WASHINGTON -- Researchers at NOAA's National Climate Data Center (NCDC) have found evidence that the rate of global warming is accelerating and that in the past 25 years it achieved the rate of two degrees Celsius (four degrees Fahrenheit) per century. This rate had previously been predicted for the 21st Century.
Writing in the March 1 issue of Geophysical Research Letters, Dr. Thomas R. Karl, Director of NCDC, and colleagues analyze recent temperature data. They focus particularly on the years 1997 and 1998, during which a string of 16 consecutive months saw record high global mean average temperatures. This, Karl notes, was unprecedented since instruments began systematically recording temperature in the 19th Century. During much of 1998, records set just the previous year were broken.
Karl and his colleagues conclude that there is only a one-in-20 chance that the string of record high temperatures in 1997-1998 was simply an unusual event, rather than a change point, the start of a new and faster ongoing trend. Since completing the research, the data for 1999 have been compiled. They found that 1999 was the fifth warmest year on record, although as a La Nina year it would normally be cooler. Outside the band between 20 degrees north latitude and 20 degrees south latitude, 1999 was the second warmest year of the 20th Century, just behind 1998, an El Nino year.
The researchers at NCDC, part of the National Oceanic and Atmospheric Administration (NOAA), based in Asheville, North Carolina, analyzed data from land based and satellite instruments for their study. They conclude that the rate of warming since 1976 is clearly greater than the average rate over the late 19th and 20th Centuries. To account for the string of record setting temperatures, the average rate of global temperature increase since 1976 would have to be three degrees Celsius (five degrees Fahrenheit) per century.