A Revisionist View of the Milankovitch
Hypothesis for Climate Change

Carl Wunsch

Professor of Physical Oceanography
Massachusetts Institute of Technology

Much of the paleoclimate literature is built around the hypothesis that small insolation changes, induced by variations in the earth's orbital parameters, control climate change over the last several million years. At least two, not completely consistent, versions of the hypothesis exist: (1) that the spectrum of climate change is dominated by the Milankovitch obliquity and precessional terms, and/or (2) that the energy in a band of periods around 100,000 years is controlled by these terms (the "pacemaker" hypothesis). Hypothesis (1) has led to the further assertion that low frequency climate change is mainly one of "cyclicities" or near-periodic fluctuations. The evidence for and against these assumptions is evaluated by re-examining a number of core records. The results suggest reasonably clear evidence for a weak response to obliquity forcing, and a tenuous presence of precessional terms. The 100,000 year fluctuations are not demonstrably periodic, and could possibly be controlled by the high frequency insolation changes, but the data are so-far inadequate to resolve the issue. Such a response requires an unusual non-linear system.

About the Lecturer

Carl Wunsch is Cecil and Ida Green Professor of Physical Oceanography at Massachusetts Institute of Technology. He holds a bachelors degree in mathematics and a PhD in geophysics, both from MIT. He has worked on many aspects of physical oceanography, including internal waves, mixing, tides, mesoscale eddies, and the general circulation of the ocean. A particular interest has been the use of new observational methods, including satellite altimetry and acoustic tomography as well as in mathematical techniques for using oceanographic data, including inverse and data assimilation (state estimation) methods. He was an organizer of the recent World Ocean Circulation Experiment and has been deeply involved in the analysis of its results, including the use of general circulation models. A more recent interest is in the low frequency oceanic variability with its inevitable need to understand the paleoclimate record.

More Information

http://puddle.mit.edu/~cwunsch/

Carl Wunsch