Lecture www.thelancet.com Vol 367 June 24, 2006 2101 Harben Lecture Climate change and human health: impacts, vulnerability, and mitigation A Haines, R S Kovats, D Campbell-Lendrum, C Corvalan It is now widely accepted that climate change is occurring as a result of the accumulation of greenhouse gases in the atmosphere arising from the combustion of fossil fuels. Climate change may affect health through a range of pathways— eg, as a result of increased frequency and intensity of heat waves, reduction in cold-related deaths, increased floods and droughts, changes in the distribution of vector-borne diseases, and effects on the risk of disasters and malnutrition. The overall balance of effects on health is likely to be negative and populations in low-income countries are likely to be particularly vulnerable to the adverse effects. The experience of the 2003 heat wave in Europe shows that high-income countries might also be adversely affected. Adaptation to climate change requires public-health strategies and improved surveillance. Mitigation of climate change by reducing the use of fossil fuels and increasing the use of a number of renewable energy technologies should improve health in the near term by reducing exposure to air pollution. Introduction It has been known for thousands of years, at least since the time of Hippocrates, that climate has wide ranging impacts on health. Increasing recognition of the process of climate change has led to a growing interest by health researchers in assessing the potential mechanisms by which changes in climate could influence health (figure 1). Such health effects will be modulated by factors such as socioeconomic development and by the degree to which effective adaptation measures are implemented. Although most studies have assessed the potential impacts of climate change in isolation from other environmental changes, in reality climate change will be experienced against a background of other global changes—eg, population growth, urbanisation, land use changes, and depletion of fresh water resources—that themselves have implications for health and that could, in some instances, interact with climate change to magnify the impacts. This article was the subject of the 2005 Harben Lecture of the Royal Institute of Public Health given by one of us (AH). It covers some of the ground of previous overviews 1,2 but adds discussion of adaptation options and the potential use of “mitigation strategies”—eg, energy efficiency and renewable technologies—to contribute to near-term reductions in mortality. There are several mechanisms by which climate can affect health. Extremes of temperature and rainfall—eg, heat waves, floods, and drought—have direct immediate effects on mortality as well as longer-term effects. For example, populations that have experienced flooding may suffer from sustained increases in common mental disorders. 3 Climate change is also likely to affect biodiversity and the ecosystem goods and services that we rely on for human health. Changes in temperature and rainfall may also affect the distribution of disease vectors—eg, those of malaria and dengue—and the incidence of diarrhoeal diseases. Climate can affect levels of air pollutants—eg, tropospheric ozone pollution may be higher in some areas of Europe and lower in others— but the relations are still imperfectly understood. 4 Sea level rise is likely to threaten low lying coastal populations, particularly in countries where economic conditions do not allow construction of sea defences and other counter measures. There are also concerns that flooding, drought, and environmental degradation associated with climate change may lead to population displacement and more environmental refugees. Research on the health impacts of climate change addresses three main topics: current associations between climate and disease, the effect of recent changes in climate, and the evidence base for projecting the future impacts of climate change on health (figure 2). Temperatures have been increasing globally for the past two to three decades. The detection and attribution of health effects to these changes has become a key research challenge. 5 This climate warming is projected to continue and accelerate, so that by the end of this century global mean temperature will have increased by 1·4–5·8°C. 6 Effects at the upper end of the range are more difficult to predict and likely to be more seriously adverse. 7 Has observed climate change already been affecting human health? A growing number of studies present evidence for the effects of observed climate change on vector-borne and other infectious diseases. Although the literature to date does not constitute strong evidence of an impact of climate change on human vector-borne diseases (eg, malaria), there is now evidence of vector species responding to recent climate change in Europe. 8 There have been latitudinal shifts in ticks that carry tick-borne encephalitis in northern Europe, 9,10 although alternative explanations—eg, changes in confounding factors like land use or in socioeconomic, demographic, and other environmental factors—remain plausible. Lancet 2006; 367: 2101–09 See Comment page 2039 London School of Hygiene and Tropical Medicine, London, UK (Prof A Haines MD, R S Kovats MSc); and WHO, Geneva, Switzerland (D Campbell-Lendrum DPhil, C Corvalan PhD) Correspondence to: Prof A Haines, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK Andy.Haines@lshtm.ac.uk Published simultaneously with Public Health; DOI:10.1016/ j.puhe.2006.01.002