Global warming is likely to have wide-ranging and mostly adverse impacts on human health, with significant loss of life. The most vulnerable populations to the impacts of climate change will be those already under pressure from social, economic and existing climate stresses. These will include those in developing countries, in the lower income groups, residents of coastal lowlands and islands, populations in semi-arid grasslands, and the urban poor. Increased exposure to natural hazards and extreme weather, such as coastal or river flooding, drought, landslides, storms and hurricanes, will prove detrimental to those most at risk.
Direct health impacts from climate change are likely to arise from the increased occurrence and magnitude of extreme weather events. Such direct effects may include heat-related stress and death, and deaths from flooding and landslides. An increased frequency or severity of heat waves would cause an increase in mortality, heart attacks and breathing illnesses. In very large cities, this would represent several thousand extra deaths annually. However, the number of cold-related deaths may decrease, partially offsetting deaths due to heat waves.
A significant indirect effect arising from global warming will be an increase in the range of vector-borne diseases such as malaria. Malarial mosquitoes may spread to higher latitudes and higher altitudes, taking advantage of the warmer temperatures. Approximately 45% of the world's population presently live in the climate zone where mosquitoes transmit malaria. Climate models predict that this will increase to about 60% by the second half of the 21st century, with maybe 80 million extra cases of malaria occurring each year. Increases in food- and water-related infections could also occur, particularly in tropical and subtropical regions. Warmer temperatures, reduced water supplies, and proliferating micro-organisms would lead to a higher incidence of diarrhoea, cholera, salmonellosis, and other such infections. Local reductions in food production could increase malnutrition and hunger, with long-term health consequences, particularly for children.
Warming of local and regional climates may enhance episodes of air pollution, particularly in urban centres, increasing the incidence of respiratory diseases. Asthma and other allergic disorders could result from climate-induced changes in the formation and persistence of pollens, spores, and certain air pollutants.
Poorer communities will be more vulnerable than richer ones. However, richer countries will also be increasingly vulnerable as their populations age. Health risks can be addressed through various adaptation strategies. Adaptive options to minimise health impacts may include improved and extended medical care services, better housing and air conditioning, water purification and public education. The lack of resources will be a constraint in many regions, but negative health effects can be minimised through a transfer of technological, educational and medical expertise from the more developed nations to the less developed nations.