Increase of carbon cycle feedback with climate sensitivity: results from a coupled climate and carbon cycle model

B Govindasamy,S Thompson,A Mirin,M Wickett,C Delire,K Caldeira

doi:10.1111/j.1600-0889.2005.00135.x

B Govindasamy, S Thompson + Show 4 more

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https://doi.org/10.1111/j.1600-0889.2005.00135.x

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Abstract

Coupled climate and carbon cycle modelling studies have shown that the feedback between global warming and the carbon cycle, in particular the terrestrial carbon cycle, could accelerate climate change and result in greater warming. In this paper we investigate the sensitivity of this feedback for year 2100 global warming in the range of 0 to 8 K. Differing climate sensitivities to increased CO2content are imposed on the carbon cycle models for the same emissions. Emissions from the SRES A2 scenario are used. We use a fully coupled climate and carbon cycle model, the INtegrated Climate and CArbon model (INCCA), the NCAR/DOE Parallel Climate Model coupled to the IBIS terrestrial biosphere model and a modified OCMIP ocean biogeochemistry model. In our integrated model, for scenarios with year 2100 global warming increasing from 0 to 8 K, land uptake decreases from 47% to 29% of total CO2emissions. Due to competing effects, ocean uptake (16%) shows almost no change at all. Atmospheric CO2 concentration increases are 48% higher in the run with 8 K global climate warming than in the case with no warming. Our results indicate that carbon cycle amplification of climate warming will be greater if there is higher climate sensitivity to increased atmospheric CO2 content; the carbon cycle feedback factor increases from 1.13 to 1.48 when global warming increases from 3.2 to 8 K.

Highlights

The physical climate system and the global carbon cycle are tightly coupled, as changes in climate affect exchange of atmospheric CO2 with the land surface and ocean, and changes in CO2 fluxes affect Earth’s radiative forcing and the physical climate system
Our results indicate that carbon cycle amplification of climate warming will be greater if there is higher climate sensitivity to increased atmospheric CO2 content; the carbon cycle feedback factor increases from 1.13 to 1.48 when global warming increases from 3.2 to 8 K
The climate model used here has equilibrium climate sensitivity to increased CO2 (2.1 K per doubling) that is at the lower end of the range of the general model population (IPCC, 2001)

Summary

Introduction

The physical climate system and the global carbon cycle are tightly coupled, as changes in climate affect exchange of atmospheric CO2 with the land surface and ocean, and changes in CO2 fluxes affect Earth’s radiative forcing and the physical climate system. Anthropogenic emissions of fossil fuels and land use change are expected to lead to significant climate change in the future (IPCC, 2001). Both climate change and elevated CO2 have impact on land and ocean carbon uptake. Studies on ocean carbon uptake have suggested that global warming reduces uptake of carbon by oceans (Sarmiento and Le Quere, 1996; Sarmiento et al, 1998). This occurs primarily because CO2 is less soluble in warmer water and increased stratification would tend to inhibit downward transport of anthropogenic carbon

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