Annual Average Global Temperature Variations
                           for the Period 1860–2002

The basis for comparison is the average for the 1961–90 period (the 0.0 line on the graph). Each narrow bar on the graph represents the departure of the global mean temperature from the 1961–1990 average for one year. For example, the global mean temperature for 1862 was more than 0.5° C (1° F) below the 1961–90 average, whereas the global mean for 1998 was more than 0.5° C above. (Specifically, 1998 was 0.56° C warmer.) The bar graph clearly indicates that there can be significant variations from year to year. But the graph also shows a trend. Estimated global mean temperatures have been above the 1961–90 average every year since 1978. Globally the 1990s was the warmest decade—and the years 1998 and 2002 the warmest years—since 1861.