It is a hopeful sign. It is a scientific measurement of improvement in the atmosphere. It demonstrates that governments can create and stick to an agreement that has a positive effect on global warming. It is years ahead of schedule and it all started in Montreal, Canada. 
NASA Ozone Hole Watch
Let’s back up for a moment. In the 1980s we noticed that there was a growing hole in the ozone layer. This was a problem because ozone forms a barrier against UV radiation. Sometimes atmospheric ozone is referred to as “a layer of sunscreen.” Less ozone means higher rates of health problems like skin cancer and cataracts. Why was the ozone missing? Ozone-depleting substances such as chlorofluorocarbons (CFCs) rise into the stratosphere and release chlorine atoms which react with ozone. Where did these CFCs come from? They were chemicals commonly used to create aerosol sprays (think hairspray), foams, packing materials and refrigerants.
In 1987 countries got together in Montreal Canada to stop the usage of CFCs with the goal of slowing and reversing the hole in the ozone layer. They put together the Montreal Protocol -- pledging to stop using CFCs by 2010. Initially CFCs were replaced with hydrochlorofluorocarbons (HCFCs) but then it was discovered that HCFCs were powerful greenhouse gasses, with a global warming potential 2000 times stronger than carbon dioxide. Amendments were added to the Protocol in 1992 and 1999 to phase out HCFCs. The Montreal Protocol was eventually signed by 197 countries -- every country in the world.
People don’t replace their refrigerators every year. Even when you stop selling refrigerators with HCFCs there will still be HCFCs released from refrigerators that have already been sold. (This is one reason why it’s important to recycle your refrigerators, see https://www.largeappliancerecycling.ca/.) However, scientists modeled the effect of the Montreal Protocol on the rise of HCFCs and predicted that the chemical would start declining in the atmosphere in 2029.
So here is the exciting news: HCFCs in the atmosphere have already started declining. It is likely that they reached their peak in 2021. In a paper published in Nature Climate Change on June 11, 2024 Luke Western (and twenty co-authors) showed that according to two different measurements HCFC had peaked in 2021 and declined in 2022.
What made the Montreal Protocol so effective? The general public, aided by videos created by scientists, understood the concept of the hole in the ozone layer. The threat was clear -- missing ozone would lead to a higher rate of skin cancer. The solution was clear -- stop using CFCs (and later HCFCs). The Montreal Protocol also had an effective funding program where money from developed nations was donated to developing nations so they could retool and switch refrigerants.
What kind of impact does the decline of HCFCs due to the Montreal Protocol have on climate change? First, because HCFCs are powerful greenhouse gasses, it is important in their own right that they are beginning to decline. Second, while scientific evidence for global warming has been around for decades, people now feel the impact on their daily lives through warmer winters, heat waves, changes in rainfall (both droughts and increase in tropical storms) and increases in wildfires. If you need a video to convince you, I recommend the NASA climate spiral video https://www.youtube.com/watch?v=jWoCXLuTIkI&ab_channel=NASAClimateChange
But perhaps more critically this demonstrates that countries across the world are capable of identifying a problem (the hole in the ozone layer or global warming), coming together to draft a treaty and then honoring that treaty -- leading to a measurable decline. Now is the time to double down, pressuring countries and governments to sign and comply with the Paris agreement. We can do this -- we already have.
Image caption/credit: False-color view of total ozone over the Antarctic pole. Purple and blue represent areas where there is the least ozone, yellows and reds where there is more ozone.
NASA Ozone Hole Watch.
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