Complex impact of large wildfires on ozone layer dynamics

In a revelation highlighting the fragile balance of our planet's atmosphere, scientists from China, Germany, and the USA have uncovered an unexpected link between massive wildfire events and the chemistry of the ozone layer. Using satellite data and numerical modelling, the team discovered that an enormous smoke-charged vortex nearly doubles the southern hemispheric aerosol burden in the middle stratosphere of the Earth and reorders ozone depletion at different heights. Published in Science Advances, this study reveals how wildfires, such as the catastrophic 2019/20 Australian bushfires, impact the stratosphere in previously unseen ways.

The ozone layer, a crucial shield protecting life on Earth from harmful ultraviolet (UV) radiation, has been on a path to recovery thanks to the Montreal Protocol. This landmark international treaty, adopted in 1987, successfully led to phasing out the production of numerous substances responsible for ozone depletion. Over the past decades, the ozone layer has shown significant signs of healing, a testament to global cooperation and environmental policy.

However, the stability of this vital atmospheric layer is now facing a new and unexpected challenge. During the 2019/20 Australian wildfires, researchers observed a dramatic increase in stratospheric aerosols -- tiny particles that can influence climate, health, and atmospheric chemistry.

Smoke-charged vortex transports aerosol up to 35 kilometers

Utilizing new satellite data and numerical modeling, the research team successfully demonstrated the impact of wildfires through a novel phenomenon: the smoke-charged vortex (SCV).

"The SCV is a powerful, smoke-laden whirlpool that transports wildfire smoke into the middle stratosphere, reaching altitudes of up to 35 kilometers," explained Prof. Hang Su from the Institute of Atmospheric Physics at the Chinese Academy of Sciences, one of the corresponding authors of the study. "This process led to at least a doubling of the aerosol burden in the southern hemisphere's middle stratosphere. Once reaching such high altitudes, these aerosols initiated a series of chemical reactions at their surface that impacted ozone concentrations."

The international team discovered that these wildfire-induced aerosols facilitated heterogeneous chemical reactions in the stratosphere, which paradoxically led to both ozone depletion and ozone increase at different atmospheric layers.

While the lower stratosphere experienced significant ozone depletion, the new study shows that the increase of smoke aerosol particles in the middle stratosphere enhances the heterogeneous uptake and hydrolysis of N2O5, which leads to a decrease of reactive nitrogen gases, e.g., NOx, and an increase of ozone. In Southern Mid-Latitudes, the complex interplay managed to buffer approximately 40% (up to 70%) of the ozone depletion observed in the lower stratosphere in the following months of the mega-bushfire events.

So why does this matter?

"Our study uncovers an unexpected and crucial mechanism by which the absorbing aerosols in wildfire smoke, such as black carbon, can induce and sustain enormous smoke-charged vortices spanning thousands of kilometers, fundamentally changing the stratospheric circulation. The vortices can persist for months, carrying aerosols deeply into the stratosphere and affecting the ozone layer in distinct ways at different altitudes. This highlights the need for continued vigilance and research as climate change progresses," said Prof. Yafang Cheng, another leading author from the Max Planck Institute for Chemistry.

"We've made a significant step forward in simulating the SCV as a new effective pathway for wildfires to modify stratospheric dynamics and chemistry, especially the ozone layer. I love this study because it once again demonstrates how closely different parts of the Earth system are connected. Smoke from a forest fire can significantly change the wind and circulation tens of kilometers above the ground, which allows the smoke to modify the ozone layer, influencing life on our planet," said Dr. Chaoqun Ma, the first author of the study and postdoc researcher in Cheng's team at the MPIC.

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Climate change and mercury pollution stressed plants for millions of years

The link between massive flood basalt volcanism and the end-Triassic (201 million years ago) mass-extinction is commonly accepted. However, exactly how volcanism led to the collapse of ecosystems and the extinction of entire families of organisms is difficult to establish. Extreme climate change from the release of carbon dioxide, degradation of the ozone layer due to the injection of damaging chemicals, and the emissions of toxic pollutants, are all seen as contributing factors. One toxic element stands out: mercury. As one of the most toxic elements on Earth, Hg is a metal that is emitted from volcanoes in gaseous form, and thus has the capacity to spread worldwide. A new study in Nature Communications adds new compelling evidence for the combined effects of global warming and widespread mercury pollution that continued to stress plants long after volcanic activity had ceased.

