last
updated 31st August 05
by 4ecotips.com
 NCAR
climate model reveals all
Scientists at the National Center
for Atmospheric Research (NCAR) have
created a computer simulation showing
Earth's climate in unprecedented detail
at the time of the greatest mass extinction
in the planet's history.
The work gives support to a theory
that an abrupt and dramatic rise in
atmospheric levels of carbon dioxide
triggered the massive die-off 251
million years ago. The research appears
in the September issue of Geology.
“The results demonstrate how
rapidly rising temperatures in the
atmosphere can affect ocean circulation,
cutting off oxygen to lower depths
and extinguishing most life,”
says NCAR scientist Jeffrey Kiehl,
the lead author.
Kiehl and co-author Christine Shields
focused on the dramatic events at
the end of the Permian Era, when an
estimated 90 to 95% of all marine
species, as well as about 70% of all
terrestrial species, became extinct.
At the time of the event, higher-latitude
temperatures were 18o to 54o Fahrenheit
(10 o to 30 o C) higher than today,
and extensive volcanic activity had
released large amounts of carbon dioxide
and sulfur dioxide into the atmosphere
over a 700,000-year period.
 To
solve the puzzle of how those conditions
may have affected climate and life
around the globe, the researchers
turned to the Community Climate System
Model (CCSM). One of the world's premier
climate research tools, the model
can integrate changes in atmospheric
temperatures with ocean temperatures
and currents. Research teams had previously
studied the Permian extinction with
more limited computer models that
focused on a single component of Earth's
climate system, such as the ocean.
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.
 "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.
The CCSM's simulations showed that
ocean circulation was even more stagnant
than previously thought. In addition,
the research demonstrated the extent
to which computer models can successfully
simulate past climate events. The
CCSM appeared to correctly capture
key details of the late Permian, including
increased ocean salinity and sea surface
temperatures in the high latitudes
that paleontologists believe were
14 o F (8 oC) higher than present.
Helen Briggs, BBC News science reporter,
points out that until recently, computer
models of past climate have been hampered
by the difficulty of accounting for
complex interactions between the various
components of the Earth's climate
system.
She spoke to Professor Paul Wignall,
of the University of Leeds, UK, who
studies the Permian-Triassic boundary.
He says the models have not been sophisticated
enough to recreate such “lethal
super-greenhouse climates”.
“I suspect many in the modelling
community have been sceptical about
just how bad conditions were 250 million
years ago, even though the evidence
is in the rocks; but now the latest
climate system modelling is able to
replicate climatic conditions that
came close to destroying life on Earth.”
Pictures show NCAR scientist Jeffrey
Kiehl and trilobites which were one
of the groups wiped out in the extinction
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