A model investigation of vegetation-atmosphere interactions on a millennial timescale

N Devaraju,K Caldeira,R Nemani,G Bala,L Cao

doi:10.5194/bg-8-3677-2011

Abstract

Abstract. A terrestrial biosphere model with dynamic vegetation capability, Integrated Biosphere Simulator (IBIS2), coupled to the NCAR Community Atmosphere Model (CAM2) is used to investigate the multiple climate-forest equilibrium states of the climate system. A 1000-year control simulation and another 1000-year land cover change simulation that consisted of global deforestation for 100 years followed by re-growth of forests for the subsequent 900 years were performed. After several centuries of interactive climate-vegetation dynamics, the land cover change simulation converged to essentially the same climate state as the control simulation. However, the climate system takes about a millennium to reach the control forest state. In the absence of deep ocean feedbacks in our model, the millennial time scale for converging to the original climate state is dictated by long time scales of the vegetation dynamics in the northern high latitudes. Our idealized modeling study suggests that the equilibrium state reached after complete global deforestation followed by re-growth of forests is unlikely to be distinguishable from the control climate. The real world, however, could have multiple climate-forest states since our modeling study is unlikely to have represented all the essential ecological processes (e.g. altered fire regimes, seed sources and seedling establishment dynamics) for the re-establishment of major biomes.

Highlights

IntroductionDeforestation has both biogeochemical and biogeophysical influences on the climate: besides releasing carbon from land to the atmosphere (a biogeochemical effect), deforestation has biogeophysical effects such as changes in land surface albedo, surface roughness, surface energy fluxes, and cloud cover (Betts et al, 1996; Govindasamy et al, 2001; Betts, 2001; Brovkin et al, 1999; Feddema et al, 2005; Brovkin et al, 2006; Bala et al, 2007; Bonan, 2008; Brovkin et al, 2009; Findell et al, 2009)
We find that the time scale of slow component is dictated by the recovery of net primary productivity (NPP) in high latitudes which is similar to the vegetation fraction dynamics there as discussed below (Fig. 2)
We examined the possibility of multiple climate-forest states using a terrestrial biosphere model IBIS2 coupled to NCAR Community Atmosphere Model 2.0 of NCAR (CAM2)

Summary

Introduction

Deforestation has both biogeochemical and biogeophysical influences on the climate: besides releasing carbon from land to the atmosphere (a biogeochemical effect), deforestation has biogeophysical effects such as changes in land surface albedo, surface roughness, surface energy fluxes, and cloud cover (Betts et al, 1996; Govindasamy et al, 2001; Betts, 2001; Brovkin et al, 1999; Feddema et al, 2005; Brovkin et al, 2006; Bala et al, 2007; Bonan, 2008; Brovkin et al, 2009; Findell et al, 2009). Land cover changes alter the climate through physical, chemical, and biological processes and thereby could affect temperature, the hydrologic cycle, and atmospheric composition. Lawrence et al (2010) and Zhongfeng et al (2009) found that for land cover change, surface hydrology and its interaction with vegetation and soils has large impacts on the climate. Changes in land cover can have remote effects: Chen et al (2001); Snyder et al (2004) and Avissar et al (2004) have found that tropical deforestation is likely to induce changes in atmospheric circulation, and that these changes may have consequences on precipitation and temperature patterns on a global scale. Are there interactions between forests and the atmosphere (i.e. vegetationprecipitation feedback, vegetation-temperature feedback) that gets severely altered for large scale land cover change?

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Conclusion