A new study published in Nature Geoscience by an international team of scientists provides new insights into the natural mechanisms behind century-scale increases in atmospheric carbon dioxide (CO₂), known as CO₂ jumps. The study, led by Etienne Legrain, paleoclimatologist at the Department of Water and Climate at the Vrije Universiteit Brussel, the Glaciology Laboratory of the Université Libre de Bruxelles and the Environmental Geosciences Institute of Université Grenoble-Alpes provides findings based on high-resolution measurements from Antarctic ice cores. The results reveal the significant role that Earth's orbital conditions play in triggering rapid CO₂ increases, particularly during periods of high obliquity. The research offers critical context for understanding natural CO₂ variability and its interaction with human-induced climate change.

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Scientist sampling ice from an Antarctic ice core. © Etienne Legrain

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Sample of ice mounted on a glass slide for further analysis. © Etienne Legrain.

"We discovered seven CO₂ jumps that happened between 260,000 and 190,000 years ago. 22 of these jumps have now been identified for the last 500,000 years. The analyses show that 18 of these CO₂ jumps happened when Earth’s axis was tilted more than usual. The tilt changes naturally over time periods of about 41,000 years, and it affects how sunlight hits Earth. This impacts how much CO₂ is released from places like oceans and continental vegetation. Our study shows that when major oceanic currents, like the Atlantic Meridional Overturning Circulation (AMOC), slow down, it can cause more CO₂ to be released from the ocean and land, especially when Earth’s tilt is high, causing these jumps." Etienne Legrain says.
"While these natural CO₂ jumps are important, they are much smaller than the amount of CO₂ humans are adding to the atmosphere today. Natural jumps increased CO₂ by about 10 parts per million (ppm) per century, while human activities are raising it by more 100 ppm per century in half of a century —20 times more. Nevertheless, if the AMOC weakens in the future, as some scientists think could happen due to anthropogenic-induced climate change, another CO₂ jump might occurs. It would release the equivalent of 4 years of anthropogenic greenhouse gas emissions over a period of a century. This would be added to the CO₂ humans are already putting in the atmosphere, increasing the global greenhouse effect." Legrain concludes.

The authors affirm that we need to learn more about how these natural processes and human-caused climate changes interact and what it may imply for future climate evolution.

Reference:

Legrain, E., et al. "Centennial-scale increases of atmospheric carbon dioxide linked to obliquity-driven climate changes," *Nature Climate Change*, [DOI: 10.1038/sXXXX].

Contact:

Etienne Legrain:

Email: etienne.legrain@vub.be

Phone: +33767883755

This work is the result of a thesis conducted at the Environmental Geosciences Institute in Grenoble at the Université Grenoble Alpes, which was completed as part of a postdoctoral fellowship jointly carried out at the Glaciology Laboratory of the Université Libre de Bruxelles and the Department of Water and Climate at the Vrije Universiteit Brussel.