Thawing permafrost raised carbon dioxide levels after the last ice age, study shows

Carbon dioxide levels in the atmosphere vary naturally between glacial ages and interglacial periods. A new study carried out by researchers from the University of Gothenburg shows that an unexpected proportion of carbon dioxide emissions after the ice age can come from the defrosting of pergialisol.

For a long time, it was the changes between the ice ages and the interglacial periods that determined the amount of carbon dioxide in the atmosphere. During ice cream, Co₂ The levels dropped, only to increase by around 100 ppm (parts per million) during interglacial periods.

Previously, the main reason for this was considered that of the warmer and more mixed oceans cannot store as much carbon and therefore release it in the atmosphere between the ice age.

However, new research from the University of Gothenburg show that the Décongeon du Pergélisol may have explained a significant proportion of carbon dioxide emissions. The work is published in the journal Scientific advances.

“We have concluded that the earth in the north of the Tropic of Cancer, at 23.5 degrees to the north, emitted a lot of carbon when the average temperature increased in the northern hemisphere after our last glacial age. We believe that this carbon exchange may have represented almost half of the rise in carbon dioxide in the atmosphere,” said Amelie Lindgren, researcher ecosyletic at the University of Godenburg.

Carbon froze in the ground

The researchers believe that large quantities of carbon were stored during the ice age when the grass and other plants were simply frozen in the ground, with rock dust at the origin of the wind set up on top. Such deposits, called “loess”, are created during ice times and can reach tens of meters in thickness. They are in large regions of Europe and Asia, but also in North America.

Pergélisc is necessary for the trapping of organic matter in these deposits, and even normal soil with permafrost contains more organic carbon than the unprotected soil because the cold slows down decomposition rates.

Pollen analysis

By combining pollen analyzes of the last 21,000 years with the climatic data of the models, the researchers have been able to estimate the types of vegetation that existed in different places through history.

“We have chosen to take an instantaneous every thousand years. Once we know what type of vegetation has prevailed, we can estimate the quantity of carbon stored in the soil. In this way, we can model the way in which the carbon exchange between the soil and the atmosphere looked since the last glacial period,” explains Lindgren.

About 21,000 years ago, continental glacial caps reached their maximum extent in the northern hemisphere. The whole of Scandinavia and what is now Canada was covered in ice at the time, and permafrost prevailed in large parts of Siberia, China and parts of Central Europe.

During the period 17,000 to 11,000 years ago, it became warmer. This led to the thaw of permafrost, which led to an increase in CO emissions₂ From soil to atmosphere.

Natural variation

Anterior analyzes of ice nuclei show that the carbon dioxide content in the atmosphere has increased as follows:

• 180 ppm (parts per million) Co₂ 21,000 years ago, when the ice age reached its peak.
• 270 ppm Co₂ 11,000 years ago, for a normal interglacial period.

According to the researchers, this is a natural variation between the age of the ice and the interglacial periods. However, despite the reduction in the glacial cap and the continuous thawing of new permafrost zones, the carbon dioxide content has not increased much more after that.

“We see that peat bogs stored large quantities of carbon during the Holocene. Over time, the absorption of peat bogs in fact compensated for the emissions that occurred by the permafrost,” explains Lindgren.

Humans disrupt the carbon cycle

However, over the past 250 years, humans have disrupted the cycle of natural carbon by burning large amounts of fossil carbon, mainly coal and oil. Since the industrial revolution in the 19th century, the carbon dioxide content in the atmosphere has increased from 280 ppm to 420 ppm today.

“There are extremely high levels of carbon dioxide in the atmosphere at the moment, and degree permafrost as temperatures increases. What helped us the last time that permafrost has decreased was an increase in carbon storage in peat bogs and new areas of terrain that will become available in continental ice sheets.