There are as far as I can tell two currents of thought. One says major climatic changes are more localized, the other that they are world wide. Though it should be noted that the major changes are always worldwide. So you have this condition that circa 800 things were warm and then a cooling set in that ended with what is termed the 'little Ice Age' in the 18th century. The earth has been warming ever since. For the past century that warming trend seems to be accelerating. Many people seem to think the actual climate change happens in the end rapidly, in less than a few years.
As for the CO2, we do know that the levels are rising and we do know we are helping them along. The Clean Air Act of the 70s was actually a great success. People who monitor these things can point to the changes to the atmosphere that occurred at the time. One thing that confuses many people is that back then the suggestion was global cooling because the gases and particulate being released were fouling the atmosphere in much the same way a major volcanic eruption does. A major volcanic eruption in 1815 resulted in a year with no summer.
[read the Three Mile Time Machine. It is a book on Ice cores in Greenland. Very Good]
As for the Norsemen, by the 12th century they controlled everything from Russia to Jerusalem, Tunis, Spain, to England. Though it was all a bit splintered and some were by then Franks. A people who were hated in the 'levant'. Though Saladin, the Kurd took possession of Jerusalem about that time.
Or something like that.
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