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 LUO ET AL.SOIL CARBON MODELING 40 PUBLICATIONS

Estimating global cropland production from 1961 to 2010

“…More work should be directed to reduce uncertainties in regional model parameterizations (Le Quéré et al, 2015;Luo et al, 2016). This paper focuses on both the continental and country scales to calibrate key parameters to better constrain the future projections of global cropland NPP.…”

“…The importance of parameter calibration has been recognized and addressed by numerous modeling studies Chen et al, 2011;Crowther et al, 2016;Luo et al, 2016;Ogle et al, 2010;Peng et al, 2013). In addition, regional calibrated parameters are critical for global-scale modeling (Le Quéré et al, 2016).…”

ORCHIDEE-SOM: modeling soil organic carbon (SOC) and dissolved organic carbon (DOC) dynamics along vertical soil profiles in Europe

“…Several studies have recognized these processes as key emergent properties for understanding soil C dynamics; however, they have not yet been explicitly integrated into land surface models (Davidson et al, 2014;Finke and Hutson, 2008;Schmidt et al, 2011). Since it is not feasible to incorporate all the involved factors and processes into a global soil model, further research is still needed to elucidate which processes should be explicitly represented and which can be neglected in order to achieve the best simulations and predictions of SOC dynamics (Luo et al, 2016). Future model applications will require further empirical parameterization.…”

Ideas and perspectives: Can we use the soil carbon saturation deficit to quantitatively assess the soil carbon storage potential, or should we explore other strategies?

“…Second, SOC dynamic models can still be significantly improved, in particular their initialization is still very problematic, and they do not accurately simulate the effect on SOC stocks of 15 management practices such as no tillage with permanent cover crop or agroforestry (e.g. Luo et al, 2016). Third, the model predictions need to be validated using data from resampled monitoring networks.…”