Where is ozone depletion most severe

This thinning of the ozone layer over Antarctica came to be known as the ozone hole. This series of images shows the size and shape of the ozone hole each year from through no data are available for Red and yellow areas indicate the ozone hole.

Scientists use the word hole as a metaphor for the area in which ozone concentrations drop below the historical threshold of Dobson Units. These maps show the state of the ozone hole each year on the day of maximum depth—the day the lowest ozone concentrations were measured.

The series begins in The maximum depth of the hole that year was Dobson Units DU —not far below the previous historical low. For several years, the minimum concentrations stayed in the s, but then the minimums rapidly grew deeper: DU in , in , in By , a new threshold was passed, as the ozone concentration fell below DU for the first time. Since then, concentrations below became more common. The rapid decline in emissions of ozone-depleting substances shown above was driven by international agreement to phase out their production.

In the Vienna Convention for the Protection of the Ozone Layer was adopted and entered into force in In the chart we see the evolution of global parties signing on to the Vienna Convention. In its first year there were only 29 parties signed to the agreement.

This rapidly increased in the years to follow, reaching parties by In , the Vienna Convention became the first of any Convention to achieve universal ratification. The Vienna Convention, despite not mandating parties to take concrete actions on ozone protection laid the foundations for adoption of The Montreal Protocol.

The Montreal Protocol on Substances that Deplete the Ozone Layer is arguably the most successful international treaty to date. The Montreal Protocol is an international protocol to the Vienna Convention, agreed in before entering into force in Its purpose was to phase-out reduce and eventually eliminate the use of man-made ozone-depleting substances for protection of the ozone layer.

The Protocol has now reached universal ratification, with South Sudan as the final signatory in Since its first draft in , the Montreal Protocol has undergone numerous amendments of increasing ambition and reduction targets. In the chart we see various projections of historic and future concentrations of effective chlorine substances i.

These are mapped from assumptions of no international protocol, the first Montreal treaty in , followed by subsequent revisions of increasing ambition. However, even under the initial Montreal Protocol, and subsequent London amendment, reduction controls and targets would have been too relaxed to have resulted in a reduction in ODS emissions. However, the Copenhagen and its subsequent revisions greatly increased controls and ambition in global commitments, leading to a peak in stratospheric concentrations in the early s and projected declines in the decades to follow.

In the chart we see average stratospheric ozone concentrations in the Southern Hemisphere where ozone depletion has been most severe from to Ozone concentrations are measured in Dobson Units DU : this is number of molecules of ozone that would be required to create a layer of pure ozone 0. For several decades since the s, concentrations have continued to approximate around or below DU. Over the last few years since , however, ozone concentrations have started to slowly recover.

Has the fall of stratospheric ozone concentrations been reflected in an ozone hole? In the chart we see the maximum and mean ozone hole area over Antarctica, measured in square kilometres km 2. Like gas concentrations, ozone hole area is monitored daily by NASA via satellite instruments. Since we see a distinct increase in the Antarctic ozone hole area, reaching a maximum of 30 million km 2 in the early s.

However, since the late s, the ozone hole area had approximately stabilised between 20 to 25 million km 2. Full recovery is, however, expected to take until at least the second half is this century as described in the entry below.

The Ozone Layer has recently shown early signs of recovery. However, full recovery of stratospheric ozone concentrations to historical levels is projected to take many more decades. In the charts we profile historic levels and future projections of recovery in two forms: equivalent stratospheric chlorine i. ODS concentrations, and stratospheric ozone concentrations through to This is measured as the global average, as well as concentrations Antarctic and Artic zones.

Note that such projections are given as the median lines from a range of chemistry-climate; true modelled results presented in the Montreal Protocol Scientific Assessment Panel report present the full range of modelled estimates, with notable confidence intervals. The data presented is measured relative to concentrations in where is equal to 0.

ODS can have a significant lifetime in the atmosphere, for some between 50 and years on average. This means that despite reductions in ODS emissions and eventually complete phase-out of these substances , equivalent stratospheric chlorine ESC concentrations are expected to remain higher than levels through to the end of the century.

