Sick of It?

CDC:PHIL:CORBIS
PHOTO BY CDC:PHIL:CORBIS

Some climate scientists predict big impacts on public health. Others say implications remain unclear.

When a freakish heat wave struck France and central Europe in 2003, more than 50,000 people died in 11 days.

Were they casualties of climate change?

“That was a public health disaster,” says Jonathan Patz, professor of environmental studies and population health sciences at the University of Wisconsin–Madison. “Attribution to climate change is a difficult thing.”

And not simply because it is impossible to pin singular events on a changing climate. Other factors—changing land use, trade and travel, pest control, and air and water pollution—obscure and overwhelm the effects of climate change.

“It is really quite impossible to disentangle the many confounding factors,” says Patz.

That, however, has not kept experts from warning that climate change has the potential to affect health in many ways. In considering just four diseases – cardiovascular disease, malnutrition, diarrhea and malaria – and death from flooding, the World Health Organization estimated 166,000 deaths could be attributed to the effects of climate change in 2000.

“Unlike a single agent of disease, or single toxic element or pollutant, climate change is something that cuts across many exposure pathways to affect our health,” says Patz. “These range from the direct effects of heat waves and even stagnant air masses and air pollution, to more of these ecologically mediated effects on infectious diseases.”

Myriad Consequences

Public health and disease specialists have warned for more than a decade that a warming planet could threaten health, especially of the world’s poor.

A 2009 report of the U.S. Interagency Working Group on Climate Change and Health noted that “climate change is currently affecting public health through myriad environmental consequences, such as sea-level rise, changes in precipitation resulting in flooding and drought, heat waves, changes in intensity of hurricanes and storms, and degraded air quality, that are anticipated to continue into the foreseeable future.”

Some impacts are intuitive. If warming leads to more and bigger tropical storms – a hypothesis still in doubt – then catastrophes like Hurricane Katrina will become more common. If climate change amplifies the world’s water cycle, as is generally accepted, increased rainfall and floods are likely. Worldwide, floods are the most common weather disaster. According to the United Nations, the number of people affected by floods and storms worldwide has risen steadily since 1975. Besides killing people outright, floods also pollute water supplies and lead to widespread waterborne disease such as cholera, cryptosporidiosis and giardiasis.

Also unsurprising are predictions of more killer heat waves. Writing in Nature, a team from Britain estimated “it is very likely” that human-caused global warming at least doubled the chances of the 2003 European heat wave. In the U.S., according to the Intergovernmental Panel on Climate Change, Chicago is expected to brave heat waves with 25 percent greater frequency by the end of the century. Los Angeles can expect a four- to eightfold increase in heat wave days. According to the U.S. Environmental Protection Agency, heat is already the leading cause of weather-related death. The heat wave that hit Chicago in 1995 is estimated to have killed more than 700 people.

But of all health hazards posed by climate change, one of the most intriguing is the expansion of infectious diseases. In a 2000 Scientific American article, Paul Epstein, associate director of the Center for Health and the Global Environment at Harvard Medical School, predicted the spread of tropical diseases, with maps of lurid colors forecasting an increase in malaria risk across Europe and the eastern United States. In 2007 the IPCC stated, “climate change currently contributes to the global burden of disease and premature deaths.” It makes sense: The world gets warmer; tropical and subtropical diseases move to higher latitudes.

Change Mappers

Sudipto Banerjee applies math to maps in a way that’s improving our ability to identify the location and severity of climate-related health changes. The goal: to figure out – and ultimately counteract – factors most closely associated with particular health problems. Read the article by Ashley Kuehl