Newman et al.'s model predicts the size of the hole in the Antarctic ozone layer based on the level of ozone-depleting substances in the atmosphere.

Their model predicts that the hole is expected to fully recover around 2068 because the levels of ozone-depleting substances have been declining.

Solomon et al. used a model to identify key factors influencing chemically induced ozone depletion.

For example, they found that polar ozone loss is particularly sensitive to temperature and the presence of sulfate aerosols from volcanic eruptions.

The model's predictions are in good agreement with measured ozone-abundance data.

Kuttippurath et al. reported that from 2004 to 2013, the level of ozone-depleting substances was relatively stable. Thus, they conclude that naturally occurring climate variations produced the year-to-year variations in the ozone hole depth.

In this review paper, Solomon explains that human-made chlorofluorocarbons (CFCs) are the primary cause of the hole in the ozone layer.

Also, the paper emphasizes that more ozone depletion occurs in the Antarctic and Arctic regions due to surface chemistry on cold polar clouds.

Kuttippurath et al. reported signs of ozone-layer recovery by using September-to-November averaged data collected from 1979 to 2010.

They attributed these signs of recovery to the reduction in ozone-depleting substances.

Salby et al. demonstrate that naturally occurring changes, or variability, in the ozone layer must be taken into account to observe human-induced changes.<br> Here, they report that after accounting for the naturally occurring changes, a trend of increasing ozone levels is observed.

Salby et al. look for signs of ozone healing using September-to-November averages, but the current paper by Solomon et al. uses data from September when there is less variability.

Shepherd et al. show that in order to predict the effects of human-induced climate change, models must include more than just surface temperature conditions.

These models must also account for uncertainties arising from circulation, or the movement of air, within the atmosphere.

Typically every 4 years, the World Meteorological Organization and the United Nations Environment Programme publish a joint assessment of the state of the ozone layer based on the latest scientific findings. The report helps to guide policy makers in making science-based policy decisions.

The 2014 assessment concludes that nearly half of the improvement in stratospheric ozone levels since the year 2000 is due to a reduction in ozone-depleting substances.

The Montreal Protocol was established to heal the hole in the ozone layer by phasing out the release of ozone-depleting substances. This paper concludes that the hole in the Antarctic ozone layer is starting to heal as a result of the reduction in ozone-depleting substances.

This paper's findings that the Antarctic ozone hole is beginning to heal provided evidence that the Montreal Protocol is having the intended effect.

Read more at BBC News: https://www.bbc.com/news/science-environment-36674996

This paper shows that in order to draw a conclusion about the healing of the Antarctic ozone hole, the following is required:

1. Gathering data on the amount of atmospheric ozone over time using balloons and satellites.

2. Since aerosols released by volcanic eruptions can deplete ozone, volcanic aerosols must be measured.

3. Ozone-depletion models which account for climate and chemistry must be used to interpret ozone-abundance data.

Since the ozone-depleting substances released by humans were not increasing, it was important to understand why the Antarctic ozone hole was so large in the year 2015.

The paper concludes that the unusually large hole was due to a volcanic eruption in Calbuco, Chile.

The sulfur-based aerosols released from volcanoes can also deplete the ozone layer, so they must be accounted for when tracking the hole over time.

If the effects of the volcanic eruptions in 2011 and 2015 are removed, the chemically induced Antarctic ozone hole shows signs of healing.

The model is accurately simulating the ozone trends, and it shows that the decline in ozone-depleting chemicals is driving the healing.

While October is the month when the Antarctic ozone hole was originally discovered, the smaller variations from non-chemical factors make it easier to observe healing in September.

The polar cap is the region of each pole that is covered in ice.

Interannual events take place in different years.

Here, it refers to variations that occur from year to year.

Forcings refer to factors that drive changes in the climate.

Light absorption occurs when light transfers energy to an object.

Here, sunlight's energy is transferred to ozone in the form of heat.

While the chem-only simulation is intended to determine the effect of chemistry on ozone depletion, it cannot fully capture this effect because the chemical reaction rates also depend on temperature.

As the amount of ozone changes, the atmospheric temperature also changes.

If these temperature-driven variations in chemistry were fully accounted for, the effect of chemistry on ozone depletion could be even larger.

This approach only includes sulfur-based aerosols that did not originate from a volcanic eruption.

Thus, the effect of the volcanic eruption on ozone depletion is removed.

