That ancient seabed methane is the real old fart. Our contributions (personally and via cattle) may pale in comparison.
Agreed that methane releases from the tundra and seabed may turn out to be the Black Swan that trumps our other concerns.

It's the most ominous news since the report of arctic ice melting 30 years ahead of schedule.

But, but, but.. I was told that we have nothing to worry about - it's snowing in the Himalaya's for Pete's sake!

But in all seriousness. It's only a matter of time before the the remaining deniers are forced to sing a different, and unfortunately accurate, tune: "Climate change is real, but it's far too late to do anything."

What a disgrace.

Thank god for Leanan's inclusive drumbeats.

In reality, we don't know if this is dangerous or not. In absence of certain knowledge though this is like driving along a cliff with the wheels just at the edge.

We often read stories about old people who grew up in the horse and buggy age and now have witnessed space flight, computers, flat screen TVs and such. I often think about how I was born into a world that was still safe and now we have driven the climate to the edge with CO2 emissions, forest clearings, pollution and such.

Words can't express how much this story affects me.

James Hansen and other scientists have been stressing the probability of tipping points for some time.The methane release in the Arctic could be a tipping point.We don't know but by the time we do it will be too late.
Meanwhile the naysayers relish their moment in the spotlight.The Yale Forum article linked by Leanan has some interesting comments on this phenomenen.

Any idea how much? If it's a small amount it will dissolve in the sea before reaching the atmosphere.

We need a measure of quantity -- I suggest MCE (Million Cow Equivalents).