The central argument of the paper is provocative precisely because it challenges a widespread assumption: that access to air conditioning guarantees protection from dangerous heat. According to the authors, air conditioning only protects people if they can afford to run it, maintain it, and use it safely. Rising utility costs, the expense of repairing or replacing aging cooling systems, mobility limitations that make installing window units difficult, and an aging housing stock that was never designed to withstand prolonged extreme heat all combine to leave many older Americans exposed even when they technically have cooling equipment in their homes. Cognitive decline adds another layer of risk, because some individuals may fail to recognize when indoor temperatures have reached dangerous levels or may be unable to take appropriate action on their own behalf.

The physiological reasons behind this vulnerability are well established. Aging reduces the body’s ability to regulate temperature, making older adults less efficient at dissipating heat through sweating and cardiovascular adjustments. Common chronic conditions, including diabetes and neurodegenerative diseases, further heighten heat-related risks, as do many medications frequently prescribed to older adults, which can interfere with thermoregulation or hydration. The health consequences of extreme heat exposure are not limited to heat stroke. The analysis links exposure to cardiovascular and respiratory problems, sleep disruption, cognitive impairment, reduced attention, and mental health concerns, painting a picture of heat as a systemic threat to the health of aging populations rather than a short-lived inconvenience.

Heat is, as co-author Amir Baniassadi, PhD, Assistant Scientist II at the Marcus Institute, notes, one of the deadliest weather-related hazards in the United States, and older adults are among those at greatest risk. But the analysis emphasizes that the nature of that risk varies dramatically from region to region, which means a one-size-fits-all national policy is unlikely to succeed. In the Desert Southwest, where air conditioning is often essential for survival, questions of affordability and performance standards have become critical public health concerns. Some Arizona cities have responded with rental housing laws that require air-conditioning systems to be operational, repaired promptly, and capable of cooling a residence to as much as 20 degrees Fahrenheit below outdoor temperatures. These are among the strongest such protections in the country, yet the analysis shows they may still fall short in a rapidly warming climate.

The numbers from Phoenix illustrate the problem starkly. In 2024, the city experienced 70 days on which temperatures reached 110 degrees Fahrenheit or higher. Under the local rules, a legally compliant cooling system could still leave indoor temperatures above 90 degrees Fahrenheit on such days. Lead author Peter Crank, PhD, Assistant Professor in the Department of Geography and Environmental Management at the University of Waterloo, states that indoor temperatures above 90 degrees are not safe for many older adults, and that clear, objective standards for cooling performance are critical to protecting health and ensuring safe living conditions. In other words, even the regulatory gold standard in the hottest part of the country leaves a gap between legal compliance and genuine physiological safety, a gap that widens with every additional extreme heat day.

The analysis also scrutinizes cooling centers, which are frequently promoted by municipalities as a frontline public response to extreme heat. While these facilities can provide meaningful relief, the authors document a series of barriers that limit their usefulness for the very population they are meant to serve. Transportation challenges can make reaching a cooling center difficult or impossible for people with mobility limitations. Limited operating hours, particularly the lack of overnight and weekend availability, mean that the most dangerous hours of a heatwave often occur when centers are closed. Safety concerns and simple lack of awareness of available services further reduce utilization. A resource that exists on paper but cannot be reached, or is closed during the hottest hours, offers little protection to a frail older adult in an overheated apartment.

The challenges look strikingly different in historically colder climates, and the analysis devotes particular attention to the Northeast. In cities such as Boston, many older adults live in older buildings designed to retain heat during harsh winters, a feature that becomes a liability during prolonged hot weather. Much of this housing stock lacks central air conditioning and can trap heat indoors, exposing residents to dangerous temperatures even during periods when outdoor conditions might seem manageable. Yet the regulatory and social safety net in the region has not adapted. Regulations governing indoor cooling, renter protections, and utility assistance have not kept pace with increasingly frequent heatwaves, leaving a mismatch between the climate older Americans actually face and the policies built for the climate of the past.

The financial asymmetry the authors identify is particularly striking. Substantial public resources exist to help households cover heating costs during the winter months, reflecting decades of policy attention to cold-related mortality. Comparable protections for cooling remain limited across much of the Northeast. Maximum indoor temperature standards are largely absent from housing codes, and most energy-assistance programs continue to focus primarily on winter heating needs despite rising summertime heat risks. For an older adult on a fixed income, this means the choice between an unbearable utility bill and an unsafe indoor environment is one that policy has largely left unaddressed, even as summer temperatures in northern cities increasingly rival those of southern ones.

