"Climate change now represents at least as great a threat to the number of species surviving on Earth as habitat-destruction and modification," said Chris Thomas, a conservation biologist at the University of Leeds in the United Kingdom.
Thomas is the lead author of the study published in tomorrow's issue of the science journal Nature. His co-authors include 18 scientists from around the world, making this the largest collaboration of its type.
Townsend Peterson, an evolutionary biologist at the University of Kansas in Lawrence and one of the study's co-authors, said the paper allows scientists for the first time to "get a grip" on the impact of climate change as far as natural systems are concerned.
"A lot of us are in this to start to get a handle on what we are talking about," he said. "When we talk about the difference between half a percent and one percent of carbon dioxide emissions what does that mean?"
The researchers worked independently in six biodiversity-rich regions around the world, from Australia to South Africa, plugging field data on species distribution and regional climate into computer models that simulated the ways species' ranges are expected to move in response to temperature and climate changes.
"We later met and decided to pool results to produce a more globally relevant look at the issue," said Lee Hannah, a climate change biologist with Conservation International's Center for Applied Biodiversity Science in Washington, D.C.
Study Results
According to the researchers' collective results, the predicted range of climate change by 2050 will place 15 to 35 percent of the 1,103 species studied at risk of extinction. The numbers are expected to hold up when extrapolated globally, potentially dooming more than a million species.
"These are first-pass estimates, but they put the problem in the right ballpark : I expect more detailed studies to refine these numbers and to add data for additional regions, but not to change the general import of these findings," said Hannah.
Writing in an accompanying commentary to the study in Nature, J. Alan Pounds of the Monteverde Cloud Forest Reserve in Costa Rica, and Robert Puschendorf, a biologist at the University of Costa Rica, say these estimates "might be optimistic."
As global warming interacts with other factors such as habitat-destruction, invasive species, and the build up of carbon dioxide in the landscape, the risk of extinction increases even further, they say.
In agreement with the study authors, Pounds and Puschendorf say taking immediate steps to reduce greenhouse gas emissions is imperative to constrain global warming to the minimum predicted levels and thus prevent many of the extinctions from occurring.
"The threat to life on Earth is not just a problem for the future. It is part of the here and now," they write.
Climate Scenarios
The researchers based their study on minimum, mid-range, and maximum future climate scenarios based on information released by the United Nation's Intergovernmental Panel on Climate Change (IPCC) in 2001.
According to the IPCC, temperatures are expected to rise from somewhere between 1.5 and more than 4 degrees Fahrenheit (0.8 and more than 2 degrees Celsius) by the year 2050.
"Few climate scientists around the world think that 2050 temperatures will fall outside those bounds," said Thomas. "In some respects, we have been conservative because almost all future climate projections expect more warming and hence more extinction between 2050 and 2100."
In addition, the researchers accounted for the ability of species to disperse or successfully move to a new area, thus preventing climate change-induced extinction. They used two alternatives: one where species couldn't move at all, the other assuming unlimited abilities for movement.
"We are trying to bracket the truth," said Peterson. "If you bracket the truth and look at the two endpoints and they give the same general message, then you can start to believe it."
Outside of the small group of researchers working directly on the impacts of climate change to species diversity, "the numbers will come as a huge shock," said Thomas.
Extinction Prevention
The researchers point out that there is a significant gap between the low and high ends of the species predicted to be on the road to extinction by 2050. Taking action to ensure the climate ends up on the low end of the range is vital to prevent catastrophic extinctions.
"We need to start thinking about the fullest of costs involved with our activities, the real costs of what we do in modern society," said Peterson.
Thomas said that since there may be a large time lag between the climate changing and the last individual of a doomed species dying off, rapid reductions of greenhouse gas emissions may allow some of these species to hang on.
"The only conservation action that really makes sense, at a global scale, is for the international community to minimize warming through reduced emissions and the potential establishment of carbon-sequestration programs," he said.
