Update: Jamais Cascio posted more about the ice core studies at WorldChanging.com.

Researchers have pulled the oldest-yet core of ice from the Antarctic, according to this article in Nature. The core includes a section from a time when the earth's orbit was near what it is today, so the expectation is that it will provide insight into the progress of contemporary climate change. [Link]

A million years ago, ice ages recurred about every 40,000 years — the same timescale on which wobbles in the Earth's tilt alter the amount of sunlight hitting its surface. But now our ice ages return every 100,000 years. This is the timescale on which Earth's orbit becomes more or less elliptical, but this does not provide enough of a change in the amount of sunlight to explain the ice ages. So why should the cycle length have changed?

One possible explanation is that CO2 levels may have gradually fallen, making the world progressively colder, says Wolff. This would have caused successive ice ages to grow larger and larger ice sheets — something that marine records suggest has been occurring over the past 2 million years.

Eventually, the ice may simply have become too slow on its feet to respond to the 40,000-year beat, and could have been forced to adopt the more stately, 100,000-year driving force. The Dome C core should soon reveal whether this is right. "If carbon dioxide really is the key, this is the only convincing way of getting it," says Wolff.

An article in the Straits Times says the evidence suggests that we're "not even half way through the current warm area," however "there was now a wild card that could cause the current era to stray from past patterns: the intensification of the earth's insulating 'greenhouse effect' by smokestack and tailpipe emissions of carbon dioxide and other gases."