February 28, 2007
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FROM VOLUME 9, NUMBER 6, JUNE 1996
"A la Recherche
du Temps Perdu," P. Jones, (Clim. Res. Unit, Univ. E. Anglia, Norwich NR4
7TJ, UK), Nature, 381(6581), 375-376, May 30, 1996.
Discusses recent workshops in Australia and New Zealand that have helped
exploit a wealth of natural archives (tree rings, corals and ice records) to
delineate the nature of climate change over the past 150 years in Oceania
(Australia, New Zealand and the South Pacific).
Surprises," J.T. Overpeck (Paleoclim. Prog., NGDC, NOAA, 325 Broadway,
Boulder CO 80303), Science, 271(5257), 1820-1821, Mar. 29, 1996.
Reviews growing paleoclimatic evidence that, even in the absence of human
forcing, warm interglacial climates (such as the present Holocene) are capable
of generating significant decade- to century-scale climatic surprises, which may
be our biggest worry in the years to come. We are beginning to be able to map
the patterns of these variations, but unraveling their causes remains a major
challenge. If the climate system also turns out to be highly sensitive to
elevated trace gas concentrations, we may be confronted with modes of climate
variability without precedent.
Things Past: Greenhouse Lessons from the Geologic Record," T.J. Crowley
(Dept. Oceanog., Texas A & M Univ., College Sta. TX 77843), ibid.,
A review for non-specialists. For most of the last two million years, there
is little evidence for global temperatures more than one degree higher than
those of the present warm interglacial period. The possibility of an enhanced
greenhouse effect thus comes at a time of high temperatures that are rare in the
span of human history. Moreover, the concentrations of carbon dioxide and other
greenhouse gases are today as high as any that are known in the 200,000 years
for which measurements are available, and we know that they played a significant
role in climatic changes of the past. While questions remain regarding possible,
ameliorating feedbacks from other elements of the climate system, all that is
known from the record of the past confirms a direct connection between
greenhouse gases and surface temperatures.
Depression in the Lowland Tropics in Glacial Times," P.A. Colinvaux
(Smithsonian Tropical Res. Inst., POB 2072, Balboa, Panama), K.-B. Liu et al.,
Clim. Change, 32(1), 19-33, Jan. 1996.
Presents pollen and other data confirming the recently recognized existence
of a general tropical cooling during the last ice age. Climate models used to
predict future effects of greenhouse gases must also be able to simulate the
significant cooling of the large tropical land masses at glacial times with
reduced greenhouse gas concentrations.
Holocene Climate as Reconstructed from a Greenland Ice Core," S.R. O'Brien
(Paragon Environ. Services Inc., 153 Washington, E. Walpole MA 02032), P.A.
Mayewski et al., Science, 270(5244), Dec. 22, 1995.
(See Research News, this Digest issue--June 1996.) Elevated
concentrations of sea salt and terrestrial dusts detected in ice cores show that
the chemical composition of the atmosphere was dynamic throughout the Holocene
epoch. The most recent and abrupt increase coincides with the Little Ice Age.
These changes imply that temperatures in the mid-to-high northern latitudes
during those periods were potentially the coldest since the Younger Dryas event.
"Profiles of the
Past," D.A. Peel (Brit. Antarctic Survey, High Cross, Madingley Rd.,
Cambridge CB3 0ET, UK), Nature, 378(6554), 234-235, Nov. 16,
Discusses a joint GISP2-GRIP workshop (Sep. 1995, Wolfeboro, New Hampshire)
involving the U.S. and European teams that have been drilling deep ice cores 30
km apart on the Greenland ice cap. Comparison of the two cores has been
augmented by new high-resolution data on methane and oxygen, and this approach
is helping to forge a long-awaited direct link between the Greenland, Antarctic
and marine sediment paleoclimate records. One result suggests that high-latitude
climate may be more sensitive than previously thought, and changes in global
temperatures may be amplified in the polar regions. (Another account of the
workshop appears in EOS, pp. 209, 213, May 28, 1996.)
Interdecadal and Century-Scale Climate Oscillations During the Past Five
Centuries," M.E. Mann (Dept. Geol., Yale Univ., POB 208109, New Haven CT
06520), J. Park, R.S. Bradley, Nature, 378(6554), 266-270, Nov.
Reports a multivariate statistical analysis of a small but global set of
high-quality temperature proxy records, extending over several centuries. The
results strengthen evidence for persistent, natural interdecadal and
century-scale climate oscillations, and reveal both the spatial patterns and
temporal histories of these signals.
Two related items in
Science, 270(5235), Oct. 20, 1995:
"Challenging an Ice-Core Paleothermometer," D. MacAyeal (Dept.
Geophys. Sci., Univ. Chicago, Chicago IL 60637), 444-445. Discusses the
following article, which uses temperature profile inversion analysis to
challenge and refine the temperature history deduced from the GISP2 ice core.
The outcome implies that past estimates of the amount of warming after the last
glacial period have been too low, and confirms that polar amplification of
climate change is a central characteristic of Earth's climate.
"Large Arctic Temperature Change at the Wisconsin-Holocene Glacial
Transition," K.M. Cuffey (Dept. Geol. Sci., Box 351310, Univ. Washington,
Seattle WA 98195), G.D. Clow et al., 455-458. Combined analysis of borehole
temperature and oxygen isotope composition for the GISP2 Greenland ice core
shows that the warming from the last glacial period was 15£ C, about three
times the coincident temperature change in the tropics and mid-latitudes.
Effort Helps Decipher Mysteries of Paleoclimate from Antarctic Ice Cores,"
Vostok Project Members (c/o J. Jouzel, Lab. Clim. & Environ. Modeling, Bâitment
709, Orme des Merisiers, CE Saclay, 91191 Gif-sur-Yvette Cedex, France), Eos,
76(17), 169, 179, Apr. 25, 1995.
Summarizes results of studies of ice cores drilled at Vostok Station,
Antarctica, over the past ten years by Russia, France and the U.S., which are
revealing a wealth of information about past climate and environmental changes
over more than a full glacial-interglacial cycle. The data suggest that CO2
and methane have amplified the initial orbital forcing and account for about
half of the glacial-interglacial climate change. They also suggest that positive
feedbacks operate in the climate system and support the idea that significant
greenhouse warming will occur in the next century.
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