A paper published today in Nature Climate Change updates records of large volcanic eruptions from Antarctic ice cores and finds
"Assessments of climate sensitivity to projected greenhouse gas concentrations underpin environmental policy decisions, with such assessments often based on model simulations of climate during recent centuries and millennia. These simulations depend critically on accurate records of past aerosol forcing"
"that prior to the year 1500 the reconstructions [of volcanic eruptions] were either previously overestimating global aerosol forcing by 20–30% or underestimating it by 20–50%. This has implications for estimates of climate sensitivity" to CO2.
"Simulations of climate impacts after large eruptions predict stronger cooling than is found from temperature reconstructions, although the reasons for the mismatch are widely debated."Perhaps the reason why ""simulations of climate impacts after large eruptions predict stronger cooling than is found from temperature reconstructions" is because, as Willis Eschenbach has shown, the climate really cares little about radiative forcing at the top of the atmosphere, and the real control knob is the emergent thermodynamics of the lower atmosphere.
Summary of the paper from Nature Climate Change:
Historical aerosol forcing from large volcanic eruptions are reconstructed from sulphate deposition measured in ice cores. This study updates these records by using a more extensive collection of Antarctic ice cores, which provide new records and accurate dating of published records. The results show that prior to the year 1500 the reconstructions were either previously overestimating global aerosol forcing by 20–30% or underestimating it by 20–50%. This has implications for estimates of climate sensitivity.
Nature Climate Change 4 693 doi: 10.1038/nclimate2293