The clamour about the warming planet and the changing climate is growing louder by the day as we worry about the implications of greenhouse gases on the earth. But, did you know that our planet has seen many such ‘greenhouse periods’ in the past where the concentrations of greenhouse gases were significantly higher, resulting in higher temperatures? Yes, you read that right, and one such period was about 56 to 34 million years ago, called the Eocene epoch.
While we know that high concentration of greenhouse gases resulted in a substantial increase in the temperature, there is little knowledge about the exact climatic conditions during this period. Now, a collaborative study by researchers from the Indian Institute of Technology Bombay, Yale University, University of Florida, Natural History Museum, London, KU Leuven, Cardiff University and the Hebrew University has provided reliable answers to these questions. The researchers believe that the findings of the study may help understand our present climate too.
The Eocene epoch is estimated to have seen a concentration of atmospheric carbon dioxide (CO2) of more than 560 ppm; twice as much as the pre-industrial concentration of 280 ppm, and higher than today’s level of 410 ppm. The high concentration of CO2 led to significant increase in the land and sea temperatures. The findings of this study, published in the Proceedings of the National Academy of Sciences (PNAS), help scientists in understanding and improving present climate models, and the relationship between ocean temperatures and seawater chemistry.
Since 1880, the average temperature of our planet has risen by 0.9°C. While the temperatures in the tropics have modestly increased, the maximum increase has been at the poles. This phenomenon, called the polar amplification, has been observed in the past and is seen in the present too. Polar amplification could lead to melting of glaciers at a higher speed, resulting in a significant rise in the sea-level and increase in the frequency of extreme weather events.
Previous studies trying to understand past climatic changes have faced challenges in precisely determining the past climatic conditions due to poor preservation of samples, impacts of salinity, calibration complications and the seasonal variations. Hence, there was no scientific consensus about how warmer the polar regions were when compared to the tropics. In this study, the researchers have reconstructed the sea surface temperature that prevailed during the Eocene to understand the extent of polar amplification by addressing the drawbacks in the past methods.
The researchers have used fossil samples from the Eocene period collected from seven sites across the world and have assessed them using isotopic analysis. These samples were well-preserved and the method chosen was immune to the impacts of salinity, making the results reliable.
The findings of the study state that the mean tropical sea surface temperature during the Eocene was about 32.5 ± 2.5 °C. The mean difference in the temperature between tropics and the polar regions was at least 32 ± 10% compared to the present day—a greater polar amplification than what we have been assuming till date. The results also provide a direction towards understanding the potential mechanisms for polar amplification.
The study shows how our understanding of past climatic conditions has downplayed the extent of polar amplification—a phenomenon that needs further understanding. While responding to climatic changes that are complex and dynamic is always challenging, such accurate assessments can help us face the future with greater confidence.