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. In one of the first analyses of extinction rates to incorporate the most recent climate change scenarios set forth in the IPCC 2007 reports, researchers say that by 2100 up to 30 percent of land-bird species may be extinct.