Another great Peter Sinclair video about a denier favorite: the Medieval Warm Period.
You can read about this crock here at SkepticalScience:
The skeptic argument: The Medieval Warm Period was warmer than current conditions. This means recent warming is not unusual and hence must be natural, not man-made.
What the science says: While the Medieval Warm Period saw unusually warm temperatures in some regions, globally the planet was cooler than current conditions.
The Medieval Warm Period spanned 950 to 1250 AD and corresponded with warmer temperatures in certain regions. During this time, ice-free seas allowed the Vikings to colonize Greenland. North America experienced prolonged droughts.
The Medieval Warm Period was not a global phenomenon. Warmer conditions were concentrated in certain regions. Some regions were even colder than during the Little Ice Age. To claim the Medieval Warm Period was warmer than today is to narrowly focus on a few regions that showed unusual warmth. However, when we look at the broader picture, we see that the Medieval Warm Period was a regional phenomenon with other regions showing strong cooling. Globally, temperatures during the Medieval Period were less than today.
Also see articles on the RealClimate site on the MWP here and here.