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A sustained decline in the levels of carbon dioxide (CO2) in the atmosphere and the removal of rocky soils overlying the bedrock have resulted in a crucial change in the structure of the Earth's glacial and interglacial cycles approximately one million years ago. years, according to a new German study.
A team led by Matteo Willeit of the Potsdam Institute for Climate Impact Research used a terrestrial system model to demonstrate that the gradual reduction of CO2 caused a glaciation of the northern hemisphere and was likely to The origin of the increasing temperature differences between the glacial and interglacial periods during the Quaternary period. extends from 2.6 million years to the present day.
This, they suggest, when they are combined with the removal of rocks and loose soils collectively called the regolith, by scouring glaciers, "best explains the transition of a more muted cycle." from 41,000 years to the much larger cycle of 100,000-year-old glaciers that has dominated the last million years. "
The two hypotheses of the so-called Mid-Pleistocene transition (MPT) have already been examined, but this is the first study to suggest that they were actually at stake.
Together, they are "essential to reproduce the realistic evolution of climate variability during the Quaternary and their combination controls the timing of regime changes in climate variability," the researchers write in an article published in the journal. Progress of science.
Perhaps more immediately, their results also confirm that the current concentration of atmospheric CO2 is unprecedented over the last three million years and that world temperatures in the Quaternary have never exceeded more than two degrees Celsius pre-industrial temperatures. 1750.
Human activity has warmed the planet about a degree since then.
"In the context of future climate change, this implies a failure in substantially reducing CO2 emissions to comply with the Paris Agreement's goal of limiting global warming well below two degrees Celsius not only will move Earth's climate away from conditions similar to the Holocene, but beyond the climatic conditions encountered throughout the current geological period, "the researchers write.
For the study, Willeit and his colleagues performed a large number of transient simulations with a terrestrial model called CLIMBER-2, which includes models of atmosphere, ocean, vegetation, carbon, and dust in the world and the three-dimensional model of thermomechanical ice cap SICOPOLIS.
They note that CLIMBER-2 is only of "intermediate complexity", requiring "a rather coarse spatial resolution and considerable simplifications in the description of individual processes, in particular atmospheric dynamics".
The study did not seek to find the reason for the gradual decrease in CO2.
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