In late winter the weather was so warm it was called Summer in March. When the actual summer came around, it was one for the record books. Now that the end of the year is rolling around, it is no surprise that 2012 will rank as the warmest calendar year ever for the contiguous United States (along with various other geographical zones).
It is not that the entire year has been warm, but it is warm again now, with November-like weather in the middle of December. Not far away in Greenland, above-freezing temperatures in December are another sign of a shifting climate. Realistically, the climate will change almost detectably from year to year for the next two generations before human patterns of activity have a chance to change enough to permit climate to settle into a new, relatively stable pattern.