Toward more realistic projections of soil carbon dynamics by Earth system models

TY - JOUR

T1 - Toward more realistic projections of soil carbon dynamics by Earth system models

AU - Luo, Yiqi

AU - Ahlström, Anders

AU - Allison, Steven D.

AU - Batjes, Niels H.

AU - Brovkin, Victor

AU - Carvalhais, Nuno

AU - Chappell, Adrian

AU - Ciais, Philippe

AU - Davidson, Eric A.

AU - Finzi, Adien

AU - Georgiou, Katerina

AU - Guenet, Bertrand

AU - Hararuk, Oleksandra

AU - Harden, Jennifer W.

AU - He, Yujie

AU - Hopkins, Francesca

AU - Jiang, Lifen

AU - Koven, Charlie

AU - Jackson, Robert B.

AU - Jones, Chris D.

AU - Lara, Mark J.

AU - Liang, Junyi

AU - McGuire, A. David

AU - Parton, William

AU - Peng, Changhui

AU - Randerson, James T.

AU - Salazar, Alejandro

AU - Sierra, Carlos A.

AU - Smith, Matthew J.

AU - Tian, Hanqin

AU - Todd-Brown, Katherine E.O.

AU - Torn, Margaret

AU - Van Groenigen, Kees Jan

AU - Wang, Ying Ping

AU - West, Tristram O.

AU - Wei, Yaxing

AU - Wieder, William R.

AU - Xia, Jianyang

AU - Xu, Xia

AU - Xu, Xiaofeng

AU - Zhou, Tao

PY - 2016/1/1

Y1 - 2016/1/1

N2 - 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.

AB - 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.

KW - CMIP5

KW - Earth system models

KW - realistic projections

KW - recommendations

KW - soil carbon dynamics

U2 - 10.1002/2015GB005239

DO - 10.1002/2015GB005239

M3 - Article

AN - SCOPUS:84956641600

VL - 30

SP - 40

EP - 56

JO - Global Biogeochemical Cycles

JF - Global Biogeochemical Cycles

SN - 0886-6236

IS - 1

ER -