UK: Arctic thawed in prehistoric global warming

Scientists - Arctic Core Expedition (Acex) - have discovered that the complete disappearance of the Arctic sea ice, 55 million years ago, coincided with a dramatic increase in concentrations of carbon dioxide or methane in the atmosphere - which must have caused global warming.
[...]
The scientists also found that the Arctic is currently experiencing one of the fastest temperature rises on record, with more sea ice melting each summer than at any time in hundreds and possibly thousands of years.
http://news.independent.co.uk/environment/article1218041.ece