Could humans recreate Permian-like extinction?-IPT

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Global warming may have triggered worst mass extinction
mongabay.com, National Center for Atmospheric Research release
August 29, 2005


SUMMARY: A dramatic rise in carbon dioxide 250 million years ago may have caused global temperatures to soar and result in Earth's greatest mass extinction, according to a study published in the September issue of Geology. Global warming, which may have produced temperatures 10 to 30 degrees Celsius higher than today, would have had a significant impact both on oceans, where about 95% of lifeforms became extinct, and on land, where almost 75% of species died out.

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The CCSM indicated that ocean waters warmed significantly at higher latitudes because of rising atmospheric levels of carbon dioxide (CO2), a greenhouse gas. The warming reached a depth of about 10,000 feet (4,000 meters), interfering with the normal circulation process in which colder surface water descends, taking oxygen and nutrients deep into the ocean.

As a result, ocean waters became stratified with little oxygen, a condition that proved deadly to marine life. This in turn accelerated the warming, since marine organisms were no longer removing carbon dioxide from the atmosphere.

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"The implication of our study is that elevated CO2 is sufficient to lead to inhospitable conditions for marine life and excessively high temperatures over land would contribute to the demise of terrestrial life," the authors concluded in the article.

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Methane hydrate gasification

In 2002, a BBC2 'Horizon' documentary, 'The Day the Earth Almost Died' summarized some recent findings and speculation concerning the Permian extinction event. Paul Wignall examined Permian strata in Greenland, where the rock layers devoid of marine life are tens of meters thick. With such an expanded scale, he could judge the timing of deposition more accurately and ascertained that the entire extinction lasted merely 80,000 years and showed three distinctive phases in the plant and animal fossils they contained. The extinction appeared to kill land and marine life selectively at different times. Two periods of extinctions of terrestrial life were separated by a brief, sharp, almost total extinction of marine life. Such a process seemed too long, however, to be accounted for by a meteorite strike. His best clue was the carbon isotope balance in the rock, which showed an increase in carbon-12 over time. The standard explanation for such a spike – rotting vegetation – seemed insufficient.

Geologist Gerry Dickens suggested that the increased carbon-12 could have been rapidly released by upwellings of frozen methane hydrate from the seabeds. Experiments to assess how large a rise in deep sea temperature would be required to gasify solid methane hydrate suggested that a rise of 5°C would be sufficient. Released from the pressures of the ocean depths, methane hydrate expands to create huge volumes of methane gas, one of the most powerful of the greenhouse gases. The resulting additional 5°C rise in average temperatures would have been sufficient to kill off most of the life on earth.

Sudden release of methane hydrate has also been hypothesized as a cause of the Paleocene-Eocene Thermal Maximum extinction event.

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Edited by: AAdmin  at: 8/16/07 6:25 am

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Edited by: AAdmin  at: 8/27/07 5:42 pm