Study by IIT Kharagpur scientists debunks claims of ozone hole in the tropics

New Delhi: A study led by Professor 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 debunked previous assertions of a severe ozone hole in the tropical stratosphere. The study concludes that there is no significant ozone depletion in the tropics and, consequently, no associated health threat.

Published under the title “No Severe Ozone Depletion in the Tropical Stratosphere in Recent Decades,” the study challenges earlier assertions of a year-round massive ozone hole in the tropics, which could potentially impact the health of about half of the world’s population residing in tropical regions.

Stratospheric ozone is a crucial component of the atmosphere, and significant changes in its concentrations can have serious environmental, ecological, and health consequences.

The researchers analyzed ground-based, ozonesonde, and satellite ozone measurements to examine ozone depletion and trends in the tropics over the past five decades (1980–2022). The findings revealed 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, which is used to define an ozone hole.

The study identified flaws in the previous research that reported an ozone hole, noting that the earlier study relied on inadequate data primarily from the surface to an altitude of 11 km.This limited data was insufficient to accurately assess ozone levels at the vital altitude of 15–20 km, leading to erroneous conclusions. The IIT-Kharagpur study identified high uncertainty and gaps in the dataset used by the previous researcher.

The study also found that any observed decrease in tropical ozone levels is due to atmospheric dynamics rather than chemical depletion. Contrary to earlier claims, the researchers observed either a small increase or no significant trend in ozone levels in the tropical lower stratosphere. Furthermore, the study confirmed that based on current atmospheric halogen levels, there is no immediate risk of an ozone hole forming outside the Polar Regions, and thus, no associated health threat to the tropical population. 

“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,” said Prof. Jayanarayanan Kuttippurath, lead author of the study. “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. 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.”

Research scholar and author of the study GS Gopikrishnan, CORAL, IIT Kharagpur stated, “The study that claimed a tropical ozone hole used data from surface to 11 km altitude, which are insufficient to assess ozone distribution at 15–20 km, the core ozone region in the atmosphere. Also, the dataset used in that study has high uncertainty and large gaps, which make it unfit to claim any scientific findings. On the other hand, we have used all the available datasets in the tropical region and found that there is no severe ozone depletion.”

“Ozone holes are confined to Antarctica due to unique conditions such as extremely cold temperatures, strong polar vortex and presence of polar stratospheric clouds for 4-5 months, and this particular state of the atmosphere is absent in the tropics. Ozone dynamics in the tropics are primarily influenced by atmospheric circulation patterns. Thus, the study that claimed a tropical ozone hole is based on a flawed theoretical framework and inadequate measurements,” added Prof. Kuttippurath.

Collaborators Rolf Müller, Sophie Godin-Beekmann, and Jerome Brioude from Germany and France concurred with the study’s findings, which align with the current scientific consensus on ozone dynamics and atmospheric conditions.