The disease burden of a population, and how that burden is distributed, are important pieces of information for prioritizing and defining strategies to protect population health. For policy-makers, disease burden estimates provide an indication of the current and future health gains that could be achieved by targeted protection from specific risks. To help provide a reliable source of information for policy-makers, WHO has developed methods to analyse the impacts of risks for health, and has estimated the impacts of 26 risk factors worldwide, including climate change (WHO, 2002; McMichael et al., 2004).

The Environmental Burden of Disease (EBD) series aims at supporting countries to generate reliable information for policy-making, by presenting methods for estimating the environmental burden at national and regional levels. The introductory volume in the series outlines the general method (Prüss-Üstün et al., 2003), while subsequent volumes address specific environmental risk factors. The guides on specific risk factors are organized similarly, first outlining the evidence linking the risk factor to health, and then describing a method for estimating the health impact of that risk factor on the population.

All the guides take a practical, step-by-step approach and use numerical examples. The methods described can be adapted both to regional and national levels, and can be tailored to suit data availability.

It has been shown that climate change causes impacts on various communicable and noncommunicable diseases and injuries (WHO, 2002; McMichael et al., 2003a; Ezzati et al.,2004). While the environmental risk is distributed globally, most of the actions that are necessary to protect health under a changing climate are local. Quantitative assessment of the size and distribution of health risks can therefore be an important tool in identifying which actions will be most effective in adapting to climate change. They may also provide an incentive to cooperate at the international level to reduce our impacts on the global climate.

Climate change is unusual in its global scope, its irreversibility (over human timescales), and the very wide range of threats that it poses to health and other aspects of human wellbeing. While methods for describing and measuring health effects are still at an early stage of development and many uncertainties remain, it is important to provide a framework and first set of guidance for assessing health impacts, so that societies are better equipped to address this emerging threat.

This is a World Health Organization, Environmental Burden of Disease Series No. 14.