Lauren Marshall, Anja Schmidt, Jill Johnson, Graham Mann, Lindsay Lee, Ken Carslaw

Reconstructions of volcanic aerosol radiative forcing are required to understand past climate variability. Currently, reconstructions of pre-20th century volcanic forcing are derived from sulfate concentrations measured in polar ice cores, predominantly using a relationship between average ice sheet sulfate deposition and stratospheric sulfate aerosol based on a single explosive eruption - the 1991 eruption of Mt. Pinatubo. Here we derive volcanic radiative forcing from ice-core-records using a perturbed parameter ensemble of aerosol-climate model simulations of explosive eruptions, which enables the uncertainty to be estimated. We find that a very wide range of eruptions with different sulfur dioxide emissions, eruption latitudes, emission altitudes and in different seasons produce ice-sheet sulfate deposition consistent with ice-core-derived values for eruptions during the last 2500 years. Consequently, we find a large uncertainty in the volcanic forcing, suggesting uncertainties on the global mean temperature response of more than 1C for several past explosive eruptions, which has not been previously accounted for.