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An international Treaty that works! The Montreal Protocol and the healing of the ozone layer.

Each year, during the southern spring, a hole appears in the ozone layer above Antarctica. This is due to the extremely cold temperatures in the winter stratosphere (above 10km altitude) that allow byproducts of CFCsand related gases to be converted into forms that destroy ozone when the sunlight returns in spring.

As ozone-destroying gases are phased out, the annual ozone hole is generally getting smaller – a rare success story for international environmentalism.

Back in 2012, our Saving the Ozone series marked the Montreal Protocol’s silver jubilee and reflected on its success. But how has the ozone hole fared in the five years since?

The Antarctic ozone hole has continued to appear each spring, as it has since the late 1970s. This is expected, as levels of the ozone-destroying halocarbon gases controlled by the Montreal Protocol are still relatively high. The figure below shows that concentrations of these human-made substances over Antarctica have fallen by 14% since their peak in about 2000.

It typically takes a few decades for these gases to cycle between the lower atmosphere and the stratosphere, and then ultimately to disappear. The most recent official assessment, released in 2014, predicted that it will take 30-40 years for the Antarctic ozone hole to shrink to the size it was in 1980………

Reassuringly, a recent study showed that the size of the ozone hole each September has shrunk overall since the turn of the century, and that more than half of this shrinking trend is consistent with reductions in ozone-depleting substances. However, another study warns that careful analysis is needed to account for a variety of natural factors that could confound our detection of ozone recovery……..

While annual monitoring continues, which includes measurements under the Australian Antarctic Program, a more comprehensive assessment of the ozone layer’s prospects is set to arrive late next year. Scientists across the globe, coordinated by the UN Environment Program and the World Meteorological Organisation, are busy preparing the next report required under the Montreal Protocol, called the Scientific Assessment of Ozone Depletion: 2018.

This peer-reviewed report will examine the recent state of the ozone layer and the atmospheric concentration of ozone-depleting chemicals, how the ozone layer is projected to change, and links between ozone change and climate.

In the meantime we’ll watch the 2017 hole as it peaks then shrinks over the remainder of the year, as well as the ozone holes of future years, which will tend to grow less and less large as the ozone layer heals. https://theconversation.com/after-30-years-of-the-montreal-protocol-the-ozone-layer-is-gradually-healing-84051

September 18, 2017 - Posted by Christina Macpherson | 2 WORLD, climate change, environment, politics international