If there's a methane tipping point, we may have already passed it. Have a look on YouTube, and you'll see people in Siberia happily creating fireballs by poking

If there's a methane tipping point, we may have already passed it. Have a look on YouTube, and you'll see people in Siberia happily creating fireballs by poking a stick in the ground and holding a lighter over the hole they've just created. And more methane is bubbling up from the Arctic continental shelf every year.