178 The impactsof climate change
whether the reduction in winter mortality will be greater or less than
the increase in summer mortality. These studies have largely been con-
fined to populations in developed countries, precluding a more general
comparison between changes in summer and winter mortality.
A further likely impact of climate change on health is the increased
spreading of diseases in a warmer world. Many insect carriers of dis-
ease thrive better in warmer and wetter conditions. For instance, epi-
demics of diseases such as viral encephalitides carried by mosquitoes
are known to be associated with the unusually wet conditions that oc-
cur in the Australian, American and African continents associated with
different phases of the El Ni ̃no cycle.^59 Some diseases, currently largely
confined to tropical regions, with warmer conditions could spread into
mid latitudes. Malaria is an example of such a disease thatis spread
by mosquitoes under conditions which are optimum in the tempera-
ture range of 15–32◦C with humidities of fifty to sixty per cent. It
currently represents a huge global public health problem, causing an-
nually around 300 million new infections and over one million deaths.
Under climate change scenarios, most predictive model studies indi-
cate a net increase in the geographic range (and in the populations at
risk) of potential transmission of malaria and dengue infections, each
of which currently impinge on forty to fifty per cent of the world’s
population. Other diseases that are likely to spread for the same rea-
son are yellow fever and some viral encephalitis. In all cases, how-
ever, actual disease occurrence will be strongly influenced by local envi-
ronmental conditions, socio-economic circumstances and public health
infrastructure.
The potential impact of climate change on human health could be
large. However, the factors involved are highly complex; any quanti-
tative conclusions will require careful study of the direct effects of
climate on humans and of the epidemiology of the diseases that are
likely to be particularly affected. Some remarks about how the health
impacts of extremes and disasters might be reduced are given in the next
section.Adaptationto climate change
As we have seen, some of the impacts of climate change are already
becoming apparent. A degree of adaptation therefore has already be-
come a necessity. Numerous possible adaptation options for responding
to climate change have already been identified. These can reduce ad-
verse impacts and enhance beneficial effects of climate change and can
also produce immediate ancillary benefits, but they cannot prevent all