Climate change and the spread of disease
One of the under-reported consequences of global warming is the inevitable spread of infectious diseases, such as malaria, schistosomiasis, dengue fever, and many others. The World Health Organization has been predicting for several years that climate change will probably cause significant spread of these and other diseases into areas where they've been unknown in the past.
This fact sheet from the WHO enumerates several reasons for the spread:
- Increasing frequencies of heatwaves: recent analyses show that human-induced climate change significantly increased the likelihood of the European summer heatwave of 2003.
- More variable precipitation patterns are likely to compromise the supply of freshwater, increasing risks of water-borne disease.
- Rising temperatures and variable precipitation are likely to decrease the production of staple foods in many of the poorest regions, increasing risks of malnutrition.
- Rising sea levels increase the risk of coastal flooding, and may necessitate population displacement. More than half of the world's population now lives within 60km of the sea. Some of the most vulnerable regions are the Nile delta in Egypt, the Ganges-Brahmaputra delta in Bangladesh, and many small islands, such as the Maldives, the Marshall Islands and Tuvalu.
- Changes in climate are likely to lengthen the transmission seasons of important vector-borne diseases, and to alter their geographic range, potentially bringing them to regions which lack either population immunity or a strong public health infrastructure.
Sure enough, that last point has proven true in the highlands of Kenya. That region had never known malaria before now, due to the fact that its 6,000-foot elevation was too cold for anopheles mosquitoes to reproduce. Now, the warming climate has made those highlands more suitable for mosquito infestation:
Worldwide temperatures rose 1.3 degrees Fahrenheit during the last 100 years, but recent studies suggest temperatures in Africa are climbing faster. In Kenya's western highlands, maximum annual temperatures over the last 20 years are up about 1.8 degrees, according to Kenya's Centre for Global Health Research.
Fifteen years ago, malaria couldn't reach Thangathi, perched at nearly 6,000 feet amid steep, coffee-covered mountains. The 1970 national atlas declared the region "malaria-free," thanks to cool weather year-round, with temperatures often dipping below 65 degrees — too cold for the strains of anopheles mosquito that carry malaria.
Today, however, malaria beats AIDS, stomach parasites and skin infections as a cause of illness here, said Peter Mbugua, regional medical officer for Nyeri district, which includes Thangathi. Since 2001, his malaria caseload has nearly doubled, reaching 206,369 last year; the disease's prevalence in the region is now second only to pneumonia.
"The situation changed very quickly," Mbugua said. "Malaria became a concern all of a sudden."
That last point is the kicker -- because these new outbreaks will happen suddenly and in areas without adequate prevention mechanisms, they'll hit those areas harder. Poor regions of the world (which will bear an unevenly large proportion of the total temperature change) will seldom be prepared to spray for new insects previously unknown to them, and they will lack the appropriate medications to deal with these new illnesses.