Read here. It's been well documented that global warming ideologists will always make every attempt to slant paleo-climate research in such a way that modern warming appears to be "unprecedented." This built-in research bias is very prevalent in tree-ring studies, which the infamous 'hockey-stick' fraud is the classic example - e.g., over-weighting a single tree species by 390 times in the hockey-stick study revealed how desperate researchers have been to create a warming bias.
Despite the efforts of some researchers, more objective and impartial scientists are conducting peer-reviewed studies that avoid the significant problems (flim-flam) of tree-ring analysis. The vast preponderance of these studies reveal the wide natural variations in both temperatures and climates over thousands of years. In addition, most establish that the Medieval Warming Period (MWP) was indeed warmer than our modern warming (but not always).
As an example, the recent Moschen et al. German peat bog research confirms that area of the world had considerably higher temperatures for an extended period during the MWP.
Their research also provided a unique indicator for the extreme temperatures of natural climate - varying without any industrial/consumer CO2 emission impact. As the adjacent chart shows, there is a large, multi-century gap with no peat bog data recorded (where the bold blue curve goes missing). That's when the post-Medieval Warming era became so freaking cold the natives actually dug up (The 'Big Dig') the bog's empirical evidence to burn in their homes to keep warm.
"A new paper by Moschen et al appearing in the journal Climate of the Past presents a high resolution reconstruction of local growing season temperature (GST) anomalies at Dürres Maar, Germany over the last two thousand years...In 2007, a 5.5 m long core was recovered from the centre of Dürres Maar peat bog in the mountainous West Eifel Volcanic Field in southwestern Germany...I got a copy of the paper from a source, who wrote: “The ex-hockey team will hate it”. The paper’s Figure 6 tells quite the story. Indeed there was a lot of climate change in the past when CO2 was more or less stagnant." [R. Moschen, N. Kuhl, S. Peters, H. Vos, A. Lucke 2011: Climate of the Past]