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Low atmospheric CO2 levels before the rise of forested ecosystems

Dahl, Tais W.; Harding, Magnus A. R.; Brugger, Julia; Feulner, Georg; Norrman, Kion; Lomax, Barry H.; Junium, Christopher K.


Tais W. Dahl

Magnus A. R. Harding

Julia Brugger

Georg Feulner

Kion Norrman

Barry H. Lomax

Christopher K. Junium


The emergence of forests on Earth (~385 million years ago, Ma)1 has been linked to an order-of-magnitude decline in atmospheric CO2 levels and global climatic cooling by altering continental weathering processes, but observational constraints on atmospheric CO2 before the rise of forests carry large, often unbound, uncertainties. Here, we calibrate a mechanistic model for gas exchange in modern lycophytes and constrain atmospheric CO2 levels 410–380 Ma from related fossilized plants with bound uncertainties of approximately ±100 ppm (1 sd). We find that the atmosphere contained ~525–715 ppm CO2 before continents were afforested, and that Earth was partially glaciated according to a palaeoclimate model. A process-driven biogeochemical model (COPSE) shows the appearance of trees with deep roots did not dramatically enhance atmospheric CO2 removal. Rather, shallow-rooted vascular ecosystems could have simultaneously caused abrupt atmospheric oxygenation and climatic cooling long before the rise of forests, although earlier CO2 levels are still unknown.


Dahl, T. W., Harding, M. A. R., Brugger, J., Feulner, G., Norrman, K., Lomax, B. H., & Junium, C. K. (2022). Low atmospheric CO2 levels before the rise of forested ecosystems. Nature Communications, 13(1), Article 7616.

Journal Article Type Article
Acceptance Date Nov 18, 2022
Online Publication Date Dec 20, 2022
Publication Date Dec 20, 2022
Deposit Date Dec 23, 2022
Publicly Available Date Jan 4, 2023
Journal Nature Communications
Electronic ISSN 2041-1723
Publisher Springer Science and Business Media LLC
Peer Reviewed Peer Reviewed
Volume 13
Issue 1
Article Number 7616
Keywords General Physics and Astronomy; General Biochemistry, Genetics and Molecular Biology; General Chemistry; Multidisciplinary
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