Researchers say they have discovered the first real evidence that the thinning in the ozone layer above Antarctica is starting to recover.

Researchers detected the hole decreased by more than 1.5 million square miles - roughly half the area of the contiguous United States - since 2000, when ozone depletion was at its highest point.

"It's a big surprise," said Susan Solomon, an atmospheric chemist at the Massachusetts Institute of Technology and lead author of the study published Thursday in the journal Science. "I didn't think it (the healing) would be this early."

The study were published Thursday in the journal Science.

"We can now be confident that the things we've done have put the planet on a path to heal," added Susan Solomon, the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science at MIT, said in a press release. "Which is pretty good for us, isn't it? Aren't we amazing humans, that we did something that created a situation that we decided collectively, as a world, 'Let's get rid of these molecules'? We got rid of them, and now we're seeing the planet respond."

The team then used computer model simulations to compare September ozone measurements year-to-year and project what ozone levels would be in the future. The ozone hole was at its largest in 2000, but decreased by more than 4 million square kilometers over the course of the next 15 years. These changes ended up matching the predictions of the computer models.

The ozone hole was first found in the 1950s using ground-based data.

"It's been interesting to think about this in a different month, and looking in September was a novel way," co-author Diane Ivy, a researcher at MIT's Department of Earth, Atmospheric and Planetary Sciences, said in the release. "It showed we can actually see a chemical fingerprint, which is sensitive to the levels of chlorine, finally emerging as a sign of recovery."

After Solomon's paper on the irreversibility of climate change came out, she noted with another paper in Science, explaining that "irreversible" doesn't mean "unstoppable."