In a boost to the CO2 mass extinction idea, a computer simulation of the Earth's climate 250 million years
ago suggests that global warming triggered the so-called "great
dying" in the Permian-Triassic boundary extinction.
A dramatic rise in carbon dioxide caused temperatures to soar to
between 10 to 30 degrees Celsius higher than today, US researchers
found. The warming had a profound impact on the oceans, cutting off
oxygen to the lower depths and extinguishing most lifeforms.
The research added to the growing body of evidence that higher
temperatures, rather than a giant space rock hitting the planet, led
to the greatest mass extinction in history.
The extinction, at the end of the Permian Period and the
beginning of the Triassic, had puzzled scientists for many years. Some 95% of lifeforms in the oceans became extinct, along with
about three-quarters of land species.
Many possible reasons for this catastrophic event have been
proposed - including impacts, volcanism, climate change and
glaciation. Hard evidence, however, has been difficult to find.
This latest data from scientists at the National Center for
Atmospheric Research (NCAR) in Boulder, Colorado, supported the view
that extensive volcanic activity over the course of hundreds of
thousands of years released large amounts of carbon dioxide and
sulphur dioxide into the air, gradually warming up the planet.
The NCAR team used a research tool known as the Community
Climate System Model (CSSM) which looks at the combined effects of
atmospheric temperatures, ocean temperatures and currents.
Their work indicated that temperatures in higher latitudes rose
so much that the oceans warmed to a depth of about 3,000m
This interfered with the circulation process that takes colder
water, carrying oxygen and nutrients, into lower levels. The water
became depleted of oxygen and was unable to support marine life.
"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," Jeffrey Kiehl and colleagues wrote in Geology.
Until shortly before this study, computer models of past climate had been
hampered by the difficulty of accounting for complex interactions
between the various components of the Earth's climate system.
Professor Paul Wignall, of the University of Leeds, UK, who
studies the Permian-Triassic boundary, said the models had not been
sophisticated enough to recreate such "lethal super-greenhouse
"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," he said.