In this approach, the primary contributors to ozone depletion are included in the model, and it is expected to be the closest to the actual measured trends.

The human-made substances that are primarily responsible for the hole in the ozone layer are chlorine- and bromine-based chemicals.

Thus, chemical reactions involving chlorine and bromine are included in the model to simulate the ozone depletion process.

The goal of this paper is to determine if the reduction in human-made ozone-depleting chemicals is healing the hole in the Antarctic ozone layer. It studies ozone-layer trends over the time period of 2000 to 2015. However, in the year 2002, the Antarctic weather conditions were unusual compared to other years within this time period.

Since ozone depletion in the atmosphere is extremely sensitive to weather conditions, the year 2002 was not included in this analysis.

To understand the impact of human-made substances on the ozone hole, researchers have been tracking the level of ozone-depleting substances in the atmosphere.

Due to the Montreal Protocol, levels of these substances have been declining.

Thus, researchers are investigating whether the ozone layer has begun to heal as a result of this decline.

High latitudes are approximately 60 degrees from the equator and higher. This includes the polar regions.

Here, modal refers to the aerosols in the atmosphere which have a distribution of sizes.

The size distribution used in this model includes 3 modes corresponding to smaller (Aitken), intermediate (accumulation), and larger (coarse) diameter aerosols. Read more here: https://www.dwd.de/EN/research/observing_atmosphere/composition_atmosphere/aerosol/cont_nav/particle_size_distribution_node.html

A specified dynamics model incorporates actual temperature and wind measurement data.

This approach improves the specified dynamics model's accuracy compared to a model which does not include measured data.

The CESM1 version of this model includes effects which extend from the Earth's oceans to the second-highest layer of the atmosphere (thermosphere). This allows for a more accurate representation of how different parts of the Earth's climate system influence the ozone layer.

In addition, the model accounts for how the climate system interacts with chemical reactions in the atmosphere. This is important for modeling how chemicals deplete the ozone layer.

The model can be used to calculate historical ozone trends and to make predictions about future trends.

Balloon ozone data is collected by attaching an ozone-measuring device to a balloon that carries the device into the atmosphere. As the device travels through the atmosphere, it transmits data back to the ground station. Read more here: https://gml.noaa.gov/ozwv/ozsondes/

The Syowa Station is a Japanese research post in the Antarctic which collects data on atmospheric ozone as well as other scientific data. Read more here: https://www.nipr.ac.jp/english/antarctic/center.html

The Amundsen–Scott South Pole Station is a research site in the Antarctic administered by the United States' National Science Foundation. The station collects a variety of scientific data including data on atmospheric ozone. Read more here: https://www.nsf.gov/geo/opp/support/southp.jsp

See animations of yearly South Pole Station ozone data here: https://gml.noaa.gov/dv/spo_oz/movies/index.html

It has been well established that human-made chemicals are the primary cause of the hole in the ozone layer. These chemicals are called ozone-depleting substances.

In reference 12, Solomon details the chemical process of ozone depletion in the atmosphere.

Ozone-depleting substances (ODS) had already been declining for many years prior to 2015. Thus, it is noteworthy that the hole in the Antarctic ozone layer would reach record size in 2015.

Why such a large hole was observed in 2015 when ODS have been on the decline is one of the key questions investigated in the current paper.

Dynamical variability refers to naturally occurring changes in the climate from year to year.

Halogen-induced changes become more apparent when naturally occurring changes are removed from the analysis.

The low latitudes are approximately between 0 degrees (equator) and 30 degrees.

Hofmann et al. in Reference 3 used 10 years (1986-1996) of Antarctic ozone level measurements to show how ozone recovery occurs over time.

They show that before an increase in ozone levels occurs, the rate of ozone loss slows down over time.

They predicted that conclusive signs of Antarctic ozone layer healing could be detected as early as 2008.

In the 2016 Kigali amendment to the Montreal Protocol, countries will also begin phasing out the use of hydrofluorocarbons (HFCs) because they contribute to global warming.

Read more at the Weather Channel: https://weather.com/en-IN/india/environment/news/2021-08-20-boost-for-cooling-industry-as-india-approves-kigali-ratification

Halocarbons are chemicals that contain bonds between carbon and halogen atoms.

Halogens are a group of elements that includes fluorine, chlorine, bromine, iodine, astatine, and tennessine.

