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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Radiocarbon constraints imply reduced carbon uptake by soils during the 21st century

Margaret Torn
Lawrence Berkeley National Lab

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22 September 2016
Analysis of carbon isotope data suggests Earth system models overestimate soil carbon sequestration potential.

The Science
Researchers from the University of California Irvine, Germany's Max Planck Institute for Biogeochemistry, Lawrence Berkeley National Laboratory, and Stanford University/US Geological Survey used 14C data from 157 globally distributed soil profiles to show that Earth system models (ESMs) from the fifth Coupled Model Intercomparison Project (CMIP5) underestimated the mean age of soil carbon by about a factor of six, resulting in an overestimate of soil carbon sequestration potential by a factor of nearly two. These findings, which have important implications for future atmospheric CO2 levels, emphasize the need to incorporate better understanding of soil carbon cycling as well as 14C and other tracer diagnostics into ESMs to improve the quality of future climate projections. The work also illustrates the potential value of systematically exploiting available ecosystem measurements during model development to create more robust models.

The Impact
Our analysis suggests that the carbon–concentration feedback may be weaker in the 21st century than currently expected from ESMs. Therefore, a greater fraction of CO2 emissions than previously thought could remain in the atmosphere and contribute to global warming.

Summary
Soil is the largest terrestrial carbon reservoir and may influence the sign and magnitude of carbon cycle–climate feedbacks. Many Earth system models (ESMs) estimate a significant soil carbon sink by 2100, yet the underlying carbon dynamics determining this response have not been systematically tested against observations. We used 14C data from 157 globally distributed soil profiles sampled to 1-meter depth to show that ESMs underestimated the mean age of soil carbon by a factor of more than six (430 ± 50 years versus 3100 ± 1800 years). Consequently, ESMs overestimated the carbon sequestration potential of soils by a factor of nearly two (40 ± 27%). ESMs must better represent carbon stabilization processes and the turnover time of slow and passive soil C reservoirs when simulating future atmospheric carbon dioxide dynamics.

Contacts (BER PM)
Dan Stover,
SC23.1,
Daniel.Stover@science.doe.gov
301-903-0289
ALSO:  Renu Joseph SC-23.1 Renu.Jospeph@science.doe.gov (301-903-9237)
(Author Contact)
Dr. James T. Randerson
Department of Earth System Science, University of California Irvine
jranders@uci.edu (949-824-9030)
(PI Contact)
Dr. Margaret Torn, TES SFA PI. See also Forrest Hoffman for BGC–Climate Feedbacks Scientific Focus Area
Climate and Ecosystem Sciences Division
mstorn@lbl.gov  (510-495-2223)

Funding
This research was performed for the Biogeochemistry–Climate Feedbacks Scientific Focus Area (SFA) and the Berkeley Lab Terrestrial Ecosystem Science (TES) SFA, which are sponsored by DOE Regional and Global Climate Modeling (RGCM) Program and TES Programs, respectively, in the Climate and Environmental Sciences Division (CESD) of the Office of Biological and Environmental Research (BER) in the US Department of Energy Office of Science.

Publications
He, Yujie, Susan E. Trumbore, Margaret S. Torn, Jennifer W. Harden, Lydia J. S. Vaughn, Steven D. Allison, and James T. Randerson (2016), Radiocarbon constraints imply reduced carbon uptake by soils during the 21st century, Science, 353(6306):1419–1424, doi: 10.1126/science.aad4273.

Related Links

TES SFA and BGC-Climate SFA

DOE Office of Science, BER, CESD: TES and Regional Modeling programs (see highlight Docx for funding)
 


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