Toward more realistic projections of soil carbon dynamics by Earth system models
Creators: name: Luo, Yiqi
name: Ahlstrom, Anders
name: Allison, Steven D.
name: Batjes, Niles H.
name: Brovkin, Victor
name: Carvalhais, Nuno
name: Chappell, Adrian
name: Ciais, Philippe
name: Davidson, Eric A.
name: Finzi, Adrien C.
name: Georgiou, Katerina
name: Guenet, Bertrand
name: Hararuk, Oleksandra
name: Harden, Jennifer W.
name: He, Yujie
name: Hopkins, Francesca
name: Jiang, Lifen
name: Koven, Charlie
name: Jackson, Robert B.
name: Jones, Chris D.
name: Lara, Mark J.
name: Liang, Junyi
name: McGuire, A. David
name: Parton, William
name: Peng, Changhui
name: Randerson, James T.
name: Salazar, Alejandro
name: Sierra, Carlos A.
name: Smith, Mathew J.
name: Tian, Hanqin
name: Todd-Brown, Katherine E.O.
name: Torn, Margaret
name: Van Groenigen, Kees Jan
name: Wang, Ying Ping
name: West, Tristram O.
name: Wei, Yaxing
name: Wieder, William R
name: Xia, Jianyang
name: Xu, Xia
name: Xu, Xiaofeng
name: Zhou, Tao
Publisher: name: AMER GEOPHYSICAL UNION
Year: 2016
Subjects: GLOBAL CLIMATE-CHANGE
ORGANIC-CARBON
DATA-ASSIMILATION
HETEROTROPHIC RESPIRATION
TEMPERATURE SENSITIVITY
TERRESTRIAL ECOSYSTEMS
LITTER DECOMPOSITION
PARAMETER-ESTIMATION
MICROBIAL MODELS
LAND MODELS

description: Soil carbon (C) is a critical component of Earth system models (ESMs), and its diverse representations are a major source of the large spread across models in the terrestrial C sink from the third to fifth assessment reports of the Intergovernmental Panel on Climate Change (IPCC). Improving soil C projections is of a high priority for Earth system modeling in the future IPCC and other assessments. To achieve this goal, we suggest that (1) model structures should reflect real-world processes, (2) parameters should be calibrated to match model outputs with observations, and (3) external forcing variables should accurately prescribe the environmental conditions that soils experience. First, most soil C cycle models simulate C input from litter production and C release through decomposition. The latter process has traditionally been represented by first-order decay functions, regulated primarily by temperature, moisture, litter quality, and soil texture. While this formulation well captures macroscopic soil organic C (SOC) dynamics, better understanding is needed of their underlying mechanisms as related to microbial processes, depth-dependent environmental controls, and other processes that strongly affect soil C dynamics. Second, incomplete use of observations in model parameterization is a major cause of bias in soil C projections from ESMs. Optimal parameter calibration with both pool-and flux-based data sets through data assimilation is among the highest priorities for near-term research to reduce biases among ESMs. Third, external variables are represented inconsistently among ESMs, leading to differences in modeled soil C dynamics. We recommend the implementation of traceability analyses to identify how external variables and model parameterizations influence SOC dynamics in different ESMs. Overall, projections of the terrestrial C sink can be substantially improved when reliable data sets are available to select the most representative model structure, constrain parameters, and prescribe forcing fields.