Halocarbons are highly reactive in the Earth's atmosphere and lead to ozone depletion.

Anthropogenic means caused by human activity.

In this context, humans released chemicals into the atmosphere, and these chemicals produced the hole in the ozone layer.

While the current publication focuses on ozone depletion in the Antarctic, WMO/UNEP periodically reports the state of the ozone layers in the Arctic and in the Antarctic. The reports also provide updates on the levels of ozone-depleting substances over time.

Latitude is the coordinate that specifies the north-south location on the surface of the Earth and ranges from 0 degrees at the equator to 90 degrees at the North and South Poles.

Mid(or middle)-latitudes are approximately between 30 degrees and 60 degrees.

The integrated column is a way to quantify how much of a particular gas is found in the Earth's atmosphere.

For a vertical path, or column, that extends through the atmosphere, the number of gas molecules is measured at each point along the path. Then, the sum total is calculated for the entire path.

In this case, it is used to measure the amount of ozone in the atmosphere.

Ozone is a gaseous molecule composed of 3 oxygen atoms with the chemical formula O\(_{3}\).

Here, the authors are referring to the layer of ozone in the Earth's atmosphere that filters harmful ultraviolet radiation from the sun.

Butchart reviews scientific studies of climate change's effect on the stratospheric overturning circulation.

The review shows that a variety of models agree that greenhouse gas-induced climate change should strengthen the overturning circulation. However, it has been difficult to confirm these models using actual measurements.

Portmann et al.'s models showed that both colder temperatures and particles from volcanic eruption can delay the healing of the ozone layer.

Thus, these factors must be accounted for when tracking human-caused ozone depletion.

Hofmann and Oltmans demonstrated that the unusually large Antarctic ozone hole in 1992 was most likely caused by the 1991 Pinatubo volcanic eruption.

They concluded that sulfuric acid droplets released from the eruption were responsible for the abnormally large Antarctic ozone hole.

Livesey et al. determined how much polar ozone loss was caused by chemicals versus other sources of ozone variation.

This was accomplished by tracking how much ozone varies within the same air mass over time.

Farman et al. reported that October Antarctic ozone levels had dropped significantly.

The authors suggested that Cl based chemicals could play a significant role in the ozone depletion.

Total ozone column data can be obtained by combining balloon data with data measured using satellites.

Satellites are able to obtain data at higher altitudes than balloons, which are limited to around 30 kilometers.

The earliest October ozone hole measurements are used as a reference for the trends that follow.

Nevertheless, September and November data can still be used to track the impact human-made chemicals, climate variations, and volcanic eruptions are having on the ozone layer over time.

This approach removes the contributions of climate variation and volcanic eruptions to ozone depletion.

Thus, only the effects of variations in chemistry would remain.

Since aerosols released from volcanic eruptions can also contribute to ozone depletion, the researchers must account for this contribution as accurately as possible.

To calculate the accuracy of the model, the modeled data is compared to measurement data during the years that volcanic eruptions occurred.

Modal refers to the mode, or most frequently occurring value in a distribution.

Here, modal describes the distribution of particle sizes.

In order to verify the model, Solomon et al. in Reference 24 compared the model's predictions to actual ozone abundance measurements.

After accounting for temperature variations and the particles released from volcanic eruptions, the model was in good agreement with actual measurements.

Models have demonstrated that aerosol particles released from volcanic eruptions can deplete the ozone layer.

Specifically, this modeling work demonstrated that the unusually large ozone hole in 1992 was caused by the eruption of Mount Pinatubo in 1991.

Human-made chemicals are primarily responsible for the formation of the hole in the ozone layer. However, other factors such as variations in weather conditions can produce variations in the size of the ozone hole from one year to the next.

Researchers in the field have worked to separate the human-made variations from those caused by other factors such as weather.

The WHO/UNEP scientific assessment reviews ozone hole data from numerous scientific studies.

While the 2015 assessment did not report healing in the polar regions, it did conclude that ozone levels had increased in other regions of the Earth since the year 2000.

Farman et al. were the first to publish the observation that a hole was forming in the Antarctic ozone layer, and they proposed that chemicals played a key role.

A recent study has shown that if the hole in the ozone layer had not been addressed, it could have made global warming worse by killing carbon-consuming plants.

