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Melting Permafrost Will Boost Temps, But Not Quickly

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Climate scientists have long known that human-generated greenhouse emissions are only part of the story with global warming. A rising planetary temperature sets in motion all sorts of secondary effects that can boost the temperature even higher — effects like melting Arctic sea ice, rising levels of heat-trapping water vapor in the atmosphere, and more. When researches try to figure out how high the thermometer will go over the next century or two, it’s important to figure in these so-called feedbacks into their calculations. But they don’t fully understand how feedbacks will play out.

A recent study in Nature Geoscience is helping reduce some of that uncertainty. By 2100, say Andrew MacDougall and his co-authors, the melting of Arctic permafrost will release enough carbon dioxide to boost global temperatures by up to an extra half a degree Fahrenheit, and by 2300, the extra heating could add up to as much as 3°F.

Arctic Tundra.
Credit: shane9218/flickr

So that’s not good, obviously, especially since the permafrost feedback is just one of many that will add to global warming. But two really intriguing things about that become clear when you look more closely. The first is that the half-degree by 2100 is likely to happen whether or not we slow our emissions from fossil-fuel burning or not.

If that sounds crazy, the second seems even crazier: when you go beyond 2100, the extra warming from permafrost is less if our greenhouse emissions are higher.

Both of these facts sound as absurd to me as they probably do to you — but it makes sense when you understand a couple of basic scientific facts.

Fact No. 1: carbon emissions from melting permafrost take a while to get going. First you have to add CO2 to the atmosphere by burning coal or oil. The CO2 starts trapping heat right away, but the heat still takes time to build.

Then the permafrost has to melt, and as MacDougall said in an interview, “the thawing takes several years, because it takes a lot of energy to melt frozen soil. It takes a long time for the temperature signal to penetrate into the ground.” 

It’s only after the soil thaws that the organic matter trapped within it can begin to decay and release its load of CO2 — and the decay proceeds slowly as well. “The temperature is still hovering just above freezing,” MacDougall said. It’s similar to the way a head of lettuce rots a lot more quickly out on the kitchen counter than inside the refrigerator. 

By the time you add all these delays, it can take decades for permafrost-related warming to kick in. That’s why emissions don’t affect the permafrost feedback all that much for most of this century. By the 2100’s, however, it’s definitely kicking in.

Full Mauna Loa CO2 record.
Credit: NOAA

Now comes the really counter-intuitive part: the more CO2 that’s already in the atmosphere from other sources (that is, from human emissions), the less impact the extra CO2 from permafrost will have, thanks to the physics of the greenhouse effect.

“It’s a logarithmic forcing,” MacDougall said, which in plain English means that whatever temperature increase you get from, say doubling the amount of CO2 in the atmosphere, you’ll get the same increase if you double it again.

So for example, doubling of CO2 from its pre-industrial level of about 270 parts per million to 540 parts (we’re now at about 393) should raise temperatures by somewhere between 3.2°F and 7.2°F. But you’d have to double it again to 1080 to get another 3.2°F - 7.2°F. And you’d have to double it to 2160 to get yet another.

So if we fail to cut back emissions and there’s a lot more CO2 in the air by 2100, the extra emissions from permafrost will be less, percentagewise, than they would if we do curb emissions. And their warming effect will be less.

That’s hardly a reason to abandon efforts to reduce greenhouse gas emissions, since the overall heating would be far more without such reductions, even if the contribution from permafrost would be less. It’s kind of like continuing to smoke because it helps you lose weight, even though the health risks from smoking are vastly worse than the risks from chubbiness.

But it is a reason to keep studying the climate. Scientists don’t have all the answers yet, and sometimes those answers can be surprising.

Related Coverage 
Permafrost Time Bomb
Why Temperatures Could Eventually Go Higher Than We Think
Tracking Temperature for a Better Look at Climate Change

« Climate in Context

Comments

By km
on October 5th, 2012

Minor point, but to be technically correct, permafrost, which may include ice, but certainly includes sediment, soil, and/or rock, does not actually melt—it thaws.

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By Christopher Shaw (Seaford)
on October 5th, 2012

What about the potential for increased methane releases that I have read about elsewhere. Will that not be a forcing factor?

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By mlemonick
on October 5th, 2012

km is right, of course, but journalists hate to use the same word too many times in the same story. That’s why earthquake stories frequently mix it up with the word “temblor,” which nobody ever actually says. (Can you imagine someone saying “hey, was that a temblor I just felt?” No, I didn’t think you could). I could have used “softens,” though, come to think of it, which would have been less inaccurate. Next time I will!

Christopher Shaw is also correct: as tundra thaws, swampy areas will emit methane, while drier areas will emit CO2. The greatest potential for methane release, however, could be for methane hydrates buried in the seafloor. We’ll have a story on that coming out very soon.

Reply to this comment

By Wes Hopper (AZ)
on October 5th, 2012

This article is so optimistic as to be almost delusional. At what temperature does the ecosystem collapse? At what point does the warming become irreversible? Considering what we’re seeing already, can any rational human believe that we can take 7 deg F more and survive? The chances of any human being around to document the effects of 1080ppm are small indeed.

