- At least 15% of the Northern Hemisphere has permafrost underneath it.

Technically, that's ground that's been frozen for at least two years, but much of it has been frozen for millennia and it stores a staggering amount of carbon locked safely away in the soil, as long as it stays below 32 degrees.

I don't think viewers of this channel will be surprised to learn that it's already begun thawing due to global warming.

But new research shows that, with just a little bit more warming, a tipping point could be reached, causing a sudden and widespread change to this frozen ground.

- So around about 1500 gigatons of carbon locked in this permafrost that becomes available for release when it thaws.

That's actually about two and a half times the amount that humanity has emitted so far.

- This is one of the first major climate tipping points that human emissions could trigger.

And it's a feedback loop where global warming releases carbon, which speeds up warming.

So what does this mean for our planet's climate?

And are any efforts to slow global warming totally doomed if this carbon bomb is triggered?

In this episode of Weathered, we're talking to the scientists behind this new research who actually have a pretty good answer to that question.

So watch till the end to find out.

And if you appreciate this kind of science-based climate content, hit like and subscribe.

(dramatic music) Back in 2008, Tim Lenton published a groundbreaking paper outlining nine climate tipping points that, once triggered, could be irreversible, leading to the collapse of many important earth systems and contributing significantly to global warming.

At that time, other scientists were skeptical, but now sadly, his work has become highly respected.

Back then, permafrost didn't make the list.

So we were very interested to read Dr. David Armstrong McKay's New Research, which finds that a permafrost abrupt thaw could be triggered, even if we meet the most aggressive targets of the Paris Agreement.

That would suddenly make a lot of carbon available to be released as carbon dioxide, as well as methane, which is some 85 times more potent of a greenhouse gas than CO2 over its first 20 years in the atmosphere.

Because permafrost is deep underground, it's hard to measure, but we know that a gradual thaw of permafrost is already happening.

- When we try to to quantify it, this change in permafrost extent, you just look for where on the globe do we still have a temperature below zero degrees in the ground.

- And they found that since 1997, in fact, this permafrost extent has decreased by two and a half percent.

Much of this ground that remains below zero degrees has been frozen since the last ice age, keeping dormant all of the tiny microbes that break down organic matter and release greenhouse gases.

It's almost all in latitudes far north where it's warming four times faster than the global average.

And when it thaws, those little microbes start quickly digesting carbon into either CO2 if they're dry, or methane, if they're under water.

It's a process called "soil respiration."

Dr. David Armstrong McKay's new paper breaks down permafrost tipping points into two stages.

The first and most likely is the abrupt thaw.

- This is something a bit newer that's been researched recently.

This is not in most climate models and this is that the, you can get all these localized tipping point starting.

- David outlined three related examples for us.

The first is landslides known as slumps or thaw slumps.

- So you can imagine these more steeper slopes that have permafrost underneath them.

If you are melting some of the the ice blocks that are in them, you can get little slumps happening and that can turn into landslides, effectively.

And that gouges out large amounts of land that leads to all of the carbon exposed to be degraded and rot and release greenhouse gases as well.

- And there are several hundreds of thousands of these thaw slumps across the Arctic.

It's a really huge number.

You find them in North America, you find them all across Siberia.

- The ground subsiding as permafrost thaws can also lead to the second local tipping point, known as Thermokarst Lakes.

- It starts off with a little bit of slumping that forms a lake above it and effectively it keeps on spreading outwards as this lake forms.

The lake forming accelerates and amplifies the decay of permafrost underneath it.

So effectively, each Thermokarst Lake is kind of like a little tipping point in action.

These sort of features like slumping and Thermokarst Lakes can make deeper carbon more available more quickly than if you're just thawing gradually from the top down.

And that's something that can really amplify emissions.

- And the third example of a localized tipping point came as a real surprise to scientists and everyone, really.

- So maybe you have heard about these craters in Siberia, really in a lot in the news.

And that's from this really old methane in the ground.

Yeah, so that's a kind of trapped beneath the permafrost.

And some researchers, they think it's due to the thawing permafrost that hot summers triggered the the release.

- Since they became newsworthy back in 2014, at least 17 of these craters have been found.

And there are even reports of locals in Siberia hearing loud explosions before finding new ones.

Many scientists now agree that these craters were caused by a sudden release of a pocket of methane that was capped and held underground by permafrost.

