WASHINGTON - As world leaders meet in Bali this week to find new ways to battle global warming, some of the nation's top climate change scientists yesterday argued that there's little concrete evidence connecting global warming to the spread of infectious diseases, while others said the link is crystal clear.
The debate before an Institute of Medicine panel on global health, occurring less than a mile from the US Capitol building, was far from an academic exercise. A similar review in 2001, which found little conclusive data that climate change is adversely affecting human health, was among the arguments the Environmental Protection Agency used in denying states the ability to curb emissions from new motor vehicles.
Now, after the US Supreme Court ordered the EPA to review that decision earlier this year, the scientific disagreement yesterday - particularly the clash between an academic from Harvard University and one from the University of Pittsburgh - paralleled an ongoing political battle between the Bush administration and several states, including Massachusetts.
Donald S. Burke, dean of Pittsburgh's Graduate School of Public Health, noted that the 2001 study found that weather fluctuation and seasonal variability may influence the spread of infectious disease. But he also noted that such conclusions should be interpreted with caution.
"There are no apocalyptic pronouncements," Burke said. "There's an awful lot we don't know."
Burke said he is not convinced that climate change can be proven to cause the spread of many diseases, specifically naming dengue fever, influenza, and West Nile virus.
But Paul R. Epstein, associate director of the Center for Health and the Global Environment at Harvard Medical School, said clusters of disease outbreaks spread by water, mosquitoes, and rats could clearly be traced to global warming.
"Extreme weather changes have the biggest effect on the environment and on human health," he said in an interview after his talk. "It's about heat waves, flooding, extreme storms - all of those affect human health and are related to climate change."
Epstein said those who "just look at specific diseases can miss the broader picture. If you look at ecological systems, water systems, the extreme weather, the range of wildlife . . . or more profoundly everything that supports a health system, then you can see the linkages. Scope is really important when you look at this."
The global health specialists, though, heard about the spread of several diseases, including an outbreak of chikungunya fever in northern Italy recently. The disease, normally found in Africa and Asia, is transmitted by mosquitoes and can cause fever, chills, vomiting, and nausea.
Jean-Paul Chretien, the Defense Department's coordinator of overseas laboratories, said there was "anecdotal evidence" from Italy that the mosquito population had risen significantly, this year, perhaps because of a warmer-than-normal summer.
He said an earlier outbreak of chikungunya fever on Kenya's coast had a more documented link to climate change. Weather patterns caused by the atmospheric phenomenon La Niña contributed to a drought in east Africa in 2004. Because of a shortage of fresh water, people rarely emptied buckets around their homes, giving mosquitoes an ideal breeding ground of standing water.
"An outbreak like that is from a convergence of factors, and climate is one of them," Chretien said in an interview.
While scientific proceedings in Washington often are related to political developments, the forum yesterday was unusually close to the politics of the day.
In addition to the Bali gathering and the EPA deliberations, the US Senate Environment and Public Works Committee said it would debate amendments today on a global warming bill that would create a "cap and trade" system designed to restrict US greenhouse gas emissions.
Also, the House today is expected to vote on an energy bill, which calls for increasing fuel economy standards for new cars and trucks to an average of 35 miles per gallon by 2020 - a provision that not only saves fuel, but could cut carbon dioxide emissions.
Representative Edward J. Markey, chairman of the House Select Committee on Energy Independence and Global Warming, said he expects the bill to pass today; the Senate is expected to debate the energy bill next week.
Markey said he has no doubt that climate change is affecting human health.
"It leads to the migration of animals, who are bearing disease, and brings them close to population areas that they otherwise had not been exposed to," he said. "Before climate change, mosquitoes were not present in Nairobi because of the elevation. But as it warms, these insects are moving higher and they bring malaria and other diseases with them."
John Donnelly can be reached at firstname.lastname@example.org.