Effects of forcing differences and initial conditions on inter-model agreement in the VolMIP volc-pinatubo-full experiment

Davide Zanchettin (1) , Claudia Timmreck (2) , Myriam Khodri (3) , Anja Schmidt (4, 5) , Matthew Toohey (6) , Manabu Abe (7) , Slimane Bekki (8) , Jason Cole (9) , Shih-Wei Fang (2) , Wuhu Feng (10) , Gabriele Hegerl (11) , Ben Johnson (12) , Nicolas Lebas (3) , Allegra N. Legrande (13, 14) , Graham W. Mann (10) , Lauren Marshall (5) , Landon Rieger (6) , Alan Robock (15) , Sara Rubinetti (1) , Kostas Tsigaridis (14, 13) , Helen Weierbach (16, 17)

1 Department of Environmental Sciences, Informatics and Statistics [Venezia]
2 MPI-M - Max-Planck-Institut für Meteorologie
3 VARCLIM - Océan et variabilité du climat
4 Department of Geography [Cambridge, UK]
5 Department of Chemistry [Cambridge, UK]
6 ISAS - Institute of Space and Atmospheric Studies [Saskatoon]
7 RIGC - Research Institute for Global Change
8 STRATO - LATMOS
9 Environment and Climate Change Canada
10 SEE - School of Earth and Environment [Leeds]
11 University of Edinburgh
12 MOHC - Met Office Hadley Centre for Climate Change
13 GISS - NASA Goddard Institute for Space Studies
14 CCSR - Center for Climate Systems Research [New York]
15 Department of Environmental Sciences [New Brunswick]
16 Earth and Environmental Sciences Area [LBNL Berkeley]
17 LDEO - Lamont-Doherty Earth Observatory

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 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 pre-industrial 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 scale 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 modeling 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.

Domains: Atmospheric and Oceanic Physics [physics.ao-ph]; Climatology; Volcanology

Davide Zanchettin, Claudia Timmreck, Myriam Khodri, Anja Schmidt, Matthew Toohey, et al.. Effects of forcing differences and initial conditions on inter-model agreement in the VolMIP volc-pinatubo-full experiment. Geoscientific Model Development, 2022, 15 (5), pp.2265-2292. ⟨10.5194/gmd-15-2265-2022⟩. ⟨insu-03466056v2⟩