The study ran as the cover article in Nature. In the popular press, the
welter of numbers the researchers came up with was condensed down to
just one. “Climate Change Could Drive a Million of the World’s Species to
Extinction,” the BBC declared. “By 2050 Warming to Doom a Million
Species” is how the headline in National Geographic put it.
The study has since been challenged on a number of grounds. It
ignores interactions between organisms. It doesn’t account for the
possibility that plants and animals can tolerate a broader range of
climates than their current range suggests. It looks only as far as 2050
when, under any remotely plausible scenario, warming will continue far
beyond that. It applies the species-area relationship to a new, and
therefore untested, set of conditions.
More recent studies have come down on both sides of the Nature
paper. Some have concluded that the paper overestimated the number of
extinctions likely to be caused by climate change, others that it
understated it. For his part, Thomas has acknowledged that many of the
objections to the 2004 paper may be valid. But he has pointed out that
every estimate that’s been proposed since then has been the same order
of magnitude. Thus, he’s observed, “around 10 or more percent of species,
and not 1 percent, or .01 percent,” are likely to be done in by climate
change.
In a recent article, Thomas suggested that it would be useful to place
these numbers “in a geological context.” Climate change alone “is
unlikely to generate a mass extinction as large as one of the Big Five,” he
wrote. However, there’s a “high likelihood that climate change on its own
could generate a level of extinction on par with, or exceeding, the slightly
‘lesser’ extinction events” of the past.
“The potential impacts,” he concluded, “support the notion that we
have recently entered the Anthropocene.”
“THE Brits like to mark everything in plastic,” Silman told me. “We
think it’s kind of gauche.” It was our third day on the trail, and we were