A Monthly and Latitudinally Varying Volcanic Forcing Dataset in Simulations of 20th Century Climate
C.M. Ammann, G.A. Meehl, W.M Washington, C.S. Zender
National Center for Atmospheric Research
P. O. Box 3000
Boulder, CO 80307
email: meehl@cgd.ucar.edu
voice: (303) 497 1331
A new zonally averaged monthly volcanic forcing dataset that is consistent for each eruption is included in a global coupled GCM for improved treatment of stratospheric sulfate aerosol from explosive volcanism. The volcanic forcing is different from previous versions in that there is an individual evolution of the volcanic aerosols spread over three layers in the lower stratosphere in the model. Thus the seasonal and latitudinal dependence of the volcanic aerosols can affect global climate in a more realistic way, compared to earlier volcanic forcing datasets that specify a latitudinally uniform annual mean forcing prior to the satellite period. Negative radiative forcing from volcanic activity is greatest in the early 20th century prior to about 1915 and in the late 20th century after the 1950s. The combination of volcanic and solar forcing contributes to a mid-20th century warming, followed by relative cooling in the late 20th century. Consequently, the addition of natural forcing factors in the anthropogenic GHG forcing in late 20th century is required to simulate the observed late 20th century warming.
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Cassidy P. Rush: cassrush@ucar.edu