Edited by A. J. McMichael, A. Haines, R. Slooff and S. Kovats
the world's climate system and its dependent ecosystems, we are posing
new and widespread risks to the health of human populations.
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 most direct health
effects would be those caused by heatwaves, storms, and floods. These
may increase in frequency and intensity as mean temperature and precipitation
rise. However, the regional pattern of increases in these extreme events
remains difficult to predict with existing climate models.
Stressful hot weather
episodes are a known cause of short-term mortality excesses. An increase
in the frequency and severity of heatwaves would obviously exacerbate
The extent to which
increases in heat-related deaths would be offset by a reduction in cold-related
deaths is unresolved. On balance, evidence suggests that increases in
"acute" mortality in response to more frequent hot weather episodes would
outweigh decreases in winter-related mortality.
Current models indicate
that, by around 2050, many major cities around the world could be experiencing
up to several thousand extra heat-related deaths annually, independent
of any increases due to population growth.
Climate change would
exacerbate the production of some types of air pollutants and thus increase
the incidence of associated health effects, such as cardiovascular and
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.
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.
Climate change would
tend to alter the geographic distribution (altitude and latitude) of disease
vectors and to affect the behavior and seasonal activity of vectors and
parasites. These effects could amplify the transmission of many vector-borne
diseases in many parts of the world.
In the next century,
climate change is expected to increase the global incidence of malaria
by 50-80 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 45 percent to around 60 percent.
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.
The predicted rise
in sea level would have several adverse effects, apart from population
displacement and the loss of agricultural land. These effects include
saltwater intrusion and contamination of water supplies, changes in the
distribution of vector-borne diseases, and increases in death and injury
due to flooding.
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 responses of
essential food crops to a change in climate will depend much on other
ecological determinants such as soil erosion, saltwater intrusion or salination,
the balance between pests and predators, and increases in ultraviolet
effects on health would result from the social-demographic disruptions
caused by rising sea-level and from those caused by climate-related regional
shortages in fresh water, food and other natural resources.
Many health consequences
would arise via disturbances of complex biotic and other natural systems,
reflecting the fundamental link between the integrity of natural ecosystems
and the long-term health of human populations.
depletion coincides with, but is separate from, troposphere-based climate
change. Sustained depletion of ozone, resulting in increased exposure
to ultraviolet radiation, would cause an increase in the incidence of
skin cancer. It may also increase the incidence of ocular lesions, such
as cataracts, and possibly cause weakening of the immune system, with
a corresponding increased susceptibility to infections and altered responsiveness
and communities vary markedly in their vulnerability to climatic change
and in the resources available to them for protection and mitigation.
Many of the anticipated consequences would be greatest in the world's
poor and disadvantaged populations.
While there can as yet be no certainty in forecasts of the future health effects of climate change, the role of science in this context must be to assist adoption of precautionary policies that balance current social needs against serious future risks.
Work on the report began in 1993 following receipt of a grant from the United States Environmental Protection Agency. Further financial resources were obtained from the government of the Netherlands and the three participating UN agencies (WHO,WMO, and UNEP, with WHO designated the coordinating agency). An international task group of experts was formed under the direction of A. J. Michael, and met three times in two years. The views expressed in the report reflect the consensus reached by this Task Group and do not necessarily reflect the the policies of the participating agencies.