An international team of Dutch, Chinese, Danish, British, and Czech scientists studied sediments from Northern-Germany in a drill-core (Schandelah-1) that spans the uppermost Triassic to lower Jurassic for microfossils and geochemical signals. A study of pollen and spore abundances revealed a profusion of fern spores showing a range of malformations, from abnormalities in wall structure to evidence for botched meiotic divisions, leading to unseparated, dwarfed, and fused fern spores. "Seeing the sheer amount and different types of malformed fern spores in sediment samples from a coastal lagoon, dating back 201 million years ago is truly astonishing. It means there must have been very many ferns being stressed," explains Remco Bos, a PhD candidate at Utrecht University and lead author of the study. "It is also not something we see regularly during other periods that also contain many fern fossils, making it a true signal connected to the end-Triassic mass-extinction event."

Deforestation and ferns

The results from Bos and co-authors confirm earlier work by co-authors Sofie Lindström (University of Copenhagen), Hamed Sanei (Aarhus University), and Bas van de Schootbrugge (Utrecht University), who previously produced similar data obtained from cores from Denmark and from nearby outcrops in Sweden. According to Sofie Lindström: "Ferns replaced trees across the extinction interval in response to dramatic environmental changes likely driven by heat stress, strongly increased monsoonal rainfall, and increased forest fire activity. Palynological results show that a pioneering fern vegetation spread across vast swaths of coastal lowlands in Northwestern Europe from Sweden and Denmark to Germany, France, Luxemburg, and Austria in response to widespread deforestation." Ferns are hardy plants, often colonizing disturbed environments, including newly formed volcanic islands or landscapes devastated by volcanism or wildfires. "What is extraordinary here is that the ferns that produced all these malformed spores in all these different sites, did not go extinct. While other plants went extinct, ferns were apparently robust enough to continue, which could also be related to their different mercury tolerance."

Climate variability

In this new study, Bos and co-authors show that the ferns, which took advantage of the dieback of forests, themselves were subjected to stress from Hg-pollution well beyond the immediate extinction interval. "We found four more intervals with high levels of Hg concentrations and high numbers of malformed spores in the 1.3 to 2 million years following the extinction interval," explains Remco Bos. This interval, known as the Hettangian, was a time of continuing adverse conditions in the oceans, with generally low diversities among marine invertebrates, such as ammonites and bivalves. On land, however, vegetation appeared to have recovered quicker. "We now show that this forest ecosystem continued to be perturbed repeatedly for at least 1.3 million years, but perhaps as long as 2 million years," Bos explains.

The four additional episodes of high Hg concentrations and high fern spore malformations were unlikely connected to later phases of Central Atlantic Magmatic Province volcanism. Instead, Bos and co-authors show that these periods correspond closely to the long eccentricity cycle, the major variation in the shape of Earth's orbit that moves Earth closer or further away from the Sun every 405 thousand years. During eccentricity maxima Earth moves closer to the Sun allowing for more sunlight to reach the Earth surface. As the Earth's atmosphere was already supercharged with carbon dioxide from the large-scale volcanism, this cyclic modulation of the climate system repeatedly triggered forest dieback, allowing for the renewed spread of pioneer ferns. As is shown by the correlation with high Hg contents, malformations in fern spores during these episodes were also the result of mercury poisoning. But where did this Hg come from?

Hg-isotopes

A crucial data set was generated at Tianjin University (China) by Wang Zheng, a co-corresponding author and geochemist specialized in metal isotope studies, especially Hg-isotopes. Mercury has different stable isotopes that behave differently in the environment. During reactions in nature, for example the expulsion from volcanism, deposition from the atmosphere, and the uptake by organisms, Hg-isotopes can become fractionated, enriching one pool in heavier isotopes, and others in lighter isotopes. Sediments with elevated levels of Hg and malformed spores also show clear variations in Hg-isotopes. "Based on the Hg-isotope variations we were able to link an initial pulse in Hg enrichment at the Triassic-Jurassic boundary to the emission of mercury from flood basalt volcanism," Wang Zheng explains. "However, the four other pulses in mercury had a different isotopic composition, indicating they were mainly driven by Hg input from soil erosion and photochemical reduction."

