Smoke from wildfires in Canada has created a crisis in the American Northeast and beyond, with air pollution in New York reaching its worst level in modern history.

David Wallace-Wells, a climate columnist for The Times, explains why this happened, and why there is so little we can do to keep it from happening again.

Guest: David Wallace-Wells, a climate columnist correspondent for The New York Times.

Background reading: 

• New York City experienced its worst air quality on record. Here’s how to stay safe as the smoke spreads.
• David Wallace-Well’s column on the smoke that shrouded New York City.

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