Over the past 60 years, 100 million to 300 million metric tons of methane have streamed up from once-frozen lake beds in the Arctic, concludes a study " 

That's a lot of variation 100/300 million. And it's expected to double. That sounds bad. And plants on land will release even more than the lakes. But new plant growth is expected to completely mitigate it through the 21 century. Oh well, I was expecting an end of the world report and got a scientific study that raises as many questions as it answers.