Abstract
Abstract. This paper provides initial results from a multi-model ensemble analysis based on the volc-pinatubo-full experiment performed within the Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP) as part of the sixth phase of the Coupled Model Intercomparison Project (CMIP6). The volc-pinatubo-full experiment is based on an ensemble of volcanic forcing-only climate simulations with the same volcanic aerosol dataset across the participating models (the 1991–1993 Pinatubo period from the CMIP6-GloSSAC dataset). The simulations are conducted within an idealized experimental design where initial states are sampled consistently across models from the CMIP6-piControl simulation providing unperturbed preindustrial background conditions. The multi-model ensemble includes output from an initial set of six participating Earth system models (CanESM5, GISS-E2.1-G, IPSL-CM6A-LR, MIROC-E2SL, MPI-ESM1.2-LR and UKESM1). The results show overall good agreement between the different models on the global and hemispheric scales concerning the surface climate responses, thus demonstrating the overall effectiveness of VolMIP's experimental design. However, small yet significant inter-model discrepancies are found in radiative fluxes, especially in the tropics, that preliminary analyses link with minor differences in forcing implementation; model physics, notably aerosol–radiation interactions; the simulation and sampling of El Niño–Southern Oscillation (ENSO); and, possibly, the simulation of climate feedbacks operating in the tropics. We discuss the volc-pinatubo-full protocol and highlight the advantages of volcanic forcing experiments defined within a carefully designed protocol with respect to emerging modelling approaches based on large ensemble transient simulations. We identify how the VolMIP strategy could be improved in future phases of the initiative to ensure a cleaner sampling protocol with greater focus on the evolving state of ENSO in the pre-eruption period.
Highlights
The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP; Zanchettin et al, 2016) defined a coordinated set of idealized volcanic perturbation experiments to be carried out in alignment with the protocol of the sixth phase of the Coupled Model Intercomparison Project (CMIP6; Eyring et al, 2016)
This paper provides initial results from a multimodel ensemble analysis based on the volc-pinatubofull experiment performed within the Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP) as part of the sixth phase of the Coupled Model Intercomparison Project (CMIP6)
The climate state in piControl is illustrated in the form of box–whisker plots of relevant diagnostics calculated for the whole length of the simulations, including global and regional averages of annualmean near-surface air temperature (Fig. 3a–d), and winter El Niño–Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) indices as defined by the VolMIP protocol (Fig. 3e and f)
Summary
The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP; Zanchettin et al, 2016) defined a coordinated set of idealized volcanic perturbation experiments to be carried out in alignment with the protocol of the sixth phase of the Coupled Model Intercomparison Project (CMIP6; Eyring et al, 2016). Climate conditions defining the initial states of individual members of the ensemble must be selected in a consistent manner across the participating models so that the diagnosed expected climate response is not biased by potential effects of a preferential phase of ongoing internal variability at the time of the eruption (see Zanchettin et al, 2013; Swingedouw et al, 2015; Lehner et al, 2016; Khodri et al, 2017; Coupe and Robock, 2021). This is achieved by defining desired states of climate variability modes to be sampled along the parent
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