Predictions of how much seas will rise as a result of climate change continue to differ. Some say the global seas will rise by 20 feet or more by the end of this century. Now the University of Colorado at Boulder has issued a study concluding that the seas cannot rise more than 6 feet.

The university researchers made calculations based on melting of Greenland, Antarctica and the world’s smaller glaciers and ice caps. They considered conditions required for large sea level rises and concluded that a total rise of two meters (slightly more than six and a half feet) by 2100 could occur only if all variables were accelerated. All outlet glaciers in Greenland would have to move three times faster than the fastest outlet glaciers ever observed or more than 70 times faster than they presently move to increase sea level by 6 feet  by the end of the century. Furthermore, they would have to be moving that fast now.

Tad Pfeffer, a fellow of CU-Boulder’s Institute of Arctic and Alpine Research, and his colleagues made calculations using conservative, medium and extreme assumptions for sea rise expected from Greenland, Antarctica and smaller glaciers and ice caps — the three primary contributors to rise in sea level. The team concluded that a global sea rise of more than 6 feet is “a near physical impossibility.” The most plausible scenario will lead to a total sea level rise of roughly 3 to 6 feet by 2100.

Yet, Pfeffer points out that an estimate of 3 to 6 feet by 2100 is “potentially devastating to huge areas of the world in low-lying coastal areas.” Why a difference of a few feet matters is the planning that should take place. “If we plan for 6 feet and only get 2 feet,“ says Pfeffer, “or visa versa, we could spend billions of dollars of resources solving the wrong problems.”