One in six species at risk of extinction without action on climate change, study finds

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Earth is on a course to lose biodiversity by degrees – literally – as climate change exacts an inexorable toll on species around the globe, a new analysis suggests.

The analysis is one of the most comprehensive efforts to date to quantify something that scientists have long warned of: that the warming of the planet, primarily because of fossil fuel emissions, is having a negative impact on the viability of a growing number of plant and animal species.

The results show not only that extinction risk tracks climate change, but also that the risk accelerates as the planet warms. In the most extreme case, where global warming is allowed to proceed unabated, the analysis projects that one in six species will ultimately be at risk of extinction.

"We can now see what effects different emission strategies will have on biodiversity loss," said Mark Urban, an ecologist at the University of Connecticut who performed the analysis, published Thursday in the journal Science.

Not all species threatened by climate change will go extinct, Dr. Urban added, and those that do may persist long after the climate puts them into decline. But, armed with such the projections, he said, "we can try to pinpoint those species that are most at risk and begin to design and implement conservation strategies designed to protect them."

Other researchers caution that the study should be read with some important caveats.

"The problem with projecting the future of extinction rates is that these projections don't rest on well-known physical processes that track known atmospheric differences," said Jeremy Kerr, a professor of biology at the University of Ottawa.

Nevertheless, Dr. Kerr added, the new analysis underscores the seriousness of the problem that species face as the world warms at a rate that fast outpaces biological evolution. "We are already paying for climate change. The price is going up all the time," he said.

In preparing his analysis, Dr. Urban spent a year combing through roughly 1,000 studies that document climate impacts on multiple species around the world. He whittled that down to 131 studies that were combined to yield his global analysis.

The analysis reveals that about 2.8 per cent of species are already at risk because of climate change. Even if nations manage to curb emissions enough to hold the planet's rise in average temperature to no more than two degrees Celsius above the pre-industrial level – an internationally agreed-to target – the percentage of species at risk will grow to 5.2 per cent. A business-as-usual scenario, with little or no control on emissions, will drive that number up to 16 per cent, or one in six, the study found.

Dr. Urban said his study is still a far cry from the detailed computer models that atmospheric scientists use to forecast the physical effects of climate change on future temperature and precipitation.

However, he added it helps to narrow the range of possible outcomes for species under climate change, and helps to identify areas that are most at risk of losing species, which include South America, Australia and New Zealand.

"The value of this paper is on the fact that it put all the pieces together," said Camilo Mora, a researcher in biogeography at the University of Hawaii, who was not involved in the analysis. "What we have to ask ourselves is what else do we have to do to demonstrate the need for prompt actions on climate change?"