Warming climate drives disease surge, study shows

Warmer weather across the globe is reshaping the landscape of human health. Case in point: dengue fever, a mosquito-borne disease once confined largely to the tropics which often brings flu-like symptoms and without proper medical care can escalate to severe bleeding, organ failure, and even death. Cases of dengue could rise as much as 76% across a large swath of Asia and the Americas by 2050, according to a new study by researchers at Stanford, Harvard, Arizona State University, and the National Bureau of Economic Research. The analysis, published Sept. 9 in PNAS, is the most comprehensive estimate yet of how temperature shifts affect dengue’s spread. It provides the first direct evidence that a warming climate has already increased the disease’s toll.

A dangerous sweet spot

The study analyzed over 1.4 million observations of local dengue incidence across 21 countries in Central and South America and Southeast and South Asia, capturing both epidemic spikes and background levels of infection. Dengue thrives in a “Goldilocks zone” of temperatures – incidence peaks at about 27.8°C (82°F), rising sharply as cooler regions warm but dropping slightly when already-hot areas exceed the optimal range. As a result, some of the largest increases are projected for cooler, high-population regions in countries such as Mexico, Peru, and Brazil. Many other endemic regions will continue to experience larger, warming-fueled dengue burdens. By contrast, a few of the hottest lowland areas may see slight declines. Still, the net global effect is a steep rise in disease.

The findings suggest that higher temperatures from climate change were responsible for an average 18% of dengue incidence across 21 countries in Asia and the Americas from 1995 to 2014 — translating to more than 4.6 million extra infections annually, based on current incidence estimates. Cases could climb another 49% to 76% by 2050 depending on greenhouse gas emissions levels, according to the study. At the higher end of the projections, incidence of dengue would more than double in many cooler locations, including areas in the study countries that are already home to over 260 million people.

Combatting a disease on the move

The researchers cautioned that their estimates are likely conservative. They do not account for regions where dengue transmission is sporadic or poorly reported, nor do they include large endemic areas such as India or Africa where detailed data is lacking or not publicly available. The researchers highlight recent locally acquired cases in California, Texas, Hawaii, Florida, and in Europe—a signal of the expanding range of dengue. Urbanization, human migration, and the evolution of the virus could amplify risks, while medical advances may help blunt them, making projections uncertain.

Aggressive climate mitigation would significantly reduce the dengue disease burden, according to the study. At the same time, adaptation will be essential: better mosquito control, stronger health systems, and potential widespread use of new dengue vaccines.

In the meantime, the findings could help guide public health planning and strengthen efforts to hold governments and fossil fuel companies accountable for the damages of climate change. Attribution studies like this one are increasingly entering courtrooms and policy debates, used to assign responsibility for climate damages and to support funds compensating countries most affected.