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Study: The ozone hole is healing, thanks to global reduction of CFCs Study: The ozone hole is healing, thanks to global reduction of CFCs New results show with high statistical confidence that ozone recovery is going strong. Jennifer Chu | MIT News Publication Date: March 5, 2025 Press Inquiries Press Contact: Abby Abazorius Email: abbya@mit.edu Phone: 617-253-2709 MIT News Office Media Download An image from the ozone layer in September 2024 is in front of smaller images showing the evolution of the ozone layer from 1979-2018. | Download Image Caption: An MIT-led study confirms the Antarctic ozone layer is healing as a direct result of global efforts to reduce ozone-depleting substances. Foreground image of the ozone layer is from Sept. 28, 2024. Credits: Credit: figures courtesy of NASA; MIT News Views show "satellite trend patterns ending in" 2008-2018. | Download Image Caption: The left panels show satellite-observed Antarctic ozone trends by month and altitude, starting in 2005 with varying end years. The right panel displays model-simulated ozone changes driven by human activities. Colors indicate ozone changes relative to natural variability spread, with green for increases and blue for decreases. A higher signal-to-noise ratio suggests changes are less likely due to natural variability. As satellite records extend, observed trend patterns align more closely with modeled human fingerprint, confirming that significant Antarctic ozone recovery is now detectable from space. Credits: Credit: Courtesy of the researchers *Terms of Use: Images for download on the MIT News office website are made available to non-commercial entities, press and the general public under a Creative Commons Attribution Non-Commercial No Derivatives license. You may not alter the images provided, other than to crop them to size. A credit line must be used when reproducing images; if one is not provided below, credit the images to "MIT." Close An image from the ozone layer in September 2024 is in front of smaller images showing the evolution of the ozone layer from 1979-2018. Caption: An MIT-led study confirms the Antarctic ozone layer is healing as a direct result of global efforts to reduce ozone-depleting substances. Foreground image of the ozone layer is from Sept. 28, 2024. Credits: Credit: figures courtesy of NASA; MIT News Views show "satellite trend patterns ending in" 2008-2018. Caption: The left panels show satellite-observed Antarctic ozone trends by month and altitude, starting in 2005 with varying end years. The right panel displays model-simulated ozone changes driven by human activities. Colors indicate ozone changes relative to natural variability spread, with green for increases and blue for decreases. A higher signal-to-noise ratio suggests changes are less likely due to natural variability. As satellite records extend, observed trend patterns align more closely with modeled human fingerprint, confirming that significant Antarctic ozone recovery is now detectable from space. Credits: Credit: Courtesy of the researchers Previous image Next image A new MIT-led study confirms that the Antarctic ozone layer is healing, as a direct result of global efforts to reduce ozone-depleting substances. Scientists including the MIT team have observed signs of ozone recovery in the past. But the new study is the first to show, with high statistical confidence, that this recovery is due primarily to the reduction of ozone-depleting substances, versus other influences such as natural weather variability or increased greenhouse gas emissions to the stratosphere. "There's been a lot of qualitative evidence showing that the Antarctic ozone hole is getting better. This is really the first study that has quantified confidence in the recovery of the ozone hole," says study author Susan Solomon, the Lee and Geraldine Martin Professor of Environmental Studies and Chemistry. "The conclusion is, with 95 percent confidence, it is recovering. Which is awesome. And it shows we can actually solve environmental problems." The new study appears today in the journal Nature. Graduate student Peidong Wang from the Solomon group in the Department of Earth, Atmospheric and Planetary Sciences (EAPS) is the lead author. His co-authors include Solomon and EAPS Research Scientist Kane Stone, along with collaborators from multiple other institutions. Roots of ozone recovery Within the Earth's stratosphere, ozone is a naturally occurring gas that acts as a sort of sunscreen, protecting the planet from the sun's harmful ultraviolet radiation. In 1985, scientists discovered a "hole" in the ozone layer over Antarctica that opened up during the austral spring, between September and December. This seasonal ozone depletion was suddenly allowing UV rays to filter down to the surface, leading to skin cancer and other adverse health effects. In 1986, Solomon, who was then working at the National Oceanic and Atmospheric Administration (NOAA), led expeditions to the Antarctic, where she and her colleagues gathered evidence that quickly confirmed the ozone hole's cause: chlorofluorocarbons, or CFCs -- chemicals that were then used in refrigeration, air conditioning, insulation, and aerosol propellants. When CFCs drift up into the stratosphere, they can break down ozone under certain seasonal conditions. The following year, those relevations led to the drafting of the Montreal Protocol -- an international treaty that aimed to phase out the production of CFCs and other ozone-depleting substances, in hopes of healing the ozone hole. In 2016, Solomon led a study reporting