Though the recent uproar concerning global warming has placed the blame on the human population, natural warming and changing weather patterns have also played a part in the gradual warm up.
In fact, the earth has been going through heating and cooling cycles long before people started pumping carbon dioxide into the atmosphere.
As part of this natural cycle, scientists have observed a strange weather pattern over the past twenty or so years. Normally, cold winds from the Arctic blow south, however, during the past few decades, warmer air and clouds from the south have blown north toward the Arctic. All that warm air is a big reason why so much Arctic ice has melted.
This natural warming combined with man-made warming has melted so much Arctic ice that it's created a sort of feedback loop. Snow and ice reflect sunlight, but the darker ocean water absorbs light and heat, causing even more ice to melt.
Though natural warming and man-made warming alone cause some ice to melt, the forces combined have put us in the situation we are in today concerning global warming.