IIT Kharagpur Study Finds Tropical Rainforests Will Survive Global Warming

IIT Kharagpur-led study suggests tropical rainforests could endure global warming. The research, published in Elsevier, analysed rainforest records from sediments in Gujarat's Vastan coal mines, dating back 56 million years. Check details

A team of scientists from IIT Kharagpur, Calcutta University, and the University of Western Ontario has analyzed detailed records of tropical rainforests (TRFs) preserved in sediments from the Vastan coal mines in Gujarat, which date back around 56 million years. During this time, India was a tropical island, surrounded by oceans, with the Himalayas yet to form. This period, known as the Palaeocene-Eocene Thermal Maximum (PETM), was marked by a dramatic rise in global carbon dioxide levels to over 1000 ppmv—an abnormally high concentration that future global warming may approach.

The PETM represents the most rapid global warming event in Earth's history, during which an amount of carbon equivalent to the entire modern fossil fuel reservoir was released into the ocean-atmosphere system, largely due to the release of carbon stored in sea-floor sediments. The coal layers in Vastan offer a stunningly well-preserved fossil record of a tropical rainforest, rich in plant material, pollen, and remains of a variety of mammals and insects that once thrived in these forests. In fact, it was during this climate shift at the PETM that the world's earliest mammals evolved.

Prof. Anindya Sarkar, the lead researcher of IIT Kharagpur said,“The study took several years of field and laboratory investigation. We had to date the sediments to confirm its PETM age and collected samples at centimeter intervals, analyzed the pollens to understand how the TRF community evolved in response to such extreme global warming. To understand how the climate changed during this super-greenhouse globe we analyzed isotopes of carbon in the plant organic matter and developed special techniques of measuring isotopes of oxygen and hydrogen in micron size clay mineral kaolinite that precipitated in these lagoonal water. The climate was also monitored by analyzing oxygen isotopes in fossil teeth of small horse-like ungulate mammals those once roamed in these forests.”

“Pollens are widely dispersed by air and water, resistant to decay and are invaluable indicators for reconstructing ancient biomes. Evidence of huge diversity (70 families and 256 taxa) of dense tropical rainforest trees like Sal, Mahogany, Palm, a variety of evergreen and mangrove plants are preserved in the sediment and coal beds of Vastan. No wonder that such rain forest harbored diverse animals including ancestors of early horses, snakes and insects,” said Prof. Subir K Bera of Calcutta University.

Arpita Samanta, a former PhD student at IIT Kharagpur, Assistant Professor at Asutosh College, Calcutta said, “We found a large anomaly in carbon isotopes exactly at 56 million years. This was such a characteristic signal for a super greenhouse globe with very high atmospheric CO2. The hydrogen and oxygen isotope compositions in clays depend on land temperature and amount of rainfall and act as snapshots of past climate. Likewise, the isotopes in fossil teeth record the history of what water animals drank. As the CO2 began to increase, the land became abnormally hot >40oC. But to our surprise, we found that the temperature came down to ~30oC during the later period, almost similar to today. The rainforest not only survived but also diversified during and after this global warming phase.”

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