This chapter describes the observed and projected health impacts of climate change, current and future populations at risk, and the strategies, policies and measures that have been and can be taken to reduce impacts. The chapter reviews the knowledge that has emerged since the Third Assessment Report (TAR) (McMichael et al., 2001). Published research continues to focus on effects in high-income countries, and there remain important gaps in information for the more vulnerable populations in low-and middle-income countries.

8.1.1 State of health in the world

Health includes physical, social and psychological well-being. Population health is a primary goal of sustainable development. Human beings are exposed to climate change through changing weather patterns (for example more intense and frequent extreme events) and indirectly though changes in water, air, food quality and quantity, ecosystems, agriculture, livelihoods and infrastructure (Figure 8.1). These direct and indirect exposures can cause death, disability and suffering. Ill-health increases vulnerability and reduces the capacity of individuals and groups to adapt to climate change. Populations with high rates of disease and debility cope less successfully with stresses of all kinds, including those related to climate change.

In many respects, population health has improved remarkably over the last 50 years. For instance, average life expectancy at birth has increased worldwide since the 1950s (WHO, 2003b, 2004b). However, improvement is not apparent everywhere, and substantial inequalities in health persist within and between countries (Casas-Zamora and Ibrahim, 2004; McMichael et al., 2004; Marmot, 2005; People's Health Movement et al., 2005). In parts of Africa, life expectancy has fallen in the last 20 years, largely as a consequence of HIV/AIDS; in some countries more than 20% of the adult population is infected (UNDP, 2005). Globally, child mortality decreased from 147 to 80 deaths per 1,000 live births from 1970 to 2002 (WHO, 2002b). Reductions were largest in countries in the World Health Organization (WHO) regions of the Eastern Mediterranean, South-East Asia and Latin America. In sixteen countries (fourteen of which are in Africa), current levels of under-five mortality are higher than those observed in 1990 (Anand and Barnighausen, 2004). The Millennium Development Goal (MDG) of reducing under-five mortality rates by two-thirds by 2015 is unlikely to be reached in these countries.

Non-communicable diseases, such as heart disease, diabetes, stroke and cancer, account for nearly half of the global burden of disease (at all ages) and the burden is growing fastest in low-and middle-income countries (Mascie-Taylor and Karim, 2003). Communicable diseases are still a serious threat to public health in many parts of the world (WHO, 2003a) despite immunisation programmes and many other measures that have improved the control of once-common human infections. Almost 2 million deaths a year, mostly in young children, are caused by diarrhoeal diseases and other conditions that are attributable to unsafe water and lack of basic sanitation (Ezzati et al., 2003). Malaria, another common disease whose geographical range may be affected by climate change, causes around 1 million child deaths annually (WHO, 2003b). Worldwide, 840 million people were undernourished in 1998-2000 (FAO, 2002). Progress in overcoming hunger is very uneven. Based on current trends, only Latin America and the Caribbean will achieve the MDG target of halving the proportion of people who are hungry by 2015 (FAO, 2005; UN, 2006a).

8.1.2 Findings from the Third Assessment Report

The main findings of the IPCC TAR (McMichael et al., 2001) were as follows.

• An increase in the frequency or intensity of heatwaves will increase the risk of mortality and morbidity, principally in older age groups and among the urban poor.

• Any regional increases in climate extremes (e.g., storms, floods, cyclones, droughts) associated with climate change would cause deaths and injuries, population displacement, and adverse effects on food production, freshwater availability and quality, and would increase the risks of infectious disease, particularly in low-income countries.

• In some settings, the impacts of climate change may cause social disruption, economic decline, and displacement of populations. The health impacts associated with such socioeconomic dislocation and population displacement are substantial.

• Changes in climate, including changes in climate variability, would affect many vector-borne infections. Populations at the margins of the current distribution of diseases might be particularly affected.

• Climate change represents an additional pressure on the world's food supply system and is expected to increase yields at higher latitudes and decrease yields at lower latitudes. This would increase the number of undernourished people in the low-income world, unless there was a major redistribution of food around the world.

• Assuming that current emission levels continue, air quality in many large urban areas will deteriorate. Increases in exposure to ozone and other air pollutants (e.g., particulates) could increase morbidity and mortality.

8.1.3 Key developments since the Third Assessment Report

Overall, research over the last 6 years has provided new evidence to expand the findings of the TAR. Empirical research has further quantified the health effects of heatwaves (see Section 8.2.1). There has been little additional research on the health effects of other extreme weather events. The early effects of climate change on health-relevant exposures have been investigated in the context of changes in air quality and plant and animal phenology (see Chapter 1 and Sections 8.2.7 and 8.2.8). There has been research on a wider range of health issues, including food safety and water-related infections. The contribution made by climate change to the overall burden of disease has been estimated (see Section 8.4.1) (McMichael, 2004). Several countries have conducted health-impact assessments of climate change; either as part of a multi-sectoral study or as a stand-alone project (see Tables 8.1, 8.3 and 8.4). These provide more detailed information on population vulnerability to climate change (see Section 8.4.2). The effect of climate has been studied in the context of other social and environmental determinants of health outcomes (McMichael et al., 2003a; Izmerov et al., 2005). Little advancement has been made in the development of climate-health impact models that project future health effects. Climate change is now an issue of concern for health policy in many countries. Some adaptation measures specific to climate variability have been developed and implemented within and beyond the health sector (see Section 8.6). Many challenges remain for climate- and health-impact and adaptation research. The most important of these is the limited capacity for research and adaptation in low- and middle-income countries.

