Permafrost can be defined as the perpetually frozen subsoil that occurs in the northernmost regions of Earth. Since the last Ice Age, permafrost has been gathering and preserving animal and plant matter.
When some of this organic matter becomes decomposed, it naturally discharges carbon dioxide (CO2) gas into the air throughout the year. This decomposed organic matter is absorbed by plants during the period of warmer months.
However, it is difficult to investigate this region, known as the northern permafrost region, and not many experiments have been performed when compared to those conducted in less remote and warmer places.
But according to a novel synthesis that integrates datasets collected from over 100 Arctic study locations by numerous institutions, such as the U.S. Department of Energy’s (DOE) Argonne National Laboratory, as global temperatures increase, the breakdown of organic matter in permafrost soil during the time of winter months can be considerably higher than assumed previously.
The latest numbers indicate CO2 emissions that far surpass the corresponding uptake during the summer months.
More significantly, if greenhouse gas emissions caused by humans continue at their present rate, the CO2 discharged by permafrost soil during the winter season may probably increase by 41% by 2100. This was the conclusion reached by the researchers when they were modeling the carbon balance using the large datasets.
Published in the Nature Climate Change journal in October 2019, the study represents the most in-depth analysis of this phenomenon so far. It underscores the need for additional studies on the net CO2 emissions of the permafrost region, and shows how these emissions can have a major impact on global warming and the greenhouse effect.
The research brings together in-field measurements as well as lab-based analyses—or soil incubations—similar to those conducted at Argonne National Laboratory.
The researchers at Argonne National Laboratory sampled a wide range of permafrost soils to gain a better understanding of how upcoming warming is likely to impact the release of CO2 in permafrost regions. They tracked CO2 emissions at a range of laboratory-regulated temperatures that were below and above the freezing level mimicking standard Arctic conditions.
The aim of this study was to detect the way different properties of the soil or other factors have an impact on the speed of decomposition and the emission of CO2 from thawing and frozen soils. Such data can help in improving the Earth and climate system models.
Climate and Earth system models often treat these winter permafrost CO2 emissions as insignificant or even non-existent. But this study, with its large volume of data extending over multiple seasons, shows that winter respiration is substantial and significant. The study should convince modelers that this flux of winter-time carbon to the atmosphere can no longer be overlooked. It is not small, and it needs to be taken into account.
Roser Matamala, Study Contributor and Scientist, Environmental Science Division, Argonne National Laboratory
About 15% of the Earth’s land area is covered by the northern permafrost region, which extends from the coastline of the Arctic Ocean through a large part of northern Eurasia, northern Canada, and Alaska. The soil, which is ubiquitously frozen in these kinds of regions, contains more carbon levels than ever released by humans. The region also contains about a third of the carbon preserved in all of the soil on Earth.
During summertime, plants absorb the CO2 gas as they photosynthesize, specifically those plants with roots that grow in thawed soil over the constantly frozen subsoil. Simultaneously, microorganisms discharge the CO2 gas into the air as they intensely breakdown the organic matter in the soil.
When the surface soil and the underlying permafrost freeze during wintertime, the amount of CO2 returned to the air and the rate of decomposition decrease considerably.
However, some of the organic matter present in thin and unfrozen water films enclosing the soil particles are continuously decomposed by a tiny amount of microbial activity. This process discharges CO2 in smaller amounts.
For decades, this balance was tipped toward higher absorption instead of emitting the CO2 gas. However, the new study shows that the year-round release of CO2 in the atmosphere from the permafrost soils is currently higher when compared to its uptake during the summer period.
Arctic soils have retained disproportionately large amounts of organic matter because frozen conditions greatly slow microbial decay of dead plant roots and leaves. But just as food in the freezer compartment of a refrigerator will spoil faster than it would in a chest freezer, the temperature of seasonally frozen soils and permafrost affects the amount of microbial activity and decomposition.
Julie Jastrow, Study Contributor and Soil Scientist, Argonne National Laboratory
According to the researchers at Argonne National Laboratory, the activity of the microorganisms can increase dramatically as the permafrost is warmed by the rising global temperatures to below-freezing levels. Even before the thawing of the permafrost, the speed of the microbial activity in the permafrost soil speeds up its emissions of CO2.
On the basis of these outcomes and upscaling across the Arctic region, the study authors predicted that approximately 1.7 billion metric tons of CO2 are discharged during the present winter months, but added that only 1 billion metric tons would be taken up by photosynthesizers during the summer season.
In addition, computer models revealed that even if humans were able to cut down their own emissions to a minimal extent, the winter emissions of CO2 in the permafrost region would still continue to rise by 17% by 2100.
The paper, titled “Large loss of CO2 in winter observed across northern permafrost region,” was published online on October 21st, 2019, and in the November 2019 issue of the Nature Climate Change journal.
The study was supported by the National Aeronautics and Space Administration’s (NASA) Arctic-Boreal Vulnerability Experiment and New Investigator Program, DOE’s Office of Biological and Environmental Research Terrestrial Ecosystem Science Program and Next-Generation Ecosystem Experiments Arctic Project, the National Science Foundation, and the National Research Foundation of Korea.