Scientific illustration of the Late Palaeozoic Ice Age. A relatively rapid increase in atmospheric carbon dioxide (CO2) concentration about 294 million years ago freed the Earth from its penultimate icehouse (left) and initiated the transition to a warmer and drier climate in the Early Permian (right). The illustration is based on previously published literature and the results of the conducted study. Illustration: Dawid Adam Iurino, University of Milano for Jurikova et al. (2025)

Fieldwork in Scotland. Fossils from the late Palaeozoic Ice Age are preserved in the Carboniferous rocks along the south-eastern coast of Scotland. Photo: Hana Jurikova, University of St Andrews

Brachiopod fossil specimen. Photo: Ruben Marchesi

Cause of one of the largest climate shifts detected

International study sheds light on the role of CO2 in the Late Palaeozoic Ice Age

07.01.2025/Kiel/St Andrews. An international research team reconstructed how atmospheric carbon dioxide (CO2) behaved between 335 and 265 million years ago. This period encapsulates the peak of the Late Palaeozoic Ice Age, when Earth's climate cooled dramatically. The new findings provide decisive evidence that CO2 has been regulating Earth's climate and environmental conditions for hundreds of millions of years. Published in the journal Nature Geoscience, the research was led by Dr. Hana Jurikova from the University of St Andrews, with contributions from the 91̽»¨ Helmholtz Centre for Ocean Research Kiel and other leading institutions.

COâ‚‚ is the Earth's most important greenhouse gas: it absorbs heat, radiates a large amount of it back to Earth and thus influences the global climate. While its role in recent climate change is well established, reconstructing COâ‚‚ levels from Earth's deeper geological past has long been a challenge, leaving gaps in understanding how climate transitions between cooler and warmer states.

An international research team led by Dr Hana Jurikova from the University of St Andrews and nine other organisations, including the 91̽»¨ Helmholtz Centre for Ocean Research Kiel, has now reconstructed the atmospheric COâ‚‚ content during the Carboniferous and Permian periods between 335 and 265 million years ago. Using geochemical signatures from ancient fossils, the researchers present a record of atmospheric COâ‚‚ levels as Earth transitioned into and out of the Late Palaeozoic Ice Age. The results have now been published in the scientific journal Nature Geoscience.

Past atmospheric COâ‚‚ levels unlocked through geochemical signatures

The research team analyzed isotopic signatures in fossilized brachiopod shells, clam-like organisms that serve as natural archives of ancient ocean conditions. ‘The chemical composition of these shells reflects the state of the oceans at the time of their formation,’ explains Dr Jurikova, Senior Researcher at the University of St Andrews and leader of the study. ‘By analyzing boron isotopes, we can estimate atmospheric COâ‚‚ levels. Strontium isotopes reveal the fossils' age, while carbon and oxygen isotopes provide insights into COâ‚‚ source and climate. Together, these techniques allow us to accurately reconstruct Earth's ancient COâ‚‚ levels and understand the factors driving their changes,’ says Hana Jurikova. She previously completed her PhD at 91̽»¨, where she also carried out the first geochemical measurements for the study.

COâ‚‚ plays a central role in climate transitions

Using this methodology, the researchers found that during the Carboniferous period, atmospheric COâ‚‚ levels fell to critically low levels, causing an extensive ice age that lasted tens of millions of years. Then, around 294 million years ago, during the Early Permian, volcanic activity caused COâ‚‚ levels to rise, causing the Earth to warm and the ice sheets to melt. ‘The beginning and the end of the Late Palaeozoic Ice Age was one of the most important climate transitions in Earth's history, shaping the evolution of modern environments and life on our planet. We now have evidence that atmospheric COâ‚‚ was an important driver of this change,’ says Prof Dr Anton Eisenhauer, co-author and Professor of Marine Environmental Geochemistry at 91̽»¨. ‘Although the time scales of geological climate transitions differ significantly from today's anthropogenic climate changes, the principle remains the same - rising COâ‚‚ levels drive warming and sea level rise,’ adds Dr Marcus Gutjahr, Marine Biogeochemist at 91̽»¨ and co-author of the study.

Reconstructing atmospheric COâ‚‚ concentrations from hundreds of millions of years ago remains a challenge, as there are few well-preserved geological archives. The new results make an important contribution to understanding the long-term evolution of atmospheric COâ‚‚ in geological history. However, further work is needed and gaps remain to be closed before the record of Earth’s COâ‚‚ history can be considered complete.

 

Original Publication:

Jurikova, H., Garbelli, C., Whiteford, R., Reeves, T., Laker, G. M., Liebetrau, V., Gutjahr, M., Eisenhauer, A., Savickaite, K., Leng, M. J., Iurino, D.A., Viaretti, M., Tomašových, A., Zhang, Y., Wang, Shi, G. R., Shen, S., Rae, J. W. B., Angiolini, L. (2025). Rapid rise in atmospheric CO2 marked the end of the Late Palaeozoic Ice Age. Nature Geoscience.

DOI: 10.1038/s41561-024-01610-2

Correction: Due to incorrect wording, we have replaced the sentence 'Using geochemical signatures from ancient fossils, the researchers present a 80-million-year record of atmospheric COâ‚‚ levels as Earth transitioned into and out of its penultimate ice age' with the following: 'Using geochemical signatures from ancient fossils, the researchers present a record of atmospheric COâ‚‚ levels as Earth transitioned into and out of the Late Palaeozoic Ice Age'.

Illustration showing the transition from the penultimate ice age to the early Permian.

Scientific illustration of the Late Palaeozoic Ice Age. A relatively rapid increase in atmospheric carbon dioxide (CO2) concentration about 294 million years ago freed the Earth from its penultimate icehouse (left) and initiated the transition to a warmer and drier climate in the Early Permian (right). The illustration is based on previously published literature and the results of the conducted study. Illustration: Dawid Adam Iurino, University of Milano for Jurikova et al. (2025)

Person standing on carbon stones on the coast in Scotland

Fieldwork in Scotland. Fossils from the late Palaeozoic Ice Age are preserved in the Carboniferous rocks along the south-eastern coast of Scotland. Photo: Hana Jurikova, University of St Andrews

Brachiopod fossil specimen

Brachiopod fossil specimen. Photo: Ruben Marchesi