Staying indoors and turning up the air conditioning can protect people from heat. But this study suggests those same choices may quietly increase exposure to radon, a gas linked to lung cancer. 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 study compared current conditions with increased air conditioning, more time in basements, and a combination of both, then estimated how those changes could affect lung cancer deaths. These estimates were not meant to predict that whole populations will behave in exactly the same way.

Instead, they were meant to illustrate the possible change in radon-related lung cancer risk that an individual may face after adopting these behavior patterns in response to a warming climate. The scenarios used a reference house with more radon in the basement than on the first floor, then changed how much time people spent indoors, used air conditioning, or stayed in the basement.

These scenarios were not intended to represent average behavior across entire populations, but to show how lifetime radon-related lung cancer risk may change if an individual adopts a particular pattern in response to climate change. Here is the surprising part: in the United States, the combined scenario was linked to about 46 additional lung cancer deaths per 10,000 people by age 85, compared with current exposure conditions.

The increase was larger when both changes occurred together than when air conditioning or more time indoors and downstairs was considered alone. The review identified multiple pathways through which climate change and the ways people adapt to it may increase exposure to indoor radon.

The results suggest that increased radon exposure caused by climate change could lead to significant increases in lung cancer. The researchers compared several ways of estimating risk, and their results differed: PUMA estimates were higher than EAC estimates, while the Darby model produced lower estimates.

Even so, all three models consistently showed increased lung cancer mortality risk across all four behavioral adaptation scenarios, preserving the same direction of change. The estimated size of the risk increase varied across models, with PUMA higher than EAC and the Darby model lower by comparison.

That consistency supports the main conclusion: all three models showed increased lung cancer mortality risk across the four behavioral adaptation scenarios, so the direction remained the same. The scenario analysis was not designed to produce precise national estimates or to predict that entire populations would adopt these behaviors uniformly.

It showed that behavioral changes alone, without any change in the underlying geology or building stock, could measurably increase lung cancer mortality risk. These projected increases are not inevitable. Available measures in homes can partially or substantially offset them.

Climate change adaptation should therefore be accompanied by greater attention to indoor radon, including more home testing and mitigation. Climate change can change not only the weather outside, but also how much radon people breathe indoors. Testing homes and using available fixes could help prevent that added risk.