A prescription for complexity: public health and climate change

Combine two of the biggest planetary challenges — climate change and public health — and you’ve got a problem as huge as Rupert Murdoch’s.

Most scientists would find either climate or health a challenging career on its own. But a few brave souls have recently ventured into the realm in between, a place where discerning the truth is harder than tracing a phone-hacking scandal to Scotland Yard.

At first glance, climate change and public health have some obvious links. As heat-trapping greenhouse gases build up in the atmosphere, heat waves come more often, potentially killing vulnerable populations like the poor and the elderly. Air pollution could also get worse, as warmer temperatures trap ozone and other ground-level pollutants down where people breathe. Most creepily, mosquitoes and other infectious insects could move into new territory, carrying fearsome diseases such as malaria and dengue.

Such flesh-crawling scenarios are why the intersection of climate and health has a “high dread factor” for most people, says Linda Mearns, a senior scientist at the National Center for Atmospheric Research in Boulder, Colo. Mearns spoke in July at the center’s fourth annual colloquium on climate and health, a conference series she started in 2004 to help lessen the dread for both scientists and the public.

Few would dispute the need for such research. After all, the full extent of climate’s influence on health is far less understood than its influence on other areas of society, such as agriculture or water resources. “Years ago I’d go to meetings and someone would stand up and say, ‘I went to Vietnam and it rained a lot and there was a lot of dengue,’ ” says Lyle Petersen, an epidemiologist with the U.S. Centers for Disease Control and Prevention in Fort Collins, Colo. “We’ve come a long way since then.”

But perhaps not far enough. The science of epidemiology — tracking diseases from person to person, from population to population — has always been devilishly complicated. Add climate to the mix, and figuring out how a disease circulates gets tougher than Will Smith fighting virus-infected zombies.

It’s one thing to say a disease could spread, another to show that it has spread, and yet another to confirm that climate played a role, point out epidemiologist Paul Epstein and journalist Dan Ferber in their new book, Changing Planet, Changing Health. Besides climate, a long list of other factors can also set the stage for an epidemic. Disease-carrying insects are becoming more resistant to pesticides. People are pushing into cities, where overcrowding allows disease to run rampant, as well as into rural areas where infections can jump from wildlife.

Many of the most vulnerable areas have poor public health systems to cope with outbreaks in the first place.

At the same time, medical advances that saved millions of lives have also made it harder to tease out the potential role of climate. Distributing bed nets in sub-Saharan Africa has dramatically cut the incidence of malaria. So too have better medicines and better insecticides for controlling mosquitoes’ spread.

Such public health triumphs have stoked one of the biggest battles in the climate/health arena: whether the rise of malaria seen in East Africa’s highlands is linked to local climate change.

Thanks to detailed medical records kept by a tea estate in Kenya, researchers have documented how malaria surged into higher elevations — in places where malarial mosquitoes never used to buzz — in the 1980s and 1990s.  But local climate records aren’t as good as the medical ones, and researchers have had to mathematically stretch to patch over gaps in  the temperature measurements. The result: a flurry and counterflurry of papers in the research journals, arguing for and against the idea that Kenya’s highland climate changed simultaneously with malaria’s appearance.

The scientific bloodsucking may now finally come to an end with a paper that appeared in Malaria Journal in January. With a little help from the Kenya Meteorological Department, a team led by Madeleine Thomson of Columbia University in New York tidied up a set of daily temperature and rainfall records from 1979 to 2009. Temperatures at the tea estate, the scientists found, have indeed been rising at around 0.2 degrees Celsius per decade.

Such work can’t prove that climate caused the spread of malaria, but it underscores that climate may be an important force to reckon with when fighting disease.

“Climate change is an integral part, and so are bed nets and all those other things,” says Mary Hayden, a medical epidemiologist at NCAR and organizer of the recent Colorado meeting.

Those few chances that climate scientists and health scientists have to work together may be the only thing standing between you and a mosquito with a parasite in its blood and a gleam in its eye.

SN Prime | August 15, 2011 | Vol. 1, No. 9

Alexandra Witze is a contributing correspondent for Science News. Based in Boulder, Colo., Witze specializes in earth, planetary and astronomical sciences.

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