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One of the layers of atmosphere that protects all life on our planet is the width of two pennies, and hangs out six to ten miles above the Earth’s in an environment that human activity made extremely hostile. Every year when winter ends and warmer weather returns to Antarctica, chemicals that we put into the air rip a hole in the layer. But this year, that hole is smaller than usual.

This week, NASA and NOAA announced that 2017’s ozone hole, at 7.6 million square miles, was the smallest since 1988.

Ozone is a molecule made of three oxygen atoms bonded together. On the ground, it can form harmful smog. But above the Earth, it acts like sunscreen, protecting life from harmful solar radiation. When elements like chlorine and bromine undergo a particular chemical reaction in clouds, ozone takes a beating.

This year it was warmer than usual in Antarctica’s lower stratosphere, with temperatures the likes of which you’d normally see over the Arctic. The odd weather pattern was not conducive to the formation of ozone-killing clouds, giving that precious layer of the atmosphere a break.

The ozone hole was first discovered in Antarctica in 1985, and quickly linked to the increased use of ozone-depleting chemicals like chlorofluorocarbons (CFC’s). CFC’s were everywhere at the time, and were seen as a better replacement for earlier industrial chemicals. They were non-toxic to humans, non-flammable, and used in refrigeration, air conditioning, and aerosols.

Alarmed by the effect that human actions were having on the planet, nations around the world signed the Montreal Protocol just a few years later, agreeing to ban CFC’s and other ozone-depleting chemicals. The agreement went into effect in 1989; but with CFC’s long lifetime, it wasn’t until very recently that researchers—who were constantly monitoring the health of the ozone layer—were able to truly notice signs of healing.

Last year also had a smaller ozone hole than previous years, a dramatic decrease from the 2006 peak when the gap reached record widths and depths. But despite the last few years of good ozone conditions, there’s still a long time to go before it returns to pre-1980 levels. A recent study found that the ozone hole was unlikely to recover to that extent before 2070.

Still, the fact that it is recovering—even if it’s recovering more slowly than we’d like—is notable. scientists who worked on the initial discovery of the ozone hole are thrilled that the recommendations they made 30 years ago are now showing environmental dividends. Trying to ban a valuable and useful class of chemicals was a daunting task, but with concerted effort on the part of politicians, policy makers, industries, and scientists, that decision is now paying off.

CFC’s were once a valued part of everyday human life. Most people in the industrialized world in the mid-to-late-1900’s used products that released CFC’s, just like most people today use products or energy that release carbon dioxide into the environment. Luckily, there were alternatives available—and we actually adopted them.

With the Paris Agreement on climate change still a contentious topic, the ozone news is a useful reminder that international efforts to combat environmental change can make a difference. It may be difficult—and it may take a few decades to see results—but it’s not too late to start cleaning up the mess we’ve made.