Background conditions influence the decadal climate response to strong volcanic eruptions

Abstract

[1] Background conditions have the potential to influence the climate response to strong tropical volcanic eruptions. As a case study, we systematically assess the decadal climate response to the April 1815 Tambora eruption in a set of full-complexity Earth system model simulations. Three 10-member simulation ensembles are evaluated which describe the climate evolution of the early 19th century under (1) full-forcing conditions, (2) volcanic forcing-only conditions, and (3) volcanic forcing-only conditions excluding events preceding the Tambora eruption. The amplitude of the simulated radiative perturbation induced by the Tambora eruption depends only marginally on the background conditions. In contrast, simulated nearsurface atmospheric and especially oceanic dynamics evolve significantly differently after the eruption under different background conditions. In particular, large inter-ensemble differences are found in the post-Tambora decadal evolution of oceanic heat transport and sea ice in the North Atlantic/Arctic Ocean. They reveal the existence of multiple response pathways that depend on background conditions. Background conditions are therefore not merely a source of additive noise for post-eruption decadal climate variability but actively influence the mechanisms involved in the post-eruption decadal evolution. Hence, background conditions should appropriately be accounted for in future ensemble-based numerical studies.

Persistent drying in the tropics linked to natural forcing

“…equatorial Pacific and the long-term variations of tropical Atlantic SSTs, which is governed by the Atlantic Multi-decadal Oscillation (AMO) 26 . An increasing number of climate reconstructions and simulations describe statistical and dynamical connections between volcanic forcing and both ENSO 27 and AMO [28][29][30] . Indeed, drying (recovery) phases during the volcanic clusters correspond to cold (warm) phases in a recent marine proxy-based AMO reconstruction 31 (Fig.…”

“…Further possible explanations are the common model deficiencies concerning regional precipitation variability at the decadal and multi-decadal time ARTICLE scales 37 , which are linked to poor and hence less robustly simulated representation of dominant modes of large-scale climate variability and associated teleconnections including ENSO 38 and the AMO 39 . Large uncertainties also affect the reconstructed forcing 40 and we have very limited knowledge about the background climate conditions at the time of volcanic eruptions that occurred before the last half of the twentieth century 30 .…”

An abrupt weakening of the subpolar gyre as trigger of Little Ice Age-type episodes

“…Each ensemble member is generated from the original Past1000-R3 (AllFor-1) by inducing an infinitesimal perturbation in the atmospheric vertical diffusivity during the first integration year, except for the first member of the NoVol ensemble. This method for ensemble initialization is a common procedure with MPI-ESM (e.g., Zanchettin et al 2013), as it produces a rapid divergence of climate trajectories and, therefore, an adequate ensemble spread.…”

Assessing the Impact of a Future Volcanic Eruption on Decadal Predictions

“…In section 4 we draw conclusions and discuss our results. We perform our Pinatubo forecasts with the baseline1 version of the MiKlip prediction system (Marotzke et al, 2016;Pohlmann et al, 2013) which is based on the coupled Max-Planck-Institute-Earth System Model (MPI-ESM) (Giorgetta et al, 2013;Jungclaus et al, 2013). The MPI-ESM is an Earth System model, with atmosphere, ocean, and dynamic vegetation 5 components.…”

“…The atmospheric component ECHAM6 ) is initialized with full-fields of temperature, vorticity, divergence, and sea level pressure from the ECMWF atmosphere reanalysis (Dee et al, 2011). The oceanic component MPI-OM (Jungclaus et al, 2013) is initialized using anomaly fields from the ECMWF ocean reanalysis system 4 (Balmaseda et al, 2013) including temperature 10 and salinity. For decadal forecasting, a stand-by model system for rapid model-based assessment of the decadal scale climate impact is needed, in case of any major volcanic eruption.…”