Arctic permafrost now a net source of greenhouse gases, say scientists

The northern permafrost region of the Arctic now emits more greenhouse gases than it captures, according to new research.

Permafrost underlies some 14 million sq km of land in and around the Arctic. The top 3 m contain an estimated 1 trillion metric tons of carbon and 55 billion metric tons of nitrogen. Historically, the northern permafrost region has been a sink for carbon, as frozen soils inhibit microbial decomposition. But rising temperatures are contributing to thawing permafrost and therefore enhancing the biogeochemical activities that worsen climate change by releasing greenhouse gases such as carbon dioxide, methane and nitrous oxide.

The results of a new study suggest that the northern permafrost region is now a net source of greenhouse gases (Justine Ramage).

The new study, published in Global Biogeochemical Cycles, synthesised greenhouse gas measurements of the northern permafrost region between 2000 and 2020 to provide a carbon balance for the region, as well as the first comprehensive assessment of the quantities of greenhouse gases the area takes up and emits.

The researchers' work, conducted as part of the Regional Carbon Cycle Assessment and Processes (RECCAP2) project, used a bottom-up approach, focusing on estimating emissions based on specific source categories. Their results suggest that the area has already shifted from a sink to a small source of carbon.

The researchers compiled many past estimates of greenhouse gas flux in various sections of the northern permafrost region to reveal how the entire area is responding to climate change. They found that the study area was a net source of methane and nitrous oxide between 2000 and 2020.

Wetlands were some of the largest methane emitters, and lakes contributed substantially as well. Dry tundra was the biggest driver of nitrous oxide release and permafrost bogs were a close second.

However, the researchers were unable to say definitively whether the region was a net source or sink of carbon dioxide. Terrestrial ecosystems, particularly boreal forests, still take up CO₂. But this is offset by fires, abrupt permafrost thaw and inland waters, which emitted an estimated 12 million metric tons of CO₂.

The researchers estimate that the northern permafrost region emitted 38 million metric tons of methane and 670,000 metric tons of nitrous oxide into the atmosphere between 2000 and 2020. When accounting for lateral fluxes such as erosion, the region was also a source of 144 million metric tons of carbon and 3 million metric tons of nitrogen.

Although these totals are relatively small when compared with the emissions of a major industrialised country, they may accelerate as the world warms.

Reference

Ramage, J, et al. 2024. The Net GHG Balance and Budget of the Permafrost Region (2000–2020) From Ecosystem Flux Upscaling. Global Biogeochemical Cycles. DOI: https://doi.org/10.1029/2023GB007953