Donald Worster, environmental historian
The worst environmental catastrophe in Earth’s history occurred 66 million years ago, when an asteroid struck, killing an estimated 70 percent of all species. Nothing humans have done compares. But the 1930s Dust Bowl was the worst catastrophe in America’s history, and such a phenomenon may become global as the world’s climate changes.
John McNeill, history professor, Georgetown
The deliberate rupture of the dikes on China’s Yellow River in 1938, by Chinese troops trying to halt a Japanese advance. It killed half a million Chinese, displaced millions more, and led to a decade of flooding.
David Yarnold, president and CEO, National Audubon Society
DDT was a human-made environmental disaster that caused the shells of bird eggs to thin, which crushed populations—and harmed the food chain in ways that affected humans.
John Schwartz, science writer, The New York Times
It would be hard to beat the six-mile-wide asteroid that struck Earth about 66 million years ago with an explosive force billions of times more powerful than that of the atomic bomb the United States dropped on Hiroshima.
Bill McKibben, author and environmentalist
The asteroid strike that some scientists theorize wiped out the dinosaurs was pretty significant. Of course, with climate change we’re on the path to accomplishing something on the same scale, and this time it’s entirely voluntary.