threatens millions of species
January 07, 2004
NewScientist.com news service
Global warming may drive a quarter of land animals
and plants to the edge of extinction by 2050,
a major international study has warned.
In the worst case scenario, between a third
to a half of land animal and plant species will
face extermination. The predictions come from
extinction models based on over 1100 species
covering a fifth of the Earth's land mass.
The bleak scenarios result from a study by
Chris Thomas at the University of Leeds, UK,
and colleagues, who have evaluated the impact
on species of mild, moderate and severe levels
of predicted climate change.
"The absolutely best case scenario - which
in my opinion is unrealistic - with the minimum
expected climate change and all of the species
moving completely into new areas which become
suitable for them, means we end up with an estimate
of nine per cent facing extinction," Thomas
told New Scientist.
This would mean about one million species would
be doomed, assuming there are 10 million species
Solid and sound
"The broad conclusions are very
solid, and very sound, and very alarming,"
says Stuart Pimm, an expert in extinctions and
biodiversity at Duke University, North Carolina,
US. "It's a hugely important paper."
Previous studies have looked at the effects
of global warming on individual species. The
new study is the most comprehensive analysis
to date, bringing together simulation studies
of where species may move in a warmer world.
The news is "not very encouraging",
Pimm told New Scientist. "It suggests that
species' extinctions following on from global
change will broadly be in the same order of
magnitude as species lost due to habitat destruction."
The World Conservation Union's Red Book lists
between 10 and 30 per cent of species as endangered
under due to habitat loss.
Thomas says the effects of climate change should
be considered as great a threat to biodiversity
as the "Big Three" - habitat destruction,
invasions by alien species and overexploitation
He says the study overturns the notion that
"climate change might simply result in
the reassembling of species around the planet,
without them dying out".
Thomas and colleagues around the world
statistically modelled the climates in which
each of the 1103 species considered currently
live. Whole groups of plant and animal species
confined to a particular region, for example,
the Amazon, were evaluated.
Endangered species would have been included
among these, as well as more common species,
so Thomas says there is no reason to suppose
that the organisms selected are unrepresentative
of species generally.
The survival of each species was then modelled
under the minimum, mid-range and maximum global
warming scenarios predicted by the Intergovernmental
Panel on Climate Change. Every species thrives
best in certain conditions involving factors
such as temperature and rainfall. So, Thomas
says, the question was then: "Where are
these same conditions going to be found?"
However, not all species would be physically
able to migrate to new locations with equivalent
conditions as the Earth hots up. And with lots
of species, the models predicted that their
new environment would be considerably smaller
than their old habitats - a basic tenet of ecology
is that smaller areas support fewer species.
Using the mid-range climate predictions, the
researchers found that by 2050 between 15 and
37 per cent of the species would be on the "slippery
slope" to extinction.
Both Thomas and Pimm agree that to curb climate
change, serious and immediate action must be
implemented at the highest intergovernmental
levels. This would include cutting emissions
of greenhouse gases, employing new energy efficient
technologies and using strategies to sequester
carbon dioxide from the atmosphere.
Journal reference: Nature (vol 427, p 145)