IPCC's forecast about the Arctic Sea melting entirely by 2020

Two posts ago, Scientists Jennifer Kay mentioned that it's currently too difficult to pinpoint when all the ice in the Arctic Sea will be completely melted thought they know that it will be if we don't do anything to save it. In this video, Dan Miller shows us a graph from the IPCC and a video animation of the changes happening in the Arctic Sea. They predict that the sea ice will be completely gone by 2020 and that the extent of the Arctic sea ice has halved already.

He mentions feedback, which is basically a concept where even after an event as occurred, the consequences of it carries on, making the effects stronger. In this case, when ice melts, the natural albedo is gone and with the dark water of the sea exposed, more heat is retained making the poles warmer as well.

But his claims about ice disappearing entirely by 2020 isn't backed up by any real scientific proof. He merely extrapolated the thick, black line. But it does seem quite convincing doesn't? With so much scientific uncertainty about the dynamics of the ocean-atmosphere-sea ice, continuing the linear line down to 2020 seems as possible as 2100. Unfortunately for Dan Miller, his method of proving that the ice will be completely gone by 2020 seems dubious especially since he's a businessman with stakes in green technology.