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By john harkness
on October 6th, 2012

This important article on permafrost feedback is now being discussed on most of the other major climate change related blogs, with various approaches. I find it interesting that Climate Central chose to downplay it. I think tamino got it better by titling his post on the findings: “Oh Shit!”

http://tamino.wordpress.com/2012/10/04/oh-shit/

What the article says is that, when this very narrow slice of the known and likely carbon feedbacks is included in the models, even if we cease all CO2 emissions immediately, we will see atmospheric CO2 levels remain at current high levels for centuries, at least.

But of course there are many other huge carbon feedbacks that are already underway or soon will be.

So instead of remaining steady at our current high levels for the indefinite future, this study proves that we are now, already inside the nightmare scenario of runaway global warming—no matter how much we reduce our emission at this point, atmospheric CO2 concentration will continue to increase indefinitely (though of course not infinitely) into the future, and so GW and its devastating effects will continue to worsen for (in human terms) ever.

Oh shit, indeed.

Reply to this comment

By SecularAnimist
on October 7th, 2012

One more study telling us what we already know:

1.  We need to end all anthropogenic GHG emissions as rapidly as possible—which is to say, as close to IMMEDIATELY as possible.

2.  We need to draw down the already dangerous anthropogenic excess of atmospheric GHGs to preindustrial levels as rapidly as possible.

The good news is that we already know how to do these things, and the means are at hand. 

We can end GHG emissions with a rapid phaseout of fossil fuels and conversion to renewable energy technologies—multiple “road maps” showing how to do this within 10 years have already been published, including some peer-reviewed studies. (This will also make our energy systems, e.g. the electric grid, more resilient to destructive weather, heat waves and other AGW impacts that are already occurring.)

We can draw down the excess GHGs with a world-wide conversion to organic agriculture and an aggressive global program of reforestation, to sequester carbon in soils and biomass (which will also help to restore the health of ecosystems in many other ways and make agriculture more resistant to drought and other AGW impacts that are already occurring).

There are no real technological or economic obstacles to doing any of these things.  The only real obstacle is the entrenched wealth and power of the fossil fuel corporations and others whose continued wealth and power depends on maintaining the status quo.

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By Mike Smith (Oakville, Ontario L6L 5J2)
on October 7th, 2012

This is the first time I have heard the logarithmic angle and it is strange because the relation between temperature and carbon ppm has been linear form the last 450,000 years see http://www.columbia.edu/~mhs119/Storms/ Chapter 3.

Other articles see Macdougalls article as “rosy”  see http://thinkprogress.org/climate/2012/10/06/970721/carbon-feedback-from-thawing-permafrost-will-add-04f-15f-to-total-global-warming-by-2100/

I would like to hear a little more on this before climbing on this band wagon.

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By melty (Montclair, NJ 07043)
on October 8th, 2012

“So if we fail to cut back emissions and there’s a lot more CO2 in the air by 2100, the extra emissions from permafrost will be less, percentagewise, than they would if we do curb emissions. And their warming effect will be less.”

What a strange statement. Is this merely semantics? “Percentagewise?” It’s not even a word without a hyphen! Physics dictates that the “greenhouse” warming from methane (CH4/CO2 emission ratio depends on moisture regime; wetter means more methane) and/or CO2 released from permafrost thawing (not “melting”) will be the same whatever the concentration of fossil fuel CO2. We are interested in the _absolute forcing potential, not the _relative forcing potential (yes, we know about the same forcing increase for doublings of CO2). And what about seafloor CH4 clathrates?

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By Pete Trabant (Hot Springs Village, AR 71909)
on October 10th, 2012

On the subject of our economy and CO-2 production I just calculated the cost of oil imports: Since 1975 U.S. consumers spent no less than 15-trillion dollars (2010 base) importing oil instead of developing alternative and renewable domestic sources of energy; after oil production peaked in 1971and OPEC imposed its first embargo in 1973. 
Moneys that would eventually drain the economy and enrich not just OPEC but mostly major international oil companies.
On clatherates.. they are pretty deep (100’s of feet) beneath the seafloor and not about to be affected by slightly warmer sea water and sea level rise.

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By Jan Galkowski (Westwood, MA 02090)
on February 13th, 2013

This article is misleading.  Sure, it highlights the contribution of GHGs from permafrost, but the measures of impact it proposes are worse than useless.  What happens is that, because of human produced greenhouse gases, some additional amplifying effect will be released, with some lag, from the permafrost.  If human emissions were to suddenly curtail, unfortunately, that additional permafrost contribution would still be there, because we’ve committed, already, due to our reticence to curtail greenhouse gases, to a certain degree of warming.  That will continue for quite some time.  We are truly trying to manage the world our grandchildren will live in.

But it is important to note that, if we fail to curtail emissions, at some point, emissions from permafrost and similar sources will overtake human emissions.  At that point we will lose control of something we had control, but refused to do anything about.  And at that point, runaway heating will occur.  This is one of the several scenarios possible from natural law which suggest we are in grave danger.

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