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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999
FROM VOLUME 10, NUMBER 3, MARCH 1997NEWS...
1996 GLOBAL TEMPERATURE
Item #d97mar73
 Results from three independent analyses of
worldwide surface temperatures show that, although 1996 was a fraction of a
degree Celsius cooler than 1995, the year still ranks among the ten warmest on
record. The surface measurements also indicate that this is the hottest decade
on record, and the 1980s are second.
Satellite measurements of temperatures in the lower layers of the atmosphere
also show 1996 to have been slightly cooler than 1995. But in contrast to the
recent warming trend displayed by the surface temperature record, the 18-year
satellite record exhibits a slight global cooling trend. The two data sets are
not necessarily inconsistent because they measure somewhat different properties
of the atmosphere. However, this difference complicates interpretation of the
observational record, and fuels debate over climate change. (See Science
News, p. 38, Jan. 18, 1997; The New York Times, pp. C1, C6, Jan. 14;
Global Environ. Change Rep., pp. 1-3, Jan. 17.)
At least two regional phenomena probably contributed to the lowered
global temperature for 1996 compared with 1995. La Niņa, the cool phase
of the El Niņo-Southern Oscillation of the Pacific Ocean, prevailed early
in 1996, helping to cool broad portions of the Northern Hemisphere. Even more
dramatic was the abrupt reversal in late 1995 of the North Atlantic Oscillation
(NAO). The NAO is a long-recognized tendency of the atmosphere to exhibit either
one of two patterns of circulation over the North Atlantic Ocean for a decade or
so, before shifting to the other pattern. Until 1995, the NAO had been in the
phase that is thought to have kept Europe and North America relatively warm for
the last two or three decades. The recent reversal probably accounts for the two
latest severe winters in Europe, and could contribute to lower Northern
Hemisphere temperatures in the near future.
Recently, oceanographers have proposed that the NAO and its reversals may be
controlled by pulses of warm and cool water traveling along a vast ocean current
that starts with the Gulf Stream, swings past Ireland, then heads west to the
Labrador Sea. (See feature articles in Science, pp. 754-755, Feb. 7, and
The New York Times, pp. C1, C6, Mar. 18.) A full understanding of the
NAO could lead to regional climate forecasts for Europe and North America. But
its existence also complicates the search for a human "fingerprint" of
climate change, as the Science feature discusses. Natural agents of
climate change such as the NAO and El Niņo could be masquerading as a
strengthening greenhouse. On the other hand, elevated greenhouse gases could be
altering these otherwise natural oscillations. Only time, and continued
observations, will tell.
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