Previous chapters have shown that climate change represents a serious environmental threat over the coming century. The public health community has a responsibility to provide policy-makers with evidence of the potential impacts of climate change on human population health. Policy-makers are obliged to respond to this risk even in the face of scientific uncertainties. The public health community has established methods for assessing the risks to health for a population. WHO defines health impact assessment as “a combination of procedures, methods and tools by which a policy, project or hazard may be judged as to its potential effects on the health of a population, and the distribution of those effects within the population” (1, 2). Despite recent advances in the methodology for health impact assessment, the greater goal of integration into mainstream policy-making has yet to be achieved. This objective is a long way off in both developed and developing countries.

Global climate change presents many unique problems for health impact assessment. It is a highly diffuse global exposure for which very limited information (in the form of climate projections) is available at local or national level. For many health impacts this is not an immediate problem but one that will develop over decades or longer. Action is needed now to avert the worst impacts through the reduction of greenhouse gas emissions. Further, guidance is required now on policies to enhance the capacity to deal with climate change (chapter 12). Health impact assessments typically refer to impacts in the next 10 to 20 years, rather than the 50 to 100 year time-scale of climate change projections
and the assessments of impacts in other sectors.