HR: 09:00h
AN: U21F-05    [Abstracts]
TI: Synchrony between the hemispheres from an opposite response to orbital variations.
AU: * Huybers, P
EM: phuybers@fas.harvard.edu
AF: Harvard University, Department of Earth and Planetary Sciences, Cambridge, MA 02138, United States
AU: Denton, G H
EM: gdenton@maine.edu
AF: University of Maine, Department of Earth Sciences and Climate Change Institute, Orono, ME 04469, United States
AB: Southern Hemisphere ice-core and marine records have been found to follow the phase of Northern Hemisphere summer insolation intensity. But such an inference of Arctic control of Southern climate is surprising, not least because the total heat transport across the equator in the modern climate is small as well as that glacial-interglacial variations in atmospheric CO₂ concentrations are thought to originate with changes Southern Hemisphere climate. Here we suggest that orbital-scale changes in Southern Hemisphere climate are related not to Northern Hemisphere summer insolation intensity, but to the duration of Southern Hemisphere summer. The confusion between forcing agents arises, for example, because when Northern Hemisphere summer insolation intensity is strong, Southern Hemisphere summer is long, making it appear as if Southern Hemisphere climate follows Northern Hemisphere summer intensity. The Southern Hemisphere may respond more to changes in summer duration than intensity because of the greater fraction of ocean area or because Antarctica is constantly glaciated. We support this conjecture of local Southern Hemisphere insolation control in three ways. First, through analysis of the relationship between the seasonal cycle of insolation and its relationship with temperature and sea-ice in the modern climate. Second, through simulation of the climate response over orbital timescales using energy-balance and more sophisticated climate models. And, finally, through intercomparison of continental records of glaciation in New Zealand, Chile, and North America as well as ice-core observations from the Arctic and Antarctica. If correct, this viewpoint frees southern hemisphere climate from the inferred Northern control at orbital timescales and suggests that the differing hemispheric responses to changes in seasonal insolation together determine the global climate response to orbital variations.
DE: 0724 Ice cores (4932)
DE: 4914 Continental climate records
DE: 4934 Insolation forcing
DE: 4938 Interhemispheric phasing
DE: 4946 Milankovitch theory
SC: Union [U]
MN: 2007 Fall Meeting