Climate normally, in the planet's history, changes gradually, over tens of thousands of years due to solar variation unless an event such as a meteorite strike should.happen and cause mass extinction. What we have now is a mass extinction event caused by the burning of colossal quantities of fossil fuels. If you really think that is untrue then you haven't really thought about it. Energy companies spent millions 'debunking' the obvious facts in. the 80's and 90's and unfortunately some stubborn people still refuse to accept the obvious.
Grapes have always been grown in the south of England although it's much easier nowadays of course.
The Dark Ages are so-called because of the lack of written records due to a breakdown of societal culture, not because it was dark.. There was a medieval warm period around 950-1200AD and mini-ice ages in human recorded history but none of these were. global, just localised and caused by sea current anomalies.