The CESM Last Millennium Ensemble: Tropical Response to the Samalas, Kuwae and Tambora Eruptions

Abstract:

Recent efforts in reconstructing climate variations and forcings for the Common Era have made this period ideal for studying the role of external forcing with numerical models. Large ensembles are needed to best evaluate model capabilities against paleoclimate records, as well as assess uncertainties in the attribution of a regional response to a particular forcing in the presence of intrinsic variability. The CESM Last Millennium Ensemble (CESM-LME) will be used to investigate interannual to multi-centennial scale climate variations in response to natural and anthropogenic forcing.

The CESM-LME is performed with the Community Earth System Model (CESM with CAM5) at ~2^o horizontal resolution in the atmosphere and land components and ~1^oresolution in the ocean and sea-ice components. The CESM-LME is nearly completed, and consists of more than 28 simulations over the period from 850 to 2005CE. Ten members use a full-set of CMIP5/PMIP3 forcings (volcanic aerosols, solar variability, orbital variations, greenhouse gases, and land use changes). The remaining runs consist of smaller sets with single transient forcings. Two pre-industrial controls with constant forcings at 850CE and 1850CE values enable a characterization of unforced variability. Upon release on the Earth System Grid, the CESM-LME will serve as a tremendous community resource, enabling investigations into the relative roles of external forcing and intrinsic climate variability and the impact of recent anthropogenic climate forcing over natural background variability of the Common Era.

Results presented will focus on the tropical response to the largest tropical volcanic eruptions of the last millennium: Samalas in 1257-1258, Kuwae in ~1452 and Tambora in 1815. The CESM-LME fully-forced and volcanic-only ensembles demonstrate the impact of these large volcanic eruptions on decadal scale regional climate variations, and help assess the likelihood to trigger an ENSO in the immediate aftermath of the eruption.