Environmental Engineering Reference
In-Depth Information
Figure 9.5
Estimated mean summer temperatures over the
British Isles for the last 120,000 years.
Source: After Jones and Keen (1993).
SUDDEN CLIMATE CHANGES
new developments
As dating methods have improved it has become possible to determine the rates of
temperature change in the past as indicated by ice cores and deep-sea sediments. Where
rates of accumulation or sedimentation are adequate and continuous it is possible to
record indicated temperature changes to within a decade. This is a very important feature
of previous climates, as the present increase in temperature needs to be related to what
has happened in the past. Could such a rate of change be produced by natural processes
or are the present rates of increase greater than anything that has been observed before?
As recently as the 1980s scientists became aware of the rapidity with which climate
might change within the geological record. Evidence from ice cores taken from
Greenland and deep-sea sediment from the North Atlantic clearly indicated sudden
changes in temperature conditions (Figures 9.12 and 9.13). In the last glacial period rapid
warming of about 5°-7° C in a few decades was followed by periods of slower cooling
and then a more rapid return to glacial conditions. Up to twenty such oscillations were
found during the last glacial period. These patterns are similar to those found in the North
Atlantic sediments. The most dramatic of these oscillations may be linked with the
sedimentary 'Heinrich' layers which have been interpreted as the result of massive
iceberg discharge from north east Canada leading to a decrease of oceanic salinity in the
