It will take longer -- perhaps thousands of years longer -- to melt Greenland completely, the longer it takes to reach the threshold. But once the threshold is passed, the melting will be irreversible, because CO2 stays in the atmosphere for hundreds of years, and because positive feedback cycles -- where loss of snow increases heat absorption by darker, exposed surfaces -- will propagate melting. And, the researchers emphasize, the true threshold may be lower than they calculate. "What we found here is largely an underestimate," Ramstein said. "We have a model that is quite simple, with coarse resolution so that it can simulate for thousands of years. You might actually get complete melting for lower carbon emissions." The work was published in Geophysical Research Letters. Scenarios below the 3,800-billion-ton threshold led to a reduction in the ice sheet size of 10 to 63 percent over the course of the simulations, still a concerning loss. "Even one meter of sea level rise is a complete catastrophe," Ramstein said. "Rates of a meter per century are feasible," Church said, so it will not take thousands of years to feel the effects of melting. "This is only the northern part of the story," Ramstein added. "There is also a southern part, in Antarctica. In the south there is the ice shelf. This makes west Antarctica very vulnerable to changes." Related Links: Jessica Marshall's blog: EnvironMental Case View an animation of the Greenland ice melt at Discovery Earth Live. How Stuff Works: Greenland's Geography |
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