Published: October 27 2006 03:00 | Last updated: October 27 2006 03:00

The rise of the Appalachian mountains may have caused a huge ice age 450m years ago, a study has found.

According to researchers at Ohio State University, the weathering of the mountains pulled carbon dioxide from the atmosphere, causing the opposite of a greenhouse effect - an "icehouse" effect.

Scientists have long thought that our current ice age, which began 40m years ago, was caused by the rise of the Himalayas. This new study, presented this week at the Geological Society of America meeting in Philadelphia, links a much earlier ice age to the uplift of the Appalachians. It also strengthens the idea that CO2 levels play a big role in determining climate.

Because we are living in an ice age - or in a slightly warmer interglacial period within an ice age - CO2 levels worldwide would ordinarily be low. But scientists believe humans have raised CO2 levels by burning fossil fuels.

"In this study, we're seeing remarkable evidence that suggests atmospheric CO2 levels were in fact dropping at the same time that the planet was getting colder," said Matthew Saltzman, professor of geological sciences at Ohio State. "So this significantly reinforces the idea that CO2 is a major driver of climate."