Climate change could significantly transform up to 86 percent of the planet's land ecosystems under worst-case global warming scenarios, according to researchers at Germany's Potsdam Institute for Climate Impact Research. That estimate is based on a 4 to 5 degree C temperature increase by the year 2100 — a scenario that is plausible given many nations' reluctance to enact greenhouse gas emissions limits, the researchers say. Even if global temperatures are kept to 2 degrees C above preindustrial levels, 20 percent of natural land ecosystems are at risk of moderate or major changes, especially high-altitude and high-latitude regions. Such changes could include boreal forests being transformed into temperate savannas, trees growing in thawed Arctic tundra, or even a dieback of some of the world's tropical forests. "Essentially, we would be leaving the world as we know it," says Sebastian Ostberg, who led the research.