Here's my big worry. Please excuse the electrical engineering analogy.
Sea ice acts as a thermal capacitor. It absorbs heat to cool the oceans. The oceans can absorb a lot of heat but they won't see a proportional temperature rise due to melting sea ice.
The ice is going away. If we have no sea ice there is nothing to absorb the heat. We will begin to experience more drastic temperature fluctuations in the oceans if there's no more ice. Once the ice goes it will get a whole lot worse.
I'm sure the climate folks who build these models account for that but it still concerns me.