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History of the Montreal Protocol

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.

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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 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.

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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. 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.

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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.

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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. This occurs for only months in Arctic regions, but across 5 to 6 months in Antarctica through winter and early spring.

The liquid and solid particles in PSCs allow highly reactive chlorine gas to be formed when halogen gases and sunlight are present.

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  8. This highly reactive chlorine gas is then very effective in breaking down stratospheric ozone. It is these unique conditions through the winter and early spring that result in high ozone destruction over Antarctica. As discussed earlier in this entry , stratospheric ozone plays a fundamental role in protecting surface lifeforms from exposure to harmful levels of UV-B radiation.

    In the figure we show the average percentage change in UV irradiation reach the surface in relative to levels in Shown are the changes across wavelengths from to nanometres, which is the region where DNA damage from UV irradiation has its largest health impacts. At nm, for example, irradiance at high Southern latitudes increased by more than 25 percent over this period. At the Northern poles, this was much less at between 5 to 10 percent. Ozone layer protection from UV-B irradiation is critical to the health of many lifeforms, including human health.

    Ozone depletion and the subsequent increase in UV-B irradiation, as discussed above , can increase negative health impacts such as skin cancer , and other implications such as sunburn and skin ageing. Using combined ozone, UV and dose-response models, numerous studies have attempted to quantify the potential increase in skin cancer cases as a result of ozone depletion.

    Such studies also attempt to quantify the number of skin cancer cases avoided as a result of international action through the Montreal Protocol to reduce ODS consumption. Dijk et al.

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    The study estimates that by , two million cases worldwide will be avoided per year as a result of ODS reduction from the Montreal Protocol and its later revisions. One of the first studies to attempt to quantify excess skin cancer cases, despite being published in the s correlates well with results from recent studies.

    The primary role of the Vienna Convention, Montreal Protocol and its subsequent revisions was to protect depletion of the stratospheric ozone layer. However, the ambition to reduce and eventually eliminate the use of ozone-depleting substances ODS has also produced co-benefits for greenhouse gas reduction. With a GWP up to 10, times higher than carbon dioxide CO 2 , these gases can have a notable impact on total greenhouse gas emissions, even in very small concentrations.

    The reduction in ODS, in particular CFCs has therefore had a significant impact on greenhouse gas reduction in recent years. In fact, several sources estimate that the climate benefits of the Montreal Protocol have been five to six times that of the Kyoto Protocol. In the chart we visualize the impact of the reduction in ODS emissions for climate change in terms of greenhouse gas emissions in carbon dioxide equivalents , and radiative forcing measured in watts per square metre.

    Blue trends map the estimated impact had the Montreal Protocol not been adopted: it is based on the assumption of a 2 to 3 percent dashed and solid line increase in annual production of halogen substances.

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    The blue area therefore represents the estimated quantity of GHG or radiative forcing averted as a result of the Montreal Protocol. GHG emissions from ODSs in could have reached approximately 10 billion tonnes of CO 2 -equivalents which would have been five times the annual target of the Kyoto Protocol for the period. This means HFC emissions have increased notably in recent years. However, HFCs have a large global-warming potential as shown in the table in the Data Definitions section ; and could begin to cancel out climate benefits made by the rapid reduction of CFCs and HCFCs in recent decades.

    If we are to preserve the climate benefits of the Montreal Protocol, further emissions and potential substitutes for CFC products will be important in the coming years. ODP tonnes attempt to standardise and correct for the differences in the potential ozone destruction across different substances. In the table in the section below , we provide a list of substances and their respective ODP values; ODP values provide a measure of the relative destruction potential of one tonne of that substance relative to chlorofluorocarbon CFC CFC is therefore given a value of 1.

    The sum of all of halogen gases in ODP tonnes provides a total measure of ozone-depleting substance emissions. The Montreal Protocol represents one of the biggest collective action efforts in human history with very effective stakeholder engagement on an international scale.

    It managed to take into account the interests of a broad range of stakeholders, including nation states, industry groups, scientists and NGOs throughout the negotiation of the final treaty.