“Medieval Warm Period was warmer” is not only irrelevant to future climate, but was known wrong within science by the early 1990s. In 2017, it is still repeated by climate deniers. They have long misused some version of an IPCC(1990) curve, whose abuse is the focus of this MedievalDeception series. The first known promoter now seems to be Richard S. Lindzen.
He was featured in The Greening of Planet Earth (produced 1991, published 1992), a 28-minute video,* widely promoted by the coal group Western Fuels Association (WFA), which funded many climate disinformation efforts, such as those by Pat Michaels and Robert Balling, Jr. For more, see Western Fuels Association's Decades Of Dollars For Doubt And Denial.