Halfway through 2011, the year-to-date (January-June) average temperature for the United States is just 0.15°F above the long-term (20th century) average. Although it is certainly too soon to say for sure (especially considering that a good portion of the country has been stuck in an extended heat wave), there is a good case to be made that when the final numbers are in at the end of December, that 2011 will go down as another in a recent string (which now stands at three years and counting) of rather unremarkable years when it comes to the national annual average temperature. The current run of near-normal years is growing evidence that the collection of relatively warm years experienced in the U.S. from 1998-2007 neither represented a new climate state in the U.S. nor a sustained uptick in the rate of warming which could be reliably extrapolated into the future.
Over at MasterResource.org, Chip Knappenberger elucidates why this is the case—catching us up on the temperatures thus far in 2011 and reviewing the recent behavior of the U.S. annual average temperature record.
The bottom line is presented in Figure 1 (below). Figure 1 includes a projection of the 2011 final end-of-the-year temperature placed in the context of the full U.S. temperature history from 1895-2010, and shows that the warm period from 1998-2007 in the United States appears to be over.
Figure 1. Projected value for the U.S. annual temperature for 2011 based on data for the first six months of the year. The blue dot at the end is the current year-to-date (January through June) temperature anomaly. The grey bar represents the region where there is about a 2/3rds chance that the 2011 annual temperature will end up being. The hash marks above and below the grey bar indicate the region where there is about a 95% chance the 2011 annual temperature will ultimately fall, and the vertical line represent the limits of the 2011 annual temperature, based on observations from 1895-2010. The elevated temperatures from 1998-2007 are circled—this warm period now seems to be over. (Data source: U.S. National Climatic Data Center)
“If 2011 ultimately turns out to come in in-line with the central projections in Figure , it will strengthen the suggestion that the unusually high temperature that characterized the 10-yr period from 1998-2007, were just that, unusual, and do not best represent either the expected trend or the climate state of the U.S. for the next several decades to come.”