The best climate news you may not have heard of » Yale Climate Connections

A treaty passed 35 years ago, which was supposed to solve a completely different problem, also protects the climate. And with bipartisan Senate endorsement and President Joe Biden’s signature on October 26, the US became the 139th nation in the world to pass a major amendment to that accord — the first time the US has endorsed a legally binding global measure specifically to combat the climate change have joined.

What is the Montreal Protocol?

Global warming was on the back burner in 1985 when scientists from the British Antarctic Survey discovered a gaping hole in the planet’s stratospheric ozone layer. The ozone layer is a natural feature of the atmosphere and is found about 10 to 25 miles above the Earth’s surface. It protects the planet from the sun’s ultraviolet radiation, which in large doses is harmful to our skin and myriad other aspects of plant and animal life.

Researchers quickly found the cause of ozone depletion: chlorofluorocarbons, known as CFCs, chemicals used as refrigerants and to make aerosol sprays and other materials. CFCs had been known to pose a threat to the ozone layer for years, but the ozone hole found in the mid-1980s was far worse than anything anticipated at the time.

By 1987, diplomats had drafted a treaty known as the Montreal Protocol to resolve the issue. It was an immense success that was ratified by all member states of the United Nations.

However, there was a big catch.

Both CFCs and their main substitutes – hydrofluorocarbons or HFCs – trap heat in the atmosphere and cause global warming.

Atmospheric chemist Susan Solomon led pivotal research that found CFCs reacted with polar stratospheric clouds to destroy ozone over Antarctica. In an email, Solomon pointed out that CFCs were recognized as dangerous heat storage gases as early as the mid-1970s. Once released, they remain in the atmosphere for about a century.

HFCs have much shorter atmospheric lifetimes — on the order of a decade or two. Therefore, they “were rightly considered to be less harmful both to ozone and climate and as a transitional substance,” Solomon said.

“What changed was that the developing world started to evolve much faster than originally anticipated,” Solomon said, “causing the world to realize that the demand for these molecules would increase rapidly as the number of people who owned refrigerators and use refrigeration equipment would increase rapidly [air conditioning] would increase in the 21st century.”

And it quickly became clear that a large amount of HFCs can cause a great deal of damage.

Susan Solomon conducted pioneering research on stratospheric ozone depletion over Antarctica, followed shortly thereafter by the Montreal Protocol. (Image credit: NOAA, via the Science History Institute)

What is the Kigali Amendment and why did the US Senate support it?

Enter the Kigali change.

Adopted at a United Nations meeting in the Rwandan capital in October 2016, it uses a variety of policy approaches to curb both HFC production and consumption. The change has put the world on track to eliminate more than 80% of HFCs by mid-century.

One reason the Kigali Amendment passed the Senate with bipartisan support (69-27, including 21 of the 50 House Republicans) is that national action on HFCs along the lines of Kigali was already underway. The Pandemic Stimulus Act of late 2020 called for an 85% cut in HFC production by 2030. Many legislators, particularly those in chemical-producing countries, recognized the rationale for HFC cutbacks. For one, nations that have not ratified the amendment cannot trade HFCs with those that have.

Reducing HFCs is an undisputed climate gain. If HFCs were to grow at an uncontrolled pace, as they did 20 years ago, they could add nearly 0.5 degrees Celsius (0.9 degrees Fahrenheit) to global warming expected by 2100.

“I think the US ratification of Kigali shows that there is no fundamental obstacle to ramping up ambition to reduce greenhouse gases,” Solomon said. “If we can do it with today’s fragmented Congress, we can also do other things, like reducing carbon dioxide.”

How the Montreal Protocol protected the Earth’s climate

But phasing out HFCs isn’t the Montreal Protocol’s only contribution to climate change mitigation. The climate benefits of the Montreal Protocol gained prominence in a series of world avoided papers published beginning in 2007.

Overall, researchers have found that approximately 2.5°C (4.0°F) of warming by 2100 will be averted by non-HFC aspects of the Montreal Protocol. Much of what prevented warming resulted from the Protocol’s phase-out of CFCs.

Had the world chosen not to ratify the Montreal Protocol and instead continued to deplete the ozone layer, extra ultraviolet sunlight would have harmed plants. That would have reduced their ability to remove heat-trapping carbon dioxide from the atmosphere, according to a 2021 paper, leading to even more warming.

“To date, the Montreal Protocol has done more to protect the climate than all other efforts combined,” Stephen Andersen, research director at the Institute for Governance and Sustainable Development in Washington, DC, said in an email. Andersen is co-author of a special volume published jointly by the Institute and the United Nations Environment Program on October 31, commemorating the Protocol’s 35th anniversaryth Anniversary.

“The rapid transition from an ozone treaty that also protects the climate to a hybrid ozone and climate treaty with a future focus on climate is a stunning diplomatic and environmental achievement,” Andersen said.

Diplomats celebrate the passage of the Kigali Amendment at the closing session of a United Nations meeting held in the Rwandan capital in October 2016. (Image credit: Rwanda Environment Management Authority, via Flickr, CC BY-ND 2.0)

Fight more pollutants

HFCs are a classic example of so-called short-lived climate pollutants. It takes well over a century for an atmospheric infusion of carbon dioxide to find its way back into the oceans and soil. Molecule for molecule, carbon dioxide is not a particularly potent heat-storage gas, but it is emitted in gargantuan amounts — more than 30 billion tons a year. Because of this sheer volume combined with its longevity, carbon dioxide is expected to cause most of the global warming this century and beyond.

Short-lived greenhouse gases – primarily methane, but also nitrous oxide and a few others including HFCs – pack a much stronger punch per molecule than carbon dioxide. The global warming potential of an HFC molecule is more than 10,000 times that of carbon dioxide when the effects of both are summed over a century. This effect is offset by the fact that HFCs are far less common than carbon dioxide.

Many scientists, activists and diplomats are urging immediate action on short-acting pollutants other than HFCs, particularly methane. Because these gases are usually so potent in the short term, reducing them as soon as possible would provide immediate relief, they argue.

NASA announced Oct. 26 that overall ozone depletion over Antarctica for September-October 2022 was less than a year earlier, although the maximum size of the ozone hole was slightly larger than the 2021 maximum. “Over time, steady progress is being made made and the hole is getting smaller and smaller,” said Paul Newman, senior scientist for geosciences at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. (Image credit: NASA Ozone Clock)

Lessons from Montreal and Kigali

Durwood Zaelke, president of the Institute for Governance and Sustainable Development, is optimistic that progress on other short-term pollutants is possible, with the Montreal and Kigali accords serving as key inspiration. The agreements “show that we’ve won the battle before,” he said. “Now let’s bring the whole package of short-term pollutants under regional agreements.”

Natural gas flaring in a West Texas oil field in 2020. (Image credit: Jonathan Cutrer, via Flickr, CC BY 2.0)

Methane from fossil fuels is particularly ripe for reduction, Zaelke said. Huge amounts of natural gas are lost through leaks in pipelines or burned in flares. “You can make at least 50% of methane recovery in oil and gas at a profit,” Zaelke said. At this point he added: “The oil and gas sector understands that it needs to have very low leak rates in order to keep its social license.”

A Global Methane Pledge launched in 2021 advocates a 30% reduction in global methane emissions from 2020 to 2030. This pledge now includes more than 120 countries; together they account for about 45% of global methane emissions and about 60% of global GDP.

Solomon says the same practical approach of the Montreal Protocol – developing policies that encourage new, low-cost technologies – can also be used for carbon dioxide.

“Misinformation has led many people to believe that this is not possible or that it would be enormously expensive for CO2. That’s definitely not true now.”


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