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Nearing a Tipping Point on Melting Permafrost?

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Nearly a quarter of the Northern Hemisphere’s land surface is covered in permanently frozen soil, or permafrost, which is filled with carbon-rich plant debris — enough to double the amount of heat-trapping carbon in the atmosphere if the permafrost all melted and the organic matter decomposed.

According to a paper published Thursday in Science, that melting could come sooner, and be more widespread, than experts previously believed. If global average temperature were to rise 2.5°F (1.5°C) above where it stood in pre-industrial times say earth scientist Anton Vaks of Oxford University and an international team of collaborators (and it's already more than halfway there), permafrost across much of northern Canada and Siberia could start to weaken and decay. And since climate scientists project at least that much warming by the middle of the 21st century, global warming could begin to accelerate as a result, in what’s known as a feedback mechanism.

Arctic permafrost seen from a helicopter.
Credit: Brocken Inaglory via Wikimedia Commons

How much this will affect global temperatures, which are currently projected to rise as much as 9°F by 2100, is impossible to say. It all depends on how quickly the permafrost melts, and how quickly bacteria convert the plant material into carbon dioxide and methane gas, and nobody knows the full answer to that. But since climate scientists already expect a wide range of negative consequences from rising temperatures, including higher sea level, more weather extremes and increasing risks to human health, anything that accelerates warming is a concern.

While the rate at which melting permafrost will add carbon to the atmosphere is largely unknown, a study released February 11 in Proceedings of the National Academy of Sciences at least begins to tackle the problem. It shows that when the permafrost does melt, carbon dissolved in the meltwater decomposes faster after it’s been exposed to the ultraviolet component of sunlight.

In any case, there’s no doubt that the permafrost will melt, at least in part, since it’s already starting to do so. In some parts of the Arctic, trees, buildings and roadways have started listing to one side, or even collapsing, as soil that was once hard as a rock has softened from the warming that’s already taken place.

To get an idea of what might be in store for the future, Vaks and his colleagues searched for evidence from the distant past — specifically, from stalagmites and stalactites formed over hundreds of thousands of years in underground Siberian caves. These spiky mineral deposits, known collectively as speleothems, grow layer by layer as surface water percolates through the ground dissolving limestone as it goes, and finally forms droplets that hang from the ceiling of a cave. If the water evaporates before dropping to the floor, it leaves the limestone behind, and over the centuries those bits of limestone grow into a downward-pointing stalactite. If it drops first, then evaporates, the limestone builds up from the floor, creating a stalagmite.

In places without permafrost, this process happens year-in and year-out. Where there’s permafrost, however, water can only drip when the permafrost melts. So Vaks and his colleagues enlisted members of the Arabica Speleological Club in Irkutsk, Russia — amateur cave explorers — to help identify likely caves in a north-south line across Siberia.

Once they’d found the caves, they carefully removed sample speleothems, “preferably from hidden areas, so we wouldn’t spoil the caves’ natural beauty,” Vaks said. The scientists took their samples back to the lab, sliced them lengthwise, and exposed layers laid down over nearly 500,000 years. “By using uranium/thorium dating,” Vaks said, “we could find the layers’ exact ages with high precision.”

They also found that there were long periods when the speleothems didn’t grow at all — certainly not during ice ages, when permafrost locked the soil across most of Siberia, but not even, in the northernmost caves, during warmer interglacial periods, like the one we’re in now when glaciers went into retreat. The last time these northern speleothems showed any growth, in fact, was during an unusually warm period about 400,000 years ago.

At the time, global average temperatures were some 2.5°F warmer than they were in industrial times, or about 1.5° warmer than they are today. That sort of temperature increase by itself wouldn’t make an enormous dent in the permafrost, but the Arctic is likely to warm faster than the rest of the globe — as in fact, it has already started to do.

As for the earlier study on carbon and ultraviolet light, environmental scientist Rose Cory, of the University of North Carolina, focused on sites in Alaska where melting permafrost has caused the soil to collapse into sinkholes or landslides. The soil exposed in this way is “baked” by sunlight, and said Cory in a press release, “(it) makes carbon better food for bacteria.”

