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.