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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

An Observational Benchmark and Scaling Theory for Environmental Controls on Soil Decomposition

Charles Koven

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Global benchmark shows that existing Earth system models underestimate vulnerability of soils to increased temperature.

The Science 
U.S. Department of Energy–supported researchers combined global maps of productivity, soil carbon, and environment to demonstrate a basic pattern of environmental controls on soil decomposition, which is that its temperature sensitivity is highest in cold regions. From this, they derive a theory that explains the pattern as an outcome of the scaling of soil freeze-thaw processes in time and depth, and apply the benchmark to existing Earth system models (ESMs) and newer land modeling approaches.

The Impact
The study shows via a global benchmark that existing models systematically underestimate the temperature sensitivity of soil carbon decomposition, and that the solution to this is to take into account the way in which surface soils freeze.

Summary
The results show that the sensitivity of soil carbon to temperature is highest in cold climates, even for surface rather than permafrost layers, and that this global pattern can most simply be explained as an outcome of the way in which soils experience freeze-thaw processes. The team also show that all existing (CMIP5-era) ESMs systematically underestimate this temperature sensitivity, whereas newer approaches, such as the CLM4.5 representation that forms the basis of the E3SM soil biogeochemistry, can match observations. Thus the team's approach shows two major impacts: (1) the single most important relationship that soil models must take into account is the physical scaling of freeze and thaw and (2) existing estimates systematically underestimate the long-term temperature sensitivity of surface soil carbon.

Contacts
BER Program Managers
Renu Joseph
SC-23.1
renu.joseph@science.doe.gov (301-903-9237)

Dorothy Koch
SC-23.1
Dorothy.koch@science.doe.gov (301-903-0105)

Daniel Stover
SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigator
Charles Koven, Staff Scientist
Lawrence Berkeley National Laboratory
Berkeley, CA 94720
cdkoven@lbl.gov, 510.486.6724

Funding
CDK received support from the Regional and Global Climate Modeling program through the BGC-Feedbacks SFA and the Terrestrial Ecosystem Sciences and Earth System Modeling programs through the Next-Generation Ecosystem Experiments (NGEE)–Tropics project of the Office of Biological and Environmental Research (BER) within the U.S. Dept. of Energy Office of Science.

Publications
Koven, C.D., Hugelius, G., Lawrence, D.M., and Wieder, W. “Higher climatological temperature sensitivity of soil carbon in cold than warm climates.” Nature Climate Change 7(11), 817–822 (2017). [DOI:10.1038/NCLIMATE3421].

LBNL, BGC-Feedbacks SFA (RGCM), NGEE-Tropics, NGEE-Arctic

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