A growing body of evidence clearly shows that hydroclimatic variability during the putative MWP (more appropriately and inclusively called the "Medieval Climate Anomaly" or MCA period) was more regionally extreme (mainly in terms of the frequency and duration of megadroughts) than anything we have seen in the 20th century, except perhaps for the Sahel. So in certain ways the MCA period may have been more climatically extreme than in modern times. The problem is that we have been too fixated on temperature, especially hemispheric and global average temperature, and IPCC is enormously guilty of that. So the fact that evidence for "warming" in tree-ring records during the putative MWP is not as strong and spatially homogeneous as one would like might simply be due to the fact that it was bloody dry too in certain regions, with more spatial variability imposed on growth due to regional drought variability even if it were truly as warm as today. The Calvin cycle and evapotranspiration demand surely prevail here: warm-dry means less tree growth and a reduced expression of what the true warmth was during the MWP.
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