Is there an ozone hole over the tropics? Canadian study sparks debate among scientists

An Ontario researcher says he has discovered a new ozone hole that is seven times larger than the Antarctic ozone hole, a claim other atmospheric scientists are challenging.

Qing-Bin Lu, professor of chemical physics at the University of Waterloo, writes in a peer-reviewed article published in AIP Advances last Tuesday that since the 1980s there has been a year-round ozone hole in the tropics, affecting 50 percent of the earth’s surface. Lu says that in the center of this tropical ozone hole, about 80 percent of the ozone has been depleted.

“The tropics make up half of the planet’s surface and are home to about half of the world’s population,” Lu said in a press release last tuesday. “The existence of the tropical ozone hole may cause great global concern.”

Earth’s ozone layer is located in the stratosphere and helps absorb ultraviolet (UV) radiation from the sun. Too much exposure to ultraviolet radiation can increase the risk of skin cancer and eye damage in humans. UV exposure can also reduce photosynthesis, which can inhibit plant growth and negatively impact marine ecosystems.

In the late 1970s, researchers began to notice that the ozone layer around the polar regions had thinned due to industrial use of ozone-depleting substances such as hydrochlorofluorocarbons. When the Montreal Protocol was signed in 1987, 197 countries around the world agreed to phase out these substances, leading to slowing rates of ozone depletion.

The thickness of ozone is measured in Dobson units (DU). NASA defines an ozone hole or thinning ozone layer as less than 220 DU, since no measurements of less than 220 DU were found before 1979.

But Lu’s study uses a different metric, defining an ozone hole as a 25 percent reduction in ozone thickness. He argues that NASA’s 220 UD definition of an ozone hole is inadequate in the tropics, since ozone in the tropics would still be above 220 UD even with a 56 percent reduction in thickness.

However, several atmospheric researchers came out with a statement published in Science Media Centerquestioning the existence of a tropical ozone hole.

“I am surprised that this study has been published in its current form. The results of this work will be very controversial and I am not convinced that they are correct,” said Martyn Chipperfield, professor of atmospheric chemistry at the University of Leeds.

“The claim in this research of such large changes in ozone in the tropics has not been evident in other studies, which makes me very suspicious. Science should never depend on a single study and this new work needs careful verification before proceeding.” that can be accepted as fact.” he added.

Lancaster University atmospheric scientist Paul Young, who was the lead author of the UN’s 2022 Scientific Assessment of Ozone Depletion, says ozone depletion in the tropics does not constitute a “hole”.

“There is no ‘tropical ozone hole,’ driven by cosmic ray proponent’s proposed electrons or otherwise,” Young said in the statement. “The author’s identification of a ‘tropical ozone hole’ is because he looks at percentage changes in ozone, rather than absolute changes, the latter being much more relevant to harmful UV rays reaching the surface.”

Marta Abalos Alvarez, an Earth and Astrophysics researcher at the Complutense University of Madrid, said that the article “lacks the necessary scientific rigor to be a reliable contribution.”

“It contains many seriously flawed arguments and unsubstantiated claims, contradicting earlier, unsubstantiated results. Ozone depletion in the tropics is nothing new and is primarily due to the acceleration of the Brewer-Dobson circulation,” he said in the release.

The Brewer-Dobson circulation refers to the process in which ozone and water vapor circulate from the tropics toward the poles, a phenomenon that climate researchers say has accelerated due to the effects of climate change.

However, in an email to on Wednesday, Lu responded to these criticisms, calling them “baseless.”

“The fact of the matter is that in my article… I not only showed ozone changes in absolute values… but compared my observed results with those reported by others in the literature, all of which were obtained from multiple data sources “, said.

“None of the criticisms…could stand out from a close examination of the scientific literature.”

Addressing Abalos Alvarez’s comments, Lu said the expected changes in ozone thickness due to the Brewer-Dobson circulation are “approximately 10 times smaller than the large ozone losses observed in the 1980s and 1990s.”

Citing NASA measurements, Lu noted that the annual average value of total ozone over the tropics is around 263 DU over the past decade. By comparison, the average in Antarctica has been 275 DU while the world average is 288 DU.

“It should also be noted that even (although) ‘no tropical ozone hole has been observed’ under the above definition in previous studies, this does not mean that there has not been a large loss of ozone in the lower stratosphere in the tropics. “. Lu said.

“My discovery therefore requires further careful study of ozone depletion, UV radiation shift, increased cancer risks, and other negative effects on health and ecosystems in tropical regions,” he added.

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