For every diagnosed heat illness, Penn economist Dr. R. Jisung Park says about 1,400 other workplace injuries are caused by heat but never recorded as such.
Most companies that track heat risk track heat illness: the cases of exhaustion or heat stroke that show up in a safety log or a sustainability report. On Aug. 25, members of Extreme Weather + Work heard from an economist whose research suggests that number captures a small fraction of what heat is actually costing them.
Dr. R. Jisung Park is an environmental and labor economist at the University of Pennsylvania, with appointments at the School of Social Policy & Practice and the Wharton School, and he directs Penn's Center for Climate Resilience. He has advised the U.S. Congress, United Nations, World Bank, EPA, and is the author of “Slow Burn: The Hidden Costs of a Warming World”, published by Princeton University Press. He joined our monthly member call to walk through what he calls the economics of heat in the workplace.
Dr. Park opened with a chart comparing the 2003 European heat wave, described at the time as a once-in-a-thousand-year event, with the summers Europe has actually experienced since. This summer was hotter than 2003. What was an extreme outlier now sits inside the normal range.
Hotter days are guaranteed, even if global emissions stop tomorrow. In an optimistic scenario, he said, the inertia of the atmosphere locks in additional warming for the next two or three decades. At 1.5°C of average global temperature rise, London sees five to 10 additional days a year above 90°F, Atlanta sees 40 to 60, and a city like Bangkok sees up to 100.
Dr. Park's team partnered with the state of California to link daily weather data at the ZIP code level to the state's full set of workers' compensation claims, which let them isolate the causal effect of temperature on workplace accidents.
Injury risk climbs well before a day looks extreme. On days at or above 85°F, same-day accident and injury rates rise by nearly 50% in agriculture and by about 20% across mining, extraction, and utility-based construction. The effect is not confined to outdoor work: manufacturing, warehousing, wholesale, retail, and food service operations all show elevated risk on hotter days.
For employers, the measurement gap matters more than any single figure.
"For every one heat illness that is medically diagnosed, there are 1,400 other accidents and injuries that are caused by hotter temperature but not associated with heat in the official record," Dr. Park said.
Those are ordinary incidents. A worker misses a rung on a ladder, or a container of hazardous material gets dropped. None of it is coded as heat, but heat is why it happened.
That gap is also part of why Dr. Park wrote “Slow Burn”. Climate has largely been treated as a symbolic and politically charged subject, he said, and it has lived inside the sustainability and corporate social responsibility function.
"It really should be an operational risk management and a cost-competitiveness issue first and foremost," he said.
His reasoning is straightforward. The path from a physical hazard to a dollar figure is dependent on a company's own operations, so the same 95°F day means something different for a logistics network than for a hospital system or a manufacturing footprint. That is why headline GDP loss estimates are hard for any single employer to use, and why his answer to "what is heat costing us" begins with where a company's value sits.
He suggested starting with the value chain rather than the hazard. Identify where most of your company's value is created, then ask which climate hazards touch those parts of it. From there, the California approach can be run on a single company: match your own historical injury, absence, and operations data against local weather to get a bespoke estimate of what weather has already cost you, then model the next five and 10 years with and without intervention.
He also shared that interventions do not have to be expensive to work. In one study, training managers on how smoke and air pollution affect labor productivity measurably reduced productivity loss within a few months.
Our members were able to ask Dr. Park questions about quantifying the risk of compounding environmental threats (e.g. concurrent heat and wildfire events), the emotional impact of weather to the workforce, and the challenges of safeguarding hybrid and remote workers.
Dr. Park directs the Center for Climate Resilience at the University of Pennsylvania, where his team quantifies the economic impact of climate risk across global operations and value chains. The center works with companies in a data-secure environment that allows for collaborative research, and Dr. Park extended an open invitation to employers interested in a bespoke analysis of their own operations. If that is useful to your team, reach out to us and we will make the introduction.
To book Dr. Park for a talk or a corporate training, contact Sydney Bartlett at Princeton University Press.
“Slow Burn: The Hidden Costs of a Warming World” is available from Princeton University Press.
Extreme Weather + Work delivers monthly insights, exclusive resources, and tools for your organization and convenes a peer community to share best practices around workforce resilience. Dr. Park is one of many guest speakers we bring to our membership group. To engage with academic subject matter experts and industry leaders like him, learn more about our coalition here.
Extreme Weather + Work is a business coalition helping employers protect their workforces from extreme weather. Sign up for our newsletter for monthly updates.
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