218 Weighingthe uncertainty
noticeable impacts are likely to be on the availability of water (especially
on the frequency and severity of droughts and floods), on the distribution
(though possibly not on the overall size) of global food production and
on sea level in low-lying areas of the world. Further, although most of
our predictions have been limited in range to the end of the twenty-first
century, it is clear that by the century beyond 2100 the magnitude of the
change in climate and the impacts resulting from that change are likely
to be very large indeed.
The statement in the box regarding scientific uncertainty was for-
mulated for the IPCC 1990 Report. Over ten years later it remains a
good statement of the main factors that underly scientific uncertainty.
That this is the case does not imply little progress in the past decade.
On the contrary, as the subsequent IPCC Reports show, a great deal of
progress has been made in scientific understanding and in the develop-
ment of models. There is now much more confidence that the signal
of anthropogenic climate change is apparent in the observed climate
record. Models now include much more sophistication in their scientific
formulationsand possess increased skill in simulating the important
climate parameters. For regional scale simulation and prediction, re-
gional climate models (RCMs) with higher resolution have been
developed that are nested within global models (seeChapters 5 and 6).
These RCMs are beginning to bring more confidence to regional projec-
tions of climate change. Further, over the last decade, a lot of progress has
been made with studies in various regions of the sensitivity to different
climates of these regions’ resources, such as water and food. Coupling
such studies with regional scenarios of climate change produced by cli-
mate models enables more meaningful impact assessments to be carried
out^2 and also enables appropriate measures to be assessed. Particularly in
some regions large uncertainties remain; it will be seen for instance from
Figure 6.5 that current models perform better for some regions than for
others.
Summarised in Figure 9.1 are the various components that are in-
cluded in the development of projections of climate change or its impacts.
All of these possess uncertainties that need to be aggregated appropri-
ately in arriving at estimates of uncertainties in different impacts.The IPCC assessments
Because of the scientific uncertainty, it has been necessary to make a
large effort to achieve the best assessment of present knowledge and to
express it as clearly as possible. For these reasons the IPCC was set up
jointly by two United Nations’ bodies, the World Meteorological Or-
ganization (WMO) and the United Nations Environmental Programme