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MIT scientists just found a hidden problem slowing the ozone comeback

A small chemical loophole could quietly delay the ozone layer’s comeback—and scientists say it’s fixable.

Date:

April 16, 2026

Source:

Massachusetts Institute of Technology

Summary:

The ozone layer has been on track to recover thanks to the Montreal Protocol—but a loophole may be holding it back. Chemicals still permitted for industrial use are leaking into the atmosphere at higher rates than expected. Scientists now estimate this could delay ozone recovery by up to seven years. Closing this gap could speed up healing and reduce harmful UV exposure worldwide.

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FULL STORY

A hidden source of ozone-damaging chemicals—leaks from industrial feedstocks—may be slowing the ozone layer’s recovery. Fixing this issue could shave years off the timeline and reduce future health risks. Credit: Shutterstock

The 1987 Montreal Protocol is often described as the most successful environmental treaty ever created. It has led to a steady global phaseout of chemicals that once damaged the ozone layer and increased risks such as skin cancer.

Research led by MIT has shown that cutting these ozone-depleting substances is allowing the ozone layer to slowly heal. (It could return to 1980 levels by as early as 2040, according to some estimates.) However, the agreement included an exception. Certain ozone-depleting chemicals can still be used as feedstocks to produce other materials, based on the belief that only a tiny fraction, about 0.5 percent, would escape into the atmosphere.

That assumption is now being challenged.

Rising Chemical Leaks Raise New Concerns

In recent years, scientists have detected higher-than-expected levels of ozone-depleting substances in the atmosphere. This has led to updated estimates showing that leakage from feedstock use is significantly greater than previously thought.

An international team of researchers, including scientists from MIT, has now examined how these higher leakage rates affect the ozone layer's recovery. Their findings show that if the issue is not addressed, ozone recovery could be delayed by about seven years.

"We've realized in the last few years that these feedstock chemicals are a bug in the system," says author Susan Solomon, the Lee and Geraldine Martin Professor of Environmental Studies and Chemistry, who helped identify the original cause of the ozone hole. "Production of ozone-depleting substances has pretty much ceased around the world except for this one use, which is when you have a chemical you convert into something else."

Industrial Uses Driving Ongoing Emissions

The study, which will appear in Nature Communications, is the first to fully measure the impact of emissions from feedstocks. These chemicals are widely used to manufacture plastics, nonstick coatings, and replacement chemicals for substances already restricted under the Montreal Protocol.

The researchers emphasize that reducing both the use of these feedstocks and their leakage is becoming increasingly important, especially as global demand for products like plastics continues to grow.

"We've gotten to the point where, if we want the protocol to be as successful in the future as it has been in the past, the parties really need to think about how to tighten up the emissions of these industrial processes," says first author Stefan Reimann of the Swiss Federal Laboratories for Materials Science and Technology.

"To me, it's only fair, because so many other things have already been completely discontinued. So why should this exemption exist if it's going to be damaging?" says Solomon.

The research team includes scientists from institutions across the United States, Europe, and Asia, including MIT, NASA, NOAA, and several universities and research centers.

How the Ozone Hole Was Discovered

The concern over ozone depletion dates back to 1985, when scientists identified a growing hole in the ozone layer above Antarctica. This thinning allowed more harmful ultraviolet radiation from the sun to reach Earth's surface.

A year later, Solomon and other researchers traveled to Antarctica and confirmed the cause. The damage was driven by chlorofluorocarbons, or CFCs, which were widely used in refrigeration, air conditioning, and aerosol products.

These findings led to the creation of the Montreal Protocol, an international agreement involving 197 countries and the European Union to limit the use of these chemicals. The decision to allow feedstock use was partly based on industry estimates that leakage would remain very low.

"It was thought that the emissions of these substances as a feedstock were minor compared to things like refrigerants and foams," Western says. "It was also believed that leakage from these sources was minor, around half a percent of what went in, because people would essentially be leaking their profits if their feedsto