Malaria may not deserve its high-profile spot as a leading public-health concern tied to global warming.
A research team has found that over the past century, malaria's prevalence has declined significantly, despite a century-long warming of global average temperatures.
The finding was published in this week's issue of the journal Nature by the Malaria Atlas Project, an international consortium of researchers that maps and tracks incidence of the disease, as well as social and environmental factors.
Warming can stimulate malaria outbreaks, as can increased rainfall and even drought, notes David Smith, an associate professor of zoology and an associate director of the Emerging Pathogens Institute at the University of Florida in Gainesville.
But the analysis holds that public-health efforts – from the expanded use of insecticide-laced mosquito nets around beds to improved treatments – and increasing urbanization have overwhelmed any climate-related effect on the incidence of the disease.
"We're not saying that weather and climate won't affect malaria," Dr. Smith writes in an e-mail exchange. "But we are arguing that there are much more powerful forces at work. The broad patterns of the last century suggest an optimistic picture for malaria."
The team compared a map it developed in 2007 showing the prevalence of malaria globally with maps based on historical data dating back to 1900, when malaria is widely considered to have peaked.
Despite the increase in global average temperatures, the prevalence of malaria fell globally. According to the team's estimates, some 58 percent of the globe's landscape was malaria prone in 1900, versus 30 percent in 2007.
Those numbers may be of little comfort to people who public-health officials say are still at risk, acknowledges Pete Gething, a researcher at Oxford University in England and leader of the team reporting the results. But the trend "is important when thinking about the effects of climate on the future of disease," he says.
To be sure, malaria is not the only public-health issue that global warming is projected to affect. But it's often been flagged as a key one to consider.
One reason: its current prevalence in many least-developed countries, which are expected to be among the hardest hit by various effects from global warming.
Beyond changes in climate, another consideration is increased resistance to drugs and insecticides by the parasite and mosquitoes that public-health officials have linked to malaria.
But ultimately, successful campaigns against the disease boil down to a question of money, Smith argues. Even though increasing resistance to DDT among mosquitoes contributed to a stall in progress against malaria in the 1960s, he says, the bigger factor could well have been political: The United States eliminated its contributions to the Global Malaria Eradication Programme in 1963.
Under the Bush administration, the US stepped up funding for several global-health challenges, including malaria.
But the needs still outstrip the resources, many say. "We need to scale up malaria control interventions in Africa and then sustain them," says Smith, adding that the effort needs an annual $7 billion to $10 billion global commitment for the next 20 years.