According to NASA scientists:

Through the first 11 months, 2007 is the second warmest year in the period of instrumental data, behind the record warmth of 2005, in the Goddard Institute for Space Studies (GISS) analysis. The unusual warmth in 2007 is noteworthy because it occurs at a time when solar irradiance is at a minimum and the equatorial Pacific Ocean has entered the cool phase of its natural El Nino — La Nina cycle.

… barring the unlikely event of a large volcanic eruption, a record global temperature exceeding that of 2005 can be expected within the next 2-3 years.

Figure (a) Annual surface temperature anomaly relative to 1951-1980 mean, based on surface air measurements at meteorological stations and ship and satellite measurements of sea surface temperature; the 2007 point is the 11-month anomaly. [Green error bar is estimated 2? uncertainty….]

Even an “unusually cold” December, would only drop 2007 to the third warmest year ever. NASA points out:

The six warmest years in the GISS record have all occurred since 1998, and the 15 warmest years in the record have all occurred since 1988.

Anyone notice a trend? And the most warming is far from the urban heat islands of major cities:

… the greatest warming has been in the Arctic. Polar amplification is an expected characteristic of global warming, as the loss of ice and snow engenders a positive feedback via increased absorption of sunlight. The large Arctic warm anomaly of 2007 is consistent with observations of record low Arctic sea ice cover in September this year.

But couldn’t this all be the sun going through a phase of high solar radiation, a favorite explanation of those who deny that human-generated greenhouse gases are the primary cause of warming? No. As NASA explains: