As global temperatures in 2012 further cement a modest warming rate in response to anthropogenic climate influences, the light burns ever brighter for the "lukewarmers"—those intrepid souls who accept that human activities are impacting the character of the world's climate, but hold the opinion that, when taken together, these influences are–and will be–relatively modest.

While lukewarmers' individual opinions of whether or how to do "something" about anthropogenic climate change vary, a future characterized by modest rather than extreme climate change elevates the role of adaptation relative to mitigation in most discussions.

A year ago, in this space, I highlighted some positive lukewarmer developments in 2011. These included findings that the observed temperature trends over (and within) the past 3 decades are lower than climate model projections and that the climate sensitivity—that is, how much the average global temperature will rise under conditions of a doubled atmospheric concentrations of carbon dioxide—has likely been overestimated.

Here, I review some significant events from 2012. Many continue these same themes. I am sure that there are others that did not make my list. If your favorite is not here, please feel free to include a brief description of it in the Comments section below.

Temperatures in 2012

First, let's have a look at the global average temperature for 2012. I am sure that most readers are already aware that in the U.S. the annual average temperature was the highest ever recorded (since 1895). But the U.S. makes up only about 2% of the globe and such small areas, especially located in the Northern Hemisphere extratropics, are subject to large regional variations.

Figure 1 shows the pattern of annual average temperature anomalies across the globe in 2012. Notice that the contiguous U.S. happens to be in the bulls-eye of higher than average temperatures. If you spent 2012 in Alaska, you'd probably be wondering what all the fuss was about, because there the state experienced its 11th coldest year on record (since 1918).

Fig. 1. The pattern of annual average temperature anomalies for 2012 (figure from the National Climate Data Center, details available here ).

But, rather than regional temperature anomalies, what I want to look at is the global temperature.

Figure 2 shows the global temperatures as compiled for the earth's surface as well as for the lower atmosphere from 1979-2012. I show just a single compilation for each, although there are several such compilations available. The differences among the various compilations are interesting, but not large enough to alter the general picture of the situation. The data in Fig. 2 begin in 1979, the year that satellite observations of the lower atmosphere begin and very near the beginning of the second warming period of the 20th century—the one which is largely associated with rising anthropogenic emissions into the atmosphere.

Fig. 2. Annual average global temperature anomalies from the surface (red, HadCRUT4 ) and from the lower atmosphere (blue, UAH MSU ), 1979-2012.

As Figure 2 shows, the global average temperature in 2012 fell below the overall linear trend line and pretty much on the same plateau as temperatures have been since 2001. Together, this has the effect of putting a bit of negative pressure on the trend in global temperatures since 1979 and further establishing it as falling below expectations (especially during the 21st century).

While we await global temperatures to start rising again, there are signs that the overall rise won't be as fast as we have once been led to believe.

Climate Sensitivity

In 2012, several papers were published in the scientific literature which provided evidence that the climate sensitivity lies towards the low end of the range of estimates provided in the most recent assessment report from the Intergovernmental Panel on Climate Change (IPCC). In its 2007 Fourth Assessment Report, the IPCC concluded that: