First of all, I think you're mixing up two terms. There was a "Holocene Climate Optimum" -- the period you're referring to is most commonly called the "Medieval Warm Period" or MWP.
Can you show provide references that indicate the MWP was truly global? The main problem is that there is so little data from the Southern Hemisphere.
By the way, Baffin Island is in the Northern Hemisphere.
For a bit of help, there is decent data showing that the cold period from 1400 - ~1850 was global, but most intense in Europe and the northern Atlantic region. Is that what you're thinking of?
You also might like to read this:
Climate in Medieval Time (PDF)
Excerpt of interest:
"There is evidence for widespread hydrological anomalies from 900 to 1300 A.D. Prolonged droughts affected many parts of the western United States (especially eastern California and the western Great Basin) (14). Other parts of the world also experienced persistent hydrological anomalies (15). For this reason, Stine (14) argues that a better term for this period is the Medieval Climatic Anomaly, removing the emphasis on temperature as its defining characteristic."
In the single figure in this reference, the Baffin Island record is #15, indicating that the warmest 30 year period in that record occurred about A.D. 1200. In the figure, records 4-6 are Southern Hemisphere, showing the warmest 30-year period between 1400-1500 -- which in Europe was the start of the Little Ice Age!
Yeah, you're right. Brain-fart on my part.
"Can you show provide references that indicate the MWP was truly global? The main problem is that there is so little data from the Southern Hemisphere."
No--I'm past the point of keeping references on this stuff--got other stuff to keep me busy. I just keep seeing different studies from widely separated geographic areas all pointing to the "globalality" of the "Medievel Warm Period". One I "do" recall was from Australia. Used proxy oxygen isotope measurements on some shellfish in sediment.