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Global Climate Change Digest

A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999



Item #d98mar118

Four separate analyses, using various combinations of land and ocean surface observations, have rated 1997 as the warmest year on record by a small margin. Estimates by the National Oceanic and Atmospheric Administration, NASA's Goddard Institute for Space Studies, the U.K. Meteorological Office, and the World Meteorological Organization range from 0.42 to 0.44°C above the 1961-1990 normal. The current El Niño is considered a major factor contributing to this outcome.

These estimates, based on surface data, continue to differ from those of lower atmospheric temperatures made by satellite, which rate 1997 in the middle of annual temperatures measured this way over nearly the last two decades. The satellite measurements also do not show the recent upward trend in temperature indicated by the surface data. There is still incomplete agreement on the reason for this discrepancy, although several recent papers have addressed the issue.

Both Tom Karl of NOAA and James Hansen of NASA interpret the warming trend over recent years in their respective data sets to be caused at least in part by anthropogenic increases in greenhouse gases. Hansen and his colleagues expect new record global temperatures in the next few years, as the effects of several cooling factors, such as ozone depletion, sunspot numbers and the thermal inertia of the oceans, start to diminish.

See Science News, p. 38, Jan. 17, 1998; Science, pp. 315-316, Jan. 16; and Global Environ. Change Rep., pp. 1-3, Jan. 16. Web sites for the various analyses are: NOAA:; NASA surface:; UKMO:; NASA satellite:

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