Mass extinction

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In a study report published from the proceedings of the Royal Society.

Warming May Bring Mass Extinctions: Study

Associated Press

WASHINGTON (AP) - Whenever the world's tropical seas warm several degrees, Earth has experienced mass extinctions over millions of years, said a first-of-its-kind statistical study of fossil records.

And scientists fear it may be about to happen again -- but in a matter of several decades, not tens of millions of years.

Four of the five major extinctions over 520 million years of Earth history have been linked to warmer tropical seas, something that indicates a warmer world overall, said the study published Wednesday.

"We found that over the fossil record as a whole, the higher the temperatures have been, the higher the extinctions have been,'' said University of York ecologist Peter Mayhew, the co-author of the peer-reviewed research published in the Proceedings of the Royal Society B, a British journal.

Earth is on track to hit that same level of extinction-connected warming in about 100 years, unless greenhouse gas emissions are curbed, top scientists say.

A second study, to be presented at a scientific convention Sunday, links high carbon dioxide levels, the chief man-made gas responsible for global warming, to past extinctions.

In the British study, Mayhew and his colleagues looked at temperatures in 10-million-year chunks because fossil records aren't that precise in time measurements. They then compared those with the number of species, the number of species families and overall biodiversity. They found more biodiversity with lower temperatures and more species dying with higher temperatures.

The researchers examined tropical sea temperatures -- the only ones that can be determined from fossil records and go back hundreds of millions of years. They indicate a natural 60-million-year climate cycle that moves from a warmer "greenhouse'' to a cooler "icehouse.'' The Earth is warming from its current colder period.

Every time the tropical sea temperatures were about four degrees C warmer than they are now and stayed that way for millions of enough years, there was a die-off. How fast extinctions happen varies in length.

The study linked mass extinctions with higher temperatures but did not try to establish a cause-and-effect. For example, the most recent mass extinction, the one 65 million years ago that included the die-off of dinosaurs, probably was caused by an asteroid collision as scientists theorize and Mayhew agrees.

But extinctions were likely happening anyway as temperatures were increasing, Mayhew said. Massive volcanic activity, which releases large amounts of carbon dioxide, has also been blamed for the dinosaur extinction.

The author of the second study, which focuses on carbon dioxide, said he does see a cause-and-effect between warmer seas and extinctions

Last Updated: Wednesday, October 24, 08:22 AM EDT

Warming May Bring Mass Extinctions: Study

Associated Press