Climate change and toxic pollution

The combined geochemical and microfossil data thus paint a picture of a much more complex and drawn-out sequence of events, starting with massive volcanism driving climate change and releasing toxic pollutants, followed by episodic pulses of disturbance in the aftermath of the extinction event lasting for at least 1.3 million years. Dr. Tomas Navratil from the Czech Academy of Sciences, a co-author on the paper and a specialist for modern-day mercury pollution, agrees with this scenario. "Our work on polluted sites in the Czech Republic does show evidence for episodic remobilization from forest soils, especially during hot summers, and in places that are more exposed to sunlight causing the photochemical reduction of mercury and re-release to the atmosphere of previously stored mercury."

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Massive 2022 eruption reduced ozone layer levels

When the Hunga Tonga-Hunga Ha'apai volcano erupted on January 15, 2022 in the South Pacific, it produced a shock wave felt around the world and triggered tsunamis in Tonga, Fiji, New Zealand, Japan, Chile, Peru and the United States. It also changed the chemistry and dynamics of the stratosphere in the year following the eruption, leading to unprecedented losses in the ozone layer of up to 7% over large areas of the Southern Hemisphere, according to a recent study published in the Proceedings of the National Academy of Sciences (PNAS) from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the University of Maryland.

Driving those atmospheric changes, according to the research, was the sheer amount of water vapor injected into the stratosphere by the undersea volcano.

The location of the stratosphere is approximately 8 -- 30 miles above Earth's surface and is where the protective ozone layer resides.

"The Hunga Tonga-Hunga Ha'apai eruption was truly extraordinary in that it injected about 300 billion pounds of water into the normally dry stratosphere, which is just an absolutely incredible amount of water from a single event," said David Wilmouth, a project scientist at SEAS and first author of the paper.

"This eruption put us in uncharted territory," said Ross Salawitch, professor at the University of Maryland's Earth System Science Interdisciplinary Center and co-author of the study.

"We've never seen, in the history of satellite records, this much water vapor injected into the atmosphere and our paper is the first that looks at the downstream consequences over broad regions of both hemispheres in the months following the eruption using satellite data and a global model."

The Hunga Tonga-Hunga Ha'apai eruption was the largest explosion ever recorded in the atmosphere.

The eruption hurled aerosols and gases deep into the stratosphere.

Some material reached the lower mesosphere, more than 30 miles above the Earth's surface, altitudes never recorded from a volcanic eruption.

Previous studies found that the eruption increased water vapor in the stratosphere by 10% worldwide, with even higher concentrations in some areas of the Southern Hemisphere.

Wilmouth, Salawitch and the rest of the research team used data from the Microwave Limb Sounder (MLS) aboard the NASA Aura satellite, to track not only how that water vapor moved across the globe but also monitor temperature and levels of chlorine monoxide (ClO), ozone (O3), nitric acid (HNO3), and hydrogen chloride (HCl) in the stratosphere for the year following the eruption.

They then compared those measurements to data collected by MLS from 2005 to 2021 prior to the eruption.

The team found that the injection of water vapor and sulfur dioxide (SO2) changed both the chemistry and the dynamics of the stratosphere.

In terms of chemistry, the SO2 led to an increase of sulfate aerosols, which provided new surfaces for chemical reactions to occur.

"Certain reactions that might not happen at all or only happen slowly can happen faster if there are aerosols available on which those reactions can take place," said Wilmouth.

"The injection of SO2 from the volcano allowed sulfate aerosols to form and the presence of water vapor led to the additional production of sulfate aerosols."

The increased sulfate aerosols and water vapor kicked off a chain of events in the complex atmospheric chemistry that led to widespread changes in the concentrations of a number of compounds, including ozone.

The extra water vapor also had a cooling effect in the stratosphere, leading to a change in circulation, which drove decreases in ozone in the southern hemisphere and an increase of ozone over the tropics.

The researchers found that the peak decrease in ozone occurred in October, nine months after the eruption.

"We had this enormous increase in water vapor in the stratosphere with modest increases in sulfate that set off a series of events that led to significant changes in temperature and circulation, ClO, HNO3, HCl, O3, and other gases," Wilmouth said.

