Southern Skies Benefit from a Rare Climate-Diplomacy Success

(Bloomberg) — Diplomacy can fix large-scale harm done to the planet by industrial pollution. That’s the conclusion of new research published today in the journal Nature showing how skies above the Southern Hemisphere have recovered since a 1987 treaty banned chemicals that eat away at the atmosphere’s protective layer. The ozone layer sits in the Earth’s stratosphere, the…

Southern Skies Benefit from a Rare Climate-Diplomacy Success

(Bloomberg) — Diplomacy can fix large-scale harm done to the planet by industrial pollution. 

That’s the conclusion of new research published today in the journal Nature showing how skies above the Southern Hemisphere have recovered since a 1987 treaty banned chemicals that eat away at the atmosphere’s protective layer. 

The ozone layer sits in the Earth’s stratosphere, the second lowest atmospheric layer. Made up of ozone gas–O₃, as opposed to the O₂ we breathe–it shields living things from the sun’s harmful ultraviolet radiation. Beginning in the 1960s, industrial chemicals called chlorofluorocarbons (CFCs)–pervasive in refrigeration, personal-care aerosol sprays, and insulating materials–reached the atmosphere, and their highly reactive chlorine began to destroy ozone, creating a massive hole. In the spring especially, concentrated pockets of cold air break down atmospheric CFCs, releasing chlorine that’s then activated by the energy of the sun.

The ozone hole not only let through UV radiation, it also changed major features of how heat and moisture circulate in the Southern Hemisphere. UV rays cause the ozone layer to heat up, therefore less ozone means less heating. The springtime stratosphere cooled by as much as 7° Celsius through the 1990s, throwing off the temperature balance between Antarctica and mid-latitude areas of the Earth and pushing the southern jet stream about 2° of latitude closer to the South Pole. The result was warming in Patagonia, New Zealand, and the Antarctic Peninsula, dryness in Tasmania and New Zealand, and changes to the Southern Ocean’s temperature, currents, and salinity levels.

Over the last 15 years, the ozone hole has shrunk by about 20%, which scientists credited to the 1987 Montreal Protocol. But the authors of the new paper, led by Antara Banerjee of the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory, say their study is the first to attribute a return of pre-pollution atmospheric behavior to the same treaty.

They used computer modeling to run simulations of atmospheric forces using data collected from 1980 to 2017, which showed a halt in the jet stream’s southward march beginning around 2000. To show the effects of the CFC ban specifically, however, the scientists first had to tease out the effects of many other factors, including greenhouse gas pollution, from the data. They found that the CFCs were far and away the biggest factor in the poleward shift. What happens next is less clear. With CFCs declining and carbon dioxide continuing to rise, there’s concern that the CO₂ could resume pushing the jet stream toward the pole, but they can’t say for sure because no one knows much CO₂ humans will eventually emit.

The effort to fix the ozone layer has faced setbacks. In recent years, scientists have documented an unexpected rise in emissions of CFCs, which has been interpreted as the start of illegal chemical production in China. Last week, a team of MIT-led researchers showed that existing stocks of CFCs embedded in equipment and materials sold legally before the full moratorium went into effect are a roadblock to faster ozone recovery.

In commentary on the paper also published in Nature, Alexey Karpechko of the Finnish Meteorological Institute wrote that the lesson of Montreal is widely applicable. “This is an object lesson in how the international community should react to global environmental challenges,” he said. “Restricting dangerous emissions and changing business practices is also the way to combat global warming caused by greenhouse gases.”

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