This chapter dealt with a single
big question and several related ones. The big question was, "Is
the atmosphere warming?" Related questions include "What
reasons do we have to suspect that the atmosphere is warming"
and "What might cause the warming?" Theory and GCM computations
point to an increase in air temperatures due to an enhanced greenhouse
effect. The observational data also indicate a modest warming
over the past 100 or so years. However, issues such as feedback
and an imperfect data record make the problem a particularly difficult
one to solve. As a result, it is not evident at this time that
an enhanced greenhouse effect has caused the warming. We reviewed scientists' projections
of the impact of global warming on the natural environments and
on human activities such as agriculture. Finally we considered
some of the options we have to respond to the threat of global
warming.
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