How much will sea level rise? 145Sensitivity, adaptive capacity and vulnerability (see box above)
vary a great deal from place to place and from country to country.
In particular, developing countries, especially the least developed
countries, have less capacity to adapt than developed countries, which
contributes to the relative high vulnerability to damaging effects of
climate change in developing countries.
The assessment of the impacts of global warming is also made more
complex because global warming is not the only human-induced envi-
ronmental problem. The loss of soil and its impoverishment (through
poor agricultural practice), the over-extraction of groundwater and the
damage due to acid rain are examples of environmental degradations on
local or regional scales that are having a substantial impact now.^3 If they
are not corrected they will tend to exacerbate the negative impacts likely
to arise from global warming. For these reasons,the various effects of
climate change so far as they concern human communities and their ac-
tivities will be put in the context of other factors that might alleviate or
exacerbate their impact.
The assessment of climate change impacts, adaptations and vulner-
ability draws on a wide range of physical, biological and social science
disciplines and consequently employs a large variety of methods and
tools. It is therefore necessary to integrate information and knowledge
from these diverse disciplines; the process is calledIntegrated Assess-
ment(see box in Chapter 9 on page 237).
The following paragraphs will look at various impacts in turn and
then bring them together in a consideration of the overall impact.
How much will sea level rise?
There is plenty of evidence for large changes in sea level during the
Earth’s history. For instance, during the warm period before the onset of
the last ice age, about 120 000 years ago, the global average temperature
was a little warmer than today (Figure 4.4). Average sea level then was
about5or 6 m higherthan it is today. When ice cover was at its maximum
towards the end of the ice age, some 18 000 years ago, sea level was over
100 m lower than today, sufficient, for instance, for Britain to be joined
to the continent of Europe.
It is often thought that the main cause of these sea level changes was
the melting or growth of the large ice-sheets that cover the polar regions.
It is certainly true that the main reason for the drop in sea level 18 000
years ago was the amount of water locked up in the large extension of the
polar ice-sheets. In the northern hemisphere these extended in Europe as
far south as southern England and in North America to south of the Great
Lakes. It must also be true that the main reason for the 5 or 6 m higher