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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 9, NUMBER 4, APRIL 1996

PROFESSIONAL PUBLICATIONS...
CLIMATE SENSITIVITY AND FEEDBACKS

Item #d96apr29

"Paleoclimate 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 agreement.

Item #d96apr30

"Some 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.

Item #d96apr31

Three related items in Nature, 378(6553), Nov. 9, 1995. (See Research News, this Digest issue--Apr. 1996.)

"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.