A geologist has discovered a link between regular changes in the Earth's orbital cycle and changes in the climate.
UC Santa Barbara's Lorraine Lisiecki examined ocean sediment cores from 57 locations around the world and covering the last 1.2 million years. These cores can be used to chart the Earth's climate.
She then compared them with data about the Earth's orbit.
The Earth's orbit around the sun changes shape every 100,000 years, becoming either more round or more elliptical - a pattern known as its eccentricity. There's also a 41,000-year cycle in the tilt of the Earth's axis.
Glaciation also occurs every 100,000 years - and Lisiecki found that 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," said Lisiecki. "It is unlikely that these events would not be related to one another."
Oddly, though, she discovered that the largest glacial cycles occurred during the weakest changes in the eccentricity of Earth's orbit – and vice versa. She found that the stronger changes in the Earth's orbit correlated to weaker changes in climate.
"I think it indicates that climate is inherently unstable - there's a lot of other processes going on," she told TG Daily. "What could be happening is that the changes in orbit are interacting with these processes to make them weaker in some way."
So will this be ammunition for climate change sceptics?
"I hope it's not used in that way," she says. "We're talking about processes over more than a million years, and the results can't be used on that timescale."