Two illustrations of arctic lakes show the relative carbon dioxide and methane release, for the cases with and without widespread permafrost
Warmer lakes have accelerated carbon cycles. High primary productivity leads to net carbon dioxide uptake, but also creates conditions favorable to methane production. By contrast, colder lakes are a net source of carbon dioxide to the atmosphere but produce less methane. Credit: Kuhn et al., 2021, Figure 4
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: AGU Advances

Of the myriad uncertainties in the far north, some are biogeochemical. For example, how will the chemical composition of permafrost carbon, and the microbial communities it supports, affect decomposition rates when thawed? What will be the balance between release of carbon dioxide (CO2) and methane (CH4)? Some questions are ecological, such as: how could increased primary productivity from invading woody plants offset soil carbon loss? Others are eco-climatic, such as: how, in the far north, might more growth in a warmer summer might offset more decomposition if the dark times of the year are warmer? Kuhn et al. [2021] focus on the role of water bodies in releasing CO2 and CHto the atmosphere, using 20 lakes along a 1600-km gradient as an experiment. They found that the warmer lakes acted as carbon sinks, because of greater hydrological connectivity and, as a result, higher nutrient availability, which led to higher productivity despite higher rates of organic matter turnover. However, the warmer lakes also had up to eight-fold higher CH4 emissions, and so, while CO2 emissions were lower, net radiative forcing was higher. Lakes, with degrading permafrost around their edges, are likely to accelerate the release of permafrost carbon into the atmosphere with warming. While productivity may compensate for these CO2 emissions, CH4 could add to climate forcing. The increase in liquid water in the north, with permafrost breakdown and associated hydrological and geomorphic changes, will undoubtedly affect the release of carbon from soils, but this study suggests an amplifier as more CH4 is produced. 

Citation: Kuhn, M., Thompson, L., Winder, J., Braga, L., Tanentzap, A., Bastviken, D., et al. [2021]. Opposing Effects of Climate and Permafrost Thaw on CH4 and CO2 Emissions from Northern Lakes. AGU Advances, 2, e2021AV000515. https://doi.org/10.1029/2021AV000515

—David Schimel, Editor, AGU Advances