As it thaws, the structure weakens and the methane can cause a bulge on the surface until it explodes, leaving behind large, mysterious craters and exposing lots of deep carbon that will thaw even more.

With more warming, they could become more common.

But when will all of these small local tipping points hit a more significant threshold?

- So a key piece of evidence here is that in one of the previous warm interglacials, the amount of permafrost thaw really expanded by around about 1.5 degrees of warming to expand over a much wider area than was seen before.

In other interglacials.

And 1.5 degrees really does mean that there's quite a lot of permafrost thaw expanding over a larger area.

So that's why we assign that as being what we call a regional impact climate tipping element.

Because even though it's not one coherent tipping element, it still affects a really large area and it does have a impact on the whole system, as well, because of the amplification of the emissions from permafrost and really has a substantial global impact as a result.

- We've already warmed the planet more than 1.1 degrees Celsius.

So 1.5 degrees could come quickly.

In fact, a number of studies show that we could cross the 1.5 degrees sometime during the 2030s, and unfortunately that number falls well within the Paris Agreement goals, which aim to keep warming under two degrees.

But as we've covered in a previous episode, we're currently on track for around 2.6 degrees of total warming.

Still, how bad is this tipping point?

- If you add it all up, it looks a bit like 10% amplification of global warming from human causes.

So it's big, but it's not dominant.

It's more of a gradual chronic leak that we're triggering that will just make it that much harder to try and actually get global warming to stop and halt preferably at the 1.5 degree level.

- So that's mixed news.

From a climate perspective, we definitely don't want 10% more warming outside of our control.

Thankfully those emissions happen over a century or more, but there's another far more dire tipping point that could be crossed if we overshoot the Paris Agreement targets by around one full degree Celsius.

- So there are some regions where permafrost is a lot deeper.

The Yedoma region, it covers parts of Eastern Siberia and far east Russia and also goes into Alaska and Northern Canada, as well.

And it's really deep deposits left from one of the previous ice ages, basically, and it's very rich in carbon.

- The large amount of carbon found in Yedoma permafrost, about 2% by mass, is the result of abundant vegetation and animals like wooly mammoths that populated the region during the last ice age, which began around 2 million years ago.

Over time, this material became frozen in the permafrost, preventing its decomposition and preserving the organic carbon within it.

And in addition to this carbon dense soil and millions of wooly mammoth tusks the Yedoma is also filled with deep ice deposits.

- The ice is important cause that's part of why you get abrupt thaw affecting these areas so badly.

Cause if you melt some of these big ice occlusions and ice layers, suddenly the whole landscape can just sort of slump, it can collapse under itself because it's losing mass from that ice melt.

And that means that you can suddenly expose a lot of deeper carbon quite quickly, and the more carbon is being exposed and the more carbon is degrading simultaneously the more warmth that's gonna release.

- And David and his team believe that the thaw of this Yedoma permafrost could begin at around three degrees of warming and becomes more likely at four degrees.

- So that's where the possibility of this self-sustaining permafrost thaw which is sometimes referred to as compost bomb instability.

The idea being it's like a compost heap that generates its own heat and keeps its, it's effectively kind of like a reaction going to itself.

- This compost bomb instability is the result of what is known as compost warming reaction, which is a process that occurs naturally when organic matter breaks down and decomposes.

As this matter breaks down, it can act as fuel for microorganisms leading to an increase in temperature.

As the temperature increases, the decomposing activity of the microorganisms also increases, leading to further release of heat.

This process creates a positive feedback loop where warming leads to further decomposition, which leads to more warming, which leads to, well, you get the idea.

- And the same thing might be possible with permafrost where there's enough of this carbon together.

So that could happen in some of the these Yedoma regions.

- One bit of good news here is that the Yedoma tends to be found very far north.

- Luckily they're some of the colder regions and that's why you tend to need a higher warming level to potentially trigger those.

- So would this tipping point be truly catastrophic for the climate?

Well, David stressed that he and his team aren't sure if or when it will happen, but he found that a collapse of the Yedoma and similar permafrost formations could increase atmospheric CO2 by up to 60 parts per million over 50 years.

We're currently at about 420 parts per million and 350 is considered safe.

That on top of the four degrees of warming it would take to trigger the thaw could mean catastrophe.

Thankfully, that level of warming is likely a long way into the future and we do have time to reduce emissions before it hits.