In response, the authors call for policies that recognize regional differences in climate, housing, and infrastructure while directly confronting affordability and accessibility challenges. Their recommended approaches include stronger renter protections, the adoption of indoor temperature standards, expanded utility assistance programs that cover cooling as well as heating, support for the maintenance and replacement of cooling systems, and improvements to the availability and accessibility of cooling centers, including extended hours. As Crank observes, the barriers facing an older adult in Phoenix are not necessarily the same as those facing someone in Boston, and effective heat policy must account for differences in climate, housing, infrastructure, and resources while ensuring that all older adults have access to safe indoor temperatures.

The broader significance of this analysis lies in its reframing of extreme heat as a policy failure rather than merely a meteorological hazard. The tools needed to protect older adults largely already exist: cooling technology, utility assistance frameworks, housing regulation, and public health infrastructure. What is missing, the authors argue, is the political and regulatory adaptation to a climate in which heat has become a chronic, deadly, and regionally diverse threat. As heatwaves intensify in both the Desert Southwest and the historically temperate Northeast, the gap between what buildings, budgets, and laws were designed for and what older Americans now experience will continue to widen. Closing that gap, the analysis suggests, is not simply a matter of installing more air conditioners, but of rethinking how housing, energy, and health policy intersect for a population whose lives increasingly depend on it.

Subject of Research: Health and policy risks of extreme heat exposure among older adults in the United States

Article Title: New analysis underscores the rising threat of extreme heat on older adults

Article References: New analysis underscores the rising threat of extreme heat on older adults. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: extreme heat, older adults, aging, air conditioning, public health, heat policy, cooling centers, housing, utility assistance, Phoenix, Boston, climate change

The research, led by Frances Moore, a professor in the UC Davis Department of Environmental Science and Policy, addresses a gap that has persisted in climate economics for years. While the deadly health consequences of extreme heat have been studied extensively, the slower, quieter erosion of human productive capacity has been harder to quantify. Moore and her colleagues argue that this omission has led policymakers to systematically underestimate the true cost of carbon emissions. Based on the new numbers, labor losses emerge as the second-largest contributor to the total social cost of carbon, trailing only heat-related deaths. That positioning is significant, because it means the economic harm flowing through sweat-soaked workdays rivals nearly every other category of climate damage except mortality itself.

At the heart of the analysis lies the social cost of carbon, often abbreviated as SC-CO2, a metric that attempts to capture the quantifiable cost of one additional ton of carbon dioxide emissions. The measure is far more than an academic curiosity. It underpins cost-benefit analyses for infrastructure planning, informs utility regulation, and provides the analytical backbone for carbon tax policies around the world. When governments weigh whether to build a pipeline, tighten emissions standards, or invest in renewable energy, the social cost of carbon determines how much weight future climate damages receive in the ledger. A metric that omits labor losses, the researchers contend, produces a distorted picture of what emissions actually cost society.

The study lends strong support for a social cost of carbon value of $200 per ton, a figure similar to the estimate produced by the U.S. Environmental Protection Agency in 2023. That alignment matters because current federal guidance does not recognize the metric and actively discourages monetizing the impacts of greenhouse gas emissions in regulatory analysis. The researchers push back against that stance with unusual directness, stating in the paper that we can confidently rule out a social cost of carbon of zero or below. In other words, whatever uncertainties remain in the models, the direction of the damage is unambiguous. Moore emphasized that the science of evaluating climate damages is maturing rapidly, and that the social cost of carbon is now a metric that should be used, one that is ready to help inform good climate policy analysis.

So how does one actually measure the productivity cost of heat? The methodological core of the study combines projections of a heat stress metric known as the wet-bulb globe temperature, or WBGT, with job- and region-specific estimates of work intensity and outdoor exposure across different economic sectors. Unlike a simple thermometer reading, WBGT captures the physical risks of hot temperatures by accounting for the weather variables that influence the body’s ability to dissipate heat, including humidity and wind speed. This distinction is critical to understanding why heat is so dangerous to workers. Human bodies cool themselves primarily through the evaporation of sweat, and when the air is already saturated with moisture, that evaporative process slows or stops entirely. A humid 35-degree day can impose far greater physiological strain than a dry 40-degree day, and WBGT is designed to reflect that reality.

The physiological mechanics are unforgiving. When the body cannot shed heat efficiently, core temperature rises, and the brain responds by reducing physical exertion, effectively forcing workers to slow down as a protective mechanism. This is not laziness or malingering; it is thermoregulation. But the economic consequence is measurable: fewer bricks laid, fewer acres harvested, fewer units assembled. The study found that exposure to heat stress among both indoor and outdoor workers varied dramatically across the globe depending on the local environment, the strenuousness of the work, and access to shade and air conditioning. Highly populated areas meeting critical thresholds for heat and humidity were particularly affected, with India, Nigeria, China and Pakistan standing out, along with countries in the Middle East and sub-Saharan Africa. The geography of the damage is thus deeply unequal, concentrating economic losses in regions that have contributed relatively little to cumulative emissions.

