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Climate change will impact infectious diseases worldwide, but questions remain as to how

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infectious disease climate change emerging pandemic spreadNEW YORK—As climatologists weather the IPCC controversy, another storm is brewing, and this one is filled with not with bloggers but with beasts, bugs and bacteria. It is the potential plague of infectious diseases—threatened to be made worse, many scientists propose, by projected changes in the Earth's climate.


At a symposium held yesterday at the New York Academy of Sciences, researchers from public health, climate, medicine and other fields gathered to discuss some of the big questions that remain in uniting these evolving fields. "The relation between climate change and infectious diseases is highly controversial to say the least," Richard Ostfeld, of the Cary Institute of Ecosystem Studies, said here.


Basic assumptions, such as the notion that rising temperatures will increase the number of mosquitoes that can transmit malaria among humans (rather than just shift their range), have been the subject of painstaking parsing over the past decade. But to Otsfeld, who is a disease ecologist, the question of whether climate change will expand the prevalence of infectious diseases "is an unequivocal 'yes,'" he said. "Climate has a strong impact on the incidence of disease." And now it is time to move on, the researchers noted, and start trying to develop real-word strategies to curtail potential pandemics before they can get started.


Stemming the tide, however, depends on a thorough understanding of both the dynamics of climate change and the behaviors of the more than 1,400 species of organisms that are pathogenic to humans—and, crucially, how the former might impact the latter.


Modeling the global climactic shifts itself—past, present or future—has proved to be no walk in the park, but the current science nearly breaks down when scientists try to pinpoint forecasts for specific locations or specific years, noted NASA researcher Gavin Schmidt. "Climate change scientists are not fortune tellers," he said. But for public health officials, government decision makers and even the biologists studying the diseases, the devil (and transmission rates) is in the details. Without a clear picture of how rainfall or daily minimum temperatures are going to change in many areas of the globe, it has been difficult to establish predictions about just how infectious diseases, such as malaria or Lyme disease, are likely to spread—or plans about how to cope with them.


One thing that Schmidt is certain of is the unexpected: "We have a lot of confidence that there are more surprises in the system," he said. Models can help predict some aspects of climate change—but only to the extent that the researchers understand possible inputs and dynamics. "They can't tell you about the unknown unknowns," Schmidt said.


And the same might be said for the current understanding of many infectious diseases—especially those that might emerge or reemerge in the future. Even for a relatively well-studied vector-borne disease such as malaria, crucial information about historical and current case numbers are often shaky in the areas that need the most intervention. "You need to know what the baseline is—and that in itself has been a huge problem" in the field, noted Madeline Thomson, of Columbia University's International Research Institute for Climate and Society.


As many of the researchers hastened to point out, however, climate is not the only force at work in increasing the spread of infectious diseases into the future. Other factors, such as expanded rapid travel and evolution of resistance, are already changing the ways pathogens infect people, plants and animals. As climate change accelerates, it is likely to work synergistically with many of these factors, especially in populations increasingly subject to massive migration and malnutrition.


But as Thompson noted, despite its challenges, climate change can be a relatively solid rock on which to moor infectious disease planning. Many functions of human populations—from geographical displacement to lifestyle changes—that influence disease transmission can be exceedingly hard to track, she said. "Climate is one thing you can actually measure."


Image of malaria-carrying genus Anopheles mosquito courtesy of Wikimedia Commons/Rsabbatini

The views expressed are those of the author and are not necessarily those of Scientific American.

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