The air quality in Portland has become the worst in the world — with Seattle, Los Angeles and Denver also ranking up there with notoriously polluted places like Delhi and Shanghai.

Why it matters: Big-city residents often consider themselves smugly immune to the physical wreckage of calamities like wildfires, floods and hurricanes. The pernicious smoke now blanketing the splendid cities of our nation's Western spine is a reminder that no one is exempt from climate change.