* Method for estimating species loss can be 160 pct too high
* Extinction crisis still looms - scientists
By Alister Doyle, Environment Correspondent
OSLO, May 18 (Reuters) - A projected spate of extinctions of
animals and plants this century may be less drastic than feared
because the most widely used scientific method can exaggerate
losses by more than 160 percent, a study said on Wednesday.
"Extinctions caused by habitat loss require greater loss of
habitat than previously thought," two experts, based in China
and the United States, wrote in the journal Nature.
Despite that good news, the report also endorsed past
findings that human activities are wrecking habitats from the
tropics to the Arctic, threatening the worst losses of species
since the dinosaurs.
"Our results must not lead to complacency about extinction
due to habitat loss, which is a real and growing threat,"
Fangliang He and Stephen Hubbell wrote.
The study, based on a survey of birds in the United States
and forests, suggested the most commonly used method can
exaggerate losses by more than 160 percent.
"The method has to be revised," Hubbell, of the University
of California, told a news conference.
Scientists have long struggled to project extinctions as a
rising human population shrinks habitats, for instance by
felling forests to clear land for farms or cities. Pollution and
global warming are also adding to threats.
The scientists stoked controversy by saying there was
"reason to question" a U.N.-led Millennium Ecosystem Assessment
that projected future extinctions at 1,000 to 10,000 times
current rates, and a 2004 study saying that 18 to 35 percent of
all species could be set on a path towards extinction by 2050.
Chris Thomas, the lead author of the latter study at the
University of York in England, said he had published an update
later in 2004 with a less severe extinction projection, broadly
using techniques advocated in Wednesday's report.
"It is a pity that the authors did not realise this," he
said. "And currently there is no reason for complacency that the
extinction risk from climate change will necessarily be lower"
than originally projected, he told Reuters.
Wednesday's report did not question findings by the U.N.
panel of climate scientists in 2007 -- used by governments to
guide climate policies -- that said 20 to 30 percent of species
may be "at increased risk of extinction" as temperatures rise.
For scientists, the problem is they can fairly easily count
species in an area -- adding one for each new bird, flower or
mammal they find. It is far harder to count extinctions since
that requires a judgment that the last individual has died.
Some studies in the 1970s, for instance, wrongly projected
that half of all species could be lost by 2000.
More recent studies have added the idea of an "extinction
debt", that species are doomed to die out once their habitat
shrinks beyond a critical point. The study said estimations used
by that technique were mathematically flawed.
Still, it said there was "no doubt whatsoever that the
Millennium Ecosystem Assessment has correctly identified habitat
loss as the primary threat to conserving the Earth's
biodiversity, and the sixth mass extinction might already be
upon us or imminent."
Scientists count five mass extinctions in the fossil record,
the most recent 65 million years ago when dinosaurs vanished.
(Editing by Mark Trevelyan)
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