The study found that carbon dioxide may have been less than 1000 parts per million, or ppm, during the Earth’s early Eocene period. This runs counter to thinking that concentration levels were as high as 2000 ppm in the same time frame.
Climate researchers focus on the early Eocene, a so-called “super greenhouse” period, to better understand how the Earth historically responds to changes in carbon dioxide levels, and to help make better climate projections. Both the Arctic and Antarctic were ice-free in this time period as temperatures averaged about 10 degrees Celsius warmer than present day.
The Dartmouth research result was derived by assessing past carbon dioxide concentrations using sediment samples found in terrestrial and deep-sea drilling sites. The ratio of carbon-12 to carbon-13 isotopes in those samples helped the team determine that the most likely source of the carbon came from thawing permafrost during the period studied.
Date: October 12, 2017
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Coordinator: EnvGuide Team
Source: https://www.sciencedaily.com/releases/2017/10/171012103737.htm