Micah Hahn, an assistant professor of environmental health at the University of Alaska Anchorage, says while it might seem obvious that wildfire smoke causes health impacts, there had actually never been a nuanced, scientific look at those impacts. The biggest impact was for asthma-related emergency department visits. This was really across the board and across age groups and in geographic areas.

Smoke and soot from central Alaska wildfires have afflicted the subarctic city of Fairbanks with some of the world's worst air pollution in recent days, forcing many residents indoors and prompting one hospital to set up a "clean air shelter."

The B.C. Centre for Disease Control recommends children and elderly stay indoors during lingering smoke from forest fires.

The smoke has pushed pollution in Calgary and other cities to dangerous levels, and cast an unsettling, spooky haze over almost every part of B.C.

Doctors urge ministers to act as 1,320 killed by asthma in England and Wales last year