The ozone hole can heal in our lives, UN reports



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When the world unites, it can solve major problems. Case in point: The ozone hole, which if everything goes according to plan, can be cured by 2060, according to a new report by the United Nations.

According to the report, a decades-long international treaty to ban the use of ozone-depleting chemicals has led to its decline and "much more severe ozone depletion in the polar regions has been avoided." There is still work to be done, but this is definitely the Good News category.

"We're at the turning point," said Paul Newman, a scientist who helps run NASA's Ozone Watch and chaired the UN report to Earther.

The report is published every four years and this is its fifth iteration. It tracks an environmental problem of the 1980s and we are still feeling the effects of today. The ozone hole is driven by a series of chemicals that were commonly found in aerosol cans, air conditioners, and refrigerators, called chlorofluorocarbons and hydrochlorofluorocarbons. These chemicals release chlorine into the stratosphere, which in turn can disintegrate ozone molecules. When this happens, more ultraviolet light from the sun comes to the surface, increasing the risk of bad things like skin cancer. The problem was particularly striking in Antarctica, where an ozone hole began to form each spring.

Scientists have identified chemicals as problematic and policymakers have actually acted on it. The Montreal Protocol was signed in 1987. After 30 years, the hole in the ozone layer remains an annual occurrence. But the new report definitely adds to a 2016 study showing that the ozone hole has been recovering since 2000. If all goes according to plan, ozone levels in the region could return to prehistoric conditions within 40 years.

In other regions where ozone depletion has been less severe, the return to normalcy may come even earlier. The Arctic and mid-latitude of the northern hemisphere could reach into the 2030s, and mid-latitudes in the southern hemisphere could reach ozone levels in the 1980s by the middle of the century.

To get to this time line of ozone recovery, the world will have to continue working to reduce other chemicals that deplete the ozone layer and not put the recovery process any other way. At some levels, there are some warning signs that scientists are observing.

The first is a mysterious increase in CFC-11, a chemical that was banned by the Montreal Protocol. Although banned, research published earlier this year has shown that it is on the rise since 2012. Most of the signals point to China as the culprit of illicit emissions, and will have to be stopped to keep the recovery on track.

Another factor is what happens to the fight to contain global warming. The ozone hole and climate change are, in general, separate problems, but overlap a bit. The warming effect in the lower atmosphere associated with the rise in greenhouse gases also leads to cooling in the stratosphere, which is about 10 to 12 kilometers above the surface of the planet. This could slow down the process of depletion of the ozone layer, which could accelerate recovery in some places.

At the same time, the report notes that rising warming due to greenhouse gases changes planetary circulation in the atmosphere in ways that can lead to less ozone in the tropics and more in the Arctic and mid-latitude. So reducing greenhouse gas emissions – including those produced by substitutes for the chemicals that deplete the ozone layer – is still probably a good idea.

The last question may be the most unnerving, because we know very little about it. The report raises concerns about what would happen if the world or even a pariah state decided to cool the planet by sending small particles into the stratosphere. The process, known as geoengineering, is made with potential consequences here on the ground and would probably also be in the stratosphere.

"The problem is that our level of knowledge of the natural levels of particles in the stratosphere is not so high," Newman said. "Geoengineering presents the challenge of disturbing the natural levels of particles in the stratosphere beyond the impact on ozone."

So maybe we do not do that and keep trying to fix the hole in the ozone layer and solve global warming here on the ground.

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