January 7, 2009

U.S. Temperatures 2008: Back to the Future?

Filed under: Surface, Temperature History

The data are just in from the National Climatic Data Center and they show that for the year 2008, the average temperature across the United States (lower 48 States) was 1.34ºF lower than last year, and a mere one-quarter of a degree above the long-term 1901-2000 average. The temperature in 2008 dropped back down to the range that characterized most of the 20th century.

Figure 1 shows the U.S. temperature history from 1895 to 2008. Notice the unusual grouping of warm years that have occurred since the 1998 El Niño. Once the 1998 El Niño elevated the temperatures across the country, they never seemed to return to where they were before. Proponents of catastrophic global warming liked to claim that is was our own doing through the burning of fossil fuels, but others were more inclined to scratch their heads at the odd nature of the record and wait to see what happened next.


Figure 1. U.S. average annual temperature history 1895-2008 (source: National Climatic Data Center, http://climvis.ncdc.noaa.gov/cgi-bin/cag3/hr-display3.pl)

You see, prior to 1998, there was little of note in the long-term U.S. temperature record. Temperatures fluctuated a bit from year to year, but the long-term trend was slight and driven by the cold string of years in the late 19th and early 20th century rather than by any warmth at the end of the record. In fact, from the period 1930 through 1997, the annual average temperature actually declined a hair—despite the on-going build-up of atmospheric greenhouse gas concentrations. The only suggestion that “global warming” had involved the U.S. was to be found in the post-1997 period—a period unusual in that the temperatures went up and stayed up at near-record levels year after year. It was not so much that temperatures continued to climb after 1998, but just that they never fell. This grouping of warm years nearly doubled the apparent overall warming trend in U.S. temperatures (starting in 1895) from 0.07ºF/dedade (ending in 1997) to 0.13ºF/decade (ending in 2007). And with this doubling of the warming trend came the big push for emissions restrictions.

But now, 2008 comes along and has broken this warm stranglehold. Perhaps this is an indication that the conditions responsible for the unusual string of warm years have broken down—and maybe they weren’t a sudden apparition of anthropogenic global warming after all.

Only time will tell for sure. But, at least for now, things seem like they have returned to a more “normal” state of being.




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