Carbon cycle feedbacks: tiptoeing forwards

This is me, tiptoeing towards the spotters guide to bloggers I promised. But I’ve been distracted, because I was pointed at Climate scientist: “Positive carbon-climate feedback is still very likely” — and even without “a runaway feedback,” warming will be “substantial and critical” Plus a review of recent research on amplifying feedbacks at ClimateProgress. I think most of it is by Brad Johnston, but there is an addendum by Romm. So, what is wrong with it?

First off, you have to wade through too much foam to get to the substance, which puts me in a bad mood. Once you know the structure of the post you blip over the goo and dribble, but for anyone coming to it fresh there is just too much “set you up in the right frame of mood to accept the framing” type stuff.

What BJ is doing is attacking some stuff in FirstPost by Tim Edwards (who he?) ‘Runaway climate change’ ‘unrealistic’, say scientists. I don’t know why. Runaway climate change *is* unrealistic (or at the very least, improbable. Certainly, I’m not worrying about it). The report isn’t wonderful, but for example it says:

Today, Sir Muir Russell’s independent review of the Climategate scandal, in which hackers stole and circulated emails from the Climatic Research Unit at the University of East Anglia, cleared climate scientists of malpractice. It is the third inquiry to do so – leading to calls of ‘whitewash’ from climate change sceptics.

I wouldn’t have put in the whitewash bits, but never mind. Or:

The Netherlands Environmental Assessment Agency (PBL) said the Intergovernmental Panel on Climate Change’s 2007 report contained “no errors that would undermine the main conclusions” … Embarrassingly for PBL, it had to admit it was the source of one of the most glaring errors – a claim that 55 per cent of the Netherlands was at risk of flooding because it lies under sea level.

Quite good, really. But the CP article rather misleadingly focuses on one line from the report:

“Climate change skeptics might say the new study is yet another nail in the coffin of the IPCC report,” Edwards writes

Now this is unfair. That line comes towards the end of the FirstPost piece, and a fuller quote is:

Climate change sceptics might say the new study is yet another nail in the coffin of the IPCC report, which says: “Anthropogenic warming could lead to some effects that are abrupt or irreversible, depending upon the rate and magnitude of the climate change.”

But mainstream scientists will just be pleased that Fluxnet has given them real-world measurements upon which to base their computer models – which could be another nail in the coffin of climate change scepticism, relying as it so often does on quibbles over the quality of data.

So while giving semi-equal weighting to the “skeptics” isn’t great, it is balanced by the sane view, which indeed is the end-of-article view.

BJ goes on the claim that “Edwards utterly misrepresented the research” and indulges in “fevered speculation”. Neither of these claims are reasonable.

I think that is enough knocking BJ. I’ll now try and talk about the actual issue involved, which is carbon cycle feedbacks.

The idea is that as the world warms, certain processes that “regulate” the atmospheric carbon diooxide get out of whack. For example, warmer oceans will absorb less CO2. Or less precipitation could lead to drying in the Amazon and dieback of the forest there, releasing CO2. And increasing soil temperatures could lead to increased life in the soils, again leading to more CO2 being produced. And more Co2 leads to more warming which feeds back into the cycle. In this case, This Week reports:

Using Fluxnet, a global network of more than 250 ‘flux towers’ to sample CO2 concentrations, a team of researchers from the Max Planck Institute has found that, actually, temperature has a much smaller effect on CO2 release than previous studies claimed. The researchers, led by Miguel Mahecha, found that the rate at which plants and microorganisms produce CO2 in ecosystems from tropical rainforests to savannah does not even double when the temperature increases by 10°C from one week to the next.

As it happens, I’ve no idea if that is a true paraphrase of the paper, but it sounds entirely plausible. The point is that just because you have *feedback* doesn’t mean you have *runaway feedback*. This study isn’t the last word on the subject, of course, but it does tell you something useful about how soils respond to temperature.

