(CN) — As if we needed any more bad news this week: A new hole in the ozone layer has been discovered by Canadian chemical physicist Qing-Bin Lu. Unlike the other two, over the North and South poles, this one is over the tropical regions and can be seen year-round. It is, according to Lu, seven times larger than the better-known hole over Antarctica, though they are similar in depth.
And like that other hole, roughly 80% of the normal ozone value is depleted at the center of the hole (the term "hole" refers to a thinning of the ozone layer past a certain threshold, and not an actual hole).
The discovery comes as something of a surprise.
"We never thought there was any possibility to see a hole over the tropics," said Lu.
Located in Earth's stratosphere, the ozone layer is a shield of chemicals (containing a high concentration of ozone) that encircle the Earth that absorbs most of the Sun's ultraviolet radiation. Without the ozone layer, that radiation would damage DNA in plants and animals and cause rampant skin cancer.
In the early 1980s, scientists began to realize that the ozone layer was thinning over the South Pole each spring. The hole in the ozone layer became the great environmental cause of the 1980s — mentioned in songs by Neil Young, Lou Reed, Elton John and Public Enemy — and led to the Montreal Protocol, an international treaty which phased out the production of ozone-depleting chemicals like chlorofluorocarbons and hydrochlorofluorocarbons (CFCs and HCFCs).
Since then, the news for the ozone layer has been mixed. A 2018 report by the United Nations, for example, revealed that the ozone layer was on track to be fully healed by 2060. But last year, scientists with the European Union’s Copernicus Atmosphere Monitoring Service said the hole over Antarctica was larger than usual.
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. A hole in the ozone layer "can increase 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," said Lu in a follow-up email.
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, states that ozone depletion is caused not just by those manmade 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 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.
So how did we miss this third ozone layer hole?
"It sounds unbelievable that the large tropical ozone hole was not noticed previously," Lu wrote in the email. "But there exists some intrinsic challenges in making this discovery."
First of all, the tropical ozone layer hole is very different than the other two holes, in that it is the same year-round, which makes it harder to detect. 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, are somehow correlated with global climate change.
"The hole in the ozone layer will affect climate changes 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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