On Sept. 2, 2026, the United Nations Environment Program report, Limiting Overshoot, declared that the world has fallen short of keeping global warming to 1.5°C above pre-industrial levels, and that urgent action is needed to course-correct. That same week, NPR reported that extreme heat killed nearly five times as many people in the United States as official records indicated. These findings followed two consecutively brutal summers.
Death counts from heatwaves across Europe dominated news cycles this year as the continent’s aging infrastructure struggled to cool down. But merely counting deaths from heat risks missing its impact on human life. Each heat dome in the U.S. affected over 100 million people.
Among them were construction workers, outdoor workers, delivery workers in unairconditioned cabs, farm workers, the unhoused, the poor who could not afford air conditioning, those on medications on whom the impact of heat was amplified, those with mental health disorders, and those with little or no access to healthcare. According to the International Labor Organization, billions of workers around the world are exposed to extreme heat every year. While the vast majority of them do not die, many suffer deeply from the arduous ignominy of a life exposed to heat, day and night, year after year.
While counting deaths from heat is an imperfect science, the quantification of heat’s impact on mental health, physical well-being, wages, food security, habitat, and infrastructure is even more complex. One thousand women working in India’s informal labor economy have set out to quantify this burden—to understand what impact the heat and humidity in their lived environments at home and at work have on their health, wages, and well-being. Partnering with our team at Harvard, the Self Employed Women’s Association in India has recruited women from trades including street vendors, waste recyclers, home-based artisans, and farmers to participate in the Community Heat Adaptation and Treatment Strategies (CommHATS) study.
For 13 months, each woman is equipped with a wrist wearable, microsensors measuring heat and humidity at home and workplaces, labs measuring critical biomarkers, and surveys documenting home and work layouts, wellbeing, and wages. Considered together, this data constructs one of the world’s largest such databases of the impact of heat on human health. Building on prior work that has shown that long exposure to heat impacts multiple organ systems, including the heart and kidneys, the CommHATS project seeks to address unanswered questions in our attempts to adapt to extreme heat: How do we know if cool roofs work?
What should our metric of success be? If the temperature drops a bit, but I still cannot sleep restfully, is the intervention valid? What should the threshold for a new heat insurance product be: the temperature at the airport where the weather station is, or the temperature in my home, which is actually how hot I feel?
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