Where FirstPost errs is in writing ‘Runaway climate change’ ‘unrealistic’, say scientists as though it was news. It isn’t; its a commonplace. But it is a mistake that many people make. Where BJ errs is in attacking a fairly harmless piece for no obvious reason, unless it was to fill up column inches. This is all assuming that ThisWeek is just some-or-another website. If it has claims to be “on the side of the angels” then I might hold it to higher standards. But BJ’s piece wouldn’t get any better.

29 thoughts on “Carbon cycle feedbacks: tiptoeing forwards”

  1. Ugh. You try to inform people that a runaway is not expected by anybody serious, and then this guy muddies the waters.


  2. I think Hansen expects it, but he seems to be an outlier.

    There does appear to be a lot of confusion about ‘tipping points’ and ‘runaway’ and ‘postive feedback’. Positive feedback is usually associated with runaway conditions, but in the case of AGW, the positive feedback does hit substantial boundaries before it can get to a Venus type situation.

    There are tipping points, such as the permafrost that, once melted, won’t be turning back into permafrost again.


  3. Positive feedback is usually associated with runaway conditions

    All runaway processes require positive feedback, but not all processes with positive feedback are subject to runaway. Also, with the possible exception of universal expansion, all runaway processes are bounded: the range where the system is unstable is limited so that when it reaches one extreme or another the feedback gain goes below unity.

    If you have a system forcing of x which causes a proportional secondary forcing y where y=kx, the net effect of forcing x is x/(1-k)

    To get runaway instability you need k≥1

    [People often get this wrong, by failing to place things correctly. When we speak of “positive feedback” we’re only talking about one component of the overall climate system. the gain of the *overall* system remains less than one. S=eT^4 is the negative feedback. [[Positive feedback#In climatology]] explains this, cos I wrote it -W]


  4. I think BJ’s main criticism was that the story (especially the headline) didn’t accurate reflect the study’s conclusions, and the researcher who was the source of Edwards’ quote about feedback agrees:

    In an email interview with the Wonk Room, Dr. Reichstein excoriated the First Post story as a “very bad report,” saying that his research does not show that runaway climate change is “unrealistic.” In fact, Reichstein told the Wonk Room that “positive carbon-climate feedback is still very likely.”

    Maybe it depends on what your definition of “runaway climate change” is.

    [I didn’t comment on R’s opinion. I think he is wrong: this is most definitely *not* a very bad report. Of its type, it is actually fairly good. I think R was fed a line by BJ and that R didn’t actually read the reporting very careffully -W]


  5. Here’s what Joe Romm thinks:

    The term “runaway feedback” is ill-defined in any case. I think the more plausible scenario is simply that if we cross a key threshold for any extended period of time, certainly 450 ppm and possibly 400 (or lower), the amplifying feedbacks will accelerate and gravely complicate any effort to constrain emissions.

    [Well, I was going to jump on that too, but I’ve stomped on Romm eniough. He is wrong. We’re already just about at 400 (385 odd). There is no evidence that “amplifying feedbacks will accelerate and gravely complicate any effort to constrain emissions”. That is just fluff -W]


  6. > the sane view, which indeed is the end-of-article view.
    Don’t journalists have some rule of thumb about what part of their audience reads to the end? “burying the lede” I think is what they call putting the facts at the end.

    [No, I don’t think that is fair. We’re talking about 2 para’s, one the second-from-last, one the last. Anyone skipping through the article is *more* likely to read the very last para -W]

    Fluxnet …

    > “CO2 in ecosystems from tropical rainforests to
    > savannah does not even double when the temperature
    > increases by 10°C from one week to the next.

    Same as saying that it almost doubles?

    [You’d have to actually read the paper I suppose 😉 -W]

    That would be an awfully fast response, wouldn’t it? Q10, the speed of enzyme reactions, is a number describing change with a 10 degree change in temperature, but that can’t be what they’re talking about. What temperature increased — average air temp for the week? Daytime? nighttime? peak? low? Or were they measuring the temperature in the cambium, the root systems, the leaves, and at what time?

