ClimateWire: A conventional historical narrative holds that the rise and expansion of the Mongol Empire -- first under Genghis Khan and, later, his progeny and successors -- were propelled by a deteriorating climate in the Mongolian steppe. Fleeing drought, the narrative runs, Ghengis Khan's Golden Horde pushed west, south and east in a bid for expansion that would someday form the world's largest contiguous empire.
Indeed, climate records indicate that the arid, landlocked steppe was seized by decades of...