This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A sea of corrugated metal roofs stretches into the distance across an informal settlement in Makassar, Indonesia. Around 40% of the industrial hub's population dwells in these makeshift communities, where a lack of basic municipal services and air conditioning leaves residents routinely exposed to temperatures above 90 degrees Fahrenheit.
In the coming months, a couple dozen roofs in the settlement will stand out with bright new coats of highly reflective white paint. They are part of a Stanford Doerr School of Sustainability project testing one of the simplest, cheapest tools available for lowering sweltering temperatures inside homes by as much as 5 degrees Fahrenheit. "Those few degrees can make a big difference," said Rishee Jain, a leader of the Makassar project and an associate professor of civil and environmental engineering at Stanford.
Lowering the temperature by even a few degrees on the hottest days matters because of the limits of our physiology. When it's too hot and humid for evaporating sweat to keep us cool and maintain our core temperature, the heart, kidneys and other organs work harder to compensate. The strain can exacerbate conditions such as cardiovascular disease, diabetes and asthma, and prolonged exposure can prove deadly even for the young and healthy.
Furthermore, during heat waves, people have trouble sleeping, leaving them susceptible to illness; in Makassar specifically, heat waves correlate with surges in work absenteeism and cases of dengue fever. "Big interventions can take decades to bring into place, and we don't have that time. People are suffering from heat events now," said John Openshaw, a Stanford assistant professor of medicine who is leading the white-roofs project team with Jain.
"We really need to start thinking about the interventions that we can implement quickly." Driven largely by climate change, heat waves are rapidly increasing in duration and frequency worldwide, with some regions now enduring 50 more heat-stress days annually than in 1950. In major U.S. cities, heat wave frequency has tripled from two events per year to six. The summer of 2026 has brought dangerous heat waves to broad swaths of India, South America, North America and Europe, the world's fastest-warming continent.
Jain and Openshaw are among a growing number of researchers seeking ways to better cool individual buildings and entire cities, where dark asphalt and impervious building materials trap heat and can drive temperatures far hotter than in nearby rural areas. The work is part of a broader push at the Doerr School of Sustainability to help people and communities adapt to growing extremes, from record wildfires and droughts to historic floods and hurricanes. "As global warming continues to unfold, we can expect accelerating occurrence of the most extreme events, particularly for heat waves but also for extreme wet events and other extremes," said climate scientist Noah Diffenbaugh, the William Wrigley Professor and Kimmelman Family Senior Fellow in the Doerr School of Sustainability.
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