Title: Volcanic forcing during the Common Era reevaluated based on new ice core evidence
Author: Sigl, M., McConnell, J.R., Toohey, M., Maselli, O.J., Pasteris, D., Layman, L., Isaksson, E.D., Kawamura, K., Motizuki, Y., Edwards, R., Curran, M.A., Das, S.B. and Krueger, K.
Periodical: American Geophysical Union, Fall Meeting 2013, abstract #PP41B-04

The attribution of observed temperature trends to external forcings strongly relies on the use of climate model simulations. The history of forcing and global temperatures of the past can be used to constrain projections into the future which are the basis for environmental policy decisions. Climate model simulations of global climate evolution during the past Millennium use reconstructions of volcanic aerosol forcing based on sulfate signals extracted from the polar ice sheets. Beside uncertainties related to the calibration of atmospheric optical depth (AOD), low spatial and temporal coverage of the proxy data and low confidence in the dating are the main sources of uncertainty for existing volcanic forcing indices. Here we reconstruct volcanic sulfate deposition over Antarctica based on a comprehensive array of existing and new ice core records, synchronized to the annually dated WAIS Divide timescale. This reconstruction for the last 2,000 years is unprecedented in robustness, dating accuracy, length and spatial coverage. We find that Antarctic average volcanic sulfate deposition for some of the largest events during the Common Era currently is overestimated by 20 to 30%, while for some other large eruptions values are underestimated by up to 160%. This implies that current volcanic aerosol forcing sets used in climate model simulations have errors of similar magnitude. Combined with a similar detailed reconstruction obtained for the Northern Hemisphere, the Antarctic sulfate record presented here provides the proxy data needed for improvement of volcanic forcing reconstructions that are widely used in climate simulations.

Year: 2013