Roughly 80% of the normal ozone value is depleted at its centre. Picture: Clker-Free-Vector-Images/Pixabay
Canadian chemical physicist, Qing-Bin Lu, recently discovered a new hole in the Earth’s ozone layer over the tropics. It is, according to Lu, seven times larger than the hole over Antarctica, though they are similar in depth.
Roughly 80% of the normal ozone value is depleted at its centre. The term “hole” refers to a thinning of the ozone layer past a certain threshold and not an actual hole.
The discovery came as something of a surprise to Lu. “We never thought there was any possibility to see a hole over the tropics,” Lu told the Courthouse News Service.
Located in Earth’s stratosphere, the ozone layer is a shield of chemicals consisting of a high concentration of ozone that encircles the Earth. This layer of ozone chemicals absorbs most of the sun’s harmful ultraviolet radiation. Without the ozone layer, that radiation would damage DNA in plants and animals and cause severe skin cancer.
It was only in the early 1980s that experts realised that the ozone layer over the South Pole was thinning each spring, and it became the great environmental issue of the 80s.
Soon after the discovery, the Montreal Protocol was established as an international treaty to phase out the production of ozone-depleting chemicals like chlorofluorocarbons and hydrochlorofluorocarbons (CFCs and HCFCs) which were widely used in refrigeration and aerosols.
We’ve seen mixed news since then, with a 2018 report by the United Nations revealing that the ozone layer was on track to be fully healed by 2060, and scientists from the European Union’s Copernicus Atmosphere Monitoring Service saying the hole over Antarctica was larger just two years later.
Now there appears to be another, even more, sprawling area of ozone layer depletion over the tropics, which covers roughly half the Earth’s surface area, and where about half the world’s population lives.
The US Environmental Protection Agency explained that ,“a hole in the ozone layer can increase the risk of skin cancer and cataracts in humans, as well as weaken human immune systems, decrease agricultural productivity, and negatively affect sensitive aquatic organisms and ecosystems. "
Mainstream theories and models of ozone layer depletion expect the ozone layer to be getting stronger, based on the reduction of CFCs and HCFCs. But an alternate theory, proposed by Lu and a few colleagues two decades ago, stated that ozone depletion is caused not just by man-made chemicals but also by cosmic rays from space, which would help explain why the hole over Antarctica has grown in the last few years.
“CFCs are undoubtedly the main ozone-depleting gases, but cosmic rays play a major triggering role in causing both polar and tropical ozone holes,” said Lu in an email to Courthouse News.
This begs the question, how did we not pick this up sooner?
“It sounds unbelievable that the large tropical ozone hole was not noticed previously,” said Lu.
“But there exists some intrinsic challenges in making this discovery.”
Lu explained that this hole, over the tropics, is very different from the holes over the ice caps in that it is the same all year round while the others fluctuate in size. Secondly, the tropical hole wouldn’t have qualified as a hole under the old definition of a hole, which was defined as having ozone levels below a certain threshold.
Lu’s study redefines a hole as an area with ozone loss greater than 25%. Lu believes that the holes in the ozone layer, which correspond with “temperature holes” observed in the stratosphere is somehow correlated with global climate change.
“The hole in the ozone layer will affect climate change in the stratosphere and on the ground because ozone itself is an effective greenhouse gas,” Lu said. “The ozone hole can reduce global warming to some degree.”
But, he added, further research on the topic is needed.
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