Stanford researchers say climate change will significantly increase impending bird e...( Where do you go when you've reached ...)

Where do you go when you've reached the top of a mountain and you can't go back down?

It's a question increasingly relevant to plants and animals, as their habitats slowly shift to higher elevations, driven by rising temperatures worldwide. The answer, unfortunately, is you can't go anywhere. Habitats shrink to the vanishing point, and species go extinct.

That scenario is likely to be played out repeatedly and at an accelerating rate as the world continues to warm, Stanford researchers say.

By 2100, climate change could cause up to 30 percent of land-bird species to go extinct worldwide, if the worst-case scenario comes to pass. Land birds constitute the vast majority of all bird species.

''Of the land-bird species predicted to go extinct, 79 percent of them are not currently considered threatened with extinction, but many will be if we cannot stop climate change,'' said Cagan Sekercioglu, a senior research scientist at Stanford and the lead author of a paper detailing the research, which is scheduled to be published online this week in Conservation Biology.

The study is one of the first analyses of extinction rates to incorporate the most recent climate change scenarios set forth earlier this year in the reports of the Intergovernmental Panel on Climate Change (IPCC), which shared the Nobel Peace Price with Al Gore.

The researchers modeled changes to the elevational limits of the ranges of more than 8,400 species of land birds using 60 scenarios. The scenarios consisted of various combinations of surface warming projections from the 2007 IPCC report, habitat loss estimates from the 2005 Millennium Ecosystem Assessment (an evaluation of the planet's ecosystems by 1,360 experts around the world), and several possibilities of shifts in elevational range limits.

The worst-case scenario of 6.4 degrees Celsius surface warming combined with extensive habitat loss produced the estimate of 30 percent of l
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