How did polar bears survive the Holocene ?

http://klimazwiebel.blogspot.com/2011/11/how-did-polar-bears-survive-holocene.html

Obviously polar bears survived the Holocene. To my knowledge -and I may be ere completely wrong here - there are no geological records of mass extinctions of Arctic species during the mid-Holocene. This does not say any thing important for or against the influence on climate of anthropogenic emissions of greenhouse gases, but it does say something about the resilience of ecosystems to climate change