The persistently wet period, which lasted from 1211 to 1225, corresponds to the time of the empire's greatest expansion under the elder Khan. A research team posits that abundant moisture could have led to plenty of steppe grass to nourish the horses of Khan's cavalry and the livestock that fed his troops.

So far, the researchers have sampled trees at one site about 150 miles northwest of the site of Genghis Khan's capital, Karakorum, and the samples suggest that fodder was abundant at the jumping-off point for Khan's armies. The team, led by Neil Pederson at Columbia University's Lamont-Doherty Earth Observatory and West Virginia University geographer Amy Hessl, is beginning to hunt for evidence of climate conditions in the conquered areas as well.

Preliminary evidence based on other climate reconstructions hint that Beijing during this period was experiencing drought, as was today's eastern Kazakhstan, Dr. Pederson says, adding that parts of the conquered lands appear to have been wetter than usual.

"It's really a complex story," he says, one that suggests that climate conditions may have been weakening some of the soon-to-be conquered groups even as conditions were contributing to the strength of Mongol forces.

Source: http://www.csmonitor.com/Science/2014/03...