Public health infrastructure has its own role to play in combating climate change. For example, hospitals can curb solid waste by promoting breast milk over formula for infants, or simply cut down on nonessential energy use. The Taiwanese branch of a network of some 800 hospitals worldwide has set itself a target of reducing emissions by 13 percent below 2007 levels by 2020. "That's equal to reforesting 34 New York City Central Parks," says Dr. Chiou Shu-ti, director-general of Taiwan's Bureau of Health Promotion and vice chairperson of the International Network of Health Promoting Hospitals.
Ultimately, however, humanity could be on course for as much as 6 degrees C of warming by century's end. Such a temperature rise would put even larger swaths of the globe in danger of breaching high temperatures of 35 degrees C on a regular basis for extended periods of time—the point at which the human body's ability to thermally regulate itself breaks down. That may be the ultimate public health impact of climate change. "It would exceed the limits for habitability," says Sir Andy Haines of the London School of Hygiene and Tropical Medicine.
Or, regardless of leishmaniasis and other potential human health concerns, as Campbell-Lendrum puts it: "If [the highest temperature estimate] happens, all bets are off."