A comprehensive study recently published in the journal Science reveals that Earth’s current carbon dioxide (CO2) levels, driven by human activity, match those last seen 14 to 16 million years ago, a significant shift from the previously estimated 3 to 5 million years.
This research, encompassing 66 million years of Earth’s history, utilized biological and geochemical data to reconstruct the historic CO2 record with unprecedented precision.
During the last period of similar CO2 levels (420 parts per million), Earth experienced drastic environmental differences: Greenland was devoid of ice, and early human ancestors were transitioning from forests to grasslands. The study highlights that the pre-industrial atmospheric CO2 concentration was around 280 ppm, indicating a 50% increase due to human activities, leading to an average global temperature rise of 1.2 degrees Celsius.
The research, conducted by a consortium of 80 scientists from 16 countries over seven years, didn’t involve new data collection. Instead, it re-evaluated and synthesized existing studies, categorizing them by confidence level. The study emphasizes the use of ‘proxies’ (like ancient leaves, minerals, and plankton) for estimating past atmospheric compositions, as ice cores only provide data for the last few hundred thousand years.
The findings confirm that the Earth’s hottest period in the last 66 million years occurred 50 million years ago, with CO2 levels spiking to 1,600 ppm and temperatures being 12C higher. Following this, a long cooling period led to the ice ages, starting around 2.5 million years ago. Modern humans evolved during a period of relatively stable CO2 levels (270-280 ppm) until the onset of large-scale fossil fuel burning.
The study predicts that a doubling of CO2 could lead to a 5-8 degrees Celsius temperature increase over hundreds of thousands of years, creating feedback loops such as reduced solar radiation reflection due to melting polar ice caps.
The paper’s lead author, Baerbel Hoenisch, emphasizes the long-term nature of the current climate challenge. She draws parallels to a rapid carbon release event 56 million years ago that drastically altered ecosystems and took 150,000 years to normalize. The study underlines the urgency of carbon sequestration and emission reduction to mitigate these long-term climate impacts.
https://www.sciencealert.com/scientists-warn-the-atmosphere-hasnt-been-like-this-in-14-million-years