Heavy smoke continues to spread across the Great Lakes region into New England and as far south as Maryland, leading to unhealthy and even hazardous air quality in a number of states.

The combination of extreme heat and dry conditions in Ontario and northern Minnesota led to significant spread of wildfires on July 13. More than 800 wildfires are actively burning in Canada, according to the Canadian Wildland Fire Information System.

Record breaking temperatures created a heat dome across western Ontario and Minnesota with some places reaching over 100 degrees. This allowed fires to continue on an “unprecedented run,” said Derek Mallia, a professor of atmospheric sciences at the University of Utah.

In Ontario, dramatic videos on social media show intense fire and smoke-filled skies. The air quality in certain areas was labeled “very high risk” by Air Quality Ontario. Thousands of people in the region have been forced to evacuate.

Air quality ranging from hazardous to unhealthy is also affecting parts of Minnesota, Wisconsin and Michigan, choking major northeastern cities like Philadelphia, New York City and Baltimore, according to AirNow.

“You have a firehose of smoke coming right now,” Mallia said.

Those areas are expected to experience smoke-filled skies at least through the weekend.

Climate change caused by humans is exacerbating these conditions. And longer and more severe droughts and prolonged heat waves are resulting in drier vegetation.

“The frequency and intensity of these wildfire smoke events are increasing,” said Dan Westervelt, an associate research professor at Columbia University’s Lamont-Doherty Earth Observatory. He added that the fires are becoming an annual occurrence and sometimes more than just annual.

Dangers from wildfire smoke

Smoke is made up of tiny particles that can be inhaled deep into a person’s lungs and even enter the bloodstream.

The data is very clear that the pollution from wildfires has all kinds of health effects, said Dr. David Eisenman, a professor of medicine at the David Geffen School of Medicine at UCLA. He points to studies showing an increase in heart attacks, heart failure, stroke and respiratory illness. Chronic exposure increases the risk of pregnancy complications and the risks of possible developmental disorders in children.