Read here and here (PDF). Scientists produced a temperature reconstruction from a cave's stalagmite. Roman and Medieval warmings found to range from 1.1°C to 2.3°C higher than the 3,000 year mean. The Little Ice Age climate temperatures documented to have been 1.2°C lower than mean. In summary, the stalagmite records reveal a climate range of temperature changes of 3.5°C, prior to any industrial/consumer CO2 emissions from fossil fuels.

"The climate record derived from China's Jingdong Cave is just another example of what is being found in paleoclimate studies all around the world. There is an externally-forced millennial-scale climatic oscillation of probable solar origin that periodically brings the world relatively warmer and colder conditions, irrespective of whatever may or may not be happening to the air's CO2 content. The Modern Warm Period would thus appear to be nothing more than the most recent expression of this phenomenon."