In the upper Midwest of the United States, Michigan, Wisconsin and Minnesota have issued air quality warnings as smoke from the Prairie wildfires is dragged south by a cold front. Those warnings expanded into the Northeast, causing some hazy skies.

A gray haze from wildfire smoke could be seen in Cincinnati, and the entire state of Minnesota is under an air quality alert.

Many fires burning across Canada, forcing evacuations and threatening air quality in the United States, cannot simply be put out, authorities and experts say.

As the climate changes, the far north is drying and warming, which means wildfires are getting bigger and more intense. The area burned in Canada is now the second largest on record for this time of year,

Fire experts call them “zombie fires.” That definition comes from a specialist in the measurement of Canada’s raging