key signs of ozone recovery. The ozone hole seemed to be shrinking with each year, especially in September, the time of year when it opens up. Still, these observations were qualitative. The study showed large uncertainties regarding how much of this recovery was due to concerted efforts to reduce ozone-depleting substances, or if the shrinking ozone hole was a result of other "forcings," such as year-to-year weather variability from El Nino, La Nina, and the polar vortex. "While detecting a statistically significant increase in ozone is relatively straightforward, attributing these changes to specific forcings is more challenging," says Wang. Anthropogenic healing In their new study, the MIT team took a quantitative approach to identify the cause of Antarctic ozone recovery. The researchers borrowed a method from the climate change community, known as "fingerprinting," which was pioneered by Klaus Hasselmann, who was awarded the Nobel Prize in Physics in 2021 for the technique. In the context of climate, fingerprinting refers to a method that isolates the influence of specific climate factors, apart from natural, meteorological noise. Hasselmann applied fingerprinting to identify, confirm, and quantify the anthropogenic fingerprint of climate change. Solomon and Wang looked to apply the fingerprinting method to identify another anthropogenic signal: the effect of human reductions in ozone-depleting substances on the recovery of the ozone hole. "The atmosphere has really chaotic variability within it," Solomon says. "What we're trying to detect is the emerging signal of ozone recovery against that kind of variability, which also occurs in the stratosphere." The researchers started with simulations of the Earth's atmosphere and generated multiple "parallel worlds," or simulations of the same global atmosphere, under different starting conditions. For instance, they ran simulations under conditions that assumed no increase in greenhouse gases or ozone-depleting substances. Under these conditions, any changes in ozone should be the result of natural weather variability. They also ran simulations with only increasing greenhouse gases, as well as only decreasing ozone-depleting substances. They compared these simulations to observe how ozone in the Antarctic stratosphere changed, both with season, and across different altitudes, in response to different starting conditions. From these simulations, they mapped out the times and altitudes where ozone recovered from month to month, over several decades, and identified a key "fingerprint," or pattern, of ozone recovery that was specifically due to conditions of declining ozone-depleting substances. The team then looked for this fingerprint in actual satellite observations of the Antarctic ozone hole from 2005 to the present day. They found that, over time, the fingerprint that they identified in simulations became clearer and clearer in observations. In 2018, the fingerprint was at its strongest, and the team could say with 95 percent confidence that ozone recovery was due mainly to reductions in ozone-depleting substances. "After 15 years of observational records, we see this signal to noise with 95 percent confidence, suggesting there's only a very small chance that the observed pattern similarity can be explained by variability noise," Wang says. "This gives us confidence in the fingerprint. It also gives us confidence that we can solve environmental problems. What we can learn from ozone studies is how different countries can swiftly follow these treaties to decrease emissions." If the trend continues, and the fingerprint of ozone recovery grows stronger, Solomon anticipates that soon there will be a year, here and there, when the ozone layer stays entirely intact. And eventually, the ozone hole should stay shut for good. "By something like 2035, we might see a year when there's no ozone hole depletion at all in the Antarctic. And that will be very exciting for me," she says. "And some of you will see the ozone hole go away completely in your lifetimes. And people did that." This research was supported, in part, by the National Science Foundation and NASA. Share this news article on: * X * Facebook * LinkedIn * Reddit * Print Paper Paper: "Fingerprinting the Recovery of Antarctic Ozone " Check for open access version(s) of the research mentioned in this article. Related Links * Susan Solomon * Department of Earth, Atmospheric and Planetary Sciences * School of Science Related Topics * Ozone * Research * Climate * Pollution * EAPS * Earth and atmospheric sciences * Emissions * Climate change * Environment * School of Science Related Articles A map shows a large red splotch with blurry yellow border, the ozone hole, on top of the South Pole, on decorative background. Study: Smoke particles from wildfires can erode the ozone layer satellite image of southeast coastline of Australia Study reveals chemical link between wildfire smoke and ozone depletion Professor Susan Solomon in a hallway Susan Solomon, scholar of atmospheric chemistry and environmental policy, delivers Killian Lecture MIT researchers have found that much of the current emission of CFC-11 and CFC-12 likely stems from large CFC "banks" -- old equipment such as building insulation foam, refrigerators and cooling systems, and foam insulation, that was manufactured before the global phaseout of CFCs and is still leaking the gases into the atmosphere. Emissions of several ozone-depleting chemicals are larger than expected A simulation of the Antarctic ozone hole, made from data taken on October 22, 2015. 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