It was a dark day in New England on May 19, 1780. Sunrise in Vermont was obscured by a thick fog, and the darkness spread to Massachusetts by the late morning. The sunlight disappeared entirely. The sky over the former colonies was soon the color of midnight. Many New Englanders believed the world was ending. Was God punishing the inhabitants of the cradle of the Revolution for their violent disobedience? Was some more general biblical prophecy being fulfilled? The answer to both questions was, of course, no. The darkness was caused by smoke from Canadian wildfires.

Now, 243 years later, the Northeast has experienced another series of dark days for the same reason. Large wildfires in the Canadian provinces of Alberta, Nova Scotia, Ontario, and Quebec have been occurring since March of this year, and smoke from the fires has now drifted and spread across 20 U.S. states. Apocalyptic images of dark orange New York skies have dominated the media. Schools and businesses were closed, flights were cancelled, and experts urged people to stay inside or wear N95 masks if they ventured out.

Also prevalent in coverage of the smoke pollution was the linking of the fires to climate change. The Intergovernmental Panel on Climate Change (IPCC) has expressed some confidence that various regions across the globe are experiencing positive trends in “fire weather”, conditions conducive to triggering and sustaining wildfires. Weather in Canada this year has been warmer and drier than in years previously, and roughly half of all wildfires in the country are attributable to lightning strikes. The other half are human-caused, usually started unintentionally by campfires or discarded cigarette butts. Obviously, if “fire weather” conditions are increasing because of climate change, it is more likely that wildfires will occur.

There is some good news, however, which is lost in the at-times hyperbolic media coverage. Data from the EU show that wildfire emissions have declined globally since 2003. Wildfires have increased in recent decades in the Western United States, but Canada has not seen such an increase. In fact, analysis in the International Journal of Wildland Fire shows that burn rates from wildfires across Canada have been much lower this century than in centuries past (the analysis goes back to the year 1700). None of this means that climate change is not occurring or that wildfire risk is not higher because of climate change. It does mean that what is happening with the climate is more complicated than one might think from reading the New York Times or Washington Post.

Nonetheless, it is crucial to recognize that wildfires pose legitimate dangers to human health, and that the current wildfires burning in Canada have caused large dips in air quality in Canada and in the United States. New York City saw its worst air quality since 1966 on June 7, with an air quality index (AQI) of 484 (anything over 200 is considered “hazardous”). Delaware also reported AQIs ranging from 300 to 500, some of the worst air quality the state has ever experienced. Conditions in the Northeast have now improved, but the smoke is moving southward. The impact will likely be less severe in other states, but if the fires continue to burn, “there is a chance the smoke could come back,” as Environment and Climate Change Canada meteorologist Gerald Chang said.

What are the effects of wildfire smoke on human health? In general, particulate matter from smoke can reduce lung function. If you have health conditions like asthma or COPD, exposure to smoke can make these conditions worse. Healthy individuals may experience some inflammation or mild negative health effects from exposure to wildfire smoke, but it also depends on the composition of the smoke, how long it’s been in the air, and how long or often you are exposed to it. Breathing air polluted with wildfire smoke for weeks can cause serious problems even in healthy individuals. Residents of Seeley Lake in Montana were exposed to wildfire smoke for 49 days in 2017, and researchers found that even a year later, there was a significant decrease in lung function.

It is a good idea to reduce your exposure to wildfire smoke if the pollution is high. Air filters can help, as can respirators such as the N95 mask. Cloth and surgical masks, unfortunately, are unlikely to provide as much protection. Air quality monitors are common in most states, and you can plug in your zip code into www.airnow.gov to see the current and forecasted air quality for your area. Individuals can then determine how at risk they are for exposure to pollution from outdoor activities (AirNow will also make recommendations, particularly for people with respiratory problems).

Staying informed about air quality is crucial not only because of the increase in wildfires, but also because many of us city-dwellers live in high-exposure zones already. Chinatown, Boston has the worst air quality in Massachusetts. This is not because of wildfires but because it is situated between two highways, and its residents are exposed to ultra fine pollutants as a consequence. Many similar neighborhoods across the United States, home to low-income and minority communities, are in high-exposure zones. Poor people and people of color breathe more hazardous air. As air quality continues to be in the news, we can only hope that policy-makers recognize the importance of building green infrastructure in the future.