The ozone layer has been on the mend thanks to global action, including a major international treaty to phase out ozone-damaging chemicals. But that doesn’t mean it’s fully healed.

A large and deep ozone hole still forms every Antarctic spring, being deepest and largest toward the end of September, Shanklin told USA TODAY in a May 15 e-mail.

The largest ozone hole ever seen opened up over Antarctica in 2000. Seen in this image released by NASA, the hole appears as a giant blue blob which spreads over about 11 million square miles.

The largest ozone hole ever seen opened up over Antarctica in 2000. Seen in this image released by NASA, the hole appears as a giant blue blob which spreads over about 11 million square miles.

It's been 40 years since groundbreaking research announced the discovery of a hole in the ozone layer, a revelation that launched a rapid and successful effort to ban chemicals in hairspray ...

The study showed large uncertainties regarding how much of this recovery was due to concerted efforts to reduce ozone-depleting substances, or if the shrinking ozone hole was a result of other ...

It's been 40 years since groundbreaking research announced the discovery of a hole in the ozone layer, a revelation that launched a rapid and successful effort to ban chemicals in hairspray ...

It's been 40 years since groundbreaking research announced the discovery of a hole in the ozone layer, a revelation that launched a rapid and successful effort to ban chemicals in hairspray ...

It's been 40 years since groundbreaking research announced the discovery of a hole in the ozone layer, a revelation that launched a rapid and successful effort to ban chemicals in hairspray ...

It's been 40 years since groundbreaking research announced the discovery of a hole in the ozone layer, a revelation that launched a rapid and successful effort to ban chemicals in hairspray ...