British and American researchers predict that global warming could mean the spread of the deadly disease malaria to places where it is practically unknown.
Writing in the journal Science, the researchers say they found what they call "indisputable evidence" of the effects of climate change.
Working in Colombia and Ethiopia, they say they discovered that malaria rises to higher elevations in warmer years and lower levels when temperatures are cooler.
They say if the planet keeps getting warmer, people living in higher level tropical regions would be especially vulnerable because they lack protection from the disease.
The World Health Organization says malaria kills more than 600,000 people a year with Africa especially hard hit.
Mosquitoes spread the disease. It can be prevented by insecticides, mosquito nets and medicine.