globeandmail.com: Ancient ice survived hotter Earth than today

A team of Canadian researchers has discovered the oldest ice in North America, 700,000-year-old wedges unearthed near Dawson City in the Yukon that stayed solid when the Earth was much hotter than it is today.

The discovery suggests that one of the most catastrophic global warming scenarios, in which melting permafrost releases vast amounts of greenhouse gases like carbon dioxide and methane into the atmosphere, may not occur as quickly as some scientists fear.

“There is a certain stubbornness to permafrost, ” says Duane Froese, an assistant professor in the Department of Earth and Atmospheric Science at the University of Alberta and lead author of a paper that will appear in Friday's edition of the journal Science.

The ice was found only a few metres beneath the surface. It formed in cracks in the permafrost, the frozen soil which covers nearly a quarter of the land in the northern hemisphere, including parts of the Klondike gold field. Some of it is rich in ice.

Normally, ice is difficult to date beyond 50,000 years. But in this case, the wedges were covered with volcanic ash that the team, including researchers at the University of Toronto and the Geological Survey of Canada, determined was roughly 700,000 years old.

This means it didn't melt during two periods when many scientists believe the planet was warmer than it is today. In the most recent of those periods, 120,000 years ago, temperatures were likely several degrees hotter than they are today. It may have been even steamier 400,000 years ago.