Next, the researchers hope to continue the study by following the impact of the volcano into 2023 and beyond as the water vapor moves from the tropics and midlatitudes to the Southern Hemisphere pole, where it has the potential to amplify ozone losses in the Antarctic.

The water vapor is expected to stay elevated in the stratosphere for a period of several years.

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Montreal protocol is delaying first ice-free Arctic summer

When scientists discovered a hole over Antarctica in 1985, countries across the globe got together and wrote a treaty designed to protect the ozone layer, which shields the Earth -- and us -- from harmful levels of ultraviolet radiation. The resulting Montreal Protocol, the only United Nations treaty ratified by every country in the world, was signed in 1987 and entered into effect in 1989, when little was known about its impact on the global climate. Its purpose was to reduce atmospheric concentrations of ozone-depleting substances (ODSs), materials commonly used in products such as refrigerators, air conditioners, fire extinguishers, and aerosols. For more than 50 years, it has been an important mitigation treaty, affecting many aspects of the global climate.

New study shows that the treaty's impact goes as far as the Arctic

A new study led by climate researchers at Columbia Engineering and the University of Exeter demonstrates that the treaty's impact reaches all the way into the Arctic: its implementation is delaying the occurrence of the first ice-free Arctic by as much as 15 years, depending on the details of future emissions. The study was published today by PNAS.

"The first ice-free Arctic summer-with the Arctic Ocean practically free of sea ice-will be a major milestone in the process of climate change, and our findings were a surprise to us," said the study's co-author Lorenzo Polvani, Maurice Ewing and J. Lamar Worzel Professor of Geophysics in the Department of Applied Physics and Applied Mathematics and professor of earth and environmental sciences. "Our results show that the climate benefits from the Montreal Protocol are not in some faraway future: the Protocol is delaying the melting of Arctic sea ice at this very moment. That's what a successful climate treaty does: it yields measurable results within a few decades of its implementation."

Impact of ODSs

Polvani noted that the rapid melting of Arctic sea ice is the largest and clearest signal of anthropogenic climate change. Current projections indicate that the first ice-free Arctic summer will likely occur by 2050, owing largely to increasing carbon dioxide concentrations in the atmosphere. However, other powerful greenhouse gases have also contributed to Arctic sea ice loss, notably ODSs. When ODSs became strictly regulated by the Montreal Protocol In the late 1980s, their atmospheric concentrations began to decline in the mid-1990s.

Polvani and his co-author Mark England, Royal Commission for the Exhibition of 1851 Senior Research Fellow at the University of Exeter and a former PhD student with Polvani, were particularly interested in exploring the impact of ODSs because their molecules, while a lot less common in the atmosphere, are tens of thousands of times more powerful at warming the planet than carbon dioxide.

Analysis of new climate model simulations

The researchers analyzed new climate model simulations and found that the Montreal Protocol is delaying the first appearance of an ice-free Arctic summer by up to 15 years, depending on future CO2 emissions. They compared the estimated warming from ODS with and without the Montreal Protocol under two scenarios of future CO2 emissions from 1985-2050. Their results show that if the Montreal Protocol had not been enacted, the estimated global mean surface temperature would be around 0.5 °C warmer and the Arctic polar cap would be almost 1 °C warmer in 2050.

"This important climate mitigation stems entirely from the reduced greenhouse gas warming from the regulated ODSs, with the avoided stratospheric ozone losses playing no role," said England. "While ODSs aren't as abundant as other greenhouse gasses such as carbon dioxide, they can have a real impact on global warming. ODSs have particularly powerful effects in the Arctic, and they were an important driver of Arctic climate change in the second half of the 20th Century. While stopping these effects was not the primary goal of the Montreal Protocol, it has been a fantastic by-product."

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Smoke particles from wildfires can erode the ozone layer

A wildfire can pump smoke up into the stratosphere, where the particles drift for over a year. A new MIT study has found that while suspended there these particles can trigger chemical reactions that erode the protective ozone layer shielding the Earth from the sun's damaging ultraviolet radiation.

The study, which will appear in Nature, focuses on the smoke from the "Black Summer" megafire in eastern Australia, which burned from December 2019 into January 2020. The fires -- the country's most devastating on record -- scorched tens of millions of acres and pumped more than 1 million tons of smoke into the atmosphere.

