The venerable Science magazine has a special issue out today on climate change. Some of the content is free, and it’s well worth checking out. That includes an article on one of the most important and perplexing areas in global-warming research: the possible connection between a changing climate and a growing threat from infectious disease.
It’s been known for a while that warming temperatures could help certain diseases. Malaria, which kills about 650,000 people a year, thrives in the hot and humid areas where the Anopheles mosquito can live. As the climate warms, the territory where the mosquito and the malaria parasite will be able to live will likely expand, putting more people at risk. Already dengue fever, another mosquito-borne tropical disease, has re-established itself in the Florida Keys, where it was wiped out decades ago. Tropical diseases will loom that much larger in a warmer world, as host-parasite cycles accelerate. In the Arctic, which is warming faster than any other region on the planet, higher temperatures are allowing parasites like the lungworm, which afflicts musk oxen, to develop faster and be transmitted over longer periods.
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But as the Science study — by American and Canadian researchers — points out, the connection between climate change and disease is actually a lot more complicated than that. It’s true that warmer temperatures may be helping dengue fever to return to the Florida Keys, but the disease was initially vanquished in the 20th century not because the climate was cooler, but because public-health officials systematically controlled mosquito populations, cutting off the spread of the dengue virus. Both Singapore and Burma are tropical countries well within the malaria belt, but rich, urban Singapore has largely eliminated malaria, while the disease is still common in impoverished, rural Burma. (I should know — I contracted a mild case of malaria while reporting along the Thai-Burmese border in 2005.) Health care infrastructure and wealth — or lack it — have a lot more to do with the spread of infectious disease than climate change does, and that will continue to be the case even as the globe warms.
Still, the study points out that climate change will be a major factor in the spread of infectious disease in the future — and the impact is likely to be even greater in wildlife and agricultural systems, which aren’t likely to be able to react as quickly as human beings can. In the Caribbean, where I was just on a reporting trip, warmer water temperatures have stressed vulnerable corals, which then leaves them less able to fight off infections by pathogenic fungi and bacteria. Whole species of coral in the Caribbean have been lost thanks to the rapid spread of disease — and since corals are the framework builders of the marine ecosystems, other species can quickly follow them into oblivion.
As co-author Richard Ostfeld of the Cary Institute of Ecosystem Studies in Millbrook, N.Y., put it in a statement:
Biodiversity loss is a well-established consequence of climate change. In a number of infectious disease systems, such as Lyme disease and West Nile virus, biodiversity loss is tied to greater pathogen transmission and increased human risk. Moving forward, we need models that are sensitive to both direct and indirect effects of climate change on infectious disease.
Climate change is likely to impact infectious disease just as it will impact other areas of life. Human beings — especially relatively rich ones — will muddle through, adapting to a warmer, more parasite-ridden world. Plants and animals, though, won’t be able to adapt as fast, or perhaps at all. Good thing we don’t need them. Right?