Declining atmospheric CO2 during the late Middle Eocene climate transition

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ID: 293602
2011
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Abstract
The transition from the extreme greenhouse of the early Paleogene (∼52 Ma) to the present-day icehouse is the most prominent change in Earth's Cenozoic climate history. During the late Middle Eocene climate transition (42-38 Ma), which preceded the onset of long-lived, continental-scale ice sheets, there is concordant evidence for brief pulses (\<1 m.y. in length) of global warmth and ice sheet growth but few constraints on atmospheric CO~2~. Here we estimate the concentration of atmospheric CO~2~ during this critical interval using stomatal indices of fossil *Metasequoia* needles from ten levels in an exceptionally well-preserved core from the Giraffe kimberlite locality in northwestern Canada. Reconstructed CO~2~ concentrations are mainly between 700 to 1000 ppm, but include a secular decline to 450 ppm towards the top of the investigated section. Because the CO~2~ threshold for nucleating continental ice sheets at this time was ∼500 to 750 ppm, the CO~2~ decline is compatible with a rapid (\<10^4^ yrs) transition from warm, largely ice-free conditions to cooler climates with ice sheets. These fossils provide direct evidence that high-latitude deciduous forests thrived in the geological past under CO~2~ concentrations that will likely be reached within the 21^st^ century (500-1000 ppm).
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Authors Gabriela Doria, Dana L. Royer, A. P. Wolfe, A. M. Fox, John A. Westgate, David J. Beerling
Journal american journal of science
Year 2011
DOI
10.2475/01.2011.03
URL
https://ajs.scholasticahq.com/article/60880.pdf
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