Bergen earth system model (BCM-C): model description and regional climate-carbon cycle feedbacks assessment

Abstract

Abstract. A complex earth system model is developed by coupling terrestrial and oceanic carbon cycle models into the Bergen Climate Model. Two model simulations (one with climate change inclusions and the other without) are generated to study the large scale climate and carbon cycle variability as well as its feedback for the period 1850–2100. The simulations are performed based on historical and future IPCC CO2 emission scenarios. Globally, a pronounced positive climate-carbon cycle feedback is simulated by the terrestrial carbon cycle model, but less significant signals are shown by the oceanic counterpart. Over land, the regional climate-carbon cycle feedback is highlighted by increased soil respiration, which exceeds the enhanced production due to the atmospheric CO2 fertilization effect, in the equatorial and northern hemisphere mid-latitude regions. Although the model generates nearly identical global oceanic carbon uptake between the coupled and uncoupled simulations, our analysis indicates that there are substantial temporal and spatial variations in air-sea CO2 fluxes. This implies feedback mechanisms act inhomogeneously in different ocean regions. In the North Atlantic subpolar gyre, the simulated future cooling of SST improves the CO2 gas solubility in seawater, and hence reduces the strength of positive climate-carbon cycle feedback in this region. In most of the ocean regions, the changes in Revelle factor is dominated by changes in surface pCO2, and not by the warming of SST. Therefore, the solubility feedback is more prominent than the buffer capacity feedback. In our climate change simulation, the opening of Southern Ocean sea ice due to melting allows an additional ~20 Pg C uptake as compared to the simulation without climate change.