US officials have yet to draw conclusions on the cause of the inferno. There is no doubt that the dry Mediterranean climate of California is susceptible to wildfires, but the natural factor is not the major cause.

First, because of global warming vegetation tends to dry out more. Statistics show that the autumn of California has been roughly three degrees Fahrenheit warmer since 1980. It makes a big difference to the moisture levels of plants, said Daniel Swain, a climate scientist at University of California at Los Angeles. Currently, the moisture levels in vegetation across California are at the lowest levels on record. Normally, by mid-November, the ground and the vegetation is damp. So sparks from cars, power lines and campfires have a difficult time growing into large fires.