Thick plumes of smoke from wildfires in Canada and the northern United States recently caused a significant decline in air quality across New England, particularly in the Greater Boston area. The smoky conditions, which reached levels deemed unhealthy for sensitive groups, were driven by hundreds of fires burning in Ontario and nearly 20 blazes in Minnesota. These fires were fueled by unusually hot and dry weather, with temperatures in some parts of Ontario reaching around 100 degrees Fahrenheit—approximately 25 to 30 degrees above average for this time of year.

Meteorologists attribute the movement of smoke eastward over New England to a heat dome centered over the upper Midwest, which created atmospheric circulation patterns that transported the smoke across long distances. While smoky days in New England are not unprecedented — with significant events recorded in 1950 and as far back as 1881 — experts note that the frequency of such events has increased in recent years. Daniel Westervelt, an associate professor at Columbia Climate School’s Lamont-Doherty Earth Observatory, observed that major smoke episodes have become nearly annual occurrences along the northeastern coast, including Boston.

Although Boston’s air quality has improved overall over recent decades, there have been no days reaching very unhealthy levels since 2002 and no unhealthy days since 2012. Nevertheless, officials and researchers caution that these temporary improvements may be offset by the increasing prevalence of wildfire smoke episodes, particularly as climate change contributes to more frequent and severe wildfires. Tori Hass-Mitchell, Boston’s air quality project manager, anticipates more days with unhealthy air for sensitive populations as heatwaves and wildfire smoke transport events become more common.

Climate scientists link the unprecedented heat and dryness fueling the fires, especially in Canada, to climate change. Shel Winkley, a meteorologist at Climate Central, noted that such extreme temperatures in Ontario would be highly unlikely without the influence of global warming. Scientists warn that as wildfires intensify and become more expansive in Canada, the risk of smoke drifting into the United States will likely rise.

However, some experts urge caution in interpreting current trends. Robert Field, an associate research scientist at Columbia University, explained that episodic smoky days remain relatively rare and complex factors govern fire occurrence, smoke production, and atmospheric transport. Consequently, it remains challenging to conclusively forecast the future frequency of smoky events in New England.

Research has detailed the public health impacts of wildfire smoke, which carries a toxic mix of pollutants including fine particulate matter known as PM2.5. These particles are small enough to penetrate deeply into the lungs and enter the bloodstream and have been linked to respiratory and cardiovascular problems as well as premature death. Studies have found that rising smoke exposure has contributed to stalled air quality improvements in parts of the Northeastern US and has been associated with tens of thousands of deaths nationwide.

Public health officials continue to advise individuals with respiratory or cardiovascular conditions to remain vigilant during fire seasons. Although forecasters expect current smoke levels to diminish over the upcoming weekend, lingering risks persist, and the possibility of smoke returning in the near term remains dependent on fire activity and weather patterns.