Humans may have prevented super ice age

Our impact on Earth's climate might be even more profound than we realise. Before we started pumping massive amounts of carbon dioxide into the atmosphere, the planet was on the brink of entering a semi-permanent ice age, two researchers have proposed.

Had we not radically altered the atmosphere, say Thomas Crowley of the University of Edinburgh, UK, and William Hyde of the University of Toronto in Canada, the current cycle of ice ages and interglacials would have given way in the not-too-distant future to an ice age lasting millions of years.

"It's not proven but it's more than just an interesting idea," says Crowley.

For much of the 500 million years or so since complex life evolved, Earth's climate has been much hotter than it is now, with no ice at the poles. During the last of these "hothouse Earth" phases, from around 100 to 50 million years ago, the Antarctic was covered by lush forests and shallow seas submerged vast areas of America, Europe and Africa.