Wildfire smoke is reversing decades of progress on clean air

After months of devastating fires, Canada’s worst wildfire season worsened even further in September. In just seven days, blazes across the country burned through as much land as is usually scorched in an entire fire season. The smoke stretched over Greenland and northern Europe, bringing with it toxic particles that can lead to everything from asthma to heart attacks.

This story is increasingly common. Canadian wildfires earlier in the year sent smoke south that blanketed much of the eastern and …