Read here, here, here, here, here, and here. Multiple research efforts have determined that a combination of natural climate forces (Arctic Oscillation, North Atlantic Oscillation, Transpolar Drift Stream, cyclical flow of atmospheric energy around Arctic Circle) have created a warming environment in the Arctic area. The research also confirms that it has been warmer in the Arctic prior to this current period. Read here about 1944 ship journey via Northwest Passage. The image below is another testament to previous Arctic warming. (click to enlarge)