OUR MISSION: ACER supports communities, government agencies and corporations in taking action to reduce biodiversity loss and strengthen climate resilience by increasing and monitoring urban and riparian zone forest canopy.

Human Health



As the world’s climate system and its dependent ecosystems become unstable, new and widespread risks to the health of human populations occur. Most of our current environmental health problems occur on a local or regional level. Many health effects of climate change are already beginning to affect large populations in areas of the planet.

The effect is mainly negative. Extreme heat and cold, floods and droughts, air pollution, and allergens all cause health problems. Less direct impacts such as increased infectious diseases, poor nutrition, and economic hardship are evident.

Human health is affected by many factors, so it is difficult to point to climate change as a specific cause unless from an extreme event or known trail of infection.

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

Heat stress is highest for cities in temperate latitudes especially those areas with limited air-conditioning. Paris and Chicago are two of the major cities around the world that have experienced several thousand extra heat-related deaths mostly the young and elderly.

Power shortages in Ontario have required people to reduce their use of electricity eg. air-conditioning.

2. Increases in the frequency and intensity of extreme events like cyclones, hurricanes and tornados have affected human health and well-being in many ways.

There has been direct loss of life and injury. Health is indirectly affected by loss of shelter, 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. One of the most recent disasters is Hurricane Katrina that wreaked havoc to the American gulf states in August 2005.

Major regional shifts in rainfall patterns have brought increased frequency or severity of droughts, floods, and brushfires. Food and water supplies and sewage treatment facilities have failed or been threatened.

3. Decreased air quality in urban areas with air pollution problems. An increase in temperature and ultraviolet (UV) radiation increases the formation of ground-level ozone and smog. Ground level ozone has adverse effects on respiratory health.

Citizens in Toronto have been asked to reduce use of automobiles to reduce air pollution. People with asthma and chronic respiratory ailments have been forced to remain indoors for many more ‘smog alert days in Ontario.

4. Range and season changes of 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 has been affected by higher temperatures, and changes in precipitation. See the spread of West Nile Virus and Lyme disease north into Ontario.

Increases in the incidence of non-vector-borne diseases, such as cholera, and other food-related and water-related infections, are feared after extreme events where basic health care has been disrupted.

5. Algal blooms threaten drinking water supplies. Contamination from E. coli and other bacteria are causing beach closings. Changes in surface water quantity and quality affect the incidence of diarrheal diseases. Marine poisonings from biotoxins need to be heeded.

6. Changes in food supply affect nutrition and health. Some areas have lost agricultural yield through drought and others through early frosts, flooding, insect invasions – even in Ontario. The most negative effects are seen at lower latitudes, in poorer tropical and semitropical countries, especially those reliant upon rain-fed, non-irrigated agriculture. The effects on essential food crops of a change in climate depends 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 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 consequences are 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. The figure below shows the estimate of the disease burden caused by climate change in 2000. The base year for comparison was 1990.

The Disability-Adjusted Life Year (DALY) is the sum of: The number of years of life lost due to premature death (YLL) and the number of years of life lived with disability (YLD).

Content Updated Sept 2005

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.

Choose an affected country and learn what other reasons have been part of the loss of food production in these latitudes in Africa which have led to starvation conditions in these countries other than those caused by government policy. Hint see also deforestation and desertification.