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

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title = "Toward more realistic projections of soil carbon dynamics by Earth system models",
abstract = "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.",
keywords = "CMIP5, Earth system models, realistic projections, recommendations, soil carbon dynamics",
author = "Yiqi Luo and Anders Ahlstr{\"o}m and Allison, {Steven D.} and Batjes, {Niels H.} and Victor Brovkin and Nuno Carvalhais and Adrian Chappell and Philippe Ciais and Davidson, {Eric A.} and Adien Finzi and Katerina Georgiou and Bertrand Guenet and Oleksandra Hararuk and Harden, {Jennifer W.} and Yujie He and Francesca Hopkins and Lifen Jiang and Charlie Koven and Jackson, {Robert B.} and Jones, {Chris D.} and Lara, {Mark J.} and Junyi Liang and McGuire, {A. David} and William Parton and Changhui Peng and Randerson, {James T.} and Alejandro Salazar and Sierra, {Carlos A.} and Smith, {Matthew J.} and Hanqin Tian and Todd-Brown, {Katherine E.O.} and Margaret Torn and {Van Groenigen}, {Kees Jan} and Wang, {Ying Ping} and West, {Tristram O.} and Yaxing Wei and Wieder, {William R.} and Jianyang Xia and Xia Xu and Xiaofeng Xu and Tao Zhou",
year = "2016",
month = jan,
day = "1",
doi = "10.1002/2015GB005239",
language = "English",
volume = "30",
pages = "40--56",
journal = "Global Biogeochemical Cycles",
issn = "0886-6236",
publisher = "American Geophysical Union (AGU)",
number = "1",