Trends in the Global Net Land Sink and Their Sensitivity to Environmental Forcing Factors: Results From the Multi-Scale Synthesis and Terrestrial Model Intercomparison Project (MsTMIP)

Deborah N Huntzinger1, Christopher Schwalm2, Anna M Michalak3, Yaxing Wei4, Robert B Cook4, Kevin M Schaefer5, Andrew R Jacobson6, Muhammad Altaf Arain7, Philippe Ciais8, Joshua Fisher9, Daniel J Hayes10, Maoyi Huang11, Suo Huang12, Dr. Akihiko Ito13, Atul K Jain14, Huimin Lei15, Chaoqun Lu16, Fabienne Maignan17, Jiafu Mao18, Nick Parazoo19, Shushi Peng17, Changhui Peng20, Benjamin Poulter21, Daniel M Ricciuto18, Xiaoying Shi10, Hanqin Tian22, Ning Zeng23, Fang Zhao23, Qiuan Zhu24 and Weile Wang25, (1)Northern Arizona University, School of Earth Sciences and Environmental Sustainability, Flagstaff, AZ, United States, (2)Northern Arizona University, Flagstaff, AZ, United States, (3)Google Research, Mountain View, United States, (4)Oak Ridge National Laboratory, Oak Ridge, TN, United States, (5)National Snow and Ice Data Center, Cooperative Institute for Research in the Environmental Sciences, University of Colorado at Boulder, Boulder, Colorado, U.S.A, Boulder, United States, (6)University of Colorado at Boulder, CIRES, Boulder, United States, (7)McMaster University, School Of Earth, Environment and Society, Hamilton, ON, Canada, (8)LSCE Laboratoire des Sciences du Climat et de l'Environnement, Gif-Sur-Yvette, France, (9)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, United States, (10)Oak Ridge National Laboratory, Oak Ridge, United States, (11)National Weather Service, National Oceanic and Atmospheric Administration, Office of Science and Technology Integration, Silver Spring, MD, United States, (12)McMaster University, Hamilton, ON, Canada, (13)The University of Tokyo, Graduate School of Agricultural and Life Sciences, Tokyo, Japan, (14)University of Illinois at Urbana Champaign, Urbana, United States, (15)Pacific NW Nat'l Lab-Atmos Sci, Richland, WA, United States, (16)Auburn University at Montgomery, Montgomery, AL, United States, (17)CEA Saclay DSM / LSCE, Gif sur Yvette, France, (18)Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, TN, United States, (19)NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, (20)University of Quebec at Montreal UQAM, Department of Biology Sciences, Montreal, QC, Canada, (21)Spark Climate Solutions, Greenbelt, United States, (22)Auburn University, Auburn, United States, (23)University of Maryland, College Park, MD, United States, (24)University of Quebec at Montreal, Institute of Environment Sciences, Montreal, QC, Canada, (25)CSUMB & NASA/AMES, Seaside, CA, United States
Abstract:
Predictions of future climate depend strongly on trends in net uptake or release of carbon by the land biosphere. However, model estimates of the strength of the net global land sink during the Industrial Era vary widely. Here we evaluate results from an ensemble of uncoupled models taken from the Multi-scale Synthesis and Terrestrial Model Intercomparison Project (MsTMIP) and forced by the same input fields. When compared to estimates inferred from atmospheric CO2 observations (i.e., fossil fuel emission + net land use change - atmospheric increase - ocean uptake), MsTMIP models estimate, on average, a stronger global net land uptake of carbon (e.g., -0.3 to 8.7 Pg C/yr from 2000 to 2010, where a negative flux represents a net release to the atmosphere). Some models consistently show the land surface as a net source of carbon to the atmosphere, which is inconsistent with the other terms in the global anthropogenic CO2 budget. In addition, regional differences in land carbon exchange are compared across models and to estimates derived from atmospheric inversions and inventory based approaches. Using the semi-factorial simulations of the MsTMIP activity, we examine how model estimates of the cumulative global net land sink diverge over the period 1900 to 2010, and the degree to which model sensitivity to forcing factors contribute to this divergence. We link differences in estimates of the cumulative land sink back to each model’s sensitivity to climate variability, CO2 fertilization, nitrogen limitation, and net land-use change. Throughout the 110-year time period, the strength of carbon uptake in most models appears to be strongly sensitive to atmospheric CO2 concentrations (CO2 fertilization effect). The strength of this relationship, however, varies across models depending on model structure (e.g., stronger CO2 fertilization effect in models without an interactive nitrogen cycle with N limitations) and across decades (e.g., strong sensitivity of net flux to increasing atmospheric CO2 concentrations after 1970s).

http://nacp.ornl.gov/MsTMIP.shtml

Huntzinger et al. (2014) NACP MsTMIP - Part 1: Overview and Experimental Design. www.geosci-model-dev.net/6/2121/2013/

Wei et al. (2014) NACP MsTMIP: Global and North American Driver Data for Multi-Model Intercomparison. DOI:  10.3334/ORNLDAAC/1220

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