- The ground around me is made up of both ice and frozen soil.

We call that permafrost.

It contains twice as much carbon as the atmosphere, and it thaws faster as the climate gets warmer.

It's like opening a freezer door and the food that's in the freezer door starts to rot.

So the dead plant and animal remains that have been locked away in permafrost for thousands of years are now becoming food for microbes that decompose it, and they make greenhouse gases, methane and carbon dioxide.

[soft music] narrator: As the permafrost thaws, the ground sinks and floods.

- Since the 1980s, the amount of lakes here around interior Alaska has increased by 40%.

narrator: In summer, there's nothing to stop the damaging greenhouse gases bubbling up into the atmosphere.

But in winter, all that changes.

- These great big dimples are telling me that there's hardly any ice there.

- Okay.

- Be careful, though.

Thin ice means a hole we could fall into.

- Fun part of the job.

- It wasn't until I went out on a lake in the winter when the ice had frozen that I learned a lot about methane bubbles.

narrator: The ice traps gases bubbling up from the decomposing permafrost.

- Oh, there we go.

We found one.

See how round that is, and you can actually see some of the bubbles there... - Mm-hmm.

- Trapped in the ice.

So that's a good candidate.

narrator: There's a surefire way of finding out what gas this is.

[dramatic music] ♪ ♪ - Okay, ready?

- Yep.

♪ ♪ - Ooh!

- Whoa!

- Nice.

[laughter] - Are you okay, Phil?

That was about as good as they get.

[laughs] I wonder how high that went.

If we see gas pockets, we try lighting a match.

And if our match lights up into a big ball of fire, we know that we have a methane lake.

Whoo!