How will climate change affect malaria?
At higher temperatures, malarial mosquitoes bite more and grow faster. The parasite develops more rapidly inside the mosquito, making it more likely that the mosquito will survive long enough to infect people.
Some climate experts have argued that because of this, increasing temperatures will mean more malaria, but it isn’t so simple. For one, if there are no available reservoirs of parasites, it doesn’t matter how many mosquitoes there are, or how quickly parasites might develop inside them. To wit, malaria receded in Europe at a time when the climate was warming.
Climate change is expected to be variable, and so it is seems safe to predict that in some places, climate change may result in less malaria. A few less puddles, an earlier cold snap: these changes can alter the ecology of malaria such that fewer people are infected.
However, malaria will likely increase in other areas as the climate changes, in ways that are potentially devastating. The most convincing evidence suggests that these will be areas where malaria is either nonexistent or only sporadically present, where people thus have little acquired immunity, and which are subject to El Nino-influenced weather.
In 1982, El Niño torched the sea by 4 degrees Celsius, the most severe El Niño since 1940. The droughts, floods, fires, and storms that followed directly killed about 2,000. According to climate scientists, human emissions of carbon dioxide and other greenhouse gases triggered the heightened ENSO, and as global warming progressed, El Niño years would continue to grow harsher, with stronger storms and warmer temperatures.
El Niño staged an unusually strong return in 1998 again. That year was the hottest of the twentieth century. Malaria emerged in the high-altitude city of Nairobi, Kenya for the first time since the 1930s. To the non-immune villagers, malaria’s ravages that followed the mosquito bites were inexplicable. “In a crowd of perhaps two dozen people,” recounted a NYT reporter who visited the area, “no one could say exactly how malaria was spread or how to prevent it.” “If you have experience, maybe you can explain it,” one girl asked the reporter. Hundreds perished. The following year, a three-month outbreak took even more lives. Plasmodium continued to colonize previously malaria-free zones across the cool African highlands in Uganda, Tanzania, and Rwanda.
According to a 2001 analysis, in El Niño’s wake, the death toll from malaria increases by 36 percent in Venezuela. The risk of malaria epidemics increases by 400 percent in Sri Lanka. In northeast India, malaria epidemics themselves increase by 500 percent. Today, fifteen districts in the highlands of Kenya are under constant threat of malaria epidemics, compared to just 3 in 1988.
For more:
R. Sari Kovats, et al, “El Nino and Health,” Lancet, November 1, 2003
Andrew K. Githenko et al, “Predicting malaria epidemics in the Kenyan highlands using climate data: a tool for decision makers,” Global Change & Human Health, Volume 1, No. 1, 2001
www.ogp.noaa.gov/mpe/csi/esd/africa/fundproj/health/malaria_epidemic.pdf
Menno J. Bouma et al, “The El Nino Southern Oscillation and the historic malaria epidemics on the Indian subcontinent and Sri Lanka: an early warning system for future epidemics?” Tropical Medicine and International Health, Vol. 1, No. 1, February 1996
Frank C. Tanser et al, “Potential effect of climate change on malaria transmission in Africa,” Lancet, November 29, 2003
“Little imagination is required to visualize the great increase in the production of food and raw materials, the stimulus to world trade….that would result from the conquest of tropical diseases.”-U.S. Secretary of State George Marshall, 1948
