Disagreement over the public health impact of global warming emerged in a symposium Monday morning (Feb. 18) at the annual meeting of the American Association for the Advancement of Science. The colloquium, titled “Sustaining Human Health in a Changing Global Environment,” addressed what hazards can be expected as a result of rapid and continuing climate change. For additional AAAS coverage, page 9 http://harvardscience.harvard.edu/topics/harvard-aaas-news

On one hand, Paul Epstein, associate director of the Center for Health and the Global Environment at Harvard Medical School, argued in prepared remarks that there is real danger in climate change, including heat waves, flooding, and the likelihood that it will open the gates to infectious diseases.

“Climate change is affecting human health indirectly by encouraging the spread of pests and diseases among livestock, wildlife and agricultural systems, forests, and coastal marine life,” Epstein said. [Health problems prevented Epstein, the organizer of the session, from attending and delivering his remarks in person.] “Heat waves affect health directly and are projected to take an increasing toll in developed and undeveloped nations,” Epstein wrote in his prepared remarks.

Arguing to the contrary, Duane Gubler, who was recently named director of Asia-Pacific Institute of Tropical Medicine and Infectious Diseases in Honolulu, said it’s too easy to blame global warming for the dangerous problem of infectious diseases spreading, or re-emerging, in areas where they’ve been absent for a century or more.

Gubler believes that public health emergencies are arising more often and in more places primarily for reasons other than climate change. And he was very blunt in his assessment. “I’ve always been the maverick,” he said, on the issue of climate change and the spread of infectious diseases, adding that in the 20th century “we had great success in controlling infectious diseases, with the exception of the 1918 flu epidemic. But in the 1980s we began to see a re-emergence of infectious diseases. Why?”

The answers have little to do with global warming, he said. Instead, they include increases in the population density of vectors such as mosquitoes and ticks, too little attention being paid to public health practices, the increasing crowding of huge cities, genetic changes in disease organisms, the rapid transportation of harmful viruses and bacteria around the globe, and complaisance about the dangers — a sense that infectious diseases had been conquered.

Gubler noted, “In the 1970s most preventive medicine departments left medical schools and went to public health schools. So the medical schools now work on ‘curative’ medicine instead.” The change has been so dramatic, he added, that “we don’t even emphasize hand-washing anymore.”

Gubler pointed out several other examples of changes outside of global warming that have allowed diseases to rebound or spread:

n Lyme disease, a tickborne infection, is directly linked to a greatly increased deer population in the northeastern United States. This resulted from farmlands returning to forest and the advent of people building homes in the woods, where deer ticks abound;

n In some Asian countries, livestock producers set up large piggeries adjacent to forests, the home of fruit bats that carry the Nipah virus, which causes flu-like symptoms and is fatal about half the time. The virus got into pigs, and from pigs into humans;

n The huge re-emergence of malaria in tropical regions is a result of “a breakdown in public health” practices, such as efforts at mosquito control.

n Dengue hemorrhagic fever, also known as “breakbone fever” and prevalent throughout the Caribbean region and in Asia, can be carried by a mosquito recently introduced into North America, Aedes albopictus. There are four strains of the dengue virus, and now all four are in this hemisphere. Infection with multiple strains is especially dangerous.

Epstein argued, however, that “excess carbon dioxide [in the air] itself carries health consequences. Ragweed grown in elevated carbon dioxide levels produces pollen disproportionate to its stem growth. Moreover, the exploration, extraction, mining, refining, transport, and combustion of fossil fuels harm health and the environment, especially in developing nations.”

But on the other hand, Epstein wrote, “clean energy solutions can stimulate business opportunities and job creation.” He also predicted that “with the proper financial incentives and the dismantling of ‘perverse’ ones, the clean energy and technology transition can improve public health, help stabilize the climate, and become the engine of economic growth and poverty alleviation in this 21st century.”