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be detected from vegetation history studies when resolution is suffi ciently
high. The “rules” or hypotheses are now being refi ned as part of various
studies, for example, of packrat middens in the arid southwest, designed
to identify Holocene refugia in the southern Sonoran Desert during cold
intervals (Camille Holmgren, work in progress).
One of the hallmarks of recent paleoclimate studies has been to dem-
onstrate that these changes in temperature, identifi ed fi rst in the North
Atlantic region, also extended into the lower latitudes. The fi rst large-
scale attempts to reconstruct Quaternary climates were the Climate Long-
Range Investigation and Mapping Program (CLIMAP 1976, 1981, 1984)
and the Cooperative Holocene Mapping Project (COHMAP 1988). These
early efforts suggested that while climates cooled signifi cantly in the north
(12°C-14°C), they waned toward the lower latitudes and cooled there only
by as much as 2°C. Guilderson and others (1994) have shown from oxygen
isotope and Sr/Ca thermometry in Barbados corals (13°11
N) that tempera-
tures there were 5°C cooler at the LGM, and in the lowlands of Brazil they
were 5°C-6°C cooler (Stute et al. 1995; Webb et al. 1997; Aeschbach-Hertig
et al. 2000). The Younger Dryas, Heinrich events, and the Medieval Warm
Period are now recognized from several sites in the equatorial regions, and
the results document that the tropics experienced a muted but nonethe-
less dynamic Quaternary climate. The related precipitation patterns were
the result of the meanderings of the Intertropical Convergence Zone and
the pulsating occurrence of El Niños. To the far south, similar Quaternary
changes in climate are also preserved in the 3623-meter Vostok and other
ice cores from Antarctica and in marine cores from the Southern Ocean.
At times the temperature shifts in the two hemispheres were out of phase,
leading to the idea of a bipolar seesaw, whereby heat was reciprocally trans-
ferred via the ocean conveyor belt. If this were the case, however, the pace
of temperature changes in the two regions should have been more or less
equal, but those in the Southern Hemisphere appear to have been slower.
Barker and colleagues 2009 now present evidence for the past 26,000 years
that, at least for surface waters during the last deglaciation, the changes in
the two hemispheres were at times opposite and abrupt (see summary by
Severinghaus 2009).
Evidence that major glacial advances and changes in climate occurred
in the relatively recent past was building during the nineteenth century,
based in part on the presence of boulder erratics on the plains and in the
mountains of Europe. These rocks, some the size of small houses, had a
composition different from the underlying substrate and had obviously
been transported some distance by powerful forces. Among the early expla-
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