Dr. David Karoly-May 9 Colloquium

Decadal variability in the Southern Hemisphere over the last millennium: paleoclimate reconstructions and evaluating climate model simulations

Paleoclimate reconstructions of temperature variations over the last millennium have been key to estimating natural climate variability and separating forced climate change from natural variations. However, there have been fewer reconstructions of Southern Hemisphere climate variability. Two separate multi-proxy ensemble reconstructions of temperature variations over the last millennium will be described, first for the combined land-ocean region of Australasia and second for the whole Southern Hemisphere. The reconstructions will be compared with a three-member ensemble of climate model simulations. Most of the decadal variability is associated with unforced internal variability, except since the mid-20th century. Combining the Southern Hemisphere reconstruction with an independent Northern Hemisphere temperature reconstruction ensemble reveals an extended cold period (1594–1677) in both hemispheres but no globally coherent warm phase during the pre-industrial era. The analysis of inter-hemispheric temperature variability in climate model simulations suggests that models tend to overemphasize synchronicity between the hemispheres by underestimating the role of internal ocean-atmosphere dynamics, particularly in the ocean-dominated Southern Hemisphere.

Dr. Karoly is an internationally recognized expert in climate change and climate variability, including greenhouse climate change, stratospheric ozone depletion, and interannual climate variations due to El Niño Southern Oscillation. He was heavily involved, in several different roles, in preparation of the Fourth Assessment Report of the IPCC  released in 2007, and was a Review Editor of the chapter ‘Australasia’ in the IPCC Fifth Assessment Report released in 2014. Before joining the University of Melbourne in 2007 he was Professor of the School of Meteorology, OU.