Discovery of Atmospheric CO2 "Jumps" Over the Last 500,000 Years in Antarctic Ice Cores

Fragment of an ice core drilled in Antarctica. Air bubbles trapped by polar ice over time allow us to reconstruct past changes in the composition of our atmosphere. © Xavier FAIN/IPEV/LGGE/CNRS Images.

A new study, supported by the Make Our Planet Great Again program as part of the HOTCLIM project, and conducted by an international scientific team led by the Institute of Environmental Geosciences in Grenoble (IGE – CNRS/INRAE/IRD/UGA - Grenoble INP-UGA) in collaboration with the Laboratory of Climate and Environmental Sciences, LSCE (CEA/CNRS/UVSQ), the University of New South Wales, and the University of Bern, has revealed new rapid variations within global fluctuations of atmospheric carbon dioxide (CO2) concentrations over the past 500,000 years. These phenomena are called "CO2 jumps" and are significant events, although their rate of increase remains 10 times lower than the current rise in CO2 concentrations caused by human activities. The article has been published in the journal Nature Geoscience on Friday, October 11, 2024.

These "CO2 jumps," corresponding to increases of about ten ppm (parts per million) in atmospheric CO2 concentrations—i.e., the number of CO2 particles observed per million air particles—over a period of a few decades to several hundred years, were recorded in ancient air trapped in Antarctic ice cores.

It is important to note that the current rate of CO2 concentration increase, approximately 2.5 ppm/year due to human activities, is 10 times higher than these jumps, which range around 10 ppm over a few decades.
Researchers at IGE measured a new high-resolution CO2 record from the EPICA Dome C Antarctic ice core, allowing them to identify seven new jumps. By comparing their data with previous studies, they were able to demonstrate that 18 out of the 22 recorded CO2 jumps over the past 500,000 years occurred during periods when the Earth’s axial tilt, or obliquity, was high.

Relying on new simulations using a climate model, the researchers showed that in the context of high obliquity, the various terrestrial carbon reservoirs, particularly continental vegetation, are particularly sensitive to climate changes linked to major shifts in Atlantic ocean circulation. The disruption of these carbon reservoirs triggers massive carbon releases into the atmosphere, which is the cause of these CO2 jumps.

What is the connection to current climate change ?

The Earth is currently in a period of high obliquity. In the event of a major disturbance to Atlantic ocean circulation, particularly a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), an amount of carbon equivalent to four years of global anthropogenic emissions (at the rate of average emissions between 2010 and 2019) could be released within a few decades, compounding current anthropogenic emissions. However, there is still considerable uncertainty regarding the future of the AMOC in response to current climate change. In the scenario of an AMOC collapse due to climate changes caused by human activities, a massive additional release of carbon from natural sources would add to anthropogenic emissions.

Emilie Capron, co-author of the study, looking at air bubbles trapped in Antarctic ice.
© Sepp Kipfstuhl, Alfred Wegener Institute.
Gregory Teste, co-author of the study, cutting an Antarctic ice core at Concordia Station, Antarctica. © Gregory Teste, Institut des géosciences de l’environnement

Référence

Centennial-scale variations in the carbon cycle enhanced by high obliquity
Etienne Legrain, Emilie Capron, Laurie Menviel, Axel Wohleber, Frédéric Parrenin, Grégory Teste, Amaëlle Landais, Marie Bouchet, Roberto Grilli, Christoph Nehrbass-Ahles, Lucas Silva, Hubertus Fischer & Thomas F. Stocker
https://doi.org/10.1038/s41561-024-01556-5

Contact scientifique local

 Etienne Legrain, Former PhD student at the Institute of Environmental Geosciences during the article’s writing, currently post-doctoral researcher at Université Libre de Bruxelles.
 Emilie Capron, CNRS Research Scientist at the Institute of Environmental Geosciences.

This press release was initially pubished by l’l’Université Grenoble Alpes.