Study throws new light on global warming
Thursday, September 20, 2007
METHANE released from wetlands turned the Earth into a hothouse 55 million years ago, according to research released yesterday 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 in just a few hundred or a few thousand years. The Arctic Ocean was at 23 degrees Celsius — 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.AFP
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 in just a few hundred or a few thousand years. The Arctic Ocean was at 23 degrees Celsius — 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.AFP
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