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\begin{document}

\title{Two decades of permafrost region CO2, CH4, and N2O budgets suggest a
small net greenhouse gas source to the atmosphere}



\author[1]{Gustaf Hugelius}%
\author[1]{Justine Lucile Ramage}%
\author[2]{Eleanor J. Burke}%
\author[3]{Abhishek Chatterjee}%
\author[4]{Thomas Luke Smallman}%
\author[5]{Tuula Aalto}%
\author[6]{Ana Bastos}%
\author[7]{Christina Biasi}%
\author[8]{Josep G. Canadell}%
\author[9]{Naveen Chandra}%
\author[10]{Frederic Chevallier}%
\author[11]{Philippe Ciais}%
\author[12]{Jinfeng Chang}%
\author[4]{Liang Feng}%
\author[13]{Matthew W Jones}%
\author[14]{Thomas Kleinen}%
\author[15]{McKenzie Kuhn}%
\author[16]{Ronny Lauerwald}%
\author[17]{Junjie Liu}%
\author[18]{Efrén López-Blanco}%
\author[19]{Ingrid Theodora Luijkx}%
\author[7]{Maija E Marushchak}%
\author[20]{Susan M. Natali}%
\author[21]{Yosuke Niwa}%
\author[22]{David Olefeldt}%
\author[4]{Paul Palmer}%
\author[23]{Prabir K. Patra}%
\author[19]{Wouter Peters}%
\author[20]{Stefano Potter}%
\author[24]{Benjamin Poulter}%
\author[20]{Brendan Rogers}%
\author[25]{William J. Riley}%
\author[26]{Marielle SAUNOIS}%
\author[27]{Ted A.G. Schuur}%
\author[28]{Rona L. Thompson}%
\author[29]{Claire Clark Treat}%
\author[30]{Aki Tsuruta}%
\author[31]{Merritt R Turetsky}%
\author[32]{Anna- Maria Virkkala}%
\author[7]{Carolina Voigt}%
\author[20]{Jennifer Watts}%
\author[25]{Qing Zhu}%
\author[33]{Bo Zheng}%
\affil[1]{Stockholm University}%
\affil[2]{Met Office Hadley Centre for Cllimate Prediction and Research}%
\affil[3]{NASA Jet Propulsion Laboratory}%
\affil[4]{University of Edinburgh}%
\affil[5]{Finnish Meteorological Institute}%
\affil[6]{Department of Biogeochemical Integration, Max Planck Institute for Biogeochemistry, 07745 Jena, Germany}%
\affil[7]{University of Eastern Finland}%
\affil[8]{Global Carbon Project, CSIRO Oceans and Atmosphere}%
\affil[9]{Japan Agency for Marine-Earth Science and Technology}%
\affil[10]{Laboratoire des Sciences du Climat et de l'Environnement (LSCE)}%
\affil[11]{Laboratory for Climate Sciences and the Environment (LSCE)}%
\affil[12]{Zhejiang University}%
\affil[13]{Tyndall Centre for Climate Change Research}%
\affil[14]{Max Planck Institute for Meteorology}%
\affil[15]{University of New Hampshire}%
\affil[16]{Université Paris Saclay}%
\affil[17]{Jet Propulsion Laboratory}%
\affil[18]{Aarhus University \& University of Edinburgh}%
\affil[19]{Wageningen University}%
\affil[20]{Woodwell Climate Research Center}%
\affil[21]{National Institute for Environmental Studies}%
\affil[22]{University of Alberta}%
\affil[23]{JAMSTEC}%
\affil[24]{NASA}%
\affil[25]{Lawrence Berkeley National Laboratory (DOE)}%
\affil[26]{LSCE-IPSL (CEA/CNRS/UVSQ)}%
\affil[27]{Northern Arizona University}%
\affil[28]{Norwegian Institute for Air Research}%
\affil[29]{Alfred Wegener Institute}%
\affil[30]{FMI}%
\affil[31]{University of Colorado Boulder}%
\affil[32]{Woodwell Climate Research Center, Falmouth, MA, USA}%
\affil[33]{Tsinghua University}%


\vspace{-1em}



  
  \date{May 25, 2024}


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\selectlanguage{english}
\begin{abstract}
The long-term net sink of carbon (C), nitrogen (N) and greenhouse gases
(GHGs) in the northern permafrost region is projected to weaken or shift
under climate change. But large uncertainties remain, even on
present-day GHG budgets. We compare bottom-up (data-driven upscaling,
process-based models) and top-down budgets (atmospheric inversion
models) of the main GHGs (CO2, CH4, and N2O) and lateral fluxes of C and
N across the region over 2000-2020. Bottom-up approaches estimate higher
land to atmosphere fluxes for all GHGs compared to top-down atmospheric
inversions. Both bottom-up and top-down approaches respectively show a
net sink of CO2 in natural ecosystems (-31 (-667, 559) and -587 (-862,
-312), respectively) but sources of CH4 (38 (23, 53) and 15 (11, 18) Tg
CH4-C yr-1) and N2O (0.6 (0.03, 1.2) and 0.09 (-0.19, 0.37) Tg N2O-N
yr-1) in natural ecosystems. Assuming equal weight to bottom-up and
top-down budgets and including anthropogenic emissions, the combined GHG
budget is a source of 147 (-492, 759) Tg CO2-Ceq yr-1 (GWP100). A net
CO2 sink in boreal forests and wetlands is offset by CO2 emissions from
inland waters and CH4 emissions from wetlands and inland waters, with a
smaller additional warming from N2O emissions. Priorities for future
research include representation of inland waters in process-based models
and 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 in-situ flux
observations and improved resolution in upscaling.%
\end{abstract}%



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