Your post made me think of something I hadn't considered before: Muhammad lived in the 7th century (600's) during the Dark Age cooling period. So his trek to Mecca would have probably been during cooler summers than what they had later in the Medieval Warm Period or today in the Modern Warm Period.
In the graph below, he would have lived in the small blue half-circle between the Roman Warm Period and the Medieval Warm Period, probably on the left side of the blue circle while average temps were still cooling until they bottomed around AD 700 or 900 (depending on who you ask).
