New paper predicts CO2 fertilization will greatly improve plant productivity by 40-60%

A paper published today in Biogeosciences finds that the increase in CO2 levels since 1850 has greatly enhanced plant fertilization and that a doubling of CO2 levels would be predicted to increase plant productivity by 40 - 60%. The study derives "a probabilistic prediction for the globally averaged strength of CO₂ fertilization in nature, for the period 1850 to 2000 AD, implicitly net of other limiting factors such as nutrient availability" and predicts, "the increase in gross primary productivity (GPP) in response to a doubling of CO₂ from pre-industrial values is very likely (90% confidence) to exceed 20%, with a most likely value of 40–60%."

Related: Greenhouse operators increase CO2 levels by 3-4 times to enhance plant productivity by up to 50%

Biogeosciences, 10, 339-355, 2013
www.biogeosciences.net/10/339/2013/
doi:10.5194/bg-10-339-2013

A model-based constraint on CO₂ fertilisation

P. B. Holden¹, N. R. Edwards¹, D. Gerten², and S. Schaphoff^2
1Environment, Earth and Ecosystems, Open University, Milton Keynes, UK
²Potsdam Institute for Climate Impact Research, Potsdam, Germany
 Abstract. We derive a constraint on the strength of CO₂ fertilisation of the terrestrial biosphere through a "top-down" approach, calibrating Earth system model parameters constrained by the post-industrial increase of atmospheric CO₂ concentration. We derive a probabilistic prediction for the globally averaged strength of CO₂ fertilisation in nature, for the period 1850 to 2000 AD, implicitly net of other limiting factors such as nutrient availability. The approach yields an estimate that is independent of CO₂ enrichment experiments. To achieve this, an essential requirement was the incorporation of a land use change (LUC) scheme into the GENIE Earth system model. Using output from a 671-member ensemble of transient GENIE simulations, we build an emulator of the change in atmospheric CO₂ concentration change since the preindustrial period. We use this emulator to sample the 28-dimensional input parameter space. A Bayesian calibration of the emulator output suggests that the increase in gross primary productivity (GPP) in response to a doubling of CO₂ from preindustrial values is very likely (90% confidence) to exceed 20%, with a most likely value of 40–60%. It is important to note that we do not represent all of the possible contributing mechanisms to the terrestrial sink. The missing processes are subsumed into our calibration of CO₂ fertilisation, which therefore represents the combined effect of CO₂ fertilisation and additional missing processes. If the missing processes are a net sink then our estimate represents an upper bound. We derive calibrated estimates of carbon fluxes that are consistent with existing estimates. The present-day land–atmosphere flux (1990–2000) is estimated at −0.7 GTC yr⁻¹ (likely, 66% confidence, in the range 0.4 to −1.7 GTC yr⁻¹). The present-day ocean–atmosphere flux (1990–2000) is estimated to be −2.3 GTC yr⁻¹ (likely in the range −1.8 to −2.7 GTC yr⁻¹). We estimate cumulative net land emissions over the post-industrial period (land use change emissions net of the CO₂ fertilisation and climate sinks) to be 66 GTC, likely to lie in the range 0 to 128 GTC.

 Final Revised Paper (PDF, 2501 KB)   Discussion Paper (BGD)