The MIT team identified a new chemical reaction by which smoke particles from the Australian wildfires made ozone depletion worse. By triggering this reaction, the fires likely contributed to a 3-5 percent depletion of total ozone at mid-latitudes in the southern hemisphere, in regions overlying Australia, New Zealand, and parts of Africa and South America.

The researchers' model also indicates the fires had an effect in the polar regions, eating away at the edges of the ozone hole over Antarctica. By late 2020, smoke particles from the Australian wildfires widened the Antarctic ozone hole by 2.5 million square kilometers -- 10 percent of its area compared to the previous year.

It's unclear what long-term effect wildfires will have on ozone recovery. The United Nations recently reported that the ozone hole, and ozone depletion around the world, is on a recovery track, thanks to a sustained international effort to phase out ozone-depleting chemicals. But the MIT study suggests that as long as these chemicals persist in the atmosphere, large fires could spark a reaction that temporarily depletes ozone.

"The Australian fires of 2020 were really a wake-up call for the science community," says Susan Solomon, the Lee and Geraldine Martin Professor of Environmental Studies at MIT and a leading climate scientist who first identified the chemicals responsible for the Antarctic ozone hole. "The effect of wildfires was not previously accounted for in [projections of] ozone recovery. And I think that effect may depend on whether fires become more frequent and intense as the planet warms."

The study is led by Solomon and MIT graduate student Peidong Wang, along with collaborators from the Institute for Environmental and Climate Research in Guangzhou, China, the National Oceanic and Atmospheric Administration, the National Center for Atmospheric Research, and Colorado State University.

Chlorine cascade

The new study expands on a 2022 discovery by Solomon and her colleagues, in which they first identified a chemical link between wildfires and ozone depletion. The researchers found that chlorine-containing compounds, originally emitted by factories in the form of chlorofluorocarbons (CFCs), could react with the surface of fire aerosols. This interaction, they found, set off a chemical cascade that produced chlorine monoxide -- the ultimate ozone-depleting molecule. Their results showed that the Australian wildfires likely depleted ozone through this newly identified chemical reaction.

"But that didn't explain all the changes that were observed in the stratosphere," Solomon says. "There was a whole bunch of chlorine-related chemistry that was totally out of whack."

In the new study, the team took a closer look at the composition of molecules in the stratosphere following the Australian wildfires. They combed through three independent sets of satellite data and observed that in the months following the fires, concentrations of hydrochloric acid dropped significantly at mid-latitudes, while chlorine monoxide spiked.

Hydrochloric acid (HCl) is present in the stratosphere as CFCs break down naturally over time. As long as chlorine is bound in the form of HCl, it doesn't have a chance to destroy ozone. But if HCl breaks apart, chlorine can react with oxygen to form ozone-depleting chlorine monoxide.

In the polar regions, HCl can break apart when it interacts with the surface of cloud particles at frigid temperatures of about 155 Kelvin. However, this reaction was not expected to occur at mid-latitudes, where temperatures are much warmer.

"The fact that HCl at mid-latitudes dropped by this unprecedented amount was to me kind of a danger signal," Solomon says.

She wondered: What if HCl could also interact with smoke particles, at warmer temperatures and in a way that released chlorine to destroy ozone? If such a reaction was possible, it would explain the imbalance of molecules and much of the ozone depletion observed following the Australian wildfires.

Smoky drift

Solomon and her colleagues dug through the chemical literature to see what sort of organic molecules could react with HCl at warmer temperatures to break it apart.

"Lo and behold, I learned that HCl is extremely soluble in a whole broad range of organic species," Solomon says. "It likes to glom on to lots of compounds."

The question then, was whether the Australian wildfires released any of those compounds that could have triggered HCl's breakup and any subsequent depletion of ozone. When the team looked at the composition of smoke particles in the first days after the fires, the picture was anything but clear.

"I looked at that stuff and threw up my hands and thought, there's so much stuff in there, how am I ever going to figure this out?" Solomon recalls. "But then I realized it had actually taken some weeks before you saw the HCl drop, so you really need to look at the data on aged wildfire particles."

When the team expanded their search, they found that smoke particles persisted over months, circulating in the stratosphere at mid-latitudes, in the same regions and times when concentrations of HCl dropped.

