Indeed, early I think a poster mentioned that we should follow the null hypothesis, in this case the IPCC has follow it by punting on the possible acceleration of the melting of the polar ice.
Back in 2007 there was still not enough information to make a good prediction on what the ice was going to do in a warming world, so it was assumed that a **potential **act of the ice would had little or no effect. Giving us the conservative estimates that by the end of the century we could expect about 50 centimeters of sea rise. Like that, other possible feed-backs have not been used or minimized in the past reports because, gosh, the IPCC did the right thing and avoided dealing with the then still uncertain feed-backs. So a conservative report was the result.
The fact that deniers even attempt to discredit the conservative reports shows that deniers are not even wrong, they do not even have a clue.