October 24, 2007 in Nation/World

Study links mass die-offs, global warming

Seth Borenstein Associated Press
 

WASHINGTON – Whenever the world’s tropical seas rose several degrees, Earth experienced mass extinctions over millions of years, according to 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, according to the new study published today.

“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, according to top scientists.

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 to 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 7 degrees 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.

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