China's skies may be toxic, and its rivers fetid and prone to sudden infestations of pig carcasses. But according to a new study, the country's environmental battle has also been making quiet, measurable progress.

The paper, a collaboration between U.S. and Chinese researchers published in this week's issue of Science, found that China's ecosystems have become healthier and more resilient against such disasters as sandstorms and flooding. The authors partly credit what they describe as the world's largest government-backed...