Thawing permafrost is known to be a substantial source of greenhouse gases to our atmosphere, yet scientists may still be underestimating this frozen giant. Permafrost soils store twice the amount of carbon than is currently in the atmosphere, but icy temperatures prevent microbes from converting carbon in the soil to greenhouse gasses. This creates a sort of carbon lockbox in the arctic. However, as climate change warms our planet, this once-frozen carbon threatens to escape to the atmosphere as the potent greenhouse gas, methane. A new study by Dr. Katey Walter Anthony and colleagues changes the paradigm of permafrost science and warns that current models underestimate the amount of methane that permafrost thaw in regions of Alaska and Siberia could release.
Dr. Walter Anthony describes the ground as a “waterbed”. Trapped beneath the grass at her central-Alaskan sampling site, bubbles of methane gas compress and shift when prodded. Most studies on methane emissions from thawing permafrost focus on wetlands. This is because the damp, stinky, ground in wetlands contains very little oxygen. Methanogens(microbes that produce methane) thrive without oxygen, making wetlands are a huge source of methane. However, these “methane waterbeds” that Dr. Walter Anthony was finding that were not near a wetland. As permafrost melts, the surrounding soil is temporarily moistened but dries out after several years. Scientists thought this would result in a temporary burp of methane that would cease once the dried-out soil became uninhabitable for methanogens and began favoring methane-consuming microbes, methanotrophs (troph means “eat”). Dr. Walter Anthony’s observations contradicted this presumption, so she started exploring further.
Her team measured methane emissions from the sampling site using two methods. First, they captured and measured methane rising from the ground using a focused approach on various 100-square-inch areas with a gas tight chamber the size of a 5-gallon bucket. Second, the team measured methane emissions on a larger scale by employing an instrument called an eddy covariance tower. The eddy covariance tower measured emissions from an area the size of 3 football fields. Combining these measurements confirmed Dr. Walter-Anthony’s suspicions. Methane emissions from this dry, upland permafrost thaw site were 3 times higher than emissions from northern wetlands. The team repeated these measurements on analogous terrain across Alaska and found similar results. Dry upland permafrost sites emit more methane than wet thaw sites, contrary to the widespread belief in permafrost science.
Dr. Walter Anthony hypothesizes that the remarkable methane emissions from drier sites result from the unique traits of central-Alaskan permafrost. Much of central Alaska and northern Siberia is classified as Yedoma, an especially carbon-rich variety of permafrost. Yedoma deposits contain more than 25% of the total carbon stored in permafrost while only accounting for 3% of the area. This is possible due to the depth that the carbon in Yedoma deposits reaches. Organic carbon in most permafrosts constitutes the top 3 meters of the ground (a single story of a building). However, in Yedoma deposits, it can extend tens of meters deep (as deep as 15 stories!). At the Yedoma deposits studied in this paper, the team discovered that sites with high methane flux had high soil water content at depths below 3 meters. While shallow soil might not have conditions conducive for methane production, the deeper soils in these Yedoma deposits do. Yedoma deposits are methane hotspots regardless of how dry they look at the surface due to the large amount of deep carbon they harbor.
With one unsuspected result already in hand, Walter-Anthony and the team decided to challenge another core principle of permafrost science – that methane emissions decrease in the winter. Using the techniques described above, the team continuously monitored methane emissions from their central Alaska site across two summers and two winters. This data disproved the previously held belief that permafrost methane emissions primarily occur in the summer. Instead, they found that roughly two thirds of the annual methane emissions occurred during the winter. DNA sequencing of the microbial community informed a hypothesis for this surprising finding. Methanotroph (methane eaters) DNA was found in the top 100 cm of the ground while methanogen (methane producers) DNA was located much deeper. In thawing permafrost, the deeper soils remain thawed year-round while, during winter, the upper soils are exposed to cold air temperatures and re-freeze. The team hypothesized that the frozen top layer of soil prevents oxygen penetration into the ground, providing deeper unfrozen methanogens with ideal conditions to produce methane throughout the winter. Additionally, the methanotrophs frozen in the top layers of soil are unable to consume methane rising from below, resulting in more methane escaping to the atmosphere.
Permafrost thaw has the potential to form a dangerous positive feedback loop where permafrost thaw yields greenhouse gas emissions, greenhouse gases heat the planet, and a hotter planet leads to more permafrost thaw. Perpetuation of this vicious cycle would move a lot of carbon from the enormous arctic soil stockpile into the atmosphere. Recent studies indicate that after the initial permafrost-thaw, arctic soils would quickly dry out, promoting methanotrophs over methanogens. It has even been suggested that these soils could become sinks for atmospheric methane, thereby disrupting the positive feedback loop. However, Walter-Anthony and her colleagues emphatically show that even drier soils can yield high methane emissions and that emissions in the winter are more substantial than during the summer. These findings have strong implications for models of greenhouse gas emissions from thawing permafrost, reshaping our understanding of permafrost carbon to reinforce its role in a dangerous positive feedback loop.
Permafrost Paradigm Shift Suggests more Methane Emissions to Come © 2025 by William Christian is licensed under Creative Commons Attribution-ShareAlike 4.0 International. To view a copy of this license, visit https://creativecommons.org/licenses/by-sa/4.0/