Tuesday, August 3, 2021

A fall in CO2 cooled the Earth’s climate 34 million years ago

Decreasing atmospheric CO2 concentration played an important role in the shift of Earth's climate from a warm greenhouse world to a cold world about 34 million years ago.

Between 40 and 34 million years ago, the Earth's climate underwent a major climatic transition. Prior to 40 million years ago, during the Eocene, Antarctica was covered with lush forests, but by 34 million years ago, in the Oligocene, these forests had been replaced by thick continental ice sheets, as we know Antarctica today.

The root cause of this transition is widely debated, and little information is available on how the climate changed on land. An international team led by Dr. Vittoria Lauretano and Dr. David Naafs of the University of Bristol used molecular fossils preserved in ancient coals to reconstruct land temperature throughout this transition.

 The team, which publishes results in Nature Geoscience, used a new approach based on the distribution of bacterial lipids preserved in ancient wetland deposits. It was developed under the ERC-funded project The Greenhouse Earth System (TGRES), which also funded this study.

TGRES principal investigator and co-author of the paper, Rich Pancost, from the University's School of Chemistry, explains that "these compounds originally made up the cell membranes of bacteria living in ancient wetlands, and their structures changed slightly to help the bacteria adapt to changes in temperature and acidity. These compounds can be preserved for tens of millions of years, allowing us to reconstruct those ancient environmental conditions," he says.

To reconstruct the temperature changes in the greenhouse-to-greenhouse transition, the team applied their new approach to the coal deposits of the Gippsland Basin in southeastern Australia. These extraordinary deposits span more than 10 million years of Earth history and have been extensively characterized by University of Melbourne study collaborators Dr. Vera Korasidis and Professor Malcolm Wallace.

 The new data show that land temperatures cooled alongside ocean temperatures and by a similar magnitude, by about 3°C. To explore the causes of this temperature decline, the team performed simulations with climate models. Most importantly, only simulations that included a decrease in atmospheric CO2 could reproduce a cooling consistent with the temperature data reconstructed from the carbons.

 These results provide further evidence that atmospheric CO2 plays a crucial role in driving the Earth's climate, including the formation of the Antarctic ice sheet.


Europa press 

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