VUB-led international study shows Earth’s obliquity triggers CO2 jumps

A new study by an international team of scientists published in Nature Geoscience 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, a paleoclimatologist at the Department of Water and Climate at the VUB (Vrije Universiteit Brussel), reveals the significant role that Earth’s orbital conditions play in triggering rapid CO₂ increases, particularly during periods of high obliquity.

‘Carbon dioxide jumps’

The scientists investigated so-called ‘carbon dioxide jumps’, which are rapid CO2 increases. Eighteen of the 22 jumps identified over the past 500,000 years occurred in high obliquity.

That obliquity changes naturally over about 41,000 years and affects how sunlight reaches Earth, affecting the amount of CO2 released from oceans and vegetation, for example.

AMOC

“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,” explains Etienne Legrain.

While those natural CO2 jumps are important, they are much smaller than the amount of CO2 added to the atmosphere by human activities. Natural jumps increased CO2 levels by about ten parts per million (ppm) per century, while human activity increased them by more than 100 ppm per century, 20 times more, in just half a century.

‘Global greenhouse effect’

Nevertheless, if the AMOC weakens in the future, as some scientists think could happen due to anthropogenic-induced climate change, another CO₂ jump might occur.

It would release the equivalent of four years of anthropogenic greenhouse gas emissions over 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 they may imply for future climate evolution.