The Green Lantern

What Ever Happened to the Ozone Layer?

Is there still a hole in it?

Is the ozone layer still at risk?

Last month, you updated us on the status of acid rain. That got me thinking about another environmental scourge of the 1980s—the hole in the ozone layer. What ever happened to that?

It’s still a problem. As of a few weeks ago, the “hole”—which isn’t so much a gap in the ozone layer as an area of seasonal thinning—is even bigger than it was at the height of the ozone panic in the 1980s. (At the moment, it spans a patch of sky almost the size of North America.) That said, the ozone layer is in much better shape today than it would have been had the world not taken decisive action 20 years ago. It’s just that the damage we did in the old days is going to take a long time to heal.

You might remember that ozone gas—made from triplets of oxygen atoms—helps shield us from the sun’s harmful UV-B rays. Most of it is in the lower stratosphere, roughly six to 30 miles above the Earth’s surface, where it’s created naturally by the interaction of sunlight and regular oxygen. Other gases, particularly those containing chlorine or bromine, can make ozone molecules break apart. Starting in the 1970s, scientists suspected that the widespread use of industrial chemicals might be putting additional chlorine and bromine into the stratosphere. In particular, researchers worried about the chlorofluorocarbons used in fridges, air conditioners, and aerosol spray cans and the halon gases used in fire extinguishers. (Human technology also creates some ozone, but that stuff tends to stay close to the ground, where it causes a range of health issues.)

By the mid-1980s, researchers knew that ozone concentrations were decreasing around the world, threatening humans with an increased incidence of skin cancer and eye cataracts and endangering plants and other kinds of animals. In 1985, following several years of U.N.-sponsored meetings, 21 nations formally agreed to cooperate on researching and monitoring the issue. It came to a head two months later, however, when a team of British researchers showed that a huge “hole” had appeared in the ozone layer above the Antarctic. What had been a predicament now started to seem like an emergency.

By 1987, 24 nations had ratified the Montreal Protocol (PDF), a landmark agreement that calls for a ban on producing and using nearly 100 of the most important ozone-depleting chemicals. As of this month, with the addition of East Timor, the protocol has been ratified by every member of the United Nations.

Ninety-seven percent of the substances regulated under the Montreal Protocol have now been phased out and replaced in manufacturing with more ozone-friendly alternatives, like hydrofluorocarbons (HFCs). The remaining gases will be phased out globally by 2040. According to the United Nations Environmental Programme, enactment of the protocol has prevented some 20 million cases of skin cancer and 130 million cases of eye cataracts. Since many ozone-depleting substances are also greenhouse gases (PDF), the treaty has also helped with global warming: A 2007 paper estimated that over the past 20 years, the protocol has prevented the emission of 10.7 to 13.8 billion tons of carbon dioxide equivalent annually.

Even so, it’s going to take several decades for the Antarctic hole to close up for good. That’s because the ozone-depleting gases we emitted before the Montreal Protocol are still floating around the stratosphere or making their way in that direction. Some of these gases can circulate for a century before their molecules break apart or air currents remove them from the sky.

While we’re waiting for the ozone layer to heal itself, a few new wrinkles have appeared in the story.Last month, researchers from the National Oceanic and Atmospheric Administration published a paper showing that nitrous oxide—which isn’t now regulated under the Montreal Protocol—is on its way to becoming the leading destroyer of ozone. It turns out that the chlorine in some of the other, more prominent ozone-depleting gases—like CFCs—dampens the effects of nitrous oxide in the stratosphere. Now that their levels are decreasing, N2O is free to do more damage on its own. (As the Lantern has noted before, nitrous oxide is also an important greenhouse gas.)

Meanwhile, fixing the hole in the ozone layer may end up worsening some other environmental problems. The hydrofluorocarbons we use in place of many CFCs don’t contribute to ozone depletion, but some of them have thousands of times the global warming potential of carbon dioxide. Given the projected boom in usage in the developing world—thanks to a growing appetite for refrigerators and air conditioners—these chemicals may end up being a major contributor to climate change. (Researchers estimate that HFCs could be one-fifth as problematic as carbon dioxide by the year 2050.) Earlier this month, the United States, Canada, and Mexico issued a joint proposal for a “phase down” in HFCs, which can be replaced in some applications with more eco-friendly options, like carbon dioxide, ammonia, or HFCs with lower global-warming potential. In November, the signatories of the Montreal Protocol will hold their annual meeting in Egypt, so we should hear more on this topic in the next few months.

Is there an environmental quandary that’s been keeping you up at night? Send it to, and check this space every Tuesday.