Last year was the eighth warmest year on record, according to the National Climatic Data Center. The world's temperature in 2008 tied that of 2001 according to the center, a division of the National Oceanic and Atmospheric Administration.
Preliminary calculations show the world's average temperature for 2008 was 0.88 degree Fahrenheit above the 20th Century average of 57.0 degrees F.
The ranking means that all of the 10 warmest years on record have occurred since 1997.
Climate scientists around the world have raised concerns about global warming caused by the so-called greenhouse effect in which chemicals, largely generated by human activity, trap solar radiation.
Researchers fear far-reaching effects ranging from changing storm patterns, damage to crops and wildlife, droughts to spread of disease.
The climate center noted that since 1880, the annual combined global land and ocean surface temperature has increased at a rate of 0.09 degree F (0.05 degree C) per decade and the rate has increased over the past 30 years.
NASA, which uses a slightly different method of calculating temperatures, has rated 2008 as the ninth warmest on record.
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