Occupation matters as much as geography. Agricultural and construction laborers are far more exposed to heat than office or service workers because they often perform strenuous work outdoors, directly under the sun, during the hottest hours of the day. Yet the study makes clear that indoor workers are not insulated from the risk. In warehouses, garment factories, and workshops across the developing world, indoor laborers with minimal or no air conditioning face heat burdens that can approach those of outdoor work. To illustrate the scale of the disparity in protective infrastructure, the researchers cite a dataset of residential air conditioning adoption across 33 countries showing penetration rates ranging from zero percent in South Sudan to 90 percent in Japan. That gap means a worker performing identical tasks in two different countries may face radically different thermal realities, and correspondingly different productivity losses.

The findings arrive at a moment when heat extremes are intensifying faster than many adaptation efforts can keep pace. Moore’s message to employers and policymakers is blunt: heat is very dangerous, and it needs to be treated as the real health hazard that it is. The study points to a menu of practical interventions that can protect workers, including more shade, access to water, more frequent breaks, and shifting work to cooler hours of the day when possible. Air conditioning remains the most powerful technological buffer, but its cost and energy demands place it out of reach for much of the world’s vulnerable workforce. The accompanying image from the research team, showing a cotton trailer outfitted with benches and a sunshade offering farmworkers a reprieve from the sun as they pick cantaloupe melons in Firebaugh, California, captures the kind of low-cost, immediately deployable adaptations that can make a difference even before large-scale infrastructure arrives.

The broader implication of the research is that the social cost of carbon has been running an understatement problem. By incorporating labor and agricultural damages that earlier estimates missed or treated crudely, the study strengthens the case for valuing carbon emissions at roughly $200 per ton, a number with real teeth for regulatory analysis. Moore noted that the research community is getting better and more confident at evaluating climate damages, and that this confidence should embolden policymakers to use the metric rather than ignore it. The work was funded by a coalition of scientific institutions, including the National Science Foundation, the National Institutes of Health, NASA, and several fellowship programs, and included co-authors from Purdue University, Stanford University, and UC Davis. As global temperatures continue to climb, the study suggests that the sweat-soaked economics of labor will only grow heavier, and that ignoring it means pricing carbon at less than it truly costs the world.

Subject of Research: Economic quantification of heat stress impacts on global worker productivity and the social cost of carbon

Article Title: The high cost of climate change on worker productivity

Article References: The high cost of climate change on worker productivity. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: climate change, heat stress, worker productivity, social cost of carbon, wet-bulb globe temperature, labor economics, UC Davis, Nature Climate Change, air conditioning, agricultural workers, carbon emissions, heat adaptation

The study’s scale and methodology set it apart from earlier work. Rather than treating air conditioning as a simple yes-or-no variable, the researchers constructed county-level estimates of annual average household AC usage and then examined how the relationship between daily temperature and mortality shifts across that usage gradient. County-specific temperature–mortality associations were first estimated for each county in the contiguous United States, and those estimates were then pooled through a meta-regression framework keyed to the counties’ average AC usage. This two-stage design allowed the team to move beyond correlation and characterize precisely how the shape of the temperature–mortality curve changes as cooling becomes more common in a population.

The technical results are striking in their internal consistency. When the researchers compared counties at the 10th percentile of household AC usage with counties at the median, three things happened simultaneously. First, the minimum mortality temperature—the outdoor temperature at which deaths are lowest—shifted downward, meaning that the human body’s apparent comfort zone extended toward cooler values. Second, the range of temperatures above that minimum mortality point for which mortality showed no statistically significant increase widened considerably, effectively flattening the most dangerous portion of the heat–death curve. Third, and most directly, the mortality odds ratio at the 95th percentile of temperature fell from 1.022, with a 95 percent confidence interval of 1.011 to 1.033, to 1.008, with a confidence interval of 0.999 to 1.017. In practical terms, an extremely hot day that would have raised mortality risk by roughly two percent in a low-AC county raised it by well under one percent where air conditioning use reached the median.

Perhaps the most policy-relevant discovery in the analysis, however, is what happened beyond the median. When household AC usage climbed further above that midpoint, the mortality odds ratio did not continue to fall. Instead, the benefit plateaued, indicating that the protective effect of residential cooling saturates once usage reaches roughly half of households in a county. Above that threshold, additional adoption delivers diminishing returns for population health. This plateau has profound implications for how governments think about adaptation investments: the priority is not maximizing AC penetration everywhere, but lifting the lowest-usage communities—often the hottest, poorest, and most vulnerable—toward the median, where each additional air-conditioned household buys the largest mortality reduction.

