World leaders are meeting in Paris this month in what amounts to a last-ditch effort to avert the worst ravages of climate change. Climatologists now say that the best-case scenario—assuming immediate and dramatic emissions curbs—is that planetary surface temperatures will increase by at least two degrees Celsius in the coming decades.

This may sound like a small uptick, but the implications are profound. Rising temperatures will destroy plant and animal habitats, and reduce yields of important food crops. More people will be exposed to the ravages of flooding and drought.

But if the nations involved in the Paris talks stay on their current emissions track and don’t reduce greenhouse-gas emissions, temperatures could go up by almost six degrees Celsius this century, according to the Committee on Climate Change, an independent body that advises the U.K. government on climate issues.

The consequences of a heating globe are already being felt in Alaska, which is warming twice as fast as the rest of the U.S. Rising temperatures have thawed frozen soil in some areas, leaving coastlines vulnerable to storms and tidal activity. Shishmaref, a remote village that sits on an island 30 miles outside the Arctic circle, is losing as many as nine feet of land a year—chunks of coastline that simply break into the sea.