232 Weighingthe uncertainty
The costs of anthropogenic climate change fall into three parts.
Firstly, there is the cost of the damage due to that change; for instance,
the cost of flooding due to sea level rise or the cost of the increase in
the number or intensity of disasters such as floods, droughts or wind-
storms, and so on. Secondly, there is the cost of adaptation that reduces
the damage or the impact of the climate change. Thirdly, there is the
cost of mitigating action to reduce the amount of climate change. The
roles of adaptation and mitigation are illustrated in Figure 1.5. Because
there is already a commitment to a significant degree of climate change,
a need for significant adaptation is apparent. That need will continue to
increase through the twenty-first century, an increase that will eventually
be mollified as the effects of mitigation begin to bite. Mitigation is be-
ginning now but the degree of mitigation that is eventually undertaken
will depend on an assessment of the effectiveness and cost of adaptation.
The costs, disadvantagesand benefits of both adaptation and mitigation
need therefore to be assessed and weighed against each other.
At the end of Chapter 7, estimates of the cost of damage from global
warming were presented. Many of these estimates of damage cost also
included some of the costs of adaptation; in general adaptation costs have
not been separately identified. Many of these cost estimates assumed
a situation for which,resulting from human activities, the increase in
greenhouse gases in the atmosphere was equivalent to a doubling of the
carbon dioxide concentration – under business-as-usual this is likely to
occur around the middle of the twenty-first century. The estimates were
typically around one to two per cent of gross domestic product (GDP)
for developed countries. In developing countries, because of their greater
vulnerability to climate change and because a greater proportion of their
expenditure is dependent on activities such as agriculture and water,
estimates of the cost of damage are greater, typically about five per cent
of GDP or more. At the present stage of knowledge, these estimates
are bound to be crude and subject to large uncertainties; nevertheless,
they give a feel for the likely range of cost. It was also pointed out in
Chapter 7 thatthe cost estimates only included those items that could
be costed in money terms. Those items of damage or disturbance for
which money is not an appropriate measure (e.g. the generation of large
numbers of environmental refugees) also need to be to exposed and taken
into account in any overall appraisal.
The longer-term damage, should greenhouse gases more than double
in concentration, is likely to rise somewhat more steeply in relation to the
concentration ofcarbon dioxide (Figure 9.3). For quadrupled equivalent
carbon dioxide concentration, for instance, estimates of damage cost
of the order of two to four times that for doubled carbon dioxide have
been made – suggesting that the damage might follow something like a
quadratic law relative to the expected temperature rise.^9 In addition the