Global-Scale Convergence Obscures Inconsistencies in Soil Carbon Change Predicted by Earth System Models

Zheng Shi, Forrest M. Hoffman, Min Xu, Umakant Mishra, Steven D. Allison, Jizhong Zhou, James T. Randerson

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

Soil carbon (C) responses to environmental change represent a major source of uncertainty in the global C cycle. Feedbacks between soil C stocks and climate drivers could impact atmospheric CO2 levels, further altering the climate. Here, we assessed the reliability of Earth system model (ESM) predictions of soil C change using the Coupled Model Intercomparison Project phases 5 and 6 (CMIP5 and CMIP6). ESMs predicted global soil C gains under the high emission scenario, with soils taking up 43.9 Pg (95% CI: 9.2–78.5 Pg) C on average during the 21st century. The variation in global soil C change declined significantly from CMIP5 (with average of 48.4 Pg [95% CI: 2.0–94.9 Pg] C) to CMIP6 models (with average of 39.3 Pg [95% CI: 23.9–54.7 Pg] C). For some models, a small C increase in all biomes contributed to this convergence. For other models, offsetting responses between cold and warm biomes contributed to convergence. Although soil C predictions appeared to converge in CMIP6, the dominant processes driving soil C change at global or biome scales differed among models and in many cases between earlier and later versions of the same model. Random Forest models, for soil carbon dynamics, accounted for more than 63% variation of the global soil C change predicted by CMIP5 ESMs, but only 36% for CMIP6 models. Although most CMIP6 models apparently agree on increased soil C storage during the 21st century, this consensus obscures substantial model disagreement on the mechanisms underlying soil C response, calling into question the reliability of model predictions.

Original languageEnglish
Article numbere2023AV001068
JournalAGU Advances
Volume5
Issue number2
DOIs
StatePublished - Apr 2024

Funding

This work was supported by the US DOE Office of Science Biological and Environmental Research RUBISCO Science Focus Area (to F.M.H., U.M, and J.T.R.), and NSF DEB Dimensions of Biodiversity Grant DEB-2129235 and the Office of the Vice President for Research at the University of Oklahoma (to J.Z.). We acknowledge the World Climate Research Programme working group on Coupled Modelling, which is responsible for CMIPs. We thank the climate modeling groups for producing and making their model outputs available, the Earth System Grid Federation (ESGF) for archiving the data and providing access, and the multiple funding agencies that support CMIP6 and ESGF. This work was supported by the US DOE Office of Science Biological and Environmental Research RUBISCO Science Focus Area (to F.M.H., U.M, and J.T.R.), and NSF DEB Dimensions of Biodiversity Grant DEB‐2129235 and the Office of the Vice President for Research at the University of Oklahoma (to J.Z.). We acknowledge the World Climate Research Programme working group on Coupled Modelling, which is responsible for CMIPs. We thank the climate modeling groups for producing and making their model outputs available, the Earth System Grid Federation (ESGF) for archiving the data and providing access, and the multiple funding agencies that support CMIP6 and ESGF.

Keywords

  • Earth system model
  • climate change
  • elevated CO
  • global warming

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