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Climate change: Fossil record points to future mass extinctions

by Staff Writers
Paris (AFP) Oct 24, 2007
Global warming could cut a swathe through the planet's species over the coming centuries, warns a study released Wednesday that shows a link between rising temperatures and mass extinctions reaching back half a billion years.

Each of five major eras of declining biodiversity -- including one in which 95 percent of the Earth's species disappeared -- correspond to cycles of severe warming over the 520-million-year period for which there are fossil records.

If emissions of greenhouse gas rise unchecked, the predicted increase in global temperature over the next several hundred years could fall within a similar range as these peaks, said the study, published in a British journal, Proceedings of The Royal Society B.

Previous studies have either looked for patterns in climate change or the causes of particular mass extinctions. But this is the first time the two been paired together to give a perspective over such a long time.

"If our results hold for current warming -- the magnitude of which is comparable with the long-term fluctuations in Earth climate -- they suggest that extinctions will increase," lead author Peter Mayhew said in a statement.

The UN's top panel of climate scientists, which won the Nobel Peace Prize earlier this month, forecasts an average increase by 2100 of between 1.1 C (1.98 F) and 6.4 C (11.52 F), compared to 1980-99 levels.

The trio of researchers, led by Timothy Benton at the University of Leeds in northern England, used sea surface temperatures -- extrapolated from fossilized records of the oxygen and acidity levels -- to determine the fluctuations over tens of millions of years between "greenhouse" and "icehouse" periods.

They then matched this data with changes in the number of plant and animal families inhabiting Earth, also based on fossil records.

The study did not dwell on the likely causes of these bouts of warming, whether natural cycles in the earth's climate or, most recently, to the burning of fossil fuels.

But whatever the causes, the result has been consistently the same: a more or less severe culling of life on Earth.

The death toll included 47 percent of all marine genera -- the classification above species -- and 18 percent of land vertebrate families.

At the end of the Permian period, some 250 million years ago, the planet's worst mass extinction wiped out 95 percent of all species, including 70 percent of land plants, insects and vertebrae.

"Our results provide the first clear evidence that global climate may explain substantial variation in the fossil record in a simple and consistent manner," the study states.

The same correlation held true for a flourishing of new species as well, with new flora and fauna multiplying during the interstices of "greenhouse" and "icehouse" cycles.

The researchers point out that the time-scale of their study does not help in making short-term predictions.

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Greenhouse Earth: Methane powered runaway global warming
Paris (AFP) Sept 19, 2007
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.

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