The Science

At high-latitudes, sunlight and air temperature change dramatically with the seasons. Summer days are warm and very long. Winter days are freezing and very short. As a result, plants and microbes are most active in summer. However, climate change will cause air temperatures to rise higher and faster at high-latitudes than anywhere else. Scientists use mathematical models to simulate how ecosystems will respond to climate change. In this study, the ecosys model was used to predict changes to the seasonality of plant and microbial activity throughout the coming century in Alaska.

The Impact

High-latitude soils store large amounts of carbon that could be released to the atmosphere, thus making it a region of interest to climate scientists and policymakers. This study predicts that high-latitude ecosystems are carbon sinks that will continue to accumulate carbon throughout the century. Analysis of seasonal dynamics provides support for these predictions. Some of the projected changes to carbon cycle seasonality are unexpected. In particular, the finding that spring uptake will outpace summer uptake by year 2100 merits further investigation. The results of this study are also used to address mismatches between recent model and observation-based studies of high-latitude carbon balance.

Summary

ecosys, a well-tested and process-rich mechanistic ecosystem model, was used to explore how climate warming will shift carbon cycle seasonality in Alaska. Model performance was evaluated using site and regional data products, and recently reported large carbon losses during the fall and winter were successfully reproduced. Nevertheless, the model predicted that the system is a carbon sink. This result helps resolve current conflicts between modeled and observation-based estimates of high-latitude carbon balance. 

The results of this study suggest that climate change will result in surprisingly large changes in carbon cycle seasonality at high-latitudes. In particular, spring net carbon uptake is projected to overtake summer net carbon uptake in the coming century. This shift is driven by a large relaxation of spring temperature limitation to plant productivity. Additionally, warmer soil temperatures and increased carbon inputs lead to combined fall and winter carbon losses that are larger than summer net uptake by year 2100. However, this increase in microbial activity leads to more rapid nitrogen cycling and increased plant nitrogen uptake during the fall and winter that supports large increases in spring plant productivity. Taken together, these results suggest that high-latitudes will continue to accumulate carbon throughout this century.

Principal Investigator

Ian Shirley
Lawrence Berkeley National Laboratory
ishirley@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 (BER) within the U.S. Department of Energy’s (DOE) Office of Science to Lawrence Berkeley National Laboratory (LBNL) as part of the Next-Generation Ecosystem Experiments—Arctic (NGEE–Arctic) project. 

References