Nonlinearity of Carbon Cycle Feedbacks

TitleNonlinearity of Carbon Cycle Feedbacks
Publication TypeJournal Article
Year of Publication2011
AuthorsZickfeld, K., M. Eby, H. D. Matthews, A. Schmittner, and A. J. Weaver
JournalJournal of Climate
Date PublishedAug
ISBN Number0894-8755
Accession NumberISI:000294490600004
Keywordsatmospheric co2, co2 fertilization, earth system model, future climate-change, photosynthesis, sinks, stomatal conductance

Coupled climate-carbon models have shown the potential for large feedbacks between climate change, atmospheric CO(2) concentrations, and global carbon sinks. Standard metrics of this feedback assume that the response of land and ocean carbon uptake to CO(2) (concentration-carbon cycle feedback) and climate change (climate-carbon cycle feedback) combine linearly. This study explores the linearity in the carbon cycle response by analyzing simulations with an earth system model of intermediate complexity [the University of Victoria Earth System Climate Model (UVic ESCM)]. The results indicate that the concentration-carbon and climate-carbon cycle feedbacks do not combine linearly to the overall carbon cycle feedback. In this model, the carbon sinks on land and in the ocean are less efficient when exposed to the combined effect of elevated CO(2) and climate change than to the linear combination of the two. The land accounts for about 80% of the nonlinearity, with the ocean accounting for the remaining 20%. On land, this nonlinearity is associated with the different response of vegetation and soil carbon uptake to climate in the presence or absence of the CO(2) fertilization effect. In the ocean, the nonlinear response is caused by the interaction of changes in physical properties and anthropogenic CO(2). These findings suggest that metrics of carbon cycle feedback that postulate linearity in the system's response may not be adequate.

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