February 28, 2007
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FROM VOLUME 7, NUMBER 2, FEBRUARY 1994
- GENERAL INTEREST--SCIENCE: PALEOCLIMATE
Temperature Variations Since 20,000 Years Ago: Modulating
Interhemispheric Climate Change," T.P. Guilderson
(Lamont-Doherty Earth Observ., Palisades NY 10964), R.G.
Fairbanks, J.L. Rubenstone, Science, 263(5147),
663-665, Feb. 4, 1994.
Results from two independent isotope techniques show that
19,000 years ago, during the last ice age, tropical sea surface
temperatures were 5·C colder than present. This suggests that
tropical temperatures are not maintained at present values by a
thermostat mechanism, as some have argued, and could change under
increased CO2 levels.
related items from Nature, 367(6462), Feb. 3, 1994:
"An Unstable Superconveyor," W.S. Broecker
(Lamont-Doherty Earth Observ., Palisades NY 10964), 414-415. The
research described in the following paper is a valuable exercise,
particularly since greenhouse gases are rising, but is haunted by
the questionable reliability of ice-core results for the Eemian
period and the suitability of the models used.
"Rapid Interglacial Climate Fluctuations Driven by North
Atlantic Ocean Circulation," A.J. Weaver (Ocean Sci., Univ.
Victoria, POB 1700, Victoria BC V8W 2Y2, Can.), T.M.C. Hughes,
447-450. Recent ice core data suggest that the climate of the
last (Eemian) interglacial period fluctuated much more than that
of the present interglacial. Results from an idealized global
ocean model suggest that the North Atlantic has three distinct
circulation modes, and rapid transitions between them can be
induced by a random component of freshwater flux. Increased
hydrologic cycle variability in the warmer Eemian climate may
have caused such transitions.
Changes in Moisture Sources for Greenland: Influences on the Ice
Core Record of Climate," C.D. Charles (Scripps Inst.
Oceanog., La Jolla CA 92093), D. Rind et al., Science, 263(5146),
508-511, Jan. 28, 1994.
Abrupt fluctuations in the oxygen isotope ratio observed in
Greenland ice cores during the last ice age could indicate
regional temperature fluctuations, but other factors might also
have influenced the isotopic composition. Support for this
possibility comes from general circulation model results
presented here, indicating that the geographical sources of
Greenland precipitation varied with different climatic states.
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