Expanding the study of prehistoric permafrost thawing to North America, researchers found evidence in mineral deposits from caves in Canada that permafrost thawing took place as recently as 400,000 years ago, in temperatures not much warmer than today. But they did not find evidence the thawing caused the release of predicted levels of carbon dioxide stored in the frozen terrain.
Click here for original story, Cave deposits reveal Pleistocene permafrost thaw, absent predicted levels of CO2 release
Source: ScienceDaily