How many Americans face unhealthy smog by 2100?

Projected air-quality decline from climate change

A new U.S. air-quality modeling study projects a major expansion of “smog season” areas where average pollution is poor enough to trigger alerts for sensitive groups (such as people with asthma, older adults, and those with heart or lung disease).

The analysis estimates that about 100 million people in the United States will live in locations where average air quality during smog season is sufficiently poor to routinely prompt “stay indoors” style guidance by the year 2100.

The scale of the change is stark: the modeling suggests that almost one in three Americans will routinely breathe air deemed unhealthy for sensitive people by 2100, which is described as a sevenfold increase compared with the baseline situation.

Why it matters

This projection matters because it links climate-driven changes to everyday health exposure. Smog season air pollution is associated with worsened respiratory and cardiovascular outcomes, especially for vulnerable populations. If large portions of the country routinely exceed sensitivity thresholds, public health burdens would likely rise in parallel—potentially increasing emergency-room visits, medication use, and missed work or school during high-pollution periods.

What the study’s projection implies

If these estimates hold, preparedness would need to shift from occasional events to more routine conditions for many communities. That includes planning for public alerts, protecting sensitive groups, and considering mitigation strategies that can reduce both pollution levels and the climate drivers that intensify pollution episodes.