A team of scientists from IIT Kharagpur and Academia Sinica, Taipei has indeed found evidence of very high annual rainfall during the catastrophic volcanism that formed the Deccan Traps in India about 66 million years back. They used a new technique — Nanoscale Secondary Ion Mass Spectrometry — to analyse three isotopes of oxygen (Oxygen-16,17, and 18) in fossil trees of the Cretaceous period and measure the isotopic composition of the lake water derived from rainfall.
The depleted values of the oxygen isotopes suggest a higher tropical rainfall (1,600 mm per year) in India during the terminal Cretaceous period. The increase in rainfall and its waning in the early Palaeocene closely follows change in palaeo-atmospheric (paleo carbon dioxide) suggesting a possible underlying link. Results were published in the Journal of Chemical Geology.
“The available records of the atmospheric carbon dioxide concentration and temperature over both land and ocean during the time of Deccan Trap eruption were analysed. Deccan trap lavas were erupting spewing huge amount of carbon dioxide thus increasing the then atmospheric carbon dioxide concentration to as high as 1,000 ppm (parts per million),” Prof. Anindya Sarkar from the Department of Geology and Geophysics at IIT Kharagpur and corresponding author of the paper said in a release.
“Excepting the arid/semi‐arid regions, the modern annual rainfall over large parts of peninsular India on an average is about 1,000‐1,200 mm. Our data suggested that these fossil trees recorded 1,800‐1,900 mm rainfall per year . This is exactly what the IPCC predicts in case of a future extreme 4 degree C warming of the planet,” said Prof. Sourendra Bhattacharya, a co‐author of the paper.
Fossil fuel emission has increased carbon dioxide from a pre‐industrial level of 280 ppm to about 420 ppm in 2023. Climate models suggest that a doubling of carbon dioxide will intensify the atmospheric circulation and consequently the rainfall. The 2023 AR6 report by the Intergovernmental Panel on Climate Change (IPCC) warns if the carbon dioxide emission and global warming continue unabated, annual wettest day precipitation will increase by manifold across all continents. Monsoon rainfall associated with tropical cyclones over India will also increase by 40%. While these predictions are made through climate models, they can only be tested by studying the rainfall record in the past when the earth went through a natural warming phase due to high carbon dioxide emission.
