Belching British Bogs Fueled Ancient Global Warming
Kate Ravilious in York, Britain
for National Geographic News
|September 19, 2007|
Huge belches of methane from bogs in what is now Britain likely contributed to global warming some 55 million years ago, a new study says.
The emissions probably amplified an ancient and extreme global warming event that heated Arctic Ocean waters to a balmy 73 degrees Fahrenheit (23 degrees Celsius).
The finding adds weight to the idea that methane being released from wetlands today may accelerate modern global warming.
Richard Pancost from Britain's University of Bristol and his colleagues studied the chemistry of 55-million-year-old sediments from the Cobham Lignite wetland in southeast England (see map of Britain).
By measuring the levels of organic compounds produced by bacteria, Pancost's team was able to estimate the levels of methane-eating microbes living in the bog in the distant past.
The researchers found a marked increase in a by-product left by methane-devouring microbes around 55 million years ago.
For the bacteria to have mushroomed so dramatically, Pancost and his colleagues suggest, methane emissions from the bog must have also radically increased.
The team's study will appear in tomorrow's issue of the journal Nature.
Warm, wet weather likely accelerated the rotting of plant material, which in turn triggered the methane burps from the Cobham Lignite bog, the researchers said.
Assuming that other wetlands responded in a similar way, such large amounts of methane could explain the extreme global warming seen at the time.
"If the increase in methane emissions were widespread, the increased methane flux from these settings could have amplified the warming occurring at this time," Pancost said.
Because methane is a key greenhouse gas, some scientists worry that a similar scenario today could trigger a runaway greenhouse effect. (Get the facts about global warming.)
"Methane is a much more powerful greenhouse gas than carbon dioxide, so a big and rapid release of methane from wetland deposits would represent a huge and rapid positive feedback," said Dave Reay, a climate scientist at Edinburgh University who was not affiliated with the research.
Study author Pancost agreed that methane from wetlands could play a key role in modern warming.
"There is a great deal of methane generated in wetlands by microbial activity. Warming or more precipitation could cause rates of microbially mediated methane production to increase," he said.
Methane already appears to be seeping out of once frozen bogs in Siberia.
"Our measurements have revealed methane-emission hot spots from the bogs in eastern Siberia," said Sergey Kirpotin, from Tomsk State University in Siberia, Russia, who wasn't involved with the study.
"The situation is quite serious and needs urgent investigation," he said.
Siberian permafrost has begun to melt, creating large lakes, Kirpotin explained.
"The frozen peat bogs used to be covered by white lichen, which reflected back sunlight. Now there is more brown surface water, which warms and stimulates the release of methane," he said.
Warmer, wetter weather is likely to promote methane release in wetlands worldwide, and scientists are concerned that this may make it almost impossible to keep a lid on greenhouse gas emissions.
"The wetland methane feedback effect could be equivalent to wiping out all the emissions cuts set out in the [1997 greenhouse gas reduction treaty] Kyoto Protocol," Edinburgh's Reay said.
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