Magny et al. utilizing advanced scientific techniques, reconstructed 1,000 years of past summer (July) temperatures for the Swiss Jura Mountains region. Unequivocally, they found that July temperatures during the Medieval Period were significantly warmer than modern summer temps.
"Working at Lake Joux in the Swiss Jura Mountains...employed a multi-proxy approach with pollen and lake-level data to develop a 1000-year history of the mean temperature of the warmest month of the year (MTWA), which was July...based on the Modern Analogue Technique. This work revealed what they describe as an "MWP between ca. AD 1100 and 1320," during which time the MTWA at Joux Lake exceeded that of the 1961-1990 reference period by fully 2.0°C....Thus, it would appear that the peak warmth of the MWP at Lake Joux exceeded that of the CWP at that location by something on the order of 0.4-1.0°C." [Michel Magnya, Odile Peyrona, Emilie Gauthiera, Boris Vannièrea, Laurent Milleta, Bruno Vermot-Desroches 2011: Quaternary Research]