Andreas Späth

The ozone hole and SA’s climate

2013-10-21 13:53

Remember the ozone hole? It was the biggest global environmental issue before climate change took centre stage. Well, it’s back - actually it never went away - and scientists think it’s been contributing to warming in our part of the world.

Ozone is a molecule that consists of three oxygen atoms - as opposed to the pairs that make up oxygen gas (O2). In the lower parts of the atmosphere it’s an air pollutant and a potent greenhouse gas.

In the stratosphere (between about 10km and 50km above the surface of the earth), where it occurs in its highest concentrations, however, ozone forms our planet's security blanket - the ozone layer - which filters out dangerous UV rays from sunlight and acts as an important life-protecting shield for all of us.

In the late 1970s, scientists first noticed an annual depletion of stratospheric ozone over Antarctica (this happens over the North Pole, too, but is most prominent over the South Pole).

It’s now generally accepted that this so-called ozone hole is caused by a group of chemicals called chlorofluorocarbons (CFCs) which were widely used in aerosol cans and refrigerators in the past. During the southern spring, chlorine radicals derived from CFCs break down stratospheric ozone molecules and eat a big, gaping hole into the ozone layer.

The perceived threat of a growing ozone hole led to the adoption of the Montreal Protocol in 1987 which banned CFCs internationally for most uses and controlled it for others. The ban has been an overwhelming success that has seen the hole shrinking in size. In 2012, the Antarctic ozone hole was reported to be smaller than it has been in the last ten years.

Unfortunately, CFCs survive in the atmosphere for a long time and even though their use is now strictly controlled, scientists estimate that it could take another decade before the ozone layer over the South Poles starts to recover fully.

It may be shrinking steadily, but the hole is still massive, covering an area of over 21 million square kilometres last year. It’s not surprising that such an enormous atmospheric phenomenon would have a significant impact on regional climate patterns.

Several recent scientific papers suggest that it has “complicated” the weather, particularly during summer, in the southern regions of the southern hemisphere, including parts of New Zealand, Patagonia, Australia and the Southern Ocean. In July, a study proposed that the ozone hole may be altering Antarctic jet stream currents, pushing reflective cloud-cover poleward, resulting in additional warming due to greater amounts of sunlight reaching the surface.

Now a new report by Desmond Manatsa of Zimbabwe’s Bindura University of Science and his colleagues argues that the Antarctic ozone hole has had a direct warming effect on Southern Africa’s summer weather.

Early summer temperatures in the region have been observed to have risen notably during the last 20 years. Since this seasonal increase is hard to explain solely as a result of rising greenhouse gas concentrations, Manatsa and co-workers looked to the Antarctic ozone hole for an explanation.

They believe that the hole has altered Southern African wind patterns, intensifying the Angola Low (a regional low-pressure system) and allowing warm equatorial air to flow into the region during summer. “The development of the ozone hole could, in fact, be the dominant cause of the increase in temperatures over Southern Africa,” contents Manatsa.

If the ozone hole closes up after 2050, as is currently projected, this effect could be reversed, leading to a relative drop in surface temperatures, although the general impact of global warming would persist.

The take-away message:

- Pumping CFCs into the atmosphere has affected our regional weather through the formation of the Antarctic ozone hole. Banning CFCs is reversing this trend.

- Pumping greenhouse gases (primarily CO2) into the atmosphere is affecting our global climate. Massively reducing CO2 emissions now will reverse this trend in the future.

- Andreas is a freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath
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