There are uncertainties regarding the sensitivity (i.e., rate of change of the outcome variable per unit change in the input/ exposure variable) of many health outcomes to climate or climate-induced environmental changes. Relatively little quantitative research, with estimation of exposure-response relationships, has been done for outcomes other than death rates associated with thermal stress and changes in the transmission potential of several vector-borne infectious diseases. There has been increased effort to map the current distribution of vectors and diseases such as malaria by using climate and other environmental data (including satellite data).
Continuation of recent climatic trends soon may result in some shifts in the
geographic range and seasonality of diseases such as malaria and dengue. In
reality, however, such shifts also would depend on local topographical and ecological
circumstances, other determinants of local population vulnerability, and the
existence and level of adaptive public health defenses. There has been some
recent debate in the scientific literature about whether there is any evidence
of such shifts yet (Epstein et al., 1997; Mouchet et al., 1998;
Reiter, 1998a,b). It is not yet clear what criteria are most appropriate for
assessment of climatic influences on such changes in infectious disease patterns.
A balance is needed between formal, statistically based analysis of changes
within a particular local setting and a more synthesizing assessment of the
consistency of patterns across diverse settings and across different systemsphysical,
biotic, social, and public health. As with climate change itself, there is an
inherent difficulty in detecting small climate-induced shifts in population
health outcomes and in attributing the shift to a change in climate.
Population vulnerability is a function of the extent to which a health outcome in that particular environmental-demographic setting is sensitive to climate change and the capacity of the population to adapt to new climate conditions. Determinants of population vulnerability to climate-related threats to health include level of material resources, effectiveness of governance and civil institutions, quality of public health infrastructure, access to relevant local information on extreme weather threats, and preexisting burden of disease (Woodward et al., 1998). Thus, vulnerability is determined by individual, community, and geographical factors:
Understanding a population's capacity to adapt to new climate conditions is crucial to realistic assessment of the potential health impacts of climate change (Smithers and Smit, 1997). This issue is addressed more fully in Section 9.11.
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