Staying cool during a warming climate sounds protective—but this paper identifies a hidden tradeoff: more air conditioning, more indoor time, and more time in lower floors could increase radon exposure and lung cancer risk. Climate change adaptation strategies, such as increased air conditioning use, greater time spent indoors, and seeking cooler lower-floor spaces, may inadvertently increase residential radon exposure and associated lung cancer risk.

The analysis combined a scoping review of literature on climate change and indoor radon with four exposure scenarios: current conditions, increased air conditioning use, increased time in basements, and a combined scenario. The study used information on plausible changes in behavior and building operation associated with climate change adaptation to derive estimates of radon-associated lung cancer risk in the pooled French-German-Italian population and the United States.

These scenario-based estimates were not intended to predict actual population behavior; they were intended to illustrate the potential magnitude of change in radon-related lung cancer risk that an individual may face if they adopt such behavior patterns in response to a warming climate.

Table two summarizes how meteorological, building, and behavioral factors may affect indoor radon exposure. It reports that meteorological effects can increase radon, although their patterns are not predictable; the cited literature reports an air-conditioning association of sixty percent higher and basement or lower-ground concentrations of one hundred fifty percent higher.

The table matters because tighter, less ventilated buildings and greater time spent below ground may alter radon exposure and related health risks. Based on the literature review, the analysis developed and analyzed scenarios of possible changes in lifestyle patterns due to climate change.

Scenario one held radon concentration constant under current conditions, while scenario two represented reduced ventilation associated with air conditioning use and an approximately sixty percent increase in indoor radon concentration. Scenario three represented one less hour outdoors and four more hours in lower, cooler indoor spaces, where concentration could increase by one hundred fifty percent; scenario four integrated scenarios two and three.

Table three compares four behavioral scenarios by air-conditioning pattern and location, reporting predicted average radon concentration and radon progeny exposure. Concentration rises from one point eight zero to two point seven two picocuries per liter, or from sixty-seven to one hundred one becquerels per cubic meter, while exposure ranges from zero point three seven six to zero point five six four working-level months per year.

The authors connect these estimates to microenvironment-specific exposure, including basement assumptions, seasonal air conditioning, and indoor and outdoor equilibrium factors. For the risk estimation, the analysis applied lung cancer risk model estimates reported in the US National Academy of Sciences BEIR VI report.

The Exposure-Age-Concentration model applied modifying factors for age and concentration. Ninety-five percent confidence intervals for cumulative excess risk were derived by substituting the lower and upper bounds of the beta coefficient directly into the cumulative excess risk calculation.

For the US, estimated cumulative excess risks by age eighty-five were ninety-one for current conditions, one hundred four with increased air conditioning use, one hundred nineteen with increased time spent indoors or on lower levels, and one hundred thirty-seven for the combined scenario.

Relative to current exposure conditions, those scenarios corresponded to about thirteen, twenty-eight, and forty-six additional lung cancer deaths per ten thousand people by age eighty-five. Table one reports cumulative excess lung-cancer mortality risk by age eighty-five, expressed as excess deaths per ten thousand people, under four climate-adaptation scenarios.

For the US, estimates rise from ninety-one in scenario one to one hundred thirty-seven in scenario four; for the pooled French-German-Italian population, they rise from eighty-six to one hundred twenty-eight. Parentheses give ninety-five-percent confidence intervals, calculated using the BEIR six exposure-age-concentration model, highlighting how climate-related adaptation and radon exposure could affect lung-cancer mortality.

PUMA-based estimates were approximately twenty-seven to thirty-one percent higher than Exposure-Age-Concentration estimates for both the US and pooled French-German-Italian populations. The Darby model yielded estimates approximately fifty-eight to sixty percent lower than Exposure-Age-Concentration estimates.

Importantly, all three models consistently showed an increase in lung cancer mortality risk across the four behavioral adaptation scenarios, supporting the robustness of the main conclusion. The review identified multiple pathways by which climate change and associated adaptations may lead to increased exposure to indoor radon.

Using literature-informed values for potential changes in radon progeny exposure, the analysis calculated estimates of increased radon-associated lung cancer mortality in the US and a pooled French-German-Italian population. The results suggest that increases in radon exposure due to climate change are anticipated to lead to significant increases in lung cancer.

The projected increases in radon-related lung cancer risk associated with climate change adaptation are not inevitable. Available radon mitigation measures in dwellings, including sub-slab depressurization, mechanical supply and exhaust ventilation with heat or energy recovery, and radon-resistant construction in new buildings, can partially or substantially offset these increases.

Climate change adaptation strategies should therefore be accompanied by greater attention to indoor radon exposure and increased uptake of radon testing and mitigation actions. The study’s central message is that climate adaptation can unintentionally raise radon-related lung cancer risk, but testing and available mitigation measures can partially or substantially offset those increases.