Fact Sheet No 266
CLIMATE AND HEALTH
People have adapted to living in a wide variety of climates around the world – from the tropics to the arctic, both climate and weather have a powerful impact on human life and health.
The extremes of weather (heavy rains, floods, hurricanes) occur over a short period of time (a few days) and can severely affect health. Poorer communities are much more vulnerable to the health impact of climate variability than rich ones. Of approximately 80,000 deaths which occur world-wide each year as a result of natural disasters about 95% of them are in poor countries. In weather-triggered disasters people and animals die; homes, crops and resources are destroyed; public health infrastructure (e.g. hospitals, roads) is damaged. Some recent examples:
Human physiology can handle most variation in weather, within certain limits. But marked short-term fluctuations in weather can cause acute adverse health effects, leading to a greater number of hospital admissions and even to increased death rate:
Climate plays an important role in vector-borne diseases – a major cause of illness and death in tropical countries – transmitted by insects such as mosquitoes, ticks, sandflies and tsetse flies. These cold-blooded vectors are sensitive to direct effects of climate such as temperature, rainfall patterns and wind. Climate also affects their distribution and abundance through its effects on host plants and animals.
Malaria transmission is particularly sensitive to weather and climate. Unusual weather conditions, for example a heavy downpour, can greatly increase the mosquito population and trigger an epidemic. This is what happened in the Wajir district of Kenya in 1998. Under normal weather conditions this region is too dry for the vectors and very little transmission occurs. There had not been a malaria epidemic since 1952 and the local health sector was unprepared for the major outbreak that followed the heavy rains. On the desert and highland fringes of malarious areas, malaria transmission is unstable and the population lacks protective immunity. Thus, when weather conditions (rainfall and temperature) favour transmission, serious epidemics may occur. In some countries, such as India, Colombia and Venezuela, fluctuations in malaria risk over the years have been linked to changes in rainfall associated with the El Niño cycle.
About two thirds of solar energy reaching Earth is absorbed by the Earth’s surface which consequently gets warmer. The heat radiates back to the atmosphere, where some of it is trapped by greenhouse gases, mostly carbon dioxide.
The average surface temperature is about 15°C – about 33°C higher than it would be in the absence of the greenhouse effect; without such gases most of the Earth’s surface would be frozen with a mean air temperature of -18° C.
Human activities have polluted the atmosphere to the extent of being able to affect the climate. The atmospheric concentration of carbon dioxide has increased by 31% since pre-industrial times, causing more heat to be trapped in the lower atmosphere. Emissions of carbon dioxide are still increasing. Many countries are working to reduce greenhouse gas emissions under the United Nations Framework Convention on Climate Change. Unfortunately, current international agreements are not sufficient to prevent the world facing significant changes in climate and a rise in sea levels.
The scientific evidence for climate change and its impacts is assessed by the Intergovernmental Panel on Climate Change (IPCC). According to IPCC's Third Assessment Report (2001), "there is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities". Some impacts include:
Projections of future climate change are derived from series of experiments with global climate models which, in turn, rely on estimates of future population growth and energy use. Climatologists of the IPCC have reviewed the results of these experiments in order to estimate changes in climate in the course of this century. They predict:
Human societies are very vulnerable to climate extremes (droughts, floods, wind storms). A changing climate would entail changes in the frequency and/or intensity of such extremes. This is a major concern for human health. To a large extent, public health depends on safe drinking water, sufficient food, secure shelter, and good social conditions. All these factors can be affected by climate change:
Changes in climate may alter the distribution of important vector species (e.g. mosquitoes) and may increase the spread of disease to new areas which lack a strong public health infrastructure.
A report by a WHO Task Group has warned that climate change may have an important impact on human health. Not only will climate change exacerbate various current health problems, it may also bring new and unexpected ones. Response strategies aimed at lessening potential health impact of the anticipated climate changes should include:
As a response to the requirements stated in Agenda 21 and in the United Nations Framework Convention on Climate Change, a number of organizations carrying out significant climate-related activities, jointly established the Inter-Agency Committee on the Climate Agenda. In 1998, the 51st World Health Assembly endorsed WHO’s participation in this group.
WHO provides input to the health aspects of the Climate Agenda within the general field of "climate impact assessment and response strategies to reduce vulnerability". WHO has been working with WMO and UNEP in this area since 1999. Joint activities of the three organizations focus on three main areas: capacity building, information exchange and research promotion.
For related information see also Fact Sheets No. 192, El Niño and its health impacts; and No. 227 Solar radiation and human health. For additional information visit the Climate and Health home page athttp://www.who.int/peh
For further information, please contact the Office of the Spokesperson, WHO, Geneva; Tel.: (+41 22) 791 2599, Fax: (+41 22) 791 4858, E-mail: email@example.com All WHO Press Releases, Fact Sheets and Features as well as other information on this subject can be obtained on Internet on the WHO home page: http://www.who.int