Thirty years after nations banded together to phase out chemicals that destroy stratospheric ozone, the gaping hole in Earth’s ultraviolet (UV) radiation shield above Antarctica is shrinking. But new findings suggest that at midlatitudes, where most people live, the ozone layer in the lower stratosphere is growing more tenuous—for reasons that scientists are struggling to fathom.
“I don’t want people to panic or get overly worried,” says William Ball, an atmospheric physicist at the Physikalisch-Meteorologisches Observatorium Davos World Radiation Centre in Switzerland. “But there is something happening in the lower stratosphere that’s important to understand.”
Several recent studies, including one published last month in Geophysical Research Letters, point to a robust recovery of stratospheric ozone concentrations over Antarctica—the long-awaited payoff after the Montreal Protocol in 1987 mandated a global phaseout of chlorofluorocarbons and other ozone-eating compounds.