IIT Kharagpur-led study debunks claims of tropical ozone hole

Pleasant news is in the air for everyone. In what comes as a reason to cheer is that apprehensions over serious health threats caused by air following significant ozone depletion are almost passé. A ground-breaking study, led by Prof. Jayanarayanan Kuttippurath from the Centre for Ocean, River, Atmosphere and Land Sciences (CORAL) at the Indian Institute of Technology Kharagpur (IIT-Kharagpur), in collaboration with international researchers, has refuted previous claims of a severe ozone hole in the tropical stratosphere and reassured that there is no such possibility and there definitely are no threats to people’s health. For years, it has been believed that ozone depletion can cause a number of health problems, including skin cancer, and increase ultraviolet (UV) radiation levels that could reach the Earth. These were considered as factors leading to skin cancer, cataracts, and impaired immune systems. Too much exposure to UV is believed to be contributing to the increase in melanoma, the most fatal of all skin cancers. Previous scientific research suggested that such an ozone hole could potentially impact the health of about half of the world’s population residing in tropical regions and mentioned that increased levels of ultraviolet B (UVB) radiation from ozone depletion can cause non-melanoma and malignant melanoma skin cancers. Melanoma is the most deadly type of skin cancer, which is killing nearly 7,000 persons in the US, each year.

The latest breakthrough study challenges earlier assertions of a year-round massive ozone hole in the tropics. The study utilized an extensive array of ground-based, satellite and reanalysis data, revealing that there is no robust observational evidence for a significant ozone hole in the tropics. Average ozone levels in these regions remain well above the critical threshold of 220 Dobson Units used to define the ozone hole. The IIT KGP-led research demonstrates that any observed decrease in tropical ozone levels is due to atmospheric dynamics, not chemical depletion. Contrary to earlier claims, the study found either a small increase or no significant trend in ozone levels in the tropical lower stratosphere. Interestingly, stratospheric ozone is an important constituent of the atmosphere. Significant changes in its concentrations have great consequences for the environment, ecosystems and public health.

The researchers analysed ground-based, ozonesonde and satellite ozone measurements to examine the ozone depletion and the spatiotemporal trends in ozone in the tropics in the last five decades (1980–2022). The amount of column ozone in the tropics is relatively small compared to the high and mid-latitudes, elsewhere. Moreover, the tropical total ozone trend is very small as estimated for the period 1998–2022. No observational evidence is found regarding indications or signatures of severe stratospheric ozone depletion in the tropics in contrast to a recent claim. Also, the current understanding and observational evidence do not provide any support for the possibility of an ozone hole occurring outside Antarctica presently with respect to the present-day stratospheric halogen levels. The slight decrease observed in the tropical ozone in recent decades is due to the changes in atmospheric dynamics, not because of chemistry, and this has also been known to the scientific community for long. So one can heave a sigh of relief and breathe fresh air!