Greenland was warm enough to graze and farm. The Vikings left because by 1400s it got too cold to live there for anyone except the Inuit. If we return to the weather conditions that existed in pre-industrial age Viking times then its the real normal climate weather is it not?
There is a lot of wine grown in upstate NY today and nobody would call that area warm so I imagine grapes could still be grown in the UK if there was any desire to do so.
Damn close. Where the Bristlecones grow in the White-Inyo range there are dead ones above the live line by about 1500-2000 feet IIRC. Baby ones are starting to sprout and grow above the current mature line. The dead ones were growing to old age (~2500-5000 years) in a significantly warmer climate as I see it.