Global Warming

I take logic class in my university every week. This week in the class, he told about the global warming. He said it less possible to melt Arctic glacier and rise the water level. He told us that because average temperature in the North Pole is about -50℃, the 3~5℃ temperature rise doesn't matter. Or, if the Arctic glacier melt, it is froating in the water, so the water level never rise from the beginning. I thought almost the same thing. The average temperature was more high when the dinosaurs lived. I think the globe is in the high tempareture time now. Optimistic to say that people care too much about the global warming. Don't you think so?