    [Why do you expect a slower response? And 10 oC is an awfully large temperature change. Clearly, they are using “weather” temperature changes as a proxy for long term changes. Clearly, this isn’t perfect. It misses a whole load of stuff – perhaps with longer term change the whole system adapts. Its just one data point -W]

    Smells funny.

    [Now I think you’re being unfair, and are leaing away from a study whose conclusions you don’t like -W]


  7. Hha, yes. It was only relatively recently that i realized that ‘runaway climate change’ means, well, Venus. Previously i’d always assumed it meant ‘whoops, shit’ – the hypothetical point at which positive feedbacks mean there’s no longer any way to stop the climate-change cart till it’s too late for human beans to survive in any substantial numbers without biological engineering or other scifiesque solutions.


  8. Outeast

    Yes, I think for ‘runaway’ to have any meaning, it has to pretty much refer to Venus. Warming that isn’t converging towards a new stable equilibrium, but rather warming that is unstable, divergent, physically unbounded, until you hit a physical constraint (the oceans boiled away) and you’ve got yourself a fundamentally different planet.

    I think for the most part, ‘runaway’ isn’t abused too much; you just get sceptics who don’t understand how you can have positive feedbacks but not a runaway.

    ‘Tipping point’ on the other hand, seems to be used somewhat indiscriminately and imprecisely.


  9. There is no evidence that “amplifying feedbacks will accelerate and gravely complicate any effort to constrain emissions”. That is just fluff

    The CP post you link to has dozens of references to just such evidence. Maybe you believe that’s all fluff, and if so, I’d like to hear about that at more length. Also, I dont think we should be surprised that CO2 concentration >350ppm for a few decades hasn’t yet triggered the kind of feedbacks that make mitigation very difficult. All that permafrost isn’t going to thaw overnight, but it will thaw eventually, and at a faster pace, if the temperature continues to rise.

    [OK, fair point. I didn’t bother look at his list because I assumed it would be just the usual. So, taking them in order:

    * clouds. A feedback, currently a somewhat uncertain one, but not an accelerating one.
    * Arctic methane. A better try, but still a fail I think.See-also Mr Methane and Methane data. Here is a pic I’ve just drawn:

    You can argue that the last few years have been an uptick, but the previous decade was very flat. There is precious little sign of an accelerating rise in methane levels.
    * Tree dying. Yes its a feedback. But that article makes no attempt to quantify it. How much as this raised CO2 levels? 10 ppm? 1? 0.1? Is it accelerating – no idea.
    * water vapour. Yes, well understood, not accelerating.

    I got bored at that point. I can’t see any evidence on accelerating feedbacks in Romm’s list. Which one did you find convincing? -W]


  10. Okay, the abstract is here:

    They “approximate the sensitivity of terrestrial ecosystem respiration to air temperature (Q10) across 60 FLUXNET sites using a methodology that circumvents confounding effects. Contrary to previous findings, our results suggest that Q10 is independent of mean annual temperature, does not differ among biomes, and is confined to values around 1.4 (±0.1) ….”

    So the abstract d the journalist’s take:
    — It’s “Q10” as I guessed (for sites not enzymes).
    — It’s for air temperature
    (Anyone recall where the enzymes for respiration are located in plants? In the roots, or stems, or leaves? Probably not the leaves. How long do they take to come to equilibrate with a change in annual air temperature?)
    — a change for “a week” says the article, but
    — the abstract says it’s a change in “mean annual”

    [Err no not quite. What you’ve quoted says that Q10 is indep of mean annual temperature. Without reading it, what I think that says is that the sensitivity doesn’t very strongly with average T – presumably these 60 sites are spread widely across different regions with differing baseline temperatures -W]

    I’d guess the journalist is reporting the press release not the actual paper. Anyone seen that?

    Yeah, I should read the article.
    So should the journalist and maybe the press release writer.
    Maybe I’m just cranky today.


