Tipping point in North American Arctic-Boreal carbon sink persists in new generation Earth system models despite reduced uncertainty
Estimating the impacts of climate change on the global carbon cycle relies on projections from Earth system models (ESMs). While ESMs currently project large warming in the high northern latitudes, the magnitude and sign of the future carbon balance of Arctic-Boreal ecosystems are highly uncertain. The new generation of increased complexity ESMs in the Intergovernmental Panel on Climate Change Sixth Assessment Report (IPCC AR6) is intended to improve future climate projections. Here, we benchmark the Coupled Model Intercomparison Project (CMIP) 5 and 6 (8 CMIP5 members and 12 CMIP6 members) with the International Land Model Benchmarking (ILAMB) tool over the region of NASA's Arctic-Boreal vulnerability experiment (ABoVE) in North America. We show that the projected average net biome production (NBP) in 2100 from CMIP6 is higher than that from CMIP5 in the ABoVE domain, despite the model spread being slightly narrower. Overall, CMIP6 shows better agreement with contemporary observed carbon cycle variables (photosynthesis, respiration, biomass) than CMIP5, except for soil carbon and turnover time. Although both CMIP ensemble members project the ABoVE domain will remain a carbon sink by the end of the 21st century, the sink strength in CMIP6 increases with CO₂ emissions. CMIP5 and CMIP6 ensembles indicate a tipping point defined here as a negative inflection point in the NBP curve by 2050–2080 independently of the shared socioeconomic pathway (SSP) for CMIP6 or representative concentration pathway (RCP) for CMIP5. The model ensembles therefore suggest that, if the carbon sink strength keeps declining throughout the 21st century, the Arctic-Boreal ecosystems in North America may become a carbon source over the next century.
© 2023 The Author(s). Published by IOP Publishing Ltd. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 license. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Special Issue: Resiliency and Vulnerability of Arctic and Boreal Ecosystems to Environmental Change: Advances and Outcomes of ABoVE (the Arctic Boreal Vulnerability Experiment) This study was part of the NASA Arctic-Boreal Vulnerability Experiment (ABoVE). RKB and JBF were supported through funding from Phase 2 of NASA ABoVE (NNX15AV77A). Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D004). California Institute of Technology. Government sponsorship acknowledged. This research used resources of the NASA ABoVE program. We acknowledge support from the NASA ABoVE (incl. 80NSSC22K1245, NNX17AD69A) and ILAMB communities. This work was supported in part by Resnick Sustainability Institute. Author contribution. RKB planned and designed the research. JBF supervised and acquired funding. RKB performed the research, data analysis, collection, and interpretation, as well as wrote the original draft and final manuscript with input from all authors. Data availability statement. The data that support the findings of this study are openly available. The CMIP6 data simulations performed by various modeling groups are available from the CMIP6 archive (https://esgf-node.llnl.gov/search/cmip6). The ILAMB package can be downloaded from (https://github.com/rubisco-sfa/ILAMB). All ILAMB plots are available from (https://braghiere.github.io/). The authors declare no competing interests.
Published - Braghiere_2023_Environ._Res._Lett._18_025008.pdf