Environmental Engineering Reference
In-Depth Information
7
The greenhouse effect and global warming
The succession of exceptional years with record
high temperatures, which characterized the
1980s, helped to generate widespread popular
interest in global warming and its many
ramifications. The decade included six of the
warmest years in the past century, and the trend
continued into the 1990s, with 1991 the second
warmest year on record. All of this fuelled
speculation—especially among the media—that
the earth's temperature had begun an inexorable
rise, and the idea was further reinforced by the
results of scientific studies which indicated that
global mean temperatures had risen by about
0.5°C since the beginning of the century (see
Figure 7.1).
Periods of rising temperature are not unknown
in the earth's past. The most significant of these
was the so-called Climatic Optimum, which
occurred some 5,000-7,000 years ago and was
associated with a level of warming that has not
been matched since. If the current global warming
continues, however, the record temperatures of
the earlier period will easily be surpassed.
Temperatures reached during a later warm spell in
the early Middle Ages may well have been
equalled already. More recently, the 1930s
Figure 7.1
Measured globally-averaged (i.e. land and ocean) surface air temperatures for this century
Source:
After Jones and Henderson-Sellers (1990)
