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clear need to obtain as much palaeoclimatic information as possible from wherever
possible if we are to accurately determine how the palaeoclimatic systems worked.
Much research is still required today. As there remains some uncertainty as to the
exact conditions in the past, the validation of climate computer models cannot be
undertaken with the exactness that policy-makers require or in a number of instances
realise (see also section 5.3.1).
If some tropical palaeoclimatic records correlate with polar records, it should not
be surprising to find that many current temperate-zone palaeorecords exhibit sim-
ilar correlations. For example, rapid environmental changes similar to those indic-
ated by Greenland ice cores are discernable in southern European palaeorecords
from Italy covering the last glacial (Allen et al., 1999). So, even though one line
of evidence - be it a drill-core alkenone-determined tropical sea-surface temper-
ature record or whatever - may not have the resolution or be as representative as
we would like, we can still place this evidence alongside that of other palaeodata
and begin to see a coherent picture emerge. Such is the amount of disparate evid-
ence that, despite shortcomings in any area, this broader coherent picture is quite
clear.
4.5.2 Iceandsealevel
During the LGM, and other recent glacial maximums, ice sheets of up to 3 km thick
covered much of northern North America down to the Great Lakes (the Laurentide
sheet, together with the Cordilleran sheet; Figure 4.3) and also much of northern
Europe, Scandinavia and the northern British Isles (the Fennoscandian sheet; Figure
4.4). Meanwhile, in the southern hemisphere, much of New Zealand, Argentina and
Chile sported ice caps, as did mountains in South Africa and southern Australia. With
so much of the Earth's water trapped on land as ice sheets, the sea level fell by about
120 m, so exposing much of the continental shelves.
4.5.3 Temperaturechangeswithintheglacial
The temperature change in the last glacial in the regions surrounding Antarctica is
depicted in detail in Figure 4.2, which is based on a deuterium isotopic analysis (see
Chapter 2) of the Vostok core. Note that most of the current (up to but not including the
incomplete present) late-Quaternary interglacials were short, of the order of 10 000
years or less, whereas glacials were about 90 000 years in duration. Also note that the
beginning and end of the glacials were comparatively sharp (critical transitions and
climate thresholds are mentioned later in the topic, e.g. section 6.6.8), as were some
of the less dramatic changes in temperature during the glacials themselves. What the
glacial-interglacial cycles are not are gently sinusoidal temperature oscillations.
The temperature graph from Figure 4.2 is shown on Figure 4.5 and added to it is
the ice-core record of past atmospheric carbon dioxide and methane concentrations
covering additional glacial-interglacial cycles. It can be seen that carbon dioxide
and temperature effectively parallel each other, which is further evidence as to the
importance of greenhouse gases in determining global climate. Methane too, as
 
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