Abstract
Abstract. The terrestrial biosphere is thought to be a key component in the climatic variability seen in the palaeo-record. It has a direct impact on surface temperature through changes in surface albedo and evapotranspiration (so-called biogeophysical effects) and, in addition, has an important indirect effect through changes in vegetation and soil carbon storage (biogeochemical effects) and hence modulates the concentrations of greenhouse gases in the atmosphere. The biogeochemical and biogeophysical effects generally have opposite signs, meaning that the terrestrial biosphere could potentially have played only a very minor role in the dynamics of the glacial–interglacial cycles of the late Quaternary. Here we use a fully coupled dynamic atmosphere–ocean–vegetation general circulation model (GCM) to generate a set of 62 equilibrium simulations spanning the last 120 kyr. The analysis of these simulations elucidates the relative importance of the biogeophysical versus biogeochemical terrestrial biosphere interactions with climate. We find that the biogeophysical effects of vegetation account for up to an additional −0.91 °C global mean cooling, with regional cooling as large as −5 °C, but with considerable variability across the glacial–interglacial cycle. By comparison, while opposite in sign, our model estimates of the biogeochemical impacts are substantially smaller in magnitude. Offline simulations show a maximum of +0.33 °C warming due to an increase of 25 ppm above our (pre-industrial) baseline atmospheric CO2 mixing ratio. In contrast to shorter (century) timescale projections of future terrestrial biosphere response where direct and indirect responses may at times cancel out, we find that the biogeophysical effects consistently and strongly dominate the biogeochemical effect over the inter-glacial cycle. On average across the period, the terrestrial biosphere has a −0.26 °C effect on temperature, with −0.58 °C at the Last Glacial Maximum. Depending on assumptions made about the destination of terrestrial carbon under ice sheets and where sea level has changed, the average terrestrial biosphere contribution over the last 120 kyr could be as much as −50 °C and −0.83 °C at the Last Glacial Maximum.
Highlights
Terrestrial vegetation interacts with the climate in complex ways, both responding to and impacting climate conditions and creating an important feedback in the Earth system (e.g. Claussen, 2009; Davies-Barnard et al, 2014b; Harrison and Prentice, 2003; Jahn et al, 2005; Matthews et al, 2003; Pongratz et al, 2010)
We present the first model analysis using a fully coupled dynamic atmosphere–ocean–vegetation general circulation model (GCM) over the last 120 kyr that quantifies the net effect of vegetation on climate. (A prior study – Singarayer and Valdes, 2010 – did not have dynamic vegetation and could not directly evaluate the biogeophysical effects.) We separate the biogeophysical and biogeochemical effects of vegetation to understand the overall climate effect of vegetation over the last glacial cycle
The shrubs and trees do not have a significant presence in northern Europe after 100 ka until the climate ameliorates into the Holocene
Summary
Terrestrial vegetation interacts with the climate in complex ways, both responding to and impacting climate conditions and creating an important feedback in the Earth system (e.g. Claussen, 2009; Davies-Barnard et al, 2014b; Harrison and Prentice, 2003; Jahn et al, 2005; Matthews et al, 2003; Pongratz et al, 2010). Terrestrial vegetation interacts with the climate in complex ways, both responding to and impacting climate conditions and creating an important feedback in the Earth system Claussen, 2009; Davies-Barnard et al, 2014b; Harrison and Prentice, 2003; Jahn et al, 2005; Matthews et al, 2003; Pongratz et al, 2010). The influence of the terrestrial biosphere on climate occurs in two distinct ways. Climate feedbacks driven by these changes in terrestrial vegetation have been hypothesised to be partially responsible for some of the major past climate states T. Davies-Barnard et al.: Terrestrial biosphere carbon emissions
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