Abstract
Abstract. Climate–vegetation feedback has the potential to significantly contribute to climate change, but little is known about its range of uncertainties. Here, using an Earth system model of intermediate complexity we address possible uncertainties in the strength of the biogeophysical climate–vegetation feedback using a single-model multi-physics ensemble. Equilibrium experiments with halving (140 ppm) and doubling (560 ppm) of CO2 give a contribution of the vegetation–climate feedback to global temperature change in the range −0.3 to −0.1 °C and −0.1 to 0.2 °C, respectively. There is an asymmetry between warming and cooling, with a larger, positive vegetation–climate feedback in the lower CO2 climate. Hotspots of climate–vegetation feedback are the boreal zone, the Amazon rainforest and the Sahara. Albedo parameterization is the dominant source of uncertainty in the subtropics and at high northern latitudes, while uncertainties in evapotranspiration are more relevant in the tropics. We analyse the separate impact of changes in stomatal conductance, leaf area index and vegetation dynamics on climate and we find that different processes are dominant in lower and higher CO2 worlds. The reduction in stomatal conductance gives the main contribution to temperature increase for a doubling of CO2, while dynamic vegetation is the dominant process in the CO2 halving experiments. Globally the climate–vegetation feedback is rather small compared to the sum of the fast climate feedbacks. However, it is comparable to the amplitude of the fast feedbacks at high northern latitudes where it can contribute considerably to polar amplification. The uncertainties in the climate–vegetation feedback are comparable to the multi-model spread of the fast climate feedbacks.
Highlights
Vegetation distribution is controlled by climate, predominantly by temperature and precipitation (e.g. Holdridge, 1947; Köppen, 1936; Prentice et al, 1992)
The third issue we explore in this study is the state-dependence of the climate–vegetation feedback, in particular the asymmetry between colder and warmer climates induced by lower and higher CO2 concentrations, respectively
Using a multi-physics ensemble we studied the uncertainties in the strength of the biogeophysical vegetation–climate feedback
Summary
Vegetation distribution is controlled by climate, predominantly by temperature and precipitation (e.g. Holdridge, 1947; Köppen, 1936; Prentice et al, 1992). Vegetation structure is influenced by the atmospheric CO2 concentration, which affects photosynthesis and the allocation of carbon to the different biomass pools. This can result in changes in physically relevant characteristics of the vegetation, such as the leaf area index (LAI) Vegetation in turn influences climate through various physical and biochemical processes. Changes in vegetation affect the fluxes of sensible and latent heat from the surface to the atmosphere, the amount of short-wave radiation absorbed by the surface and the exchange of momentum between the land surface and the air (e.g. Brovkin et al, 2009; Kleidon et al, 2000; Bala et al, 2007).
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