COS 101-7 - Land-use feedbacks constrain the land’s uptake of anthropogenic CO2

Wednesday, August 8, 2012: 3:40 PM
D135, Oregon Convention Center
Stefan Gerber1, Lars O. Hedin2, Sonja G. Keel3, Stephen W. Pacala2 and Elena Shevliakova2, (1)Soil and Water Science, University of Florida IFAS, Gainesville, FL, (2)Ecology and Evolutionary Biology, Princeton University, Princeton, NJ, (3)Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
Background/Question/Methods

Our understanding of Earth’s carbon-climate system depends critically upon interactions among the factors that govern the land carbon (C) cycle, of which ecosystem response to increasing CO2, changing land-use, and nitrogen (N) limitation of vegetation are central. Ocean-atmosphere records suggest that globally, the land has been a C source over most of the industrialized period and only recently became a sink. This net change in the biosphere is caused by two main and opposing phenomena: A C loss through land-use and a C gain in response to increased atmospheric CO2 and anthropogenic N deposition. Typically, analyses of the land carbon sink assume that the effects of land-use and the response of the terrestrial biosphere to CO2 and N enrichment on land are additive and do not interact.

Results/Conclusions

We present results from the Princeton-GFDL LM3V, a dynamic global land model that allows effects of land-use, CO2 increase, anthropogenic N deposition and recent climate change to interact and operate in concert. While our model recreates the independent records of land C dynamics over the past 200 years, our results also show critical interactions between effects of land-use and CO2 increase that reduce the capacity of the terrestrial biosphere to take up anthropogenic carbon. We quantify three sources of interactions: (i) an accelerated response of secondary vegetation to CO2 and N; (ii) a C sink foregone on agricultural lands that would have occurred if they had been left in their original state; and (iii) a compounded clearance loss of C from deforestation. We find that these effects combine to reduce the current net C uptake on land by (0.4 Pg yr-1), and that each effect is becoming increasingly important in determining the trajectory of CO2 uptake of the land biosphere.