In fact, she said, exposed organic matter releases about 40 percent more carbon, in the form of CO2 or methane, than soil that stays buried. “What that means,” Cory said, “ is that if all that stored carbon is released, exposed to sunlight and consumed by bacteria, it could double the amount of this potent greenhouse gas going into the environment.” 

Related Content
Permafrost Timebomb
Melting Permafrost Will Boost Temps, But Not Quickly
Positive Feedbacks in a Warming Arctic
Accelerated Warming Driving Arctic Into New Volatile State

Comments

By Dave (Basking Ridge, NJ 07920)
on February 21st, 2013

In terms of how fast all this happens, this would seem to suggest that the factors in play are not just trends in temperature increases and permafrost melt rates but also any trends that could occur in average sunlight and UV levels in those locations due to changes in cloud cover, pollution and perhaps also the local thickness of the ozone layer.

Reply to this comment

By Ed Leaver (Denver, CO, 80222)
on February 21st, 2013

In what sense are we now in an “interglacial”? Doesn’t that imply there’s going to be another glacial period for us to be sandwiched between? Just how optimistic is that?
Greenhouse Gases Delay the Next Ice Age and < href=“http://www.bbc.co.uk/news/science-environment-16439807”>Carbon emissions ‘will defer Ice Age’</a> both cite Determining the natural length of the current interglacial: “No glacial inception is projected to occur at the current atmospheric CO2 concentrations of 390 ppmv (ref. 1).”

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By Sasparilla
on February 22nd, 2013

I believe the paper says 1.5c higher than industrial times (not 1.5c higher than now).  It also states that the melt appears to start at southern areas earlier, while total (far northern) permafrost melt starts at 1.5c.

” in one far northern cave on the boundary of continuous permafrost grew during a period 400,000 years ago when temperatures were 1.5C higher than in pre-industrial times.”

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By Tuomo Kalliokoski (Jyväskylä/Finland)
on February 22nd, 2013

Build nuclear now!

Stop dreaming about wind and solar, they are not CO2 free (check IEA CO2 highlights and CO2/energy produced for Denmark and compare it to other countries).

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By Robert Pollard (New York, NY)
on February 22nd, 2013

Surely it is the temperature rise in the Arctic, and not the global average rise that will affect the permafrost melt and release of methane - and the Arctic temperatures have been rising much faster than the global average.

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By Bob Vos (Auburn, WA 98092)
on February 22nd, 2013

The assumption is that it will be really bad news when the carbon-rich material trapped in the permafrost “escapes” and becomes part of the atmosphere/plant/animal organic cycle.  How did this carbon get trapped in the permafrost in the first place? It was in fact part of that cycle, when those areas were warmer, before the permafrost. So what basically will have changed from then to now?

I do not claim to be a climate expert, but do have a Ph.D. in science/engineering, so please help me out. By the way, I also farm in my retirement, and would appreciate a few degrees warmer average temperature locally to improve the climate for my crops. I do understand that if climate change occurs there will be winners and losers.

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By Dave (Basking Ridge, NJ 07920)
on February 24th, 2013

BV:

GHG releases from melting permafrost is a natural positive feedback mechanism which is referred to here as a potential “tipping point” process. This is because as the GHG’s start to be released from the permafrost this in turn predictably leads to an increase in the rate of release due to the incremental enhanced warming potential of those GHG’s in the atmosphere. This then leads to faster melt rates, a faster rate of release and so on taking us faster and faster past a point of no return – hence a “tipping point”.  In other words it could suddenly escalate. There are indeed many solid reasons to be concerned about that as a bad thing. You seem to have just ‘tuned into’ this subject. Otherwise, with all due respect, with a PhD you would surely not be asking.

NASA has three nice web pages explaining the carbon cycle and the difference between the fast and slow components that may be of interest: http://earthobservatory.nasa.gov/Features/CarbonCycle/page1.php

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By Justin Bowles
on March 7th, 2013

Michael: I’ve just been exchanging e-mails with Anton Vaks, the lead author of this paper.

Sasparilla is correct. The paper says 1.5c higher than pre-industrial times (not 1.5c higher than now). 

Vaks told me that there was some ambiguity in the Oxford University press release, which has given rise to this misunderstanding, and this has now been corrected.

Accordingly, I think you need to add the correction to the post. 1.5c from pre-industrial is very different from 1.5c now; in short, it makes the problem even more urgent.

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