October 20, 2020

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Alaskan Carbon-Climate Feedbacks Will Be Weaker Than Inferred from Short-Term Experiments

The Science

Climate warming is occurring fastest at high latitudes; however, a question remains as to how representative short-term warming manipulations are of tundra responses to a changing climate. Here researchers from NGEE-Arctic use a well-tested mechanistic land model to examine differences in ecosystem carbon cycle responses between observed and modeled short-term (<10 year) warming experiments and modeled long-term (100 year) changes under 21st century expected temperature, precipitation, and COconcentrations. Their simulations show that short-term experiments disturb the tundra carbon cycle in ways that are inconsistent, and stronger, than ecosystem responses to multi-decadal climate change (Bouskill et al., 2020).

The Impact

The experimental simulations show that short-term warming resulted in a much higher rate of soil carbon loss relative to multi-decadal responses. This can partly be attributed to long-term perturbation occurring at a lower rate of change. However, the short-term warming experiments favor heterotrophic activity, and hence soil carbon loss, and generally are not designed to capture longer-term, non-linear dynamics of vegetation, that occur in response to thermal, hydrological, and nutrient transformations belowground.

Summary

Climate warming is occurring fastest at high latitudes. Based on short-term field experiments, this warming is projected to stimulate soil organic matter decomposition, and promote a positive feedback to climate change. Scientists from NGEE-Arctic show here that the tightly coupled, nonlinear nature of high-latitude ecosystems implies that short-term (< 10 year) warming experiments produce emergent ecosystem carbon stock temperature sensitivities inconsistent with emergent multi-decadal responses. They first demonstrate that a well-tested mechanistic ecosystem model accurately represents observed carbon cycle and active layer depth responses to short-term summer warming in four diverse Alaskan sites. Next they found  that short-term warming manipulations do not capture the non-linear, long-term dynamics of vegetation, and thereby soil organic matter, that occur in response to thermal, hydrological, and nutrient transformations belowground. These results demonstrate significant spatial heterogeneity in multi-decadal Arctic carbon cycle trajectories and argue for more mechanistic models to improve predictive capabilities.

Principal Investigator

Nicholas Bouskill
Lawrence Berkeley National Laboratory
njbouskill@lbl.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

This research was supported by the Director, Office of Science, Office of Biological and Environmental Research of the U.S. Department of Energy under contract DE-AC02-05CH11231 to Lawrence Berkeley National Laboratory as part of the Next-Generation Ecosystem Experiments in the Arctic (NGEE-Arctic) project.

References

Bouskill, N. J., W. J. Riley, Q. Zhu, Z. A. Mekonnen, and R. F. Grant. "Alaskan carbon-climate feedbacks will be weaker than inferred from short-term experiments". Nature Communications 11 5798  (2020). https://doi.org/10.1038/s41467-020-19574-3.