How strong is carbon cycle‐climate feedback under global warming?

Abstract

[1] The behavior of the coupled carbon cycle and physical climate system in a global warming scenario is studied using an Earth system model including the atmosphere, land, ocean, and the carbon cycle embedded in these components. A fully coupled carbon-climate simulation and several sensitivity runs were conducted for the period of 1860 -2100 with prescribed IPCC-SRES-A1B emission scenario. Results indicate a positive feedback to global warming from the interactive carbon cycle, with an additional increase of 90 ppmv in the atmospheric CO 2 , and 0.6 degree additional warming, thus confirming recent results from the Hadley Centre and IPSL. However, the changes in various carbon pools are more modest, largely due to the multiple limiting factors constraining terrestrial productivity and carbon loss. The large differences among the three models are manifestations of some of the poorly constrained processes such as the global strength of the CO 2 fertilization effect and the turnover time and rates of soil decomposition.

Ecosystems as Climate Controllers – Biotic Feedbacks

“…This is in contrast with the previous, only-ocean models according to which the ocean carbon uptake is decreased by climate change (Joos et al, 1999;Sarmiento et al, 1998). Zeng et al, 2004, Maryland University, USA, the difference between the outputs of the simulations is caused by the determination of the terrestrial carbon content.…”

Tropical forests and the changing earth system

“…However, in an alternative fully coupled model (UMD), while predicting higher atmospheric CO 2 (by 90 p.p.m.v.) and temperatures (by 0.6 8C) by 2100 compared to the uncoupled model, there is no Amazon-drought and subsequent dieback (Zeng et al 2004). This is because of the poor agreement between the fully coupled models on changing precipitation patterns, in terms of locations, durations and magnitudes (Zeng et al 2004).…”

Estimating carbon budgets for U.S. ecosystems

“…The carbon balance of terrestrial ecosys tems may become increasingly susceptible to baseline pool declines with climate warm ing [Zeng et al, 2004]. Large areas of the Pacific and Rocky Mountain regions of the country may have recently lost carbon from baseline pools, possibly due to disturbances combined with variable climate patterns.…”