A U.S. geologist says she's discovered a pattern that connects regular changes in the Earth's orbital cycle to changes in the planet's climate.

University of California-Santa Barbara Assistant Professor Lorraine Lisiecki performed her analysis of climate by examining ocean sediment cores taken from 57 locations around the world and linking that climate record to the history of the Earth's orbit.

The researchers said it's known the Earth's orbit around the sun changes shape every 100,000 years, becoming either more round or more elliptical. The shape of the orbit is known as its "eccentricity" and 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 Lisiecki found the timing of changes in climate and eccentricity coincided.

"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," Lisiecki said. She also said she discovered the largest glacial cycles occurred during the weakest changes in the eccentricity of Earth's orbit -- and vice versa, with the stronger changes in orbit correlating 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," she said.

The research is reported in the journal Nature Geoscience.