People I (Mostly) Admire 171. Measuring Pollution on Parallel Earths
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Nov 22, 2025 
Michael Greenstone, an economist from the University of Chicago, focuses on the health impacts of air pollution and practical policy solutions. He discusses the shocking life-expectancy losses linked to pollution, exemplified by China's Huai River policy. Greenstone also explains how using infants simplifies pollution measurement and shares insights on developing pollution markets in India that improved compliance and reduced emissions significantly. His work is driven by a desire to combine rigorous research with real-world impact to shape effective policies.
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Parallel Earths As The Ideal Counterfactual
- The ideal data to measure pollution effects is two parallel Earths with different exposures while people live normal lives.
- Michael Greenstone explains that natural experiments help approximate that ideal when randomization isn't possible.
Huai River Natural Experiment
- China drew a line along the Huai River and provided free winter coal heating to the north, creating an abrupt pollution jump.
- Greenstone and colleagues used that policy as a natural experiment to compare life expectancy across the boundary.
Large Health Impact From Small Geographic Jump
- Pollution jumped ~40% crossing the Huai River, from ~100 to ~140 micrograms per cubic meter, far above WHO targets.
- That discontinuity aligned with a 3–5 year reduction in life expectancy, driven by cardiorespiratory deaths.