How warm was the medieval warm period?

A frequent conclusion based on study of individual records from the so-call ed Medieval Warm Period (similar to 1000-1300 A.D.) is that the present war mth of the 20(th) century is not unusual and therefore cannot be taken as a n indication of forced climate change from greenhouse gas emissions. This c onclusion is not supported by published composites of Northern Hemisphere c limate change, but the conclusions of such syntheses are often either ignor ed or challenged. In this paper, we revisit the controversy by incorporatin g additional time series not used in earlier hemispheric compilations. Anot her difference is that the present reconstruction uses records that are onl y 900-1000 years long, thereby, avoiding the potential problem of uncertain ties introduced by using different numbers of records at different times. D espite clear evidence for Medieval warmth greater than present in some indi vidual records, the new hemispheric composite supports the principal conclu sion of earlier hemispheric reconstructions and, furthermore, indicates tha t maximum Medieval warmth was restricted to two-three 20-30 year intervals, with composite values during these times being only comparable to the mid- 20(th) century warm time interval. Failure to substantiate hemispheric warm th greater than the present consistently occurs in composites because there are significant offsets in timing of warmth in different regions; ignoring these offsets can lead to serious errors concerning inferences about the m agnitude of Medieval warmth and its relevance to interpretation of late 20( th) century warming.