Where this was said
The Clean Air Act and America's Pollution History
At 10:22 · chapter starts 10:00
Greenstone paints a vivid before-and-after: in the late 1960s, parts of the US looked like Delhi today, with white-collar workers in Gary, Indiana routinely bringing a spare shirt because coal pollution soiled the first. The Clean Air Act of 1970, signed bipartisanly and amended multiple times, changed all that. A 2021 Environmental Research Letters study confirms the downstream benefits: American crop yields are significantly higher thanks to cleaner air, though particulate matter still takes a toll. Today, the US averages just 9 micrograms per cubic meter of PM2.5 annually — above the WHO's 5 µg/m³ threshold, but dramatically better than the China average of 35. Dubner notes the uncomfortable irony: much of the US's clean-air success came by offshoring manufacturing — and its pollution — to developing nations.
As coal smoke darkened English trees, the darker variety of the peppered moth thrived because it could hide from predators. Stefan Hiblik's team used the historical ratio of dark-to-light moths as a validation tool for their pollution dispersal model — a clever bridge between microevolution and economic history.
