Read here. Map source here. For eons, Earth's climate and temperatures have changed in a cyclical pattern. In a peer-reviewed study, researchers analyzed a cave speleothem that produced a 17,000 year temperature record. The results clearly show that the climate changes naturally, and significantly, while atmospheric CO2 levels remained at levels well below current levels. They also confirmed that Roman and Medieval period temperatures equaled or exceeded modern temperatures.
"Working with stalagmite SV1 from Grotta Savi -- a cave located at the southeast margin of the European Alps in Italy.....This work revealed -- among several other things -- the occurrence of the Roman Warm Period and a Medieval Warm Period.....the five researchers say they were "characterized by temperatures that were similar to the present," while with respect to the Roman Warm Period, they say its "temperatures were similar to those of today or even slightly warmer.....we have here yet another example of the millennial-scale oscillation of climate that has characterized the earth throughout glacial and interglacial periods alike; and we note that it provides three good examples of times when temperatures were equally as warm as they are presently, or even warmer, in spite of the fact that the air's CO2 content was much lower at those earlier times than it is today."