Ecosystem effects of CO2 concentration: evidence from past climates 1QUEST, Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol BS8 1RJ, UK
2School of Geographical Sciences, University of Bristol, University Road, Bristol BS8 1SS, UK
Received: 17 Feb 2009 – Published in Clim. Past Discuss.: 12 Mar 2009 Abstract. Atmospheric CO2 concentration has varied from minima of 170–200 ppm in
glacials to maxima of 280–300 ppm in the recent interglacials.
Photosynthesis by C3 plants is highly sensitive to CO2
concentration variations in this range. Physiological consequences of the
CO2 changes should therefore be discernible in palaeodata. Several
lines of evidence support this expectation. Reduced terrestrial carbon
storage during glacials, indicated by the shift in stable isotope
composition of dissolved inorganic carbon in the ocean, cannot be explained
by climate or sea-level changes. It is however consistent with predictions
of current process-based models that propagate known physiological CO2
effects into net primary production at the ecosystem scale. Restricted
forest cover during glacial periods, indicated by pollen assemblages
dominated by non-arboreal taxa, cannot be reproduced accurately by
palaeoclimate models unless CO2 effects on C3-C4 plant
competition are also modelled. It follows that methods to reconstruct
climate from palaeodata should account for CO2 concentration changes.
When they do so, they yield results more consistent with palaeoclimate
models. In conclusion, the palaeorecord of the Late Quaternary, interpreted
with the help of climate and ecosystem models, provides evidence that
CO2 effects at the ecosystem scale are neither trivial nor transient.
Revised: 16 Jun 2009 – Accepted: 18 Jun 2009 – Published: 03 Jul 2009
Citation: Prentice, I. C. and Harrison, S. P.: Ecosystem effects of CO2 concentration: evidence from past climates, Clim. Past, 5, 297-307, doi:10.5194/cp-5-297-2009, 2009.