  11. (PS, William, if this actually is a result that changes the modeling, I’m delighted. Cranky or not, even without kids of my own, I do hope prospects for the future look better with more study rather than worse.

    I’m just wary of false hope delay-spinners, and aware there’s probably a rush to publish coming up to the next IPCC report.

    When’s the cutoff for that? It’d be interesting to chart rates of publication in the relevant fields.

    [They have only just seleted the lead authors. Cutoff must we a while away. But I’m out of that now – you could ask JA, he might care more. As to this result – I don’t know. I don’t even know what model of soil respiration *is* in the GCMs that have carbon cycle models -W]


  12. I got bored at that point. I can’t see any evidence on accelerating feedbacks in Romm’s list. Which one did you find convincing?

    I think projections for permafrost thaw are the most worrying. Even if we haven’t yet seen dramatic rises in methane levels, it’s hard to see how such thawing wouldn’t lead to highly elevated levels and drastically compound our problems. As with many aspects of climate change, if we wait until these effects are plainly visible, there will be very little we can do to prevent them.

    [Maybe. But I’d want to see at least some quantisation of the effect before I took it very seriously. People are in the habit of tossing Mtonnes around as scary numbers but forgetting that the overall total is much bigger -W]


  13. Permafrost thawing and wetlands drying strike me as largely unquantified risks. There seems to be some evidence of the latter associated with PETM.

    But then, maybe the survivors can bask with the crocodiles under the palm trees around the Arctic Ocean…


  14. As for permafrost carbon cycle feedback…

    Isn’t there a bunch of CO2 in the permafrost as well?

    I read on RealClimate that methane doesn’t stay in the atmosphere long enough to be a problem (~10 years)..It would have to come out quickly to be a problem.

    However, I think some of Romm’s concern on permafrost is the CO2 that would get released over time. If you look at the graph he posts in the article it looks like a lot would be gone by 2050…That seem concerning…

    I have no idea if that graph can be trusted or what that would translate into CO2 ppm…


  15. This whole kerfuffle can be blamed on Reichstein’s reference to “alarmist scenarios” in the press release. The fact that there hadn’t been a prior upper constraint placed on soil respiration feedback doesn’t automatically make for an alarmist scenario. Can anybody point to one? Somebody speculating outside of the literature that there might be something major to worry about doesn’t count as much of a “scenario.”

    Re Edwards, IMHO his use of that IPCC quote was a pretty major sin since it was a general statement rather than one specific to soil.

    Re the permafrost, lots of scientists, not just Reichstein, are worried about it.

    I saw this the other day on the KQED Climate Watch blog:

    According to Breck Bowden, a scientist from the University of Vermont who studies permafrost here at Toolik, the latest modeling shows that approximately half of the permafrost in the Arctic will thaw in the next 50 years. That’s significant not just for the Arctic ecosystems, but potentially for the entire planet. Scientists estimate that there’s one to two times as much carbon frozen in the Arctic soils as there is currently circulating in the atmosphere, said Bowden. The problem is that as the permafrost thaws, that carbon (mostly in the form of frozen organic matter), some of which has been frozen for thousands of years, will be processed by microbes in the soil and ultimately released into the atmosphere as greenhouse gases: CO2 and methane.

    ‘”So why should someone who is living in Alabama, or Nigeria, or the Phillippines worry about what’s going on the Arctic?” said Bowden. “Well, they should worry a lot if there’s going to be a massive amount of CO2 that gets into the atmosphere and your sea level rises or your crops fail because of changes that are related to CO2 changes globally. What happens here in the Arctic is going to affect everything on the globe.”

    Those numbers don’t sound at all good. I hadn’t seen any such results, although from the sound of it they may be unpublished. I emailed him asking for a pointer and haven’t heard back yet, but probably he’s still in the field.

    [That is better, because it is closer to numbers. However: it seems to rely on *all* the Arctic soil carbon being emitted. That seems unlikely. Soils all over the world store cabron; I’m sure as the arctic gradually unfreezes *some* will be emitted, but assuming all (or even the vast majority) doesn’t look immeadiately justified -W]


  16. > without reading the paper

    Me neither. Perhaps if we discuss it long enough someone who did will comment (grin).

