Editor’s Note: Since publishing this article, it has since come to the attention of IFLScience that many within the stratospheric ozone research community disagree with the study’s conclusions. Expert comments, some of which were published by the Science Media Centre, express that there “is no ‘tropical ozone hole’” and that long-term changes in stratospheric ozone such as that noted in the study are well documented in the Scientific Assessment of Ozone Depletion.

A new ozone hole has been detected over Earth’s tropical regions, and it stays open year-round, which the researchers behind the findings say represents "a great global concern". Having slipped past climate scientists’ models, which are usually able to predict such phenomena, the hole is thought to have been open since the 1980s.

The tropics ozone hole was found using a combination of observational data alongside cosmic-ray-driven electron reaction models, together finding physical mechanisms above the tropics that mirror the conditions at the polar ozone hole over Antarctica.

Ozone holes are defined as an area where loss of O₃ (trioxygen, an inorganic molecule) is at least 25 percent greater than that seen in the surrounding atmosphere. They represent a threat to human health because they increase ultraviolet radiation levels at Earth’s surface, exposure to which can increase the risk of developing skin cancer among other health conditions.

This latest ozone hole, reported in the journal AIP Advances, is said to be seven times the size of the Antarctic ozone hole. Situated above the tropics, it subsequently puts a large volume of the global population at increased risk of developing disease.

"The tropics constitute half the planet's surface area and are home to about half the world's population," said University of Waterloo scientist and author on the paper Qing-Bin Lu in a statement. "The existence of the tropical ozone hole may cause a great global concern.”

Since the mid-1970s, scientists have been aware of human-made industrial chemicals' role in depleting the ozone layer. As such, chemicals like chlorofluorocarbons (CFCs, the primary culprit) were banned. Unfortunately, their effects on the ozone layer appear to have endured.

The hole over the tropics differs from the one over Antarctica not just in its enormous size, but also in its seasonal endurance. The Antarctic ozone hole has a seasonal cycle, losing the most O₃ in September and October, but this later replenishes before the cycle begins again.

By contrast, the tropics ozone hole endures throughout the seasons, meaning those beneath it face the risk of exposure to greater levels of UV radiation year-round.

"The depletion of the ozone layer can lead to increased ground-level UV radiation, which 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.

"The present discovery calls for further careful studies of ozone depletion, UV radiation change, increased cancer risks, and other negative effects on health and ecosystems in the tropical regions.”