Mass-extinction study casts cloud on future
Pastor Dale Morgan
Mass-extinction study casts cloud on future*
By SETH BORENSTEIN
The 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, 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.
A second study, to be presented Sunday, links high carbon-dioxide
levels, the chief man-made gas responsible for global warming, to past
extinctions. The study was conducted by a University of Washington
scientist.
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 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 enough years, there was a die-off.
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
sees a cause and effect between warmer seas and extinctions.
Peter Ward, a University of Washington biology and paleontology
professor, said natural increases in carbon dioxide warmed the air and
ocean. The warmer water had less oxygen and spawned more microbes, which
in turn spewed toxic hydrogen sulfide into the air and water, killing
species.
Ward examined 13 major and minor extinctions in the past and found a
common link: rising carbon-dioxide levels in the air and falling oxygen
levels. Ward's study will be presented Sunday at the Geological Society
of America's annual convention in Denver.
Mayhew also found increasing carbon-dioxide levels in the air coinciding
with die-offs.
Those higher temperatures that coincided with mass extinctions are about
the same level forecast for a century from now if the world continues
its growing emissions of greenhouse gases, according to the
Intergovernmental Panel on Climate Change.
In April, the same climate panel of thousands of scientists warned that
"20 to 30 percent of animal species assessed so far are likely to be at
increased risk of extinction" if temperatures rise by about 3 to 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," said biologist
Thomas Lovejoy, president of the H. John Heinz Center for Science,
Economics and the Environment in Washington, D.C.