Climate Change Will Result in Large Increase in Methane Emissions in Polygonal Tundra

Methane emissions responded strongly to changes in temperature, atmospheric carbon dioxide, precipitation, and landscape-scale hydrology.

The Science

Scientists from the Next-Generation Ecosystem Experiments (NGEE)–Arctic project used ecosys, a mechanistic three-dimensional ecosystem model, to project how carbon dioxide (CO2) and methane (CH4) emissions at the NGEE–Arctic Utqiagvik polygonal tundra site will change over the 21st century. The model very accurately matched a wide range of NGEE–Arctic observations. CH4 emissions responded strongly to changes in temperature, atmospheric CO2, and precipitation, and they represent large potential radiative feedbacks with climate.

The Impact

Land models predict a wide range of potential permafrost tundra CO2 and CH4 emissions over the 21st century. In this study, a team of scientists from Lawrence Berkeley National Laboratory identified dominant processes responsible for variations of these emissions over time and space. They found that predicted increases in CO2 uptake were offset by large CH4 emissions, and that potential increases in drainage would decrease net CH4 emissions, highlighting the importance of landscape-scale hydrology for 21st century predictions.

Summary

Model projections of CO2 and CH4 emissions in permafrost systems vary widely between land models. In this study, the researchers used ecosys to examine how climate change will affect these emissions in a polygonal tundra site at Utqiagvik (formerly Barrow) Alaska. The model has been thoroughly tested against NGEE–Arctic thermal, hydrological, and biogeochemical observations. During the Representative Concentration Pathway (RCP) 8.5 climate change scenario from 2015 to 2085, rising air temperatures, atmospheric CO2, and precipitation (P) increased net primary productivity consistently with biometric estimates. Concurrent increases in heterotrophic respiration (Rh) were offset by increases in CH4 emissions. Both these increases were smaller if boundary conditions were altered to increase landscape drainage, highlighting the importance of these large-scale hydrological dynamics for carbon cycle predictions.

Principal Investigator

William Riley
Lawrence Berkeley National Laboratory
wjriley@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 Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, under Contract No. DE-AC02-05CH11231 as part of the Next-Generation Ecosystem Experiments (NGEE)–Arctic project.

References

Grant, R. F., Z. A. Mekonnen, W. J. Riley, and B. Arora, et al. "Modeling climate change impacts on an Arctic polygonal tundra. Part 2: Changes in CO2 and CH4 exchange depend on rates of permafrost thaw as affected by changes in vegetation and drainage". Journal of Geophysical Research: Biogeosciences 124 (5), 1323–1341  (2019). https://doi.org/10.1029/2018JG004645.