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A study released by NASA confirmed that 2005 was the warmest year on record, narrowly beating out 1998. That year a strong El Niño--a warm water event in the eastern Pacific Ocean--added significant warmth to global temperatures. The new record was set without the help of an El Niño. This suggests that a very sustantial warming trend is affecting the globe and more "warmest years ever" will continue to occur in this decade--particularly if they are El Niño years. Global warming since the middle 1970s is now about 0.6° C (1° F ). Total warming in the past century is about 0.8° C (1.4° F). The five warmest years over the last century have occurred in the last eight years. Reliable instrument records of global temperatures extend back to about 1880, but the consenus scientific view is that the current level of warmth has been unmatched for at least the past 125,000 years.
Figure 1: (Top) Global annual surface temperature relative to 1951-1980 mean based on surface air measurements at meteorological stations and ship and satellite measurements for sea surface temperature. The blue segments represent the uncertainty of of the measurements at the 95% level. (Bottom) Temperature anomaly for 2005 calendar year. Image credit: NASA Goddard.
The plot of 2005 temperature anomalies shows that virtually all land areas across the globe were warmer than average in 2005. More warming was observed in the Northern Hemisphere than the Southern Hemisphere, and the U.S. had its 13th warmest year on record. The Arctic had the most warming, helping make the extent of summer ice coverage over the Arctic Ocean in 2005 the lowest ever measured. It's sobering to note that even the Antarctic showed a net warming for 2005. The Antarctic had been the only land area on the globe to have cooler than average temperatures the past decade. If 2005 signals an end to this Antarctic cooling trend, we can expect a higher rate of global sea level rise in coming years as Antarctic melting increases.