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  National Geographic 19 Sep 07
Belching British Bogs Fueled Ancient Global Warming
Kate Ravilious in York, Britain for National Geographic News

Yahoo News 19 Sep 07
Greenhouse Earth: Methane powered runaway global warming
by Richard Ingham

Methane released from wetlands turned the Earth into a hothouse 55 million years ago, according to research released Wednesday that could shed light on a worrying aspect of today's climate-change crisis.

Scientists have long sought to understand the triggers for an extraordinary warming episode called the Palaeocene-Eocene Thermal Maximum (PETM), which occurred about 10 million years after the twilight of the dinosaurs.

Earth's surface warmed by at least five degrees Celsius (nine degrees Fahrenheit) in just a few hundred or a few thousand years. The Arctic Ocean was at 23 degrees Celsius (73 degrees Fahrenheit) -- about the same as a tepid bath -- before the planet eventually cooled.

Richard Pancost, a researcher at Britain's University of Bristol, seized an opportunity to dig, literally, into this mystery.

Excavation of a site in southeast England to set down the Channel Tunnel rail link exposed layers of sediment from a bog that had existed at the time of the PETM. Pancost's team sifted through the dirt to measure the carbon isotope values of hopanoids, which are compounds made by bacteria.

They found that levels of these isotopes suddenly fell at the onset of the PETM, yielding a signature that can only be explained if the bugs dramatically switched to a diet of methane, a powerful, naturally-occurring greenhouse gas.

Reporting in the British journal Nature, Pancost believes that the methane had remained locked up in the soil for millions of years before warming released it into the atmosphere.

As atmospheric methane levels rose, so too did Earth's temperature as a result of the famous "greenhouse" effect. In turn, that released more methane, and so on.

In other words, it was a vicious circle (a "positive feedback" in scientific parlance), in which warming begat warming.

The study has relevance because of the gigatonnes of methane locked in the Siberian permafrost today. With the permafrost slowly retreating as a result of global warming, some experts fear a threshold whereby this huge stock of greenhouse gas may also be released, unleashing unstoppable climate change.

But the temperature at which this could happen is unknown and the mechanisms by which the methane is released are unclear.

Co-author Andrew Scott of Royal Holloway University of London is cautious about making parallels.

He said the onset to the PETM was far warmer than today, which makes it risky to compare then with now, especially as the data for the new paper comes from just a single site.

However, "this does provide insight into how some ecosystems would respond to warming-induced changes in climate, and, therefore how they could respond to warming in the future," said Scott.

A study published last April in the US journal Science attributed the methane to a tectonic rather than biological source -- massive volcanic eruptions in Greenland and the British Islands.

Other hypotheses include "belches" of methane released from ice-bound bubbles in sea-floor sediment.

Pancost, though, believes that a volcanic source provided the initial heat trigger that unlocked some methane stocks in the soil and thus launched the positive feedback.

He argues that the microbes' sudden switch to methane for their diet indicates they were swamped by a local source of the gas. The explanation for this is a snap release from terrestrial sources, rather than a longer release of methane from the sea or underground, according to Pancost.

Fossil and sedimentary records show that, by the time the PETM was over, around 100,000 years later, many species of fundamental life in the sea had been wiped out and there had been a ruthless culling among mammalian species on land, opening the way to the biodiversity we see today.

National Geographic 19 Sep 07
Belching British Bogs Fueled Ancient Global Warming
Kate Ravilious in York, Britain for National Geographic News

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. 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.

Runaway Warming

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. "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.

Siberian Melt

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.

Related articles on Climate change
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