February 28, 2007
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FROM VOLUME 9, NUMBER 4, APRIL 1996
CLIMATE SENSITIVITY AND FEEDBACKS
Data Constraints on Climate Sensitivity: The Paleocalibration Method," C.
Covey (Global Clim. Res. Div., Mail Code L-264, Lawrence-Livermore Natl. Lab.,
Livermore CA 94551), L.C. Sloan, M.I. Hoffert, Clim. Change, 32(2),
165-184, Feb. 1996.
Uses a new technique to calculate the ratio of temperature response to
forcing on a global mean scale for three key intervals of Earth history (Last
Glacial Maximum, middle Cretaceous, early Eocene), to estimate the equilibrium
climate sensitivity to radiative forcing changes for different extreme climates.
Ratios for the three periods all lie in the range obtained from general
circulation models: 2° -5° C global warming for doubled atmospheric CO2.
However, when compared with paleodata on a regional scale, the models show less
Considerations on the Thermostat Hypothesis," D.E. Waliser (Inst. for
Terrestrial & Planetary Atmospheres, SUNY, Stony Brook, N.Y.), Bull.
Amer. Meteor. Soc., 77(2), 357-360, Feb. 1996.
Summarizes a symposium at the January 1995 meeting of the American
Meteorological Society concerning the manner in which the ocean-atmosphere
system limits large-scale sea surface temperatures to the observed maximum of
about 303K, and related implications for possible greenhouse warming.
Three related items in
Nature, 378(6553), Nov. 9, 1995. (See Research News, this Digest
"Driving the Ocean Conveyor," A.J. Weaver (Sch. Earth Sci., Univ.
Victoria, POB 1700, Victoria BC V8W 2Y2, Can.), 135-136. Discusses the following
two articles, emphasizing how Rahmstorf's work, combined with previous studies,
sends out a warning about the possible response of the North Atlantic deep
circulation to increasing greenhouse gases. However, a major piece of the puzzle
that remains missing is corroboration by fully coupled atmosphere-ocean models
that do not drift away from the present-day climate; this may become available
in a few years.
"Bifurcations of the Atlantic Thermohaline Circulation in Response to
Changes in the Hydrological Cycle," S. Rahmstorf (Inst. für
Meereskunde, Düsternbrooker Weg 20, 24105 Kiel, Ger.), 145-149. Studies the
sensitivity of the North Atlantic thermohaline circulation to the input of fresh
water using a global ocean circulation model coupled to a simplified model
atmosphere. Finds that substantial changes in regional climate can result from
moderate changes in freshwater input, indicating that quite small perturbations
to the present hydrological cycle may lead to temperature changes of several
degrees on timescales of only a few years.
"Simulation of Abrupt Climate Change Induced by Freshwater Input to the
North Atlantic Ocean," S. Manabe (GFDL, POB 308, Princeton NJ 08542), R.J.
Stouffer, 165-167. Uses a coupled ocean-atmosphere model to explore large and
abrupt changes of North Atlantic climate recorded in both glacial and
postglacial periods in Greenland ice cores. In response to a massive surface
flux of fresh water to the northern North Atlantic, the thermohaline circulation
in the model fluctuates, generating episodes that resemble the abrupt climate
changes observed. The associated change of surface air temperature is largest in
the North Atlantic Ocean and its neighborhood.
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