January 20, 2020

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Models Predict Rapid and Deep Soil Warming Over the 21st Century

Models predict rapid and deep soil warming over the 21st century.

The Science

The average of 14 Earth System Models predicts that globally, soils will warm by 4.5˚C or 2.3˚C by the end of the 21st century under RCP’s 8.5 or 4.5, respectively, and that deep soils (100 cm) will warm by the same amount as near surface (1 cm) soils. In regions with snow and ice, this soil warming is predicted to occur slightly slower than air warming above it.

The Impact

The impact of warming on deep soils, not just surface soils, must be taken into consideration to accurately predict carbon-climate feedbacks over the 21st century. Particularly in cold regions, using soil warming rather than air warming projections may improve predictions of temperature-sensitive soil processes, like decomposition.

Summary

Despite the fundamental importance of soil temperature for Earth’s carbon and energy budgets, ecosystem functioning, and agricultural production, studies of climate change impacts on soil processes have mainly relied on air temperatures, assuming they are accurate proxies for soil temperatures. Researchers from Lawrence Berkeley National Laboratory evaluated changes in soil temperature, moisture, and air temperature predicted over the 21st century from 14 Earth system models. The model ensemble predicted a global mean soil warming of 2.3 ± 0.7 and 4.5 ± 1.1 °C at 100‐cm depth by the end of the 21st century for RCPs 4.5 and 8.5, respectively. Soils at 100 cm warmed at almost exactly the same rate as near‐surface (~1 cm) soils. Globally, soil warming was slightly slower than air warming above it, and this difference increased over the 21st century. Regionally, soil warming kept pace with air warming in tropical and arid regions but lagged air warming in colder regions. Thus, air warming is not necessarily a good proxy for soil warming in cold regions where snow and ice impede the direct transfer of sensible heat from the atmosphere to soil. Despite this effect, high‐latitude soils were still projected to warm faster than elsewhere, albeit at slower rates than surface air above them. When compared with observations, the models were able to capture soil thermal dynamics in most biomes, but some failed to recreate thermal properties in permafrost regions. Particularly in cold regions, using soil warming rather than air warming projections may improve predictions of temperature‐sensitive soil processes.

Principal Investigator

Margaret Torn
Lawrence Berkeley National Laboratory
mstorn@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 in part by the U.S. Department of Energy Office of Science, Office of Biological and Environmental Research Terrestrial Ecosystem Science and Regional and Global Model Analysis Programs, under Award DE‐SC‐0001234.

References

Soong, J. L., C. L. Phillips, C. Ledna, and C. D. Koven, et al. "CMIP5 Models Predict Rapid and Deep Soil Warming Over the 21st Century". JGR Biogeosciences 125 (2), e2019JG005266  (2020). https://doi.org/10.1029/2019JG005266.