Links between eccentricity forcing and the 100,000-year glacial cycle (abstract)Lorraine Lisiecki of UC Santa Barbara has looked at the timing of the ice ages - as seen through 57 sediment core proxies - in the most recent 1.2 million years. The slowest cycles are believed to be linked to oscillations in the eccentricity - the deviation of our elliptical orbit from a circle. The seemingly stronger oscillation of the eccentricity has a period of 400,000 years.
Press release (UCSB)
However, the glaciation cycle data seem to ignore this cycle. Instead, they contain a stronger approximate 100,000-year periodicity which may be linked to calculably weaker variations in 90,000-year and 125,000-year cycles.
Lisiecki confirmed that the timing has been remarkably correlated with the approximate 100,000-year eccentricity variations in those 12 cycles or so. Moreover, the correlation is actually negative. When we're getting a greater amount of solar energy per year, because of the eccentricity changes, the Earth actually seems to be cooler! This fact actually seems to have been true for 5 million years.
She proposes a mechanism that explains this anticorrelation by internal feedbacks that are also influenced by the 23,000-year precession cycles and whose precise inner workings are not comprehensible to me at this point. On the other hand, the tilt-of-the-Earth's-axis 41,000-year cycles don't seem to play much role in her model.
Via Marc Morano