2025.01.10Cause of one of the largest climate shifts deciphered International study sheds light on the role of CO2 in the Late Palaeozoic Ice Age

An international research team has reconstructed how the atmospheric concentration of carbon dioxide (CO2) developed between 335 and 265 million years ago.

This period covers the peak of the late Palaeozoic ice age, when the Earth's climate cooled dramatically. The new findings provide decisive evidence that CO2 has been regulating the Earth's climate and environmental conditions for hundreds of millions of years. The researchers have summarised their findings in a study that has now been published in the journal Nature Geoscience. First author is Dr Hana Jurikova from the University of St Andrews, the GEOMAR Helmholtz Centre for Ocean Research Kiel is involved in the study with several researchers.

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CO₂ is the most important greenhouse gas on earth: it absorbs heat, radiates a large proportion of it back to the earth and thus influences the global climate. While the role of CO₂ in recent climate history is very well understood, it has long been a challenge to reconstruct the CO₂ content in the Earth's history. This left gaps in our understanding of the transitions between glacial and interglacial periods.

An international research team led by Dr Hana Jurikova from the University of St Andrews and nine other organisations, including the GEOMAR Helmholtz Centre for Ocean Research Kiel, has now reconstructed atmospheric CO₂ levels during the Carboniferous and Permian periods between 335 and 265 million years ago. Using geochemical signatures from ancient fossils, the researchers were able to create a record of atmospheric CO₂ levels during the Earth's transition to and from the late Palaeozoic ice age era. The results have now been published in the journal Nature Geoscience.

CO₂ data from the past decoded using geochemical signatures

The researchers analysed isotopic signatures in fossilised brachiopod shells, shell-like organisms that serve as a natural archive of past ocean conditions. ‘The chemical composition of these shells reflects the state of the oceans at the time of their formation,’ explains Dr Hana Jurikova, Senior Researcher at the University of St Andrews and leader of the study. ‘By analysing boron isotopes, we can determine the CO₂ content in the atmosphere. Strontium isotopes provide information about the age of the fossils, while carbon and oxygen isotopes provide information about the CO₂ source and the climate. Together, these techniques allow us to accurately reconstruct past CO₂ concentrations on Earth and understand the factors responsible for their changes,’ says Hana Jurikova. She previously completed her doctorate at GEOMAR, where she also carried out the first geochemical measurements for the study.

CO₂ plays a central role in climate transitions

Using this methodology, the researchers found that CO₂ levels fell to a critically low level during the Carboniferous period, leading to an extended ice age that lasted several million years. Around 294 million years ago, during the Early Permian, volcanic activity caused CO₂ levels to rise again, warming the Earth and melting the ice sheets. ‘The beginning and end of the Late Palaeozoic Ice Age was one of the most important climate transitions in Earth's history, shaping the development of the modern environment and life on our planet. We now have evidence that atmospheric CO₂ was an important factor in this change,’ says Prof Dr Anton Eisenhauer, co-author and Professor of Marine Environmental Geochemistry at GEOMAR. ‘Although the time scales of the geological climate transitions differ significantly from today's anthropogenic climate changes, the principle remains the same - rising CO₂ levels drive the warming of the Earth's atmosphere and sea level rise,’ adds Dr Marcus Gutjahr, marine biogeochemist at GEOMAR and co-author of the study.

Reconstructing atmospheric CO₂ concentrations from hundreds of millions of years ago is still a challenge, as there are only a few well-preserved geological archives. The results make an important contribution to understanding the long-term evolution of atmospheric CO₂ in Earth's history. However, given the gaps that still exist, further research is needed before the record of the Earth's CO₂ history can be considered complete.

Read this and more on the website of the GEOMAR Helmholtz Centre for Ocean Research Kiel