PLASIM-ENTSem v1.0: a spatio-temporal emulator of future climate change for impacts assessment

Abstract

Abstract. Many applications in the evaluation of climate impacts and environmental policy require detailed spatiotemporal projections of future climate. To capture feedbacks from impacted natural or socio-economic systems requires interactive two-way coupling, but this is generally computationally infeasible with even moderately complex general circulation models (GCMs). Dimension reduction using emulation is one solution to this problem, demonstrated here with the GCM PLASIM-ENTS (Planet Simulator coupled with the efficient numerical terrestrial scheme). Our approach generates temporally evolving spatial patterns of climate variables, considering multiple modes of variability in order to capture non-linear feedbacks. The emulator provides a 188-member ensemble of decadally and spatially resolved (∼ 5 • resolution) seasonal climate data in response to an arbitrary future CO 2 concentration and non-CO 2 radiative forcing scenario. We present the PLASIM-ENTS coupled model, the construction of its emulator from an ensemble of transient future simulations, an application of the emulator methodology to produce heating and cooling degree-day projections, the validation of the simulator (with respect to empirical data) and the validation of the emulator (with respect to highcomplexity models). We also demonstrate the application to estimates of sea-level rise and associated uncertainty.

Emulation and interpretation of high-dimensional climate model outputs

“…The climate model that was used in the simulations is the PLASIM-ENTS model [7]. It comprises the Planet Simulator [4] coupled to the terrestrial carbon model ENTS (Efficient numerical terrestrial scheme) [19].…”

“…All model parameters were set at their defaults (PLASIM Version 6 Revision 4, ENTS parameters [19]). The threshold fractional soil moisture for photosynthesis [7] was set at 0.1.…”

Visuanimation in statistics

“…To avoid running a climate model for many input values, it is possible to define a statistical model that approximates the behaviour for some inputs and extrapolates the behaviour for different inputs. These statistical models, called emulators, are useful tools for global sensitivity analysis and parameter calibration (Sacks et al ; Santner et al ; Kennedy & O'Hagan, ; Oakley & O'Hagan, ; Rougier et al ; O'Hagan, ) and impact assessment (Holden & Edwards, ; Castruccio & Stein, ; Holden et al ; Castruccio et al ). It is of interest to compare the emulated output with the original climate model, to understand how well the emulator approximates the original climate model and to detect possible differences.…”

Should we geoengineer larger ice caps?

“…Model calculations suggest that global average temperature could be anywhere from 4 to 8 K or warmer than today if anthropogenic warming melts the polar ice caps (Lenton and Ciscar 2012;Hansen et al 2013;Holden et al 2014;Haqq-Misra 2014). Most climate models today are designed to operate in a regime near present-day Earth, with accuracy up to a few degrees of warming and most of the major ice sheets present in approximately their current configuration.…”