I have been asked the following question from a reader of this web-log:
What is the evidence for the medieval warm period?
My understanding is that the Vikings were able to settle Greenland and grow grapes in Canada over several hundreds of years because the climate was significantly warmer. Yet this period is not evident in the famous ‘hockey stick’ graph.
End of question.
Jennifer Marohasy BSc PhD is a critical thinker with expertise in the scientific method.
Try reading various discussions on “warm period” and “Little Ice Age”
http://www.realclimate.org/index.php?p=64
Weren’t temperatures warmer than today during the “Medieval Warm Period”?
This is one of a number of popular myths regarding temperature variations in past centuries. At hemispheric or global scales, surface temperatures are believed to have followed the “Hockey Stick” pattern, characterized by a long-term cooling trend from the so-called “Medieval Warm Period” (broadly speaking, the 10th-mid 14th centuries) through the “Little Ice Age” (broadly speaking, the mid 15th-19th centuries), followed by a rapid warming during the 20th century that culminates in anomalous late 20th century warmth. The late 20th century warmth, at hemispheric or global scales, appears, from a number of recent peer-reviewed studies, to exceed the peak warmth of the “Medieval Warm Period”. Claims that global average temperatures during Medieval times were warmer than present-day are based on a number of false premises that a) confuse past evidence of drought/precipitation with temperature evidence, b) fail to disinguish regional from global-scale temperature variations, and c) use the entire “20th century” to describe “modern” conditions , fail to differentiate between relatively cool early 20th century conditions and the anomalously warm late 20th century conditions.
http://cfa-www.harvard.edu/press/pr0310.html
But then again the enquirer may like to peruse this web site from Harvard, which gives a different answer.
“believed” is not a scientific approach – either the temperature did, or they did not. Either the data support the thesis or they don’t.
The instant belief in something is introduced, it is religion, not science.
The Medieval Warming period is fact. What we do not understand is how Greenland froze up. But it did.
As for the infamous hockey stick, as Mcintyre and McKitrick show in peer reviewed journals, that curve cannot be created from the data set and methodology published by Mann et al.
As for the late 20th century global average temperature, there is sound evidence that this variable has not been correctly computed, involving as it does the problems associated of doing quantitative computations with “intensive” variables. And that is another issue, of course.
As long as we do not understand how Europe and Greenland in particular cooled, and for that matter Greenland remains cold, meaning we really have no idea what drives climate. whether regionally or globally, then any attempt to predict future climate states is sheer nonesense.
Loius – M&M DID NOT publish in peer reviewed journals. Their work HAS NOT been confirmed by anyone.
The work of Mann et all in contrast has been confirmed in peer reviewed journals and his methodology has been shown to be sound by independant studies.
You know this from being trounced on Deltoid whenever you show your face there on this subject.
The ‘controvosy’ about the hockey stick is one element in the FUD campaign of the paid skeptics.
Jennifer – if you read the abstract of this publication ftp://holocene.evsc.virginia.edu/pub/mann/JonesMannROG04.pdf
you will see that Mann et al do acknowledge the existance of the ‘MWP’. They argue that the exact time period of the MWP is very hard to pin down. Also the dispute that the MWP was showed as much warming as today. The Hockey Stick does not say the MWP did not happen just that it was not as warm as GW skeptics say.
Also as you read in Collapse the Greenland settlement was abandoned as much from resource depletion as climate change.