Costing the totalimpacts 185predominantly in the developed world; strongly negative effects are ex-
pected for populations that are poorly connected to regional and global
trading systems. Regions that will get drier or are already quite hot for
agriculture also will suffer, as will countries that are less well prepared
to adapt (e.g. because of lack of infrastructure, capital or education).
Overall, climate change is likely to tip agriculture production in favour
of well-to-do and well-fed regions at the expense of less well-to-do and
less well-fed regions. However, these studies have largely ignored the
increasing influence of climate extremes and as yet inadequately con-
sidered important factors such as water availability – largely because of
the lack of detailed information regarding these.
A further factor to which more consideration has recently been given
is the possibility of what are often called ‘singular events’ or irreversible
events of large or unknown impact. Some of these have been mentioned
earlier in this chapter or in previous chapters. Some examples are given
in Table 7.4. It is clearly extremely difficult to provide quantitative es-
timates of the probability of such events. Nevertheless it is important
that they arenot ignored. One recent study^66 has allocated a potential
damage cost to these of about one per cent of GWP for a warming of
2.5◦C and about seven per cent of GWP for a warming of 6◦C. Such
calculations are necessarily based on highly speculative assumptions,
but in that particular study these singular events represent the largest
single contributor to the total overall cost.
These further factors, such as more adaptation and singular events,
have worked in both directions in the estimates of cost, some reduc-
ing and some increasing them. There has tended therefore to be a
greater spread in the overall results, thus emphasising the large un-
certainties hidden in the calculations.^67 Further, little or no allowance
has been made in recent studies for the important influence of extreme
events.
If someallowance is made for the impact of extreme events (as
described in the last section), the studies so far suggest, in very gen-
eral terms, that the cost of damage due to climate change induced by a
doubling of the pre-industrial carbon dioxide concentration that can be
expressed in monetary terms is typically around one or two per cent of
GDP for developed countries and perhaps five per cent or more of GDP
in developing countries. However, what is also clear is that any estimates
at the moment must be considered as preliminary and uncertain, because
of inadequacies in both the assumptions that have to be made and the
available data necessary for the calculations.
An initial inspection of the sort of cost figures we have been pre-
senting in the last few paragraphs might suggest that the costs of global