Alarm as it warms
THE well-being of any species is dependent on the natural environment it exists in. A recent report on the effect of climate change on human health released by the Intergovernmental Panel on Climate Change (IPCC), suggests that the rise in global temperatures could directly or indirectly affect human health (Science Update, September- October, 1995).
Deaths and injuries caused due to heat waves, hurricanes and other extreme climatic conditions are some direct consequences. Skin cancers and eye disorders such as cataracts are caused due to exposure to the sun's ultra-violet rays.
The indirect effects are more complicated as they involve the study of complex ecological relationships and habitats. Factors such as drought, rising sea levels and new storm patterns could pave the way for water-borne infections and reduce drinking water sources. Reduced agricultural production could bring about famine like conditions. The lower nutritional status would bring down body-resistance to various infections.
Atmospheric change may further the spread of diseases by encouraging the breeding of microbes like the Aedes aegyph mosquitoes - prime carriers of dengue and yellow fever. According to Paul Epstein, professor of tropical medicine at the Harvard School of Public Health, these mosquitoes have increased their range of habitat. Earlier they were limited to altitudes of less than 1,000 in in Costa Rica, Colombia India and Kenya, but today they are found even above 2,000 in. Michael Loevinsohn, an ecologist at the New Delhi-based International Development Research Centre believes that a rise in temperature by 1oC in 1987 corresponded with an increase in the number of malaria cases by 337 per cent.
The El Nino effect is also stated to be a cause of greater ill-health. Such a condition occurs when warm spells followed by heavy rains lead to a cyclical warming of the tropical Pacific Ocean. This in turn causes a spate of infectious diseases. Climatic disruptions in the form of floods and droughts brought about by El Nino have been indirectly responsible for the rise in rodent populations, which are known to carry numerous infectious pathogens. The 1993 outbreak of the Hantavirus respiratory illness in the US, is a fallout of such climatic shifts. Initially, excess rainfall led to an abundance of food for the mice but the drought which followed took its toll on their predators, the end result being a 10-fold increase in the deer mice population within a year. By June 1995, 106 cases of the disease were reported from 23 states, half of them fatal.
The warming of the world's oceans may be precipitating the El Nino condition even more. Since the '80s such conditions have shown up with ever greater frequency and persistance. Temperatures in the Indian, Pacific and Atlantic oceans are reported to have gone up in the last one year. And during the last decade, even the polar ice caps registered a rise of 1oC.
Climatologists from the University of Delaware, USA, hypothesise using climate models, that a rise in temperature by 2-4oC will lead to a two-fold increase in the number of hot days during summer. Thus they suggest that the number of heat related deaths in New York would go up from 320 to 880, while in Cairo the numbers would catapult from 281 to 1,125 each summer.
Epstein suggests that an increase in the global surveillance of infectious diseases is required in order to establish the link between the two. "We also need to integrate health surveillance with environmental monitoring so we can anticipate and sometimes even predict where it is going to be hot and rainy, so we know where malaria is going to surge," he says.
The IPCC report concludes by saying that "We must see disease as the outcome of multiple conditions arising from changes not only within cells, but around the globe, including changes in climate and economic patterns."
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