A team of scientists from IIT Kharagpur, Calcutta University, and the University of Western Ontario has unlocked remarkable findings about ancient rainforests preserved in coal deposits in Gujarat’s Vastan coal mines.

Their research sheds new light on how tropical rainforests survived an intense period of warming and high carbon dioxide levels 56 million years ago, during a time known as the Paleocene-Eocene Thermal Maximum (PETM). Their findings, recently published in the Global and Planetary Change, reveal critical information about how today’s rainforests might withstand climate change, potentially offering hope amidst the global warming crisis.

During the PETM, the Earth experienced a sudden surge in atmospheric carbon dioxide, reaching levels above 1000 ppm—higher than what is currently predicted for Earth’s near future. This period saw temperatures soar above 40˚C, leading scientists to consider it the most rapid global warming event in Earth’s history. It offers an analogue for the climate stressors that today’s ecosystems, particularly tropical rainforests, may face.

Led by Professor Anindya Sarkar of IIT Kharagpur, the team analysed fossilized pollen, plant remains, and small mammal teeth from the Vastan coal mines, once home to dense, thriving tropical rainforests with a diversity of plant and animal life. These preserved records reveal insights into how the rainforest adapted to and endured extreme heat and elevated carbon levels.

The scientists found evidence of an astonishing diversity of plant life—70 families and 256 taxa, including trees like Sal, Mahogany, Palm, and various mangroves—all thriving in the PETM rainforest. These forests supported not only plants but also ancient animals, such as early horses, snakes, and a variety of insects. By studying pollen, which is resilient to decay and can provide insights into past climates, the researchers discovered that despite extreme temperatures, these forests adapted and even diversified.

A surprising discovery emerged from the study of carbon, hydrogen, and oxygen isotopes in both plant matter and small mammal teeth. Although early PETM temperatures exceeded 40˚C, the rainforest’s survival may have been due to an unusual cooling effect. Rainfall intensified alongside warming, creating a “rainfall-buffered” effect that brought temperatures down to around 30˚C, comparable to today’s tropical temperatures. This cooling, linked to increased precipitation, may have helped the forest survive under intense climate stress, according to Dr. Melinda K Bera, a co-author and isotope expert.

The study offers a valuable perspective on modern tropical rainforests, such as the Amazon, which currently store about one-third of Earth’s carbon and play a critical role in regulating the global climate. While some scientists fear these forests may collapse due to rising temperatures, the findings from Vastan suggest that intensified rainfall could mitigate some of the warming effects, allowing rainforests to persist.

However, while the PETM study offers some hope, climate experts caution that today’s warming is occurring at an unprecedented rate due to human activity. With atmospheric CO2 levels now at around 421 ppm, a future doubling could intensify rainfall patterns, potentially stabilizing rainforests as it did in ancient times.

“The Vastan record shows that these rainforests may have a higher resilience than we thought,” said Professor Sarkar, adding, “nature has experimented in the past, and there are lessons for us to learn.”