August 12, 2020

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Atmospheric CO2 and Terrestrial Carbon Feedback

CO2 effects on terrestrial ecosystem carbon subsidize CO2 emissions and are complex, uncertain, and likely to decline into the future.

The Science

The global responses of plants and soils to increasing atmospheric carbon dioxide (CO2) are slowing the rate of climate change, but these responses are complicated and their understanding lacks consensus. The research team led by scientists at Oak Ridge National Laboratory integrated a range of diverse evidence, finding support for the idea that plants and soils store more carbon in response to increasing atmospheric CO2. However, the size of this response is uncertain. Other agents of global change (e.g., land cover change) are also affecting carbon storage, complicating the attribution of change to any single factor. Despite the uncertainty, it is expected that the change in carbon storage will diminish going into the future.

The Impact

The priority of climate change mitigation efforts depends directly on how future terrestrial carbon storage will evolve. This study integrates a wide range of evidence from forests, tree-rings, experiments, volcanic CO2 springs, atmospheric and ice-core measurements, satellites, and flux towers to provide a common foundation for future research into this crucial ecosystem service. Improved understanding will help inform better management of natural resources and the services they provide to humanity.

Summary

Atmospheric CO2 is increasing, leading to climate change. Increasing CO2 also increases leaf-scale photosynthesis and water-use efficiency, which has the potential to increase plant biomass and soil organic matter. This enhanced removal of carbon from the atmosphere into terrestrial ecosystems (a carbon sink) could slow the pace of climate change. However, ecosystem CO2 responses are complex and evidence for “CO2 fertilization” of the terrestrial carbon sink can appear contradictory. An international team of over 60 scientists, led by scientists at Oak Ridge National Laboratory, synthesized theory and broad, multidisciplinary evidence for the effects of increasing CO2 on the global terrestrial carbon sink.

Evidence for increasing terrestrial ecosystem carbon storage caused by increasing atmospheric CO2 indicates a potential highly valuable ecosystem service that effectively subsidizes fossil fuel emissions by slowing the rate of CO2 accumulation in the atmosphere. But due to concurrent changes caused by other global change factors, the size of this subsidy remains unclear. Diminishing direct physiological responses, increasing mortality, nutrient limitations, and other temperature-related restrictions are highly likely to limit future increases in terrestrial carbon storage due to increasing atmospheric CO2. A decline in this subsidy will result in accelerated climate change per unit of anthropogenic CO2 emissions.

Principal Investigator

Anthony Walker
Oak Ridge National Laboratory
walkerap@ornl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

Office of Biological and Environmental Research within the U.S. Department of Energy (DOE) Office of Science: FACE Model Data Synthesis project. Lead co-authors were supported by: Australian Research Council (ARC) Discovery Grant (DP190101823), NASA Terrestrial Ecosystems Grant 80NSSC19M0103, European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 647204).

Related Links

References

Walker, A.P., M. G. De Kauwe, A. Bastos, and S. Belmecheri, et al. "Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2". New Phytologist 229 (5), 2413–2445  (2021). https://doi.org/10.1111/nph.16866.

Walker, A. P., A. S. Powell, and B. N. Taylor. "Literature synthesis and modelling data of terrestrial ecosystem responses to increasing atmospheric CO2". ESS-DIVE (2020). https://data.ess-dive.lbl.gov/view/doi:10.15485/1644687.