Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
Clim. Past, 13, 1381-1401, 2017
https://doi.org/10.5194/cp-13-1381-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
26 Oct 2017
Quantifying the influence of the terrestrial biosphere on glacial–interglacial climate dynamics
Taraka Davies-Barnard1,2, Andy Ridgwell1,3, Joy Singarayer4, and Paul Valdes1 1BRIDGE, Cabot Institute, and School of Geographical Sciences, University of Bristol, Bristol, BS8 1SS, UK
2College of Engineering, Mathematics, and Physical Sciences, University of Exeter, Exeter, EX4 4QE, UK
3Department of Earth Sciences, University of California, Riverside, CA 92521, USA
4Department of Meteorology and Centre for Past Climate Change, University of Reading, P.O. Box 243, Whiteknights Campus, Reading, RG6 6BB, UK
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.

Citation: Davies-Barnard, T., Ridgwell, A., Singarayer, J., and Valdes, P.: Quantifying the influence of the terrestrial biosphere on glacial–interglacial climate dynamics, Clim. Past, 13, 1381-1401, https://doi.org/10.5194/cp-13-1381-2017, 2017.
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Short summary
We present the first model analysis using a fully coupled dynamic atmosphere–ocean–vegetation GCM over the last 120 kyr that quantifies the net effect of vegetation on climate. This analysis shows that over the whole period the biogeophysical effect (albedo, evapotranspiration) is dominant, and that the biogeochemical impacts may have a lower possible range than typically estimated. This emphasises the temporal reliance of the balance between biogeophysical and biogeochemical effects.
We present the first model analysis using a fully coupled dynamic atmosphere–ocean–vegetation...
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