The ozone layer is healing, but not as fast as it could be. An international team of researchers, including scientists at the Massachusetts Institute of Technology, has identified a crucially overlooked source of ozone-damaging pollution: chemicals that are still legally permitted under a treaty meant to protect and heal the ozone layer. 

The 1987 Montreal Protocol, often cited as a landmark achievement in international environmental cooperation, banned many of the industrial chemicals responsible for thinning the ozone layer. 

But it carved out an exemption for industrial feedstocks: ozone-depleting substances that are used as raw ingredients to manufacture products, such as plastics and chemicals. The exemption was built on industry estimates that only about 0.5% of those chemicals would be released into the atmosphere. 

That assumption has been proven wrong by a wide margin. 

Specifically, atmospheric monitoring networks now show the real leakage rate is closer to 3.6% of production, with certain chemicals leaking even more. This new information comes on the heels of a 163% increase in feedstock use globally between 2000 and 2024, further compounding the problem.

“We’ve realized in the last few years that these feedstock chemicals are a bug in the system,” Susan Solomon, a professor at MIT and one of the scientists who discovered the cause of the ozone hole, said. “Production of ozone-depleting substances has pretty much ceased around the world except for this one use.” 

The consequences are not abstract. Without corrective action, the researchers project that the ozone layer’s return to its pre-damaged 1980 baseline could be delayed until 2073, roughly seven years later than it would otherwise occur. 

These extra years may seem insignificant, but they could mean prolonged exposure to ultraviolet radiation, which can raise the risk of skin cancer and cataracts.

Stefan Reimann, the study’s lead author, said, “We could reduce the period of ozone depletion by years. It might not sound like a long time, but if you could count the skin cancer cases you’d avoid in that time, it would seem quite significant.

Researchers said the fix does not require dismantling the agreement entirely, only closing the loophole. The ozone layer’s recovery was never going to be instantaneous, but it’s clear that it shouldn’t take this long.