Read more at Scientific American: https://www.scientificamerican.com/article/ozone-hole-would-have-killed-plants-and-raised-global-temperatures/

Stratospheric overturning circulation refers to the atmospheric "conveyor belt" that moves air from the Earth's equator toward the poles.

This system carries chemicals and ozone throughout the Earth's atmosphere.

Read more here: https://news.mit.edu/2017/strength-global-stratospheric-circulation-measured-first-time-0828

Greenhouse gases are gases which trap heat in the atmosphere and are responsible for human-caused global warming.

The Montreal Protocol is an international agreement to phase out the use and production of substances that deplete the ozone layer. The agreement was finalized in 1987.

Read more here: https://www.epa.gov/ozone-layer-protection/international-actions-montreal-protocol-substances-deplete-ozone-layer

Inline refers to the insertion of a smaller computer program into a larger, main code.

The inline code performs a specific function.

Here, the inline code generates the aerosol properties needed for the ozone calculation.

Suborbital refers to a path that is less than one full revolution around a body.

Here, it refers to data that was not obtained by satellite.

The residence time is a measure of how long a substance remains in a specific location. Here, the location is the atmosphere.

In this case, the long residence time of halocarbons means they are able to do more damage to the ozone layer.

Austral means southern. Here, it relates to the Southern Hemisphere of the Earth.

El Niño refers to a climate pattern that pushes warm water into the Pacific Ocean.

This warming of the Pacific Ocean impacts global weather patterns.

Read more here: https://oceanservice.noaa.gov/facts/ninonina.html

The prefix "geo" means Earth.

Thus, geophysical refers to physics occurring on and near the Earth.

The troposphere is one of the five major layers of the Earth's atmosphere.

It is the layer closest to the surface of the Earth.

A sonde is an instrument that measures and transmits information about a remote location.

An ozonesonde is a device that is carried by a balloon into the atmosphere. As it travels, it transmits ozone concentration information back to a station on the ground.

Balloon ozone data is measured by instruments carried into the atmosphere by balloons.

Radiation refers to energy that travels at the speed of light.

Here, it refers to a form of heat transfer that causes atmospheric temperature changes.

Something that is anomalous differs from what is normal or typical.

Climatology is the study of climate science.

OCS is carbonyl sulfide with a molecular structure consisting of an oxygen (O), carbon (C), and sulfur (S) atom.

The CCMI project develops models that describe how atmospheric chemistry and climate interact with each other.

The primary focus of the project is understanding atmospheric ozone.

A field is a property of a physical system that can be measured.

Here, it refers to properties of the atmosphere.

TOMS and OMI are instruments used to measure the total ozone in the atmosphere.

The TOMS data set has provided a record of total atmospheric ozone since 1978. OMI was launched in 2004 to continue the collection of ozone data.

Both data sets are merged to obtain a more complete record of the ozone layer over time.

The SBUV is an instrument that measures the amount of ozone in the atmosphere.

The instrument, mounted on a weather satellite, measures the sunlight reflected back from the Earth.

Since ozone is known to reflect light at a particular wavelength, the amount of light reflected at this wavelength indicates how much ozone is present in the atmosphere.

Aerosols are solid particles or liquid droplets that are suspended in a gas.

Here, the particles are suspended in air.

Meteorological variability refers to changes in atmospheric weather conditions.

Heterogeneous chemistry is a chemical process that involves different phases of matter.

Here, it refers to gaseous chlorine and bromine reacting on the surface of condensed phase cloud particles.

Polar stratospheric clouds form under extremely cold winter conditions in the Arctic and Antarctic.

They support the destructive halogen chemistry responsible for ozone depletion.

A confounding factor impacts both variables of interest and makes it more difficult to determine the cause and effect relationship between them.

A monotonic quantity is either always increasing or always decreasing.

Polar ozone refers to the ozone layer over the Arctic and Antarctic regions.

Lidar stands for "light detection and ranging" and is a technique for measuring the distance to an object. It involves shining a laser on the object and measuring the time it takes for the light to be reflected back.

The stratosphere is one of the five major layers of the Earth's atmosphere.

It is the second closest to the surface of the Earth, and it contains the ozone layer.

Halogens are a group of elements that includes fluorine, chlorine, bromine, iodine, astatine, and tennessine.

To deplete is to reduce the amount of something.

Here, the amount of ozone in the Earth's atmosphere has been reduced.