Climate indices as predictors of global soil organic carbon stocks

ABSTRACT

Global soils store more carbon than the atmosphere and terrestrial vegetation combined, with a significant proportion located in colder regions. Earth system models incorporating climate-carbon feedback suggest that a warming climate can potentially destabilize soil carbon storage, leading to carbon release into the atmosphere. However, existing models are based on limited measurements of soil organic carbon (SOC) loss and a comprehensive global-scale climate indices that effectively characterizes climate-SOC relationships is currently lacking. In this study, we present a synthetic analysis that evaluates the effectiveness of different climate indices in estimating SOC stocks using a global compilation of SOC data and the Boltzmann Sigmoidal Model (BSM). Our findings reveal that a climate index, defined as $\mathrm{TD}\text{-}\mathrm{Index}=\exp (-0.002T-0.8D)$, where T and D are mean century temperature (MCT) and dryness respectively, serves as the most reliable predictor for SOC stocks. Furthermore, we observed temperature tipping points for SOC, ranging from −4.5 to −3°C for different soil layers. As the temperature transitions from being below to above the tipping point, the SOC shifts from a stable, high state to a rapid decline. An analysis of the projected temperatures for SOC under various future greenhouse gas emissions scenarios showed a northward shift in the northern hemisphere, potentially opening up vast areas of arctic territory to increased SOC loss from the soils, with corresponding emissions of the stored carbon into the atmosphere. Our findings open up new avenues for research on and management strategies for climate-related SOC dynamics.

KEYWORDS:

• Soil organic carbon
• Boltzmann Sigmoidal Model
• future projections
• climate indices
• carbon-temperature patterns

Acknowledgements

CY completed this research when he was a Fulbright Visiting Professor at University of Innsbruck with support from the US-Austria Fulbright Program. DC is supported by the Swedish national strategic research area BECC and Swedish Research Council (VR: 2021–02163 and 2022-06011).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Long-term temperature and precipitation derived from CRU TS v. 4.04 are publicly available at https://crudata.uea.ac.uk/cru/data/hrg/cru_ts_4.04/. Long-term radiation data are publicly available at https://psl.noaa.gov/data/gridded/data.20thC_ReanV3.html. SOC data are publicly available at https://data.isric.org/geonetwork/srv/chi/catalog.search#/metadata/98062ae9-911d-4e04-80a9-e4b480f87799. The CMIP6 data are publicly available at https://esgf-node.llnl.gov/projects/cmip6/. All other data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

Additional information

Notes on contributors

Qin Zhang

Qin Zhang is a PhD student at the Dalian University of Technology, Dalian, China. His main research interest is the regulation of water on climate-carbon cycle feedback mechanism.

Chuixiang Yi

Dr. Chuixiang Yi is a professor of Queens College of City University of New York, New York, USA. His research is focused on canopy fluid mechanics including developing theoretical formulations, designing observations, and performing numerical simulations to understand the physical, biological, and chemical processes that control the exchange of trace gas between the vegetation and the atmosphere. Yi was a leading recipient of World Meteorological Organization Norbert-Gerbier-MUMM International Award in 2012. Yi was a Rossby Fellow from International Meteorological Institute at Stockholm University during 2014–2015 and a Fulbright Visiting Professor at University of Innsbruck in 2022–2023. His Lab has a broad spectrum of research projects across Forest Ecology, Remote Sensing, Micrometeorology, Climate Change, Paleoclimate, and Hydrology. The overall goal of his team is to use nonlinear system theory, stability analysis approach, resilience, and tipping point concepts to predict potential critical transitions of nature and society in facing extremes induced by the warming climate.

Georg Wohlfahrt

Dr. Georg Wohlfahrt is an associate professor of ecology at the Universität Innsbruck Innsbruck, Austria. He has a general interest in biosphere-atmosphere interactions and feedbacks with a focus on improving carbon cycle estimates, especially of gross primary productivity and ecosystem respiration.

Deliang Chen

Dr. Deliang Chen is a professor of Physical Meteorology and August Röhss Chair in Physical Geography at the University of Gothenburg, Gothenburg, Sweden. His main research interests are Earth System Science and global environmental change with a focus on climate change and impacts in Europe and Asia. He is an elected member of seven Academies in the world including the Royal Swedish Academy of Sciences and The World Academy of Sciences. He has served on numerous international and national committees and boards, as well as advised various governmental, intergovernmental, and international non-governmental bodies including funding agencies. A recent example is his role in the 6th IPCC Working Group I assessment report as a coordinating lead author.

Max Rietkerk

Dr. Max Rietkerk is a professor of Spatial Ecology and Global Change at Utrecht University, TC Utrecht, the Netherlands. His research and teaching is about Ecology, Environmental Sciences, and current topics on Global Change and Ecosystems. His research concentrates on Spatial Ecology and Global Change. His research has been published in more than 100 articles in international refereed scientific journals, including top journals such as Nature and Science.

Zhenkun Tian

Dr. Zhenkun Tian is an associate professor of Mathematics and Computer of China University of Labor Relations, Beijing, China. His main research interests are climate-carbon cycle related digital image processing, remote sensing applications, machine learning, spatial data analysis.

Mousong Wu

Dr. Mousong Wu is an associate professor of Earth System Science of Nanjing University, Nanjing, China. His main research interests are terrestrial carbon cycle and data assimilation; algorithms for assimilating data from multi-source remote sensing observations; hydrological and ecosystem processes in cold regions; development and application of coupled soil-plant-atmosphere water-heat-carbon and nitrogen models; water-carbon management in agriculture under changing climate conditions.

Eric Kutter

Dr. Eric Kutter is a researcher of Barry Commoner Center for Health & the Environment, Queens College, City University of New York, Flushing, USA. His main research interests are fluxes of CO₂, H₂O and energy in forest ecosystems using towers for eddy-covariance and vertical profile measurements; improving measurement methods and analyzing measurement data.

Jianxu Han

Jianxu Han is a PhD student at the Dalian University of Technology, Dalian, China. Her main research interest is water environment pollution management and watershed Modelling.

George Hendrey

Dr. George Hendrey is a retired Distinguished Professor in the School of Earth and Environmental Science of Queens College, City University of New York, New York, USA. He is the designer for Free-Air CO2 Enrichment (FACE) experiments, testing global ecosystem responses to future increases in atmospheric CO2. He has been working on development of a NPP correction based on photosynthesis experiments in which CO2 is oscillated in a controlled way in a leaf chamber while measuring photosynthetic fluorescence and/or CO2 assimilation.

Shiguo Xu

Dr. Shiguo Xu is a professor of hydrology of Dalian University of Technology, Dalian, China. His main research interests are rainwater resource utilization and management; Environmental water resources system analysis; Wetland water cycle and ecological environment management; Environmental protection and construction of rivers and watersheds; Reservoir pollution prevention and management.