Global Warming and its possible impacts on Essex
9
The pattern of temperature change indicates that the cold stages ended abruptly, with rapid rises of
mean annual temperature, known as terminations, in the range of 6-8°C. The consequent interglacials
were relatively short-lived, 10,000 years or perhaps a multiple thereof, then there is a slow decline
of temperature to reach a low point, with relatively short-lived full glacial conditions. Thereafter the
cycle starts again.
However, the matter is far from fully understood and there are many oddities, such as ice expansion
is often broadly synchronous in both the southern and northern hemispheres, but orbital forcing
should have different impacts in the two hemispheres.
Interaction between orbital forcing and the earth's surface
Another oddity is that the degree of cooling in glacials, 6-8°C, is more than orbital forcing would
induce. Thus it seems that other factors also control climatic events by enhancing the astronomical
patterns. Examination of gases from bubbles in ice from Antactica (from the Vostock ice core) show
carbon dioxide and methane values have varied in step with the temperature changes (Fig. 2). These
are greenhouse gases and they may have amplified the astronomical signal.
Figure 2. Pattern of variation in carbon dioxide, temperature and methane over the last
150,000 years, maximum calculated values. (Derived from A.F. Street-Perrott and N. Roberts, in
Roberts, 1994)
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Age (thousand years B.P.)
Essex Naturalist (New Series) 17 (2000)