Human Health



Global Projected Impacts on Human Health

As the world’s climate system and its dependent ecosystems are destabilized, new and widespread risks to the health of human populations are possible. While most of our current environmental health problems occur on a local or regional level, many of the anticipated health effects of climate change would affect large populations in many regions.

The effect will be mainly negative. Extreme heat and cold, floods and droughts, air pollution, and allergens all cause health problems. We must also consider the less direct impacts such as increased infectious diseases, poor nutrition, and economic hardship.

Human health is affected by many factors, so it is difficult to point to climate change as a specific cause. Research does support the following predictions:

1. An increase in the number and frequency of heat waves will increase the risk of death and illness, particularly in older people and the urban poor. Higher humidity and air pollution will intensify the effects.

Thermal stress will be highest for cities in temperate latitudes especially those with limited air-conditioning. Current models indicate that, by around 2050, many major cities around the world could experience up to several thousand extra heat-related deaths annually, independent of any increases due to population growth. Warmer winters will result in fewer cold-related deaths in many temperate countries.

2. Any increases in the frequency and intensity of extreme events like cyclones, will affect human health in many ways. There will be direct loss of life and injury. Health is indirectly affected by loss of shelter, population displacement, contamination of water supplies, loss of food production, and increased risk of infectious disease epidemics. Over recent years, major climate-related disasters have had major adverse effects on human health, including floods in China, Bangladesh, Europe, Venezuela, and Mozambique, as well as Hurricane Mitch, which devastated Central America.

Climate change is also likely to bring about major regional shifts in rainfall patterns and, with them, increased frequency or severity of droughts, floods, and brushfires. In drought-prone regions, droughts could become longer lasting and more severe.

3. Climate change will decrease air quality in urban areas with air pollution problems. An increase in temperature and ultraviolet (UV) radiation increases the formation of ground-level ozone. This type of ozone is well-known to have adverse effects on respiratory health.

Climate change would increase the production of some types of air pollutants and thus increase the incidence of associated health effects, such as cardiovascular and respiratory disorders.

A warmer and wetter climate in some regions could also result in higher airborne concentrations of various pollens and spores with likely effects on allergic disorders, such as hay fever and possibly asthma.

4. Climate change will affect vector-borne infectious diseases. Vector-borne infectious diseases are transmitted by blood-feeding organisms such as mosquitoes and ticks. The range and season for these diseases will be affected by higher temperatures, and changes in precipitation. This will extend the range and season for some infectious diseases and contract them for others.

Currently, 40% of the world population lives in malaria-infested areas. In areas with limited or deteriorating public health infrastructure, increased temperatures will tend to expand the geographic range of malaria transmission to higher altitudes and higher latitudes. Changing patterns of rainfall, combined with higher temperatures, will extend the disease transmission season. In the next century, climate change is expected to increase the global incidence of malaria by 50 to 80 million additional cases each year. The proportion of the world population exposed to the potential transmission of malaria is expected to increase from the current 40 percent to around 60 percent.

Changes in climate, will affect many other vector-borne infections (such as dengue fever, Lyme disease, and mosquito- and tick-borne encephalitis). More people will be living in disease-prone regions and will contract these diseases.

Increases in the incidence of non-vector-borne diseases, such as cholera, and other food-related and water-related infections, could also occur, particularly in tropical and sub-tropical regions, following changes in water distribution, temperature and the proliferation of microorganisms.

5. Climate change may cause changes in the marine environment that could increase biotoxin poisoning from seafood. Biotoxins associated with warmer waters could extend their range to higher latitudes. Toxic algal blooms could increase, which can poison humans and are ecologically and economically damaging. Changes in surface water quantity and quality will affect the incidence of diarrheal diseases.

6. Changes in food supply resulting from climate change could affect the nutrition and health of the poor in some regions of the world. Studies consistently predict that climate change will have significant regional impacts on agricultural yield. Some areas will gain; others will lose. Some mid-continental drying in temperate zones, such as the mid-west USA, southern Europe and Ukraine, may occur, but the most negative effects are foreseen at lower latitudes, in poorer tropical and semitropical countries, especially those reliant upon rain-fed, non-irrigated agriculture. The risk of reduced food yields is greatest in developing countries, where 790 million people are estimated to be undernourished. Climate change would increase the number of undernourished people in the developing world, particularly in the tropics.

The effects on essential food crops of a change in climate will depend on other ecological factors such as soil erosion, saltwater intrusion, the balance between pests and predators, and increases in ultraviolet radiation levels.

Natural systems are complex, and fundamentally linked to human health. Many health consequences will result from disturbances to these interactions.

Our global communities vary greatly in their vulnerability to climatic change and in the resources available to them to protect or alleviate the effects. Many of the anticipated consequences would be greatest in the world’s poor and disadvantaged populations.

Disease burdens and summary measures of population health

The World Health Organization (WHO) has estimated the global burden of disease caused by climate change. The “disease burden” is the total amount of disease or premature deaths within the population. Researchers calculated the disease burdens for 26 environmental, occupational, behavioural and life-style risk factors. Figure 1 shows the estimate of the disease burden caused by climate change in 2000. The base year for comparison was 1990. (

Figure 1. Estimated impacts of climate change in 2000 by region


ðð years of life lost due to premature death (YLL) ð years of life lived with disability (YLD).

ACTIVITY 1 Question:

1. Which three regions have suffered the greatest impact per million population?
2. Give two reasons why you think these regions have suffered the greatest impact.
3. Which region has had the least impact?
4. Give three possible reasons for this.

How much disease would climate change cause?

To inform policies, an estimation of the approximate magnitude of the health impacts of climate change is needed. This will indicate which particular impacts are likely to be greatest and in which regions, and how much of the climate-attributable disease burden could be avoided by emissions reduction. It will also guide health-protective strategies.

The global burden of disease attributable to climate change has recently been estimated as part of a comprehensive World Health Organization project (1). This project sought to quantify disease burdens attributable to 26 environmental, occupational, behavioural and life-style risk factors in 2000, and at selected future times up to 2030.

(by the World Meteorological Organization and IPCC).

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