Good news: the hole in the ozone layer is finally starting to heal

Sometimes the world really can get together and avert a major ecological catastrophe before it's too late. Case in point: A new study in Science finds evidence that the Earth's protective ozone layer is finally healing — all thanks to global efforts in the 1980s to phase out CFCs and other destructive chemicals.

This is one of the great environmental success stories of all time. Back in the 1970s, scientists first realized that we were rapidly depleting Earth's stratospheric ozone layer, which protects us from the sun's harmful ultraviolet rays.

The culprit? Chlorofluorocarbons (CFCs), a chemical widely used in refrigerators and air conditioners. These chemicals had already chewed a massive "hole" in the ozone layer above Antarctica, and the damage was poised to spread further north.

Without the ozone layer's protection, more and more people would be exposed to UV rays. Skin cancer rates would have soared in many regions, as they already have in Punta Arenas, Chile, which lies under the existing ozone hole. Those UV rays would also harm crops and the marine food chain.

Fortunately, this apocalyptic scenario never came to pass. Scientists uncovered the problem in time. And under the 1987 Montreal Protocol, world leaders agreed to phase out CFCs, despite industry warnings that abolishing the chemicals would impose steep costs. The hole in the ozone layer stopped expanding. The global economy kept chugging along.

Now comes further good news. The latest study, conducted by scientists at MIT and elsewhere, identifies several "fingerprints" suggesting that the ozone layer is on its way toward actually healing. The researchers note that the annual ozone hole that appears above Antarctica in September has shrunk by some 4 million square kilometers since 2000, although there are ups and downs each year due to volcanic eruptions.

This 2014 video from NASA illustrates the healing process, showing the minimum concentration of ozone in the Southern Hemisphere each year from 1979 to 2013. The process is sluggish: The ozone layer kept thinning in the 1980s and 1990s, even after the big agreement to phase out CFCs. In 2006, another major hole appeared. But recently, the hole has started shrinking and ozone concentrations have started rebounding:

Back in 2014, a United Nations assessment projected that the ozone layer would fully recover by 2050. "There are positive indications that the ozone layer is on track to recovery towards the middle of the century," said UN Undersecretary General Achim Steiner. "The Montreal Protocol — one of the world's most successful environmental treaties — has protected the stratospheric ozone layer and avoided enhanced UV radiation reaching the earth's surface."

Granted, just because the world banded together and saved the ozone layer doesn't ensure that we’ll also do the same for future environmental problems, like global warming. It will almost certainly be harder to reduce our reliance on fossil fuels than it was to curtail our use of CFCs. (For one thing, the DuPont chemical company developed easy substitutes to CFCs fairly quickly.) But the ozone case remains the best example of international cooperation to halt a slow-moving ecological disaster. And it worked.

We barely dodged a bullet with the ozone layer

It's worth reflecting on what a close call we had with the ozone layer. Scientists in Antarctica first began measuring stratospheric ozone levels in 1957, but it still took decades to realize how dire the situation actually was. Indeed, when researchers found signs of severe ozone depletion in the 1970s, they initially thought their instruments were faulty.

It wasn't until 1974 that chemists Mario Molina and Sherwood Rowland published a paper proposing that rising concentrations of CFCs in the atmosphere could deplete the ozone layer. These stable chemicals were widely used as refrigerants and cleaning solvents. But when CFCs wafted up into the stratosphere, they got ripped apart by UV rays, and the free chlorine atoms would catalytically destroy the ozone there.

This hypothesis was difficult to prove, and it was fiercely disputed by DuPont, the world's biggest manufacturer of CFCs, for many years. But evidence kept accumulating, and by the 1980s scientists finally had incontrovertible proof that CFCs were to blame. That's also when the massive "hole" over Antarctica received widespread attention. (This hole is a severe thinning of the ozone column throughout the atmosphere during the spring and summer.)

We were lucky that the damage wasn't even greater by that point. DuPont had been using chlorine instead of bromine to create its refrigerants. The two elements were roughly interchangeable for this purpose; it just so happened that chlorine was cheaper. Yet, as Paul Crutzen later observed in his Nobel Prize acceptance speech, bromine is 45 times more effective at destroying ozone. Had DuPont used bromine, the ozone layer might have been damaged beyond repair long before anyone even noticed.

Fortunately, that didn't happen. Under the Montreal Protocol of 1987, the world's nations agreed to phase out the use of CFCs in refrigerators, spray cans, insulation foam, and fire suppression. By and large, countries complied. Atmospheric concentrations of chlorine have stabilized and have been declining slowly over time.

In their 2014 report, the UN panel noted that without that agreement, atmospheric levels of ozone-depleting substances might have increased tenfold by midcentury. The resulting ozone loss could have led to 2 million additional cases of skin cancer by 2030 — to say nothing of crop damage or other impacts.

Today, recovery is slow, since there's still chlorine lingering in the stratosphere. The Antarctic hole still appears every spring and summer, even reaching a record size in 2006. And it's not just Antarctica: An especially cold Arctic winter in 2011 led to an ozone hole up north, too.

But the broad picture is encouraging: The ozone layer is on track to bounce back to 1980 levels by around midcentury.

Unexpected side effects of the Montreal Protocol

(DeAgostini/Getty Images)

Meanwhile, there have been a few unexpected side effects of this whole affair.

As a result of the Montreal Protocol, companies and countries stopped using CFCs and started using HFCs (hydrofluorocarbons), which have a much more benign effect on the ozone layer. That seemed like a satisfying solution — at least until global warming became a much more pressing concern.

Both CFCs and HFCs are potent greenhouse gases that help warm the planet. And on net, swapping out CFCs for HFCs reduced the overall amount of greenhouse gases in the atmosphere (making the Montreal Protocol unintentionally one of the biggest steps we've ever taken to prevent climate change).

But now HFCs are becoming a big climate problem in their own right, especially as air conditioning becomes more popular in fast-growing countries like China and India. HFCs are up to 10,000 times as effective as carbon dioxide at trapping heat, and their use is soaring.

"Hydrofluorocarbons (HFCs) do not harm the ozone layer but many of them are potent greenhouse gases," the UN panel noted in 2014. "They currently contribute about 0.5 gigatonnes of CO2-equivalent emissions per year. These emissions are growing at a rate of about 7 percent per year. Left unabated, they can be expected to contribute very significantly to climate change in the next decades."

Many environmental groups have urged world nations to revisit the Montreal Protocol and phase out HFCs in favor of chemicals that — like HFO-1234YF — that are both harmless to the ozone layer and don't warm the planet significantly.

In June 2016, the United States and India reached a side agreement to amend the Montreal Protocol in this fashion. The hope is to get a new international agreement late this year. Many companies in the United States, such as DuPont, Coca-Cola, and Target, have already pledged to shift away from using HFCs as refrigerants and toward more benign alternatives.

Further reading:

• Roger Pielke Jr. once wrote a nice essay about why the Montreal Protocol isn’t a great template for efforts to tackle climate change. Relatedly, I wrote a piece here about how the success of the Montreal Protocol in the 1980s arguably led UN climate negotiators astray in trying to craft a similar treaty for global warming.
• Back in June, the US and India agreed to tackle HFCs, a little-known (but potent) climate problem.

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