Researchers recently connected the ozone hole to summer warming over southern Africa. Source: http://commons.wikimedia.org/wiki/File:Ozone _Hole.jpg
International researchers have discovered a link between Antarctic ozone depletion and rising summer temperatures over southern Africa, as published in Nature Geoscience on October 13 (1).
Over the past two decades, there has been a substantial rise in surface air temperature over southern Africa, primarily during early summer. Previously, researchers had attributed this rise to increased emission of greenhouse gases in the atmosphere; however, climate models suggest that global warming effects should remain constant throughout all seasons, leaving the warming summer climate unexplained (2).
Desmond Manatsa and his research team found that these rising temperatures are influenced not only by greenhouse gas emission, but also by the hole in the ozone layer. Located approximately 20 to 30 kilometers above the Earth’s surface, the ozone layer absorbs ultraviolet light from the sun, protecting people from sunburn and skin cancer. This hole, which was first discovered by scientists in the early 1980’s, continues to grow every year and depletes up to 70% of the ozone concentration (2).
The ozone depletion boosts global warming slightly, allowing energy to penetrate deeper in the atmosphere. These factors shift the Southern Hemisphere wind patterns and intensify the Angola Low, an atmospheric, low-pressure system located above Angola, allowing warm air to flow into southern Africa (2).
Manatsa and his team used two independent data sets to compare the climate of southern Africa before and after the development of the ozone hole. Starting in 1979, the ozone hole greatly expanded, but its growth gradually decelerated following the mid-1990’s. As a result, the researchers split the data into two periods: Pre-Large Ozone Hole Era (1970-1993) and Large Ozone Hole Era (1993-2001) (1).
They found that during the time before and after the development of the ozone hole, the temperature in southern Africa was characterized by an increase of about one degree Celsius. This phenomenon coincides with the size of the ozone hole, which is largest in early summer, and explains the unusual rising summer temperatures (2).
Manatsa also notes that while this study demonstrates a strong correlation between the ozone hole and summer warming, it does not imply a direct causation. These conclusions can, however, lead to temperature predictability. For example, researchers can construct models based on ozone levels, which will allow them to predict the strength of the Angola Low and future summer temperatures (1).
On a more optimistic note, several studies have demonstrated that over time, the ozone levels over Antarctica may be restored to previous, normal levels. With the passage of international agreements like the Montreal Protocol, which helped phase out harmful ozone-depleting gases like chlorofluorocarbons (CFCs), ozone levels have been increasing in recent years. Scientists predict that by 2050, the ozone hole may even disappear. There is hope that as the ozone hole closes, the pressure system will weaken and gradually lead to a reduction in surface temperatures (2).
References:
1. C. Choi, Ozone Hole Over Antarctica Caused Southern Africa Warming (2013). Available at http://www.livescience.com/40388-ozone-hole-caused-southern-africa-warming.html (25 October 2013).
2. D. Manatsa et al., Link between Antarctic ozone depletion and summer warming over Southern Africa. Nature Geosci, 1038 (2013).
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