The best evidence shows warming trends similar to the Medieval Warm Period around 600 to 800 years ago (comparing 1000 years worth of tree rings from across the northern hemisphere). The glaciers are melting due to the warmup from the Little Ice Age which just ended in the 1800's.
As for the CO2 to warming models, they assume there is a "forcing" effect where increases in CO2 (a weak greenhouse gas) cause increases in water vapor (a strong greenhouse gas). This forcing effect is a hypothesis that has never been proven. In fact there is evidence that warming may cause increases in CO2. For the record, I believe mankind is increasing the CO2 in the atmosphere but that it's a small amount compared to the natural carbon cycle and will end up being rebalanced by nature.
There was a warming period when the Icelanders settled Greenland --- and then it became much colder, right? And the Greenland settlements were abandoned?
There seems to be much interesting information in the Sagas about this. And of course it had nothing to do with human activity. Unless all that cabbage and pork they ate....