Every time that Earth's
tropical oceans warm
by several degrees, a
period of mass
lasting millions of
The American Spark
Extinctions Linked To Global Warming
By Cliff Montgomery - Oct. 24th, 2007
Every time that Earth's tropical oceans have warmed by several degrees, a period of mass extinctions occur
lasting millions of years, state two new statistical reports on the subject.
Scientists add that it could well happen again--but that it may occur over the next several decades, rather than
over several million years.
Over the last 520 million years of world history, four out of the earth's five mass extinctions have been at least
partly caused by a warming of tropical seas--a pattern that indicates an increasingly warming world, according
to the breakthrough 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," University of York ecologist Peter Mayhew told Associated Press (AP). Mayhew is
co-author of the peer-reviewed study just published by the Proceedings of the Royal Society B, a British journal.
Our world will once again suffer through an extinction-connected warming cycle about 100 years from
now--unless greenhouse gases are curbed, add leading scientists.
Another scientific study on climate change, slated for release this Sunday, also has discovered a clear link
between elevated carbon dioxide levels--the man-made gas chiefly to blame for global warming--and previous
In the British report, Mayhew and his fellow researchers studied the past variations of world temperatures over
spans of 10 million years each; fossil records only reveal definite patterns over large spans of time. The team
then compared those variations to the different species, species families, and fundamental bio-diversity
existing at each period. The British scientists discovered more bio-diversity with cooler temperatures, and an
increased level of extinction with higher temperatures.
The research team studied the temperatures in tropical seas because only they provide a fossil record
spanning several hundred million years. The fossil evidence reveals that the earth experiences a natural
climate cycle of about 60 million years, in which it shifts from a cooler "icehouse" to a warmer "greenhouse".
Currently our world is heating up from a previous colder period.
Whenever tropical sea temperatures became about 7 degrees hotter than they now are and remained that
warm for millions of years, there were mass extinctions. But the time span of these extinctions is not always the
same, the report stated.
While the British study linked higher temperatures to mass extinctions, it did not attempt to prove a direct
cause-and-effect. Take the most recent grand-scale extinction, for instance. In that one, occurring about 65
million years ago, the world's dinosaurs became extinct. But most scientists believe the dinosaur extinctions
probably were the direct result of an asteroid collision with Earth. Mayhew--and, presumably, the rest of his
team--agrees with this theory.
But such mass extinctions apparently were already happening as temperatures were getting hotter before the
collision, Mayhew told AP. A great increase in volcanic activity--which pours huge levels of carbon dioxide into
the atmosphere--also has been cited as a possible cause for the extinction of the dinosaurs.
But the scientist who penned the second report, which focused on carbon dioxide fluctuations, told AP that he
did find a direct cause-and-effect between extinctions and warmer oceans.
University of Washington biology and paleontology professor Peter Ward told AP that natural carbon dioxide
increases warmed the earth's air and ocean in the past. Because the warmer water contained less oxygen, it
spawned more microbes. The larger scores of microbes spewed dangerous levels of toxic hydrogen sulfide into
the water and air, thus killing numerous species.
Ward's study of 13 past periods of extinction, both great and relatively small, revealed that in every case of
mass extinction, the world also suffered from increased carbon dioxide levels and decreased oxygen levels at
the same time. Ward's report is slated for presentation Sunday at the Geological Society of America's yearly
convention in Denver, CO.
Mayhew's team also discovered that an increased carbon dioxide level in the atmosphere consistently
coincided with the mass extinctions; but the British team concluded that the rising temperatures were a better
indication of decreased bio-diversity.
The tie between higher temperatures and mass extinctions will again assert itself about 100 years from now if
countries continue to increase their greenhouse gas emissions, predicts the Nobel Prize-winning
Intergovernmental Panel on Climate Change.
In April, that same panel--which consists of thousands of scientific experts--declared that "20 to 30 percent of
animal species assessed so far are likely to be at increased risk of extinction" if temperatures climb by about
3-4 degrees Fahrenheit.
"Since we're already seeing threshold changes in ecosystems with the relatively small amount of climate
change already taking place, one could expect there's going to be severe transformations," biologist Thomas
Lovejoy told AP. Lovejoy is president of the H. John Heinz Center for Science, Economics and the
Environment in Washington, DC.
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