OTTAWA -- Air pollution from wildfires remained well above healthy levels across much of southern and northern Ontario and several communities in British Columbia and Alberta on Thursday.

But there may be some hope on the horizon, after the number of fires burning across the country fell overnight.

The fires and the blankets of smoke affecting millions of Canadians prompted a debate in the House of Commons, during which members of Parliament expressed solidarity with the people affected and discuss the role climate change is playing in this year's more-severe fire season.

"Climate change is real and we are seeing and living its impact every day," Environment Minister Steven Guilbeault said during the debate.

This, he said, is the worst fire season Canada has ever experienced and it has had devastating consequences.

"People have lost everything," he said.

As debate continued over the motion brought forward by the Bloc Quebecois, the air outside the Parliament Buildings had mostly cleared following several days of air quality so poor people were told to limit or avoid outdoor activities completely.

But further south, towards the Greater Toronto Area and in areas around Sudbury and North Bay, the air quality remained poor.

There are also many warnings of moderate or high risks due to bad air quality in parts of British Columbia and Alberta, as out-of-control fires continued to burn in almost every province and territory across Canada.

Environment Canada's air quality forecast suggests things will remain at unhealthy levels in most of southern Ontario and in western Canada through Friday.

Multiple health studies have linked wildfire smoke to serious health consequences including heart attacks, strokes and breathing problems, and the poor air quality has prompted cancellations or changes to outdoor activities as a result.

The Toronto District School Board joined several of its counterparts across the region in cancelling outdoor activities and moving recess inside for a second straight day Thursday. The Toronto Zoo also announced it would close early.

As of midday Thursday, there were 431 fires burning in nine provinces and two territories. That was down from 441 Wednesday, with Quebec extinguishing 10 fires since Wednesday morning.

The number of out-of-control fires also fell from 256 on Wednesday to 234 on Thursday, including a change in status for more than a dozen fires in Quebec.

The eastern United States has been seeing the effects from wildfire smoke drifting south, with cities like New York and Washington, D.C., issuing air quality warnings of their own.

The U.S. Federal Aviation Administration grounded flights out of Philadelphia International Airport on Thursday morning and slowed traffic to and from New York City-area airports as wildfire smoke reduced visibility.

Prime Minister Justin Trudeau spoke on the phone with U.S. President Joe Biden about the issue on Wednesday. A readout of that call said both leaders agreed the situation pointed to the urgency of addressing climate change.

More than 42,000 square kilometres have burned so far this year, making 2023 the second-worst year for fires on record. That's before the hottest months of the year have even begun.

In 2014, more than 46,000 square kilometres burned, the most ever in a single year. At the current pace, that total is expected to be passed this weekend.

There has been no loss of life, although property and infrastructure damage has been significant. Hundreds of homes and other buildings were destroyed or damaged in Nova Scotia in recent weeks, while Quebec's fires are threatening critical infrastructure including roads and Hydro towers.

On Vancouver Island Wednesday, a small wildfire cut off the only major highway linking Port Alberni, Tofino and Ucluelet to the rest of British Columbia.

This report by The Canadian Press was first published June 8, 2023.