As seas warm, other breeders thrive. Cholera, a waterborne disease, emerged in South America in 1991 for the first time in the 20th century. Abetted by poverty and poor public health, the disease swept from Peru across the continent and into Mexico, killing more than 10,000 people.

Diseases also are expanding in a surprisingly complex dance with their environment, taking advantage of the swings from deluge to drought made more frequent by global warming

Climate change tied to spread of diseases