News & Press
Cooler, but Still Warm
The meteorological year, December 2007 through November 2008, was the coolest year since 2000, according to the Goddard Institute for Space Studies analysis of surface air temperatureIt was the ninth warmest year in the period of instrumental measurements, which extends back to 1880. The nine warmest years all occur within the eleven-year period 1998-2008.
The map of global temperature anomalies in 2008, the left panel of Figure 1 (http://data.giss.nasa.gov/gistemp/2008/), shows that most of the world was warmer than in the period of climatology (1951-1980). Eurasia, the Arctic and the Antarctic Peninsula were exceptionally warm, while much of the Pacific Ocean was cooler than the long-term average. The relatively low temperature in the tropical Pacific was due to a strong La Niña. La Niña and El Niño are opposite phases of a natural oscillation of tropical temperatures, La Niña being the cool phase.
Figure 2 (top) provides seasonal resolution of global and low latitude surface temperature, and an index that measures the state of the natural tropical temperature oscillation. The figure indicates that the La Niña cool cycle peaked in early 2008. The global effect of the tropical oscillation is made clear by the average temperature anomaly over the global ocean (Figure 2, bottom). The "El Niño of the century", in 1997-98, stands out, as well as the recent La Niña.
Figure 3 compares 2008 with the mean for the first seven years of this century. Except for the relatively cool Pacific Ocean, most of the world was unusually warm in 2008. The United States, however, was not exceptionally different than its long-term mean.
The GISS analysis of global surface temperature, documented in the scientific literature [ref. 1], incorporates data from three data bases made available monthly: (1) the Global Historical Climatology Network (GHCN) of the National Climate Data Center [ref. 2], (2) the satellite analysis of global sea surface temperature of Reynolds et al. [ref. 3], and (3) Antarctic records of the Scientific Committee on Antarctic Research (SCAR) [ref. 4].
In the past our procedure has been to run the analysis program upon receipt of all three data sets and make the analysis publicly available immediately. This procedure worked very well from a scientific perspective, with the broad availability of the analysis helping reveal any problems with input data sets. However, because confusion was generated in the media after one of the October 2008 input data sets was found to contain significant flaws (some October station records inadvertently repeated September data in the October data slot), we have instituted a new procedure. The GISS analysis is first made available internally before it is released publicly. If any suspect data are detected, they will be reported back to the data providers for resolution. This process may introduce significant delays. We apologize for any inconvenience due to this delay, but it should reduce the likelihood of instances of future confusion and misinformation.
Finally, we note that we provide the rank of global temperature for individual years because there is a high demand for it from journalists and the public. The rank has scientific significance in some cases, e.g., when a new record is established. However, otherwise rank has limited value and can be misleading. Note that, given our estimated error bar in Figure 1, we can only say that 2008 probably ranks as somewhere between the 7th and 12th warmest year. As opposed to the rank, Figure 3 provides much more information about how the 2008 temperature compares with previous years, and why it was a bit cooler (note the change in the Pacific Ocean region).
NASA's Goddard Institute for Space Studies
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