KOLKATA: A study led by a senior professor of IIT-Kharagpur, in collaboration with international researchers, has dismissed previous claims of a ‘severe ozone hole’ in the tropical stratosphere after analysing data of 42 years. The study, titled ‘No Severe Ozone Depletion in the Tropical Stratosphere in Recent Decades,’ reassures that there is no significant ozone depletion in the tropics and no associated health threat, a statement from IIT Kharagpur said.
Led by Jayanarayanan Kuttippurath from the Centre for Ocean, River, Atmosphere, and Land Sciences (CORAL) at IIT Kharagpur, his team analysed ground-based ozonesonde (instrument to measure ozone levels) and satellite ozone measurements to examine the depletion in the tropics during the past five decades (1980–2022). Their findings contradict earlier research that suggested a potential ozone hole could impact the health of about half of the world’s tropical population.
“The previous research suggested that such an ozone hole could potentially impact the health of about half of the world’s population residing in tropical regions. But there was no observational evidence,” the statement said. The researchers found that the amount of column ozone in the tropics is relatively small compared to high and mid-latitudes.
There is no observational evidence supporting severe stratospheric ozone depletion in the tropics. The study indicates that current understanding and data do not support the possibility of an ozone hole forming outside Antarctica. 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 study utilised extensive ground-based, satellite, and re-analysis data, showing no robust evidence for a significant ozone hole in the tropics. Average ozone levels in these regions remain well above the critical threshold used to define an ozone hole, the statement said. “The amount of column ozone in the tropics is relatively small compared to high and mid-latitudes. In addition, the tropical total ozone trend is very small as estimated for the period 1998-2022. No observational evidence is found regarding the indications of severe stratospheric ozone depletion in the tropics”, the statement added.
“Also, the current understanding and observational evidence do not provide any support for the possibility of an ozone hole occurring outside Antarctica these days,” it said. According to the statement, earlier studies that reported an ozone hole relied on inadequate data, primarily from the surface to 11 km altitude, which is insufficient to accurately assess ozone levels at the critical 15–20 km altitude.
The IIT-led research attributed any observed decrease in tropical ozone levels to atmospheric dynamics rather than chemical depletion. “In contrast to a previous claim, our study finds that there is no ozone hole in the tropics and therefore, no health threat associated with that. Also, it is very unlikely to have an ozone hole in the tropics with respect to the current halogen levels. The average ozone values are always about 260 DU in the tropics, which is well above the ozone hole criterion of 220 DU,” Kuttippurath said.
He further noted that any slight decrease observed in tropical ozone levels in recent decades is due to changes in atmospheric dynamics rather than chemical processes. Ozone holes, as known, are confined to Antarctica due to unique conditions such as extreme cold temperatures, he said.