"It's the aged smoke particles that really take up a lot of the HCl," Solomon says. "And then you get, amazingly, the same reactions that you get in the ozone hole, but over mid-latitudes, at much warmer temperatures."

When the team incorporated this new chemical reaction into a model of atmospheric chemistry, and simulated the conditions of the Australian wildfires, they observed a 5 percent depletion of ozone throughout the stratosphere at mid-latitudes, and a 10 percent widening of the ozone hole over Antarctica.

The reaction with HCl is likely the main pathway by which wildfires can deplete ozone. But Solomon guesses there may be other chlorine-containing compounds drifting in the stratosphere, that wildfires could unlock.

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Protecting the ozone layer is delivering vast health benefits

An international agreement to protect the ozone layer is expected to prevent 443 million cases of skin cancer and 63 million cataract cases for people born in the United States through the end of this century, according to new research.

The research team, by scientists at the National Center for Atmospheric Research (NCAR), ICF Consulting, and U.S. Environmental Protection Agency (EPA), focused on the far-reaching impacts of a landmark 1987 treaty known as the Montreal Protocol and later amendments that substantially strengthened it. The agreement phased out the use of chemicals such as chlorofluorocarbons (CFCs) that destroy ozone in the stratosphere.

Stratospheric ozone shields the planet from harmful levels of the Sun's ultraviolet (UV) radiation, protecting life on Earth.

To measure the long-term effects of the Montreal Protocol, the scientists developed a computer modeling approach that enabled them to look to both the past and the future by simulating the treaty's impact on Americans born between 1890 and 2100. The modeling revealed the treaty's effect on stratospheric ozone, the associated reductions in ultraviolet radiation, and the resulting health benefits.

In addition to the number of skin cancer and cataract cases that were avoided, the study also showed that the treaty, as most recently amended, will prevent approximately 2.3 million skin cancer deaths in the U.S.

"It's very encouraging," said NCAR scientist Julia Lee-Taylor, a co-author of the study. "It shows that, given the will, the nations of the world can come together to solve global environmental problems."

The study, funded by the EPA, was published in ACS Earth and Space Chemistry. NCAR is sponsored by the National Science Foundation.

Mounting concerns over the ozone layer

Scientists in the 1970s began highlighting the threat to the ozone layer when they found that CFCs, used as refrigerants and in other applications, release chlorine atoms in the stratosphere that set off chemical reactions that destroy ozone. Concerns mounted the following decade with the discovery of an Antarctic ozone hole.

The loss of stratospheric ozone would be catastrophic, as high levels of UV radiation have been linked to certain types of skin cancer, cataracts, and immunological disorders. The ozone layer also protects terrestrial and aquatic ecosystems, as well as agriculture.

Policy makers responded to the threat with the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer, in which nations agreed to curtail the use of certain ozone-destroying substances. Subsequent amendments strengthened the treaty by expanding the list of ozone-destroying substances (such as halons and hydrochlorofluorocarbons, or HCFCs) and accelerating the timeline for phasing out their use. The amendments were based on Input from the scientific community, including a number of NCAR scientists, that were summarized in quadrennial Ozone Assessment reports.

To quantify the impacts of the treaty, the research team built a model known as the Atmospheric and Health Effects Framework. This model, which draws on various data sources about ozone, public health, and population demographics, consists of five computational steps. These simulate past and future emissions of ozone-destroying substances, the impacts of those substances on stratospheric ozone, the resulting changes in ground-level UV radiation, the U.S. population's exposure to UV radiation, and the incidence and mortality of health effects resulting from the exposure.

The results showed UV radiation levels returning to 1980 levels by the mid-2040s under the amended treaty. In contrast, UV levels would have continued to increase throughout this century if the treaty had not been amended, and they would have soared far higher without any treaty at all.

Even with the amendments, the simulations show excess cases of cataracts and various types of skin cancer beginning to occur with the onset of ozone depletion and peaking decades later as the population exposed to the highest UV levels ages. Those born between 1900 and 2040 experience heightened cases of skin cancer and cataracts, with the worst health outcomes affecting those born between about 1950 and 2000.

However, the health impacts would have been far more severe without the treaty, with cases of skin cancer and cataracts rising at an increasingly rapid rate through the century.

