“As we get continued warming, it’s going to become more difficult to control mosquitoes,” said Andrew Monaghan, who is studying the interaction of climate and health at the National Center for Atmospheric Research in Boulder, Colo. “The warmer it is, the faster they can develop from egg to adult, and the faster they can incubate viruses.”

Already, climate change is suspected — though not proved — to have been a factor in a string of disease outbreaks afflicting both people and animals. These include the spread of malaria into the highlands of eastern Africa, the rising incidence of Lyme disease in North America, and the spread of a serious livestock ailment called bluetongue into parts of Europe that were once too cold for it to thrive.

In interviews, experts noted that no epidemic was ever the result of a single variable.

Instead, epidemics always involve interactions among genes, ecology, climate and human behavior, presenting profound difficulties for scientists trying to tease apart the contributing factors. “The complexity is enormous,” said Walter J. Tabachnick, a professor with the Florida Medical Entomology Laboratory, a unit of the University of Florida in Vero Beach.

The epidemics of Zika and dengue are cases in point. The viruses are being transmitted largely by the yellow fever mosquito, Aedes aegypti. That creature adapted long ago to live in human settlements, and developed a concomitant taste for human blood.