Preliminary calculations* show that surface temperatures** averaged over the globe in 2004 were the fourth highest (and the past decade was the warmest) since measurements began in 1861. (Actually, there are measurements at some sites before 1861, but this date is generally chosen as the first time when there is a dense enough network of data available to make a global average meaningful). 2004 was slightly cooler than 2003, 2002 and 1998, with the average world temperature exceeding the 30 year average (1961-1990) by 0.44° C. 1998 remains the warmest year, when surface temperatures averaged +0.54°C above the same 30-year mean. October 2004 was the warmest October on record. Sea-ice extent in the Arctic remains well below the long-term average. In September 2004, it was about 13% less than the 1973-2003 average. Satellite information suggests a general decline in Arctic sea-ice extent of about 8% over the last two and half decades.
For further details see the WMO Web site , go to “News” and look for Press Release 718.
You can also check the NASA-GISS news report on 2004
*Following established practice, WMO’s global temperature analyses are based on two different datasets. One is the combined dataset maintained by the Hadley Centre of the Met Office, UK, and the Climatic Research Unit, University of East Anglia, UK and the other one is maintained by the USA Department of Commerce’s National Oceanic and Atmospheric Administration (NOAA). Results from these two datasets are comparable: both indicate that 2004 is likely to be the fourth warmest year globally.
**Change of “temperatures” to “surface temperature” made, and hyperlink added 1/23/05.