8.1.4 Methods used and gaps in knowledge

The evidence for the current sensitivity of population health to weather and climate is based on five main types of empirical study:

• health impacts of individual extreme events (e.g., heatwaves, floods, storms, droughts, extreme cold);

• spatial studies where climate is an explanatory variable in the distribution of the disease or the disease vector;

• temporal studies assessing the health effects of interannual climate variability, of short-term (daily, weekly) changes in temperature or rainfall, and of longer-term (decadal) changes in the context of detecting early effects of climate change;

• experimental laboratory and field studies of vector, pathogen, or plant (allergen) biology;

• intervention studies that investigate the effectiveness of public-health measures to protect people from climate hazards.

This assessment of the potential future health impacts of climate change is conducted in the context of:

• limited region-specific projections of changes in exposures of importance to human health;

• the consideration of multiple, interacting and multi-causal health outcomes;

• the difficulty of attributing health outcomes to climate or climate change per se;

• the difficulty of generalising health outcomes from one setting to another, when many diseases (such as malaria) have important local transmission dynamics that cannot easily be represented in simple relationships;

limited inclusion of different developmental scenarios in health projections;

the difficulty in identifying climate-related thresholds for population health;

limited understanding of the extent, rate, limiting forces and major drivers of adaptation of human populations to a changing climate.

Table 8.1. National health impact assessments of climate change published since the TAR.


Key findings

Adaptation recommendations


(McMichael et al., 2003b)

Increase in heatwave-related deaths; drowning from floods; diarrhoeal disease in indigenous communities; potential change in the geographical range of dengue and malaria; likely increase in environmental refugees from Pacific islands.

Not considered.


(Programa Nacional de Cambios Climaticos Componente Salud et al., 2000)

Intensification of malaria and leishmaniasis transmission. Indigenous Not considered.

populations may be most affected by increases in infectious diseases.


(Programa Nacional de Cambios Climaticos Componente Salud et al., 2000)

Intensification of malaria and leishmaniasis transmission. Indigenous Not considered.

populations may be most affected by increases in infectious diseases.


(National Environment Commission et al., 2006)

Loss of life from frequent flash floods; glacier lake outburst floods; landslides; hunger and malnutrition; spread of vector-borne diseases into higher elevations; loss of water resources; risk of water-borne diseases.

Ensure safe drinking water; regular vector control and vaccination programmes; monitor air and drinking water quality; establishment of emergency medical services.


(Riedel, 2004)

Increase in heatwave-related deaths; increase in air pollution-related diseases; spread of vector- and rodent-borne diseases; increased problems with contamination of both domestic and imported shellfish; increase in allergic disorders; impacts on particular populations in northern Canada.

Monitoring for emerging infectious diseases; emergency management plans; early warning systems; land-use regulations; upgrading water and wastewater treatment facilities; measures for reducing the heat-island effect.

Finland Small increase in heat-related mortality; changes in phenological (Hassi and Rytkonen, 2005) phases and increased risk of allergic disorders; small reduction in winter mortality.

Awareness-building and training of medical doctors.


(Zebisch et al., 2005)

Observed excess deaths from heatwaves; changing ranges in tickborne encephalitis; impacts on health care.

Increase information to the population; early warning; emergency planning and cooling of buildings; insurance and reserve funds.


(Ministry of Environment and Forest and Government of India, 2004)

Increase in communicable diseases. Malaria projected to move to higher latitudes and altitudes in India.

Surveillance systems; vector control measures; public education.


(Koike, 2006)

Increased risk of heat-related emergency visits, Japanese cedar pollen disease patients, food poisoning; and sleep disturbance.

Heat-related emergency visit surveillance.

The Netherlands

(Bresser, 2006)

Increase in heat-related mortality, air pollutants; risk of Lyme disease, Not considered. food poisoning and allergic disorders.

New Zealand

(Woodward et al., 2001)

Increases in enteric infections (food poisoning); changes in some allergic conditions; injuries from more intense floods and storms; a small increase in heat-related deaths.

Systems to ensure food quality; information to population and health care providers; flood protection; vector control.


(Autoridad Nacional del Ambiente, 2000)

Increase of vector-borne and other infectious diseases; health problems due to high ozone levels in urban areas; increase in malnutrition.

Not considered.


(Casimiro and Calheiros, 2002; Calheiros and Casimiro, 2006)

Increase in heat-related deaths and malaria (Tables 8.2, 8.3), food-and water-borne diseases, West Nile fever, Lyme disease and Mediterranean spotted fever; a reduction in leishmaniasis risk in some areas.

Address thermal comfort; education and information as well as early warning for hot periods; and early detection of infectious diseases.


(Moreno, 2005)

Increase in heat-related mortality and air pollutants; potential change Awareness-raising; early warning systems for of ranges of vector- and rodent-borne diseases. heatwaves; surveillance and monitoring; review of health policies.


(Kaumov and Muchmadeliev, 2002)

Increase in heat-related deaths.

Not considered.


(Thommen Dombois and Braun-Fahrlaender, 2004)

Increase of heat-related mortality; changes in zoonoses; increase in cases of tick-borne encephalitis.

Heat information, early warning; greenhouse gas emissions reduction strategies to reduce secondary air pollutants; setting up a working group on climate and health.

United Kingdom

(Department of Health and Expert Group on Climate Change and Health in the UK, 2001)

Health impacts of increased flood events; increased risk of heatwave-related mortality; and increased ozone-related exposure.


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