It appears to be a pretty simple, the Earth is ~6.5B years old, if each year could be the hottest, then the odds of hitting the last 10 as the hottest is 650MM to 1. (That's realistic, right? And excellent usage of statistics. ) Kind of disappointed they didn't use the universe's age of ~15B for their basis. The odds of this are 1.5 BILLION to 1!!! There is clearly no possible way for this to NOT be a man-induced phenomenon.
But in fairness to the guy that came up w/ it, pretty sure he'd told the paper their premise was flawed but these are the #'s that result.