Mini-SymposiumClimate change and human health: Impacts, vulnerability and public health☆
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 (Fig. 1). Such health effects will be modulated by factors such as socio-economic 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 such as population growth, urbanization, land use changes and depletion of fresh water resources that themselves have implications for health and which 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 overviews1, 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.1 Extremes of temperature and rainfall, such as 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, e.g. those of malaria and dengue, and the incidence of diarrhoeal diseases. Climate can affect levels of air pollutants, for example tropospheric ozone pollution may be higher in some areas of Europe, and lower in others but the relationships 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 (Fig. 2): 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. 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 At the upper end of the range effects are more difficult to predict and likely to be more seriously adverse.7
Section snippets
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 (such as malaria), there is now evidence of vector species responding to recent climate change in Europe.8 There have been latitudinal shifts in ticks which carry Tick-Borne Encephalitis in northern Europe9, 10 but alternative
Heat waves
Mortality rises in hot weather, especially in elderly people. It is very likely that climate change will be associated with increases in the frequency of heatwaves.15 More than 2000 excess deaths were reported in England and Wales16 during the major heat wave that affected most of western Europe in 2003 (Table 1).16, 17, 18, 19, 20, 21, 22, 23 The greatest impact on mortality occurred in France, where it was estimated that 14,800 excess deaths occurred during the first 3 weeks of August 2003
Floods, droughts and storms
Natural disasters have a variety of health impacts.3, 26 These range from immediate effects of physical injury and morbidity and mortality through to potentially long lasting effects on mental health. Most flood-related deaths can be attributed to rapid rise floods27, due to the increased risk of drowning. In October 1988, a flash flood occurred in the Nimes region of France.28 Although the homes of 45,000 people were damaged and more than 1100 vehicles destroyed, only nine deaths by drowning
Infectious diseases
Transmission of many infectious disease agents is sensitive to weather conditions, particularly those spending part of their lifecycle outside the human body. Pathogens that are carried by insects are exposed to ambient weather. Vector-borne diseases typically exhibit seasonal patterns in which the role of temperature and rainfall is well documented. Some vector-borne diseases, such as malaria, also display considerable year-to-year variation in some regions that can also be partly explained by
Estimating the global burden of disease due to climate change
The WHO has recently undertaken an exercise to estimate the global burden of disease (GBD) that could be due to climate change in terms of disability adjusted life years (DALYS) lost. This measure makes it possible to take into account impacts that do not necessarily lead to death but cause disability. Climate scenarios are derived from the output of global climate models that are, in turn, driven by scenarios of future greenhouse gas emissions (Fig. 3). The attributable burden of climate
Climate change and public health
The current state of knowledge about climate change is such that some specific measures for health protection can now be recommended. The summer of 2003 illustrated a lack of public health capacity in Europe to deal with heat waves. A recent WHO publication encourages public health decision makers to act now in order to address climate hazards, as well as address adaptation strategies in the longer term.46 Although there is uncertainty about future climate change, failure to invest in
Mitigation strategies and health
Climate change poses a major threat to sustainable development because adverse effects are likely to be directed particularly at poor populations that currently also suffer disproportionately from a lack of reliable energy at the level of the household and the community. The easy availability of cheap energy from fossil fuels has underpinned the economic development of industrialised countries and has therefore contributed substantially to the dramatic advances in health observed over the past
Conclusion
The effects of climate change on health are likely to be predominately negative and impact most heavily on low-income countries where capacity to adapt is weakest, but also on the most vulnerable groups in developed countries. Adaptation strategies should blunt some of the adverse impacts but will pose difficulties of implementation, particularly in low-income countries. With climate change already underway, there is a need to assess vulnerabilities and identify cost-effective
Conflict of interest statement
AH is a reviewer and RSK a participant in the UN Intergovernmental Panel on Climate Change for the Fourth Assessment Report. DC-L and CC declare that they have no conflict of interest.
Acknowledgements
This article is based on a paper presented to the World Climate Change Conference (Moscow, Russian Federation, Sept 29–Oct 3, 2003), which has been updated for the 2005 Harben Lecture of the Royal Institute of Public Health. We thank Tony McMichael for permission to use figure 2 and acknowledge the contributions of many scientists to the Comparative quantification of health risks: global and regional burden of disease due to selected major risk factors report. The views expressed in this
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Based on a paper presented to the World Climate Change Conference, Moscow, Russian Federation, September 29–October 3, 2003 which has been updated.