B011-07
Divergence in Quantifying Terrestrial Fluxes of Carbon in Global Carbon Budgets

Monday, 7 December 2020: 16:24
Virtual
Sassan S Saatchi1, Liang Xu2, Yan Yang3, Yifan Yu2, Julia Pongratz4, A. Anthony Bloom3, Kevin W Bowman3, Junjie Liu3, John Worden3, Yi Yin5, Michael Keller6, Grant M Domke7, Ronald E McRoberts8, Christopher W Woodall9, Gert-Jan Nabuurs10, Nancy Harris11, David Schimel2 and Sergio de-Miguel Magana12, (1)NASA Jet Propulsion Laboratory, Carbon and Climate Group, Pasadena, CA, United States, (2)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (3)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, (4)Max Planck Institute for Meteorology, Hamburg, Germany, (5)California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, CA, United States, (6)USDA Forest Service, International Institute of Tropical Forestry, Rio Piedras, PR, United States, (7)US Forest Service, Northern Research Station, St. Paul, MN, United States, (8)USDA Forest Service, St. Paul, MN, United States, (9)US Forest Service St. Paul, St. Paul, MN, United States, (10)Wageningen University, Wageningen, Netherlands, (11)World Resources Institute, Washington DC, DC, United States, (12)University of Lleida, Department of Crop and Forest Sciences, Lleida, Spain
Recorded Presentation
Abstract:
The role of terrestrial ecosystems in the global carbon cycle as a significant and growing sink of atmospheric CO2 has been known for decades. This sink has been largely attributed to the forest ecosystem uptake. However, the magnitude of this sink, the location, and the cause of its interannual variability remain largely uncertain in the global carbon budget. This uncertainty is due to the complexity of quantifying two main additive fluxes: first, the net flux of carbon from land use, land use change and forestry (LULUCF) () that is estimated to be a source of carbon to the atmosphere, and second, the net flux of carbon driven by environmental changes (e.g. climate) () and is estimated to be a sink of carbon. Both fluxes include emissions from disturbance and uptakes from recovery of carbon. For , emissions are mostly from deforestation, degradation, and fire, and uptakes from secondary forest regeneration or afforestation. For , emissions are from natural or indirect human disturbances as in droughts, storms, climate change, and uptakes from regrowth, CO2 fertilization, and N deposition. Separating land use and environmental fluxes are important for carbon accounting and climate mitigations but has been proven to be difficult in practice. A combination of book-keeping models and Dynamic Global Vegetation Models (DGVMs) have been used to quantify and with divergent results at the global and regional scales.

Here we develop a global vegetation carbon stock change for this century from bottom-up techniques including forest inventory, airborne and satellite observations to quantify the contribution of live biomass carbon (forests and nonforests) to sinks and sources of carbon in this century (2000-2019). We compare our results with book-keeping models, DGVMs and top-down approaches to show, the sources of uncertainty in quantifying fluxes, and how bottom-up and top-down satellite observations can be integrated in improving terrestrial carbon fluxes.

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