The economic free fall accompanying the coronavirus pandemic has, by some measures, made the world a cleaner place. Air pollution in Chinese, Indian, and U.S. cities is way down. In China alone, lower air pollution may have saved more lives than the virus has killed so far. In New York City, some pollutants dropped by more than half in just a week. Global emissions of carbon dioxide, the chief long-term cause of climate warming, are on track to drop by eight percent this year. All that cleaner air has come at a huge, unacceptable cost. But could the pandemic lay the foundation for more serious action to protect the environment—including on the greatest of all environmental problems, climate change?