‘The Medieval Warm Period was just as warm as today’–Repeating this point does not make it true
(Part of the How to Talk to a Global Warming Skeptic guide)
Objection: It was just as warm in the Medieval Warm Period (MWP) as it is today. In fact, Greenland was green and they were growing grapes in England!
Answer: There is no good evidence that the MWP was a globally warm period comparable to today. Regionally, there may have been places that exhibited notable warmth — Europe, for example — but all global proxy reconstructions agree it is warmer now, and the temperature is rising faster now, than at any time in the last one or even two thousand years.
Anecdotal evidence of wineries in England and Norse farmers in Greenland do not amount to a global assessment.
The idea of a global or hemispheric “Medieval Warm Period” that was warmer than today, however, has turned out to be incorrect.
With regard to the “grapes used to grow in England” bit, here is some fairly solid evidence that grapes are in fact growing there now, denialist talking points aside. If that is not enough, RealClimate has a remarkably in-depth review of the history of wine in Great Britain, and how reliable it is as a proxy for global temperatures. (Hint: not very.)
More stories in this series:
(Part of the How to Talk to a Climate Skeptic guide) Objection: Despite what the computer models tell us, there is actually no evidence of significant global warming. Answer: Global warming is not an output of computer models; it is …
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: CO2 levels are recorded on top of Mauna Loa … a volcano! No wonder the levels are so high. (image courtesty of Global Warming Art)
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: The apparent rise of global average temperatures is actually an illusion due to the urbanization of land around weather stations, the Urban Heat Island effect.
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: One hundred and some years of global surface temperatures is not long enough to draw any conclusions from or worry about anyway. Answer: The reliable instrumental record …
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