Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.u22a..03r&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #U22A-03
Astronomy and Astrophysics
Astronomy
4900 Paleoceanography (0473, 3344), 4910 Astronomical Forcing, 4934 Insolation Forcing, 4946 Milankovitch Theory
Scientific paper
Two great planetary-scale systems dominate orbital-scale climate change: low-latitude monsoons and high- latitude ice sheets. Oxygen-isotopic signals from accurately dated cave calcite deposits show that the Asian monsoon system varied mainly at the 22,000-year precession cycle and with a phase of August 1. This evidence confirms the orbital monsoon hypothesis (now theory) of John Kutzbach: low-latitude insolation forces monsoon strength, with subsequent amplification from climate-system feedbacks. In contrast. the current understanding of ice-sheet variations is incomplete. Milankovitch's theory of summer insolation forcing has been confirmed in part, but discrepancies remain. High-latitude summer insolation has strong power at the 22,000-year precession period, but early glaciations (2.75-0.9 Myr ago) varied mainly at the 41,000-year obliquity (tilt) period, and subsequent glaciations occurred within a broad band of power near the ~100.000-year eccentricity band. Recent competing explanations for these discrepancies between insolation forcing and ice-responses include interhemispheric cancellation of opposite-phased 23,000-year ice volume responses, prevalence of 41,000-year insolation forcing in indices that account for changes in length of day, and strong CO2 feedback at the 41,000-year period. A major uncertainty is whether independent CO2 variations arise within the climate system and force ice sheets or whether ice sheets drive their own positive CO2 feedback.
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