Wildfires are common in Canada's western provinces, but this year the eastern provinces of Nova Scotia, Quebec and parts of Ontario are also reeling from out of control wildfires, sending plumes across much of New York and forcing authorities to issue air quality alerts for Toronto and Ottawa.
Canada is on course for its worst-ever wildfire season on record, with about 3.3 million hectares (8.2 million acres) burned so far this year, according official data.
The forest fires started in late April in British Columbia and Alberta, displacing more than 30,000 people at its peak, and shutting down oil and gas production. While most fires in the western provinces are under control, the fires have now opened new fronts spreading to the eastern provinces of Nova Scotia, Quebec and Ontario. Quebec is Canada's biggest province by area, and Ontario second-biggest by land area and biggest by population. As of Tuesday, Quebec is battling around 160 forest fires, displacing some 10,000 people, while a similar number of fires are burning in Ontario.
Quebec's multiple fires are caused by lightning.
Canadian authorities on Wednesday issued starker air quality warnings for the country's capital Ottawa and financial capital Toronto, and urged residents to limit outdoor activities.
Environment Canada has raised the air quality risk level for Toronto on Wednesday to high-risk from moderate risk on Tuesday and to very high risk for Ottawa.
Dry conditions are forecast to persist for months across Canada though occasional rains and cooler temperatures are expected to bring short-term relief. The Weather Network's longer-term forecast expects Nova Scotia temperatures to be slightly warmer than normal for the rest of the summer.
Situated on Canada's eastern seaboard, Nova Scotia's climate is heavily influenced by the North Atlantic Ocean, which brings higher humidity and more moderate temperatures than many other parts of the country. Fires are not unusual but tend to be much smaller than those in the west.
The region is covered by what is known as the 'Acadian Forest', which contains plenty of broadleaf trees like sugar maples mixed with evergreens such as conifers. Broadleaf trees are less flammable than evergreens because their branches and leaves are further from the ground, and their leaves hold more moisture.
The Acadian forest is much less prone to large wildfires than forests in western Canada.
Atlantic Canada received low snowfall this winter, followed by an exceptionally dry spring. Nova Scotia's capital Halifax received just 120 millimetres of rain between March and May, roughly a third of the average, according to Weather Network meteorologist Michael Carter.
A scorching late May heat-wave pushed temperatures in Halifax to 33 degrees Celsius (91.4 F) on Thursday, around 10 degrees Celsius above normal for this time of year.
Most of the wildfires are believed to be accidentally caused by human activity.
Ellen Whitman, a research scientist with the Canadian Forest Service, said there is also speculation that trees felled during Hurricane Fiona, which hit Atlantic Canada in September 2022, or killed by an infestation of forest pests may be providing more fuel than usual for wildfires, but that theory requires further investigation.
Whitman said it is difficult to determine the impact of climate change on a single fire season, but Atlantic Canada has been much hotter than usual and scientists expect temperatures in the region to continue to rise in coming years.
For coastal regions climate change is expected to bring more rain, which should reduce the risk of wildfires, but a warmer atmosphere is more efficient at pulling moisture out of soils, a factor that increases fire risk.
Widespread spring fires across the whole of Canada are also unusual, and research shows fire seasons across North America are getting longer.
