Talk about appealing to false causality. Was Katrina caused by GW? Who knows. One point of data trend does not make. Is the Arctic Melting caused by the fact that it's getting warmer, along with the rest of the planet on average? That's a pretty hard thing to disprove with millions of points of data all pointing to the same thing "The earth is warming."
Why is the burden of proof on the side of skepticism? If someone wants to claim that arctic melting is caused by man-made global warming, it is up to them to make their case, not the other way around.
FWIW, shipping lanes through the north pole have been possible several times in the past, and never previously have they been considered a sign of global warming.