As someone else noted, this doesn't contradict GW theory; the lack of methane increase over the past decade was the real mystery. So now it has started going up again. So there's two questions: why did methane growth in the atmosphere stop, and why did it start going up again?
(My theory: Chipotle. Have you seen how many people go to Chipotle for lunch???!!! There were 14 Chipotles in 1998 and nearly 800 now. That's a gastro-intestinally disturbing trend.)