A model-based constraint on CO<sub>2</sub> fertilisation

Abstract

Abstract. We derive a constraint on the strength of CO 2 fertilisation of the terrestrial biosphere through a "top-down" approach, calibrating Earth system model parameters constrained by the post-industrial increase of atmospheric CO 2 concentration. We derive a probabilistic prediction for the globally averaged strength of CO 2 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 CO 2 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 CO 2 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 CO 2 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 CO 2 fertilisation, which therefore represents the combined effect of CO 2 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)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(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)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(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 CO 2 fertilisation and climate sinks) to be 66 GTC, likely to lie in the range 0 to 128 GTC.

Transient Earth system responses to cumulative carbon dioxide emissions: linearities, uncertainties, and probabilities in an observation-constrained model ensemble

“…However, and in contrast to reduced-form, box-type, twodimensional, linear response models; expert assumptions; or component models applied in many earlier probabilistic assessments (e.g. Wigley and Raper, 2001;Knutti et al, 2002Knutti et al, , 2003Knutti et al, , 2005Schleussner et al, 2014;Bodman et al, 2013;Little et al, 2013;Harris et al, 2013;Holden et al, 2013;Bhat et al, 2012), Bern3D-LPJ features a dynamic threedimensional ocean with physically consistent formulations for the transport of heat, carbon, and other biogeochemical tracers, similar to work by Holden et al (2010) and Olson et al (2012), and includes a state-of-the-art dynamic global vegetation model, peat carbon, and anthropogenic land-use dynamics. The model is applied directly without using an emulator (Holden et al, 2010(Holden et al, , 2015Olson et al, 2012).…”

“…Probabilistic assessments are widely used to determine probability distributions of model parameters, climate sensitivity, and many other cli-mate variables (e.g. Wigley and Raper, 2001;Knutti et al, 2002Knutti et al, , 2003Knutti et al, , 2005Murphy et al, 2004;Schleussner et al, 2014;Bodman et al, 2013;Little et al, 2013;Harris et al, 2013;Holden et al, 2010Holden et al, , 2013Bhat et al, 2012;Olson et al, 2012;Williamson et al, 2013). The Bern3D model was used in connection with an ensemble Kalman filter to constrain model parameters and regional air-sea carbon fluxes from observations (Gerber et al, 2009;Joos, 2010, 2013).…”

Description and validation of the Simple, Efficient, Dynamic, Global, Ecological Simulator (SEDGES v.1.0)

“…In addition, we use (2015) and modeling-based results of Hemming et al (2013) and Holden et al (2013) to assess the relative performance of SEDGES.…”

PLASIM–GENIE v1.0: a new intermediate complexity AOGCM

“…The primary motivation for this would be modularity. Notably GENIEfied ENTS is coupled to the global carbon cycle and has been enabled to simulate the effects of anthropogenic land use change (Holden et al, 2013a).…”