"We peeled away from disaster," Lee-Taylor said. "What is eye popping is what would have happened by the end of this century if not for the Montreal Protocol. By 2080, the amount of UV has tripled. After that, our calculations for the health impacts start to break down because we're getting so far into conditions that have never been seen before."

The research team also found that more than half the treaty's health benefits could be traced to the later amendments rather than the original 1987 Montreal Protocol. Overall, the treaty prevented more than 99% of potential health impacts that would have otherwise occurred from ozone destruction. This showed the importance of the treaty's flexibility in adjusting to evolving scientific knowledge, the authors said.

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Damage to the ozone layer and climate change forming feedback loop

Kelp forest with school of fish.

Increased solar radiation penetrating through the damaged ozone layer is interacting with the changing climate, and the consequences are rippling through the Earth's natural systems, effecting everything from weather to the health and abundance of sea mammals like seals and penguins. These findings were detailed in a review article published today in Nature Sustainability by members of the United Nations Environment Programme's Environmental Effects Assessment Panel, which informs parties to the Montreal Protocol.

"What we're seeing is that ozone changes have shifted temperature and precipitation patterns in the southern hemisphere, and that's altering where the algae in the ocean are, which is altering where the fish are, and where the walruses and seals are, so we're seeing many changes in the food web," said Kevin Rose, a researcher at Rensselaer Polytechnic Institute who serves on the panel and is a co-author of the review article.

The 1987 Montreal Protocol on Substances that Deplete the Ozone Layer -- the first multilateral environmental agreement to be ratified by all member nations of the United Nations -- was designed to protect Earth's main filter for solar ultraviolet radiation by phasing out production of harmful humanmade substances, such as the chlorofluorocarbons class of refrigerants. The treaty has largely been considered a success, with global mean total ozone projected to recover to pre-1980 levels by the middle of the 21st century. Earlier this year, however, researchers reported detecting new emissions of ozone depleting substances emanating from East Asia, which could threaten ozone recovery.

While ozone depletion has long been known to increase harmful UV radiation at the Earth's surface, its effect on climate has only recently become evident. The report points to the Southern Hemisphere, where a hole in the ozone layer above Antarctica has pushed the Antarctic Oscillation -- the north-south movement of a wind belt that circles the Southern Hemisphere -- further south than it has been in roughly a thousand years. The movement of the Antarctic Oscillation is in turn directly contributing to climate change in the Southern Hemisphere.

As climate zones have shifted southward, rainfall patterns, sea-surface temperatures, and ocean currents across large areas of the southern hemisphere have also shifted, impacting terrestrial and aquatic ecosystems. The effects can be seen in Australia, New Zealand, Antarctica, South America, Africa, and the Southern Ocean.

In the oceans, for example, some areas have become cooler and more productive, where other areas have become warmer and less productive.

Warmer oceans are linked to declines in Tasmanian kelp beds and Brazilian coral reefs, and the ecosystems that rely on them. Cooler waters have benefitted some populations of penguins, seabirds, and seals, who profit from greater populations of krill and fish. One study reported that female albatrosses may have become a kilogram heavier in certain areas because of the more productive cooler waters linked to ozone depletion.

Rose also pointed to subtler feedback loops between climate and UV radiation described in the report. For example, higher concentrations of carbon dioxide have led to more acidic oceans, which reduces the thickness of calcified shells, rendering shellfish more vulnerable to UV radiation. Even humans, he said, are likely to wear lighter clothes in a warmer atmosphere, making themselves more susceptible to damaging UV rays.

The report found that climate change may also be affecting the ozone layer and how quickly the ozone layer is recovering.

"Greenhouse gas emissions trap more heat in the lower atmosphere which leads to a cooling of the upper atmosphere. Those colder temperatures in the upper atmosphere are slowing the recovery of the ozone layer," Rose said.

As one of three scientific panels to support the Montreal Protocol, the Environmental Effects Assessment Panel focused in particular on the effects of UV radiation, climate change, and ozone depletion. Thirty-nine researchers contributed to the article, which is titled "Ozone depletion, ultraviolet radiation, climate change and prospects for a sustainable future." Rose, an aquatic ecologist, serves on the aquatic ecosystems working group, which is one of seven working groups that are part of the panel.

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