First analyses of the longest sediment core ever collected on land in the Arctic provide dramatic, "astonishing" documentation that intense warm intervals, warmer than scientists thought possible, occurred there over the past 2.8 million years. Further, these extreme inter-glacial warm periods correspond closely with times when parts of Antarctica were ice-free and also warm, suggesting strong inter-hemispheric climate connectivity. The Polar Regions are much more vulnerable to change than once believed, they add....