The Greenland ice sheet, if melted, would raise global sea level by about 7 meters. Even a slight warming accelerates the present melt rate. Climate change models suggest that a 3°C warming over the next 100 years may be enough to eventually (over the next millennium) melt the entire ice mass (Schiermeier, 2004). Several assumptions accompany this projection, including the likelihood of more snowfall over the Greenland interior that could balance melting and change in path of the Gulf Stream which may reduce northward heat transfer to the Greenland area.
Once melted, re-establishment of permanent ice would take much more than a 3°C cooling.
Reference
Schiermeier, Q., 2004: A rising tide. Nature, 428, 114-115.