Researchers have debated for more than two decades the likely impacts of global warming on the worldwide incidence of malaria, a mosquito-borne disease that infects more than 300 million people each year.

Now, University of Michigan ecologists and their colleagues are reporting the first hard evidence that malaria does, as had long been predicted, creep to higher elevations during warmer years and back down to lower altitudes when temperatures cool.

The study, based on an analysis of records from highland regions of Ethiopia and Colombia, suggests that future climate warming will result in a significant increase in malaria cases in densely populated regions of Africa and South America, unless disease monitoring and control efforts are boosted and sustained. “We saw an upward expansion of malaria cases to higher altitudes in warmer years, which is a clear signal of a response by highland malaria to changes in climate,” said Mercedes Pascual, senior author of the research paper.

“This is indisputable evidence of a climate effect,” said Pascual.

“The main implication is that with warmer temperatures, we expect to see a higher number of people exposed to the risk of malaria in tropical highland areas like these,” she said.