The epidemiological logic behind these findings is grounded in physiology. Extreme heat stresses the cardiovascular and respiratory systems, thickens blood, impairs thermoregulation, and disproportionately kills elderly people, people with chronic disease, and those without access to cooled environments. Indoor cooling interrupts this cascade by lowering core body temperature and reducing the physiological strain of hot nights, which are increasingly recognized as a key driver of heat deaths. Earlier research, including a landmark study of the twentieth-century decline in the US temperature–mortality relationship published in the Journal of Political Economy, had pointed to air conditioning as the leading explanation for Americans’ growing resilience to heat. The new study quantifies that resilience county by county, on modern data, and with the statistical machinery needed to separate AC’s effect from other influences such as demographics, healthcare access, and long-term acclimatization.

To build their AC usage estimates, the team relied on a fine-scale dataset of multidimensional household well-being developed by co-authors Narasimha D. Rao and Karthik Akkiraju and collaborators, published in Scientific Data in 2024, which fuses multiple household surveys to produce spatially detailed portraits of American living conditions. Mortality data came from the National Center for Health Statistics Research Data Center of the US Centers for Disease Control and Prevention, while daily gridded weather data were drawn from the PRISM climate database at Oregon State University and population exposures from the LandScan Global one-kilometer population grid. The researchers also conducted an extensive battery of sensitivity analyses—varying temperature time windows, spline specifications, adjustment for fine particulate matter pollution, and restricting the analysis to summer months—finding that the core results held across all of them.

The maps of averted mortality that emerge from the analysis tell a story of deep geographic inequity. The largest avoided death burdens concentrate where the dual conditions of high heat exposure and widespread residential cooling coincide, while counties in the Southeast, Southwest, and parts of the Midwest show the biggest absolute benefits. Conversely, regions where heat risk is rising but AC adoption lags—often because of poverty, aging housing stock, or energy insecurity—stand out as areas of unmet need. The study’s authors note that in 2020, 27 percent of US households reported difficulty meeting their energy needs, according to the US Energy Information Administration, a reminder that the cooling that saves lives is itself unevenly affordable. Energy burden, in this framing, is a direct mortality risk factor.

Yet the paper is careful not to present air conditioning as an unqualified good. The authors explicitly underscore the need for strategies that balance the survival benefits of AC against the harms of overuse, which include surging electricity demand on the hottest days, greenhouse gas emissions from fossil-fueled generation, waste heat vented into urban streets, and the refrigerant emissions that potentiate further warming. The plateau finding sharpens this calculus: because health benefits saturate near median usage, the marginal emissions cost of pushing adoption far beyond that level yields little additional protective return. The rational adaptation portfolio, therefore, pairs targeted expansion of cooling access for vulnerable and low-usage populations with efficiency standards, grid decarbonization, passive cooling design, urban shade and reflective surfaces, and community interventions such as cooling centers, whose public health effectiveness has been reviewed in the European Journal of Public Health.

The stakes of getting this balance right will only grow. The Lancet Countdown’s 2024 report documented record-breaking climate-related health threats, and studies of population aging project that temperature-related mortality will rise substantially at higher levels of global warming even under optimistic scenarios. The research team’s companion work, published in JAMA Network Open in 2025, estimated the heat and cold mortality burden in the US from 2000 to 2020, providing the baseline against which the new averted-death figures are measured. Together, these findings reframe household air conditioning from a comfort appliance into critical health infrastructure—whose reach, affordability, and carbon footprint will help determine how many people the coming decades of heat will claim. As climate change pushes temperatures past thresholds the human body cannot tolerate, the authors conclude, ensuring equitable access to safe indoor cooling while managing its energy costs stands as one of the defining adaptation challenges of the century.

Subject of Research: The effect of household air conditioning usage on heat-related mortality across the contiguous United States

Article Title: Impact of household air conditioning usage on heat-related mortality in the USA

Article References: Chu, L., Akkiraju, K., Rao, N. D., Dubrow, R., & Chen, K. (2026). Impact of household air conditioning usage on heat-related mortality in the USA. Nature Health. https://doi.org/10.1038/s44360-026-00184-0

Image Credits: AI Generated

DOI: 10.1038/s44360-026-00184-0

Keywords: air conditioning, heat-related mortality, climate adaptation, public health, temperature–mortality association, heat waves, energy insecurity, meta-regression, epidemiology, United States, climate change, mortality burden