The general circulation model doesn’t account for the heating caused by greenhouse gasses. It assumes that other factors will cause the planet to heat up over a longer period of time and are easier to trace.

Aside from new shipping lanes opening up through the arctic circle numerous species will become less stable as the arctic warms more. Polar bears can already be observed to have less fat than is typical from a few years ago.http://www.greenfacts.org/en/arctic-climate-change/l-3/5-arctic-animals.htm The surface area that makes up Greenland will decrease and as it worsens the sea level will rise more. As the sea rises,eventually some small remote islands are going to wind up underwater.