The new analysis of ocean sediment cores from 57 locations around the world suggests that the pattern of climate change over the past million years likely involves complicated interactions between different parts of the climate system, as well as three different orbital systems: eccentricity, tilt, and "precession," or a change in the orientation of the rotation axis.
The Earth's orbit around the sun changes shape every 100,000 years, becoming either more round or more elliptical at these intervals. The shape of the orbit is known as its "eccentricity." A related aspect is the 41,000-year cycle in the tilt of the Earth's axis.
Glaciation of the Earth also occurs every 100,000 years, and it appears that the timing of changes in climate and eccentricity coincide. "The clear correlation between the timing of the change in orbit and the change in the Earth's climate is strong evidence of a link between the two," said UC Santa Barbara Geologist Lorraine Lisiecki. "It is unlikely that these events would not be related to one another."
The research also revealed that the largest glacial cycles occurred during the weakest changes in the eccentricity of Earth's orbit –– and vice versa. Lisiecki found that the stronger changes in the Earth's orbit correlated to weaker changes in climate. "This may mean that the Earth's climate has internal instability in addition to sensitivity to changes in the orbit," said Lisiecki.
Citation: Lorraine E. Lisiecki, 'Links between eccentricity forcing and the 100,000-year glacial cycle', Nature Geoscience, Arpil 2010; doi:10.1038/ngeo828