Antarctica, where ozone depletion has been most severe due to very low temperatures is expected to recover much more slowly. The story of international cooperation and action on addressing ozone depletion is a positive one: the Vienna Convention was the first Convention to receive universal ratification. Over the last few decades we have seen a dramatic decline in emissions of ozone-depleting substances. Montzka et al. Atmospheric concentrations of CFC have been measured and tracked back to the s via air collection and analysis with automated onsite instrumentation, such as with gas chromatography coupled with electron capture detection GC—ECD.

This allows us to track atmospheric concentrations over time. Using statistics on reported emissions of CFC submitted by parties to the Montreal Protocol, it is possible to construct estimates and projections of what change in atmospheric concentration should occur based on such levels of emissions.

In the chart we see the annual change in percent of measured concentrations of CFC shown as the solid line. As we see, actual and expected concentration changes map closely over the period up to Since , however, the annual rate of decline in concentrations has fallen almost halved from This is highly inconsistent with the expected rate of change which would have resulted in the case that reported emissions to the Montreal Protocol were correct.

This inconsistency between actual and expected rate of change particularly in the case of a slowdown in concentration decline suggests an increase in global emissions despite reports close to zero since 8. However, some additional measurements allowed the authors to provide an informed estimate.

Using combined CFC measurements in the Northern and Southern Hemisphere and atmospheric transport models, the authors suggested the likely source of additional CFC emissions was from the Northern Hemisphere. This was further supported by data from the Mauna Loa Observatory MLO in Hawaii, which also provide measurements of other chemical emissions. In correlating chemical pollution tracers and CFC emissions, the authors suggest there is strong evidence that the source of increased CFC emissions is Eastern Asia.

How much of an impact will recent emissions of CFC have on ozone layer recovery? The long-term impact of emissions for the ozone layer will depend on how long continued emissions of CFC persist. In the chart we show the absolute concentrations of CFC as opposed to the annual rate of change, shown above in terms of actual measurements solid lines, for both hemispheres and projections dashed line.

Here you see that despite recent emissions, total concentrations continue to fall but at a notably slower rate than expected.

However this could be minimised to the span of a few years if emissions are now rapidly reduced and return close to zero, as reported within the Ozone Secretariat. Nonetheless, the capacity to identify where atmospheric concentrations and reported emissions are inconsistent is an important step in itself; it makes it clear that our measurement infrastructure does not allow misreporting to go unnoticed.

Although ozone depletion has been a global issue, there is significant differences in distribution of ozone layer depletion across the world. Overall, ozone depletion increases with latitude with low levels of depletion at the equator and tropics, and highest depletion at the poles.

Why is this the case? An important condition for ozone depletion is very cold atmospheric temperatures. This factor alone explains the concentration of ozone depletion at the poles rather than at lower latitudes. Ozone depletion has been most severe over Antarctica because it provides the unique temperature and chemical conditions for effective ozone destruction by halogen gases.

The same meteorological factors also contributed to the record Arctic ozone hole. This is in contrast to the unusually small and short-lived Antarctic ozone hole in Ozone depletion is directly related to the temperature in the stratosphere, which is the layer of the atmosphere between around 10 km and round 50 km altitude.

These polar stratospheric clouds contain ice crystals that can turn non-reactive compounds into reactive ones, which can then rapidly destroy ozone as soon as light from the sun becomes available to start the chemical reactions. When temperatures high up in the atmosphere stratosphere start to rise in late Southern Hemisphere spring, ozone depletion slows, the polar vortex weakens and finally breaks down, and by the end of December ozone levels have returned to normal.

However, in , a strong, stable and cold polar vortex kept the temperature of the ozone layer over Antarctica consistently cold, preventing the mixing of ozone depleted air above Antarctica with ozone rich air from higher latitudes.

For much of the season, stratospheric ozone concentrations around 20 to 25 km of altitude hPa reached near-zero values with the ozone layer depth as low as 94 Dobson Units a unit of measurement , or approximately one third of its normal value. Every season, the appearance of the ozone hole and its evolution is monitored by means of satellites and a number of ground-based observing stations. The Montreal Protocol on Substances that Deplete the Ozone Layer is the landmark multilateral environmental agreement that regulates the production and consumption of nearly chemicals referred to as ozone depleting substances ODS.