Scientists warn that global warming could change our climate and environment. But as Mike Ahearn from the London School of Hygiene and Tropical Medicine explains, it could have consequences for our health too.

Global temperatures have risen over the last century. Evidence suggests that the human induced alteration of atmospheric composition, mainly from burning fossil fuels, contributes to this warming [1].

Current predictions are for a further rise of 1.4 - 5.80°C [1] over the next century. These changes in climatic conditions bring with them a range of hazards to human health. While their future impacts are uncertain, they can be predicted in general terms [2].

The health effects of climate change have been classified as direct and indirect, immediate and delayed [2]. Some populations would experience beneficial results. For example, winter cold-snaps would become milder in temperate countries, like the UK, where death rates usually peak at this time. But most of the anticipated health effects would be adverse [1].

Direct health effects include, changes in mortality and sickness caused by an altered pattern of exposure to thermal extremes. Respiratory illnesses could increase with more photochemical pollutants and aeroallergens in the air. And the danger of storms, floods or droughts in some regions would pose very real physical hazards too.

Indirect health effects include; a larger area at risk from 'vector borne' infectious diseases such as malaria, dengue fever, schistosomiasis, leishmaniasis, and Lyme disease. These are spread by disease-carrying mosquitoes in warmer temperatures. Other examples include various tick-borne viral encephalitis [3, 4].

Climate change is also expected to influence various directly transmitted infections, especially those due to contamination of drinking water and food. This is because many bacteria are sensitive to temperature.

Changes in the pattern of rainfall can disrupt surface water and drinking water supplies. This in turn could increase the occurrence of infectious diseases such as cryptosporidiosis and giardiasis, which are spread via contaminated drinking water.

The consequences will vary from region to region, but the burdens are likely to fall disproportionately on the poorer populations in low-income countries, and on those made vulnerable by age or pre-existing illness.

Sea levels are forecast to rise worldwide by approximately 40 centimetres by 2100 [1], and this rate of rise would be several times faster than has occurred over the past century. This is important, since over half of the world's population now lives within 60 kilometres of the sea. Sea level rise will damage coastal structures and arable land; salinate coastal freshwater aquifers, and affect sewage and wastewater disposal. This would lead to population displacement and economic disruption. And as a result, there would be inevitable adverse physical and psychological health consequences.

The effects of global climate change on food production are complex and uncertain. However, we do know that temperature and soil moisture would effect a plant's physical make-up. The climate would influence which diseases and pests attack the crops. And finally, extreme weather events would govern the extent of crop damage.

References:
1. Intergovernmental Panel on Climate Change, Third Assessment Report. 2001.
2. McMichael, A.J. and A. Haines, 'Global climate change: the potential effects on health'. BMJ, 1997.
3. Martens, W.J.M., et al., 'Climate change and future populations at risk of malaria'. Global Environmental Change, 1999. 9(Supplement)
4. Patz, J.A., 'Global climate change and emerging infectious diseases'. Journal of the American Medical Association, 1996.