Science Highlights
Permafrost Region Greenhouse Gas Budgets Suggest a Weak CO2 Sink and CH4 and N2O Sources, But Magnitudes Differ Between Top-Down and Bottom-Up Methods
G. Hugelius, J. Ramage, E. Burke, A. Chatterjee, T. L. Smallman, T. Aalto, A. Bastos, C. Biasi, J. G. Canadell, N. Chandra, F. Chevallier, P. Ciais, J. Chang, L. Feng, M. W. Jones, T. Kleinen, M. Kuhn, R. Lauerwald, J. Liu, E. López-Blanco, I. T. Luijkx, M. E. Marushchak, S. M. Natali, Y. Niwa, D. Olefeldt, P. I. Palmer, P. K. Patra, W. Peters, S. Potter, B. Poulter, B. M. Rogers, W. J. Riley, M. Saunois, E. A. G. Schuur, R. L. Thompson, C. Treat, A. Tsuruta, M. R. Turetsky, A.-M. Virkkala, C. Voigt, J. Watts, Q. Zhu & B. Zheng.
American Geophysical Union, Published 26 October 2024
DOI:10.1029/2023GB007969
Paper Abstract
Large stocks of soil carbon (C) and nitrogen (N) in northern permafrost soils are vulnerable to remobilization under climate change. However, there are large uncertainties in present-day greenhouse gas (GHG) budgets. We compare bottom-up (data-driven upscaling and process-based models) and top-down (atmospheric inversion models) budgets of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) as well as lateral fluxes of C and N across the region over 2000-2020. Bottom-up approaches estimate higher land-to-atmosphere fluxes for all GHGs. Both bottom-up and top-down approaches show a sink of CO2 in natural ecosystems (bottom-up: -29 (-709, 455), top-down: -587 (-862, -312) Tg CO2-C yr -1) and sources of CH4 (bottom-up: 38 (22, 53), top-down: 15 (11, 18) Tg CH4-C yr -1) and N2O (bottom-up: 0.7 (0.1, 1.3), top-down: 0.09 (-0.19, 0.37) Tg N2O-N yr -1). The combined global warming potential of all three gases (GWP-100) cannot be distinguished from neutral. Over shorter timescales (GWP-20), the region is a net GHG source because CH4 dominates the total forcing. The net CO2 sink in Boreal forests and wetlands is largely offset by fires and inland water CO2 emissions as well as CH4 emissions from wetlands and inland waters, with a smaller contribution from N2O emissions. Priorities for future research include the representation of inland waters in process-based models and the compilation of process-model ensembles for CH4 and N2O. Discrepancies between bottom-up and top-down methods call for analyses of how prior flux ensembles impact inversion budgets, more and well-distributed in situ GHG measurements and improved resolution in upscaling techniques.
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Access paper: https://doi.org/10.1029/2023GB007969
Media article
The Net GHG Balance and Budget of the Permafrost Region (2000-2020) From Ecosystem Flux Upscaling
Justine Ramage, McKenzie Kuhn, Anna-Maria Virkkala, Carolina Voigt, Maija E. Marushchak, Ana Bastos, Christina Biasi, Josep G. Canadell, Philippe Ciais, Efrèn López-Blanco, Susan M. Natali, David Olefeldt, Stefano Potter, Benjamin Poulter, Brendan M. Rogers, Edward A. G. Schuur, Claire Treat, Merritt R. Turetsky, Jennifer Watts & Gustaf Hugelius.
American Geophysical Union, Published 3 April 2024
DOI:10.1029/2023GB007953
Paper Abstract
The northern permafrost region has been projected to shift from a net sink to a net source of carbon under global warming. However, estimates of the contemporary net greenhouse gas (GHG) balance and budgets of the permafrost region remain highly uncertain. Here, we construct the first comprehensive bottom-up budgets of CO2, CH4, and N2O across the terrestrial permafrost region using databases of more than 1000 in situ flux measurements and a land cover-based ecosystem flux upscaling approach for the period 2000-2020. Estimates indicate that the permafrost region emitted a mean annual flux of 12 (-606, 661) Tg CO2-C yr -1, 38 (22, 53) Tg CH4-C yr -1, and 0.67 (0.07, 1.3) Tg N2O-N yr -1 to the atmosphere throughout the period. Thus, the region was a net source of CH4 and N2O, while the CO2 balance was near neutral within its large uncertainties. Undisturbed terrestrial ecosystems had a CO2 sink of -340 (-836, 156) Tg CO2-C yr -1. Vertical emissions from fire disturbances and inland waters largely offset the sink in vegetated ecosystems. When including lateral fluxes for a complete GHG budget, the permafrost region was a net source of C and N, releasing 144 (-506, 826) Tg C yr -1 and 3 (2, 5) Tg N yr -1. Large uncertainty ranges in these estimates point to a need for further expansion of monitoring networks, continued data synthesis efforts, and better integration of field observations, remote sensing data, and ecosystem models to constrain the contemporary net GHG budgets of the permafrost region and track their future trajectory.
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Access paper: https://doi.org/10.1029/2023GB007953
