SYDNEY: The amount of methane in Earth's atmosphere shot up in 2007. This brings to an end a decade in which levels of the potent greenhouse gas were relatively stable says a report in the journal Geophysical Review Letters.

Methane levels in the atmosphere have more than tripled since pre-industrial times. Though much less methane is generated than carbon dioxide, it is more effective - 25 times so - at trapping heat from the sun, accounting for around 20 per cent of the human contribution to greenhouse gas-driven global warming.

Atmospheric cleanser

Methane is produced by wetlands, rice paddies, cattle, and the gas and coal industries. It is destroyed in the atmosphere by reaction with a chemical called an hydroxyl free radical, often referred to as the atmosphere's 'cleanser'.

Until recently, experts thought that the methane produced by human activity was being roughly balanced by the rate of its destruction by the free radical in the atmosphere.

However, the new study reports that something has upset this balance since early 2007. The paper's lead authors, Matthew Rigby and Ronald Prinn both of the Massachusetts Institute of Technology, in Boston, US, say this imbalance has already resulted in several million tons of additional methane in the atmosphere.

Compensating effect

"This increase in methane is worrisome because the recent stability of methane levels was helping to compensate for the unexpectedly fast growth of carbon dioxide emissions," said climate modeller Drew Shindell at NASA's Goddard Institute for Space Studies in New York City.

"If methane continues to increase rapidly, we'll lose that offsetting effect. We will use NASA's climate modelling capability to improve our understanding of what is causing the increase and project future methane levels," said Shindell who is involved with a NASA network that collected the data for the study.

The scientists analysed air samples collected by this Advanced Global Atmospheric Gases Experiment ground network from 1997 through April 2008. The network was created in the 1970s in response to international concerns about chemicals depleting the ozone layer.

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