    Google Scholar for these terms:
    respiration rate CO2 production plants latitude
    –> no surprises, this isn’t news: “long-term temperature response of respiration was essentially flat over a wide range of ambient temperatures” for example.
    DOI 10.1111/j.1365-2486.2009.01892.x Lots more like it.
    Respiration rate for for organisms that don’t heat themselves has no call to vary greatly that I can think of — though for plants it’ll change secondary to closing the leaf pores to limit moisture loss.

    Search Google, though, and CO2Science and Wattsup are in the top ten pages found. Excitable, boy!.


  17. There is a rule of thumb that reaction rates double for a 10K temperature difference across a huge number of reactions (including complex ones). Since this is a rule of thumb, the fact that Q10 was 1.4 instead of 2 or a bit more as some previous estimates had put it is not a huge surprise. As the paper points out, the lower value was favored by carbon cycle modeling which work best for Q10 less than 2.

    However, Reichstein is right and Stoat is wrong.

    First, this is still an exponential growth, and corresponds to a significant positive feedback.

    Second, the Q10 that is talked about in the paper is the high frequency response, and as they put it
    Opposed to the global convergence in temperature sensitivities we find complex patterns in the low frequency influence of photosynthetic carbon uptake and available assimilates on ecosystem respiration dynamics. Future research should strive for an in depth understanding of carbon pathways through slow pools in terrestrial ecosystems.

    and it is there (and in a few of the outlying measurements (RTFR)) that the non-linearities in the rates (e.g. Q10) can lurk.

    [Oh go on then – email me the paper and I’ll read it -W]


  18. Eli, yes. I did find the 1.4 factor worrisome.

    And I caught the high frequency response, the problems that people are worried about are much more long term. The other problem involves the forest + savannah and ignoring the response of permafrost and marine clathrates which are much more worrisome to me. Recent papers show that clathrates are not problematic right now, but…


  19. From Eli’s comments, it makes the press release and especially Reichstein’s “alarmist scenario” rhetoric seem shakier.

    Re the issue of total permafrost carbon versus the quantity subject to emission, I noticed that too, William, but it looks to me like the reporter’s confusion. Just to be clear, the bit that I thought was alarming was the 50% melt in 50 years. That’s a big methane pulse no matter how you slice it, and also paves the way for a significant albedo change.


  20. Send twenty (20) carrots in a self addressed stamped envelope to

    Eli Rabett
    Rabett Run
    Meadow, DC

    [Don’t you owe me some from last years sea ice? Or the year before that, I forget -W}


  21. Some of you are no doubt familiar with The Register. Its coverage of breaking IT news is excellent, but it’s aggressively denialist toward AGW. Here’s an on-topic example: Mega new climate science: ‘Runaway’ effect exaggerated.

    I’m trying to recruit more people from the evidence-based community to comment on El Reg’s climate articles. My first link above is to their Science section, including a lot of recent denialist rubbish. Please pile on!

    [Well, it is a bold endeavor and I wish you will but the standard of debate on El Rego’s comments is so low I won’t be joining. I would hope that it would be obvious to the people commenting there that most of them don’t have a clue, and don’t care that they don’t know. It looks more like talking for fun than any attempt to learn anything -W]


  22. W, inline comment:

    I would hope that it would be obvious to the people commenting there that most of them don’t have a clue, and don’t care that they don’t know.

    I’d hope so too William, but El Reg gets a hellalotta traffic. Forget the DKE-afflicted commentors, there are unknown numbers of lurkers who know little of AGW but what they read on El Reg. The battle is for the hearts and minds of the uncommitted, isn’t it?


  23. Commenting on newspaper sites and other sites not directly oriented to climate is generally hopeless. It’s a large volume of people venting out remarkably stupid things.

    Even if I had infinite time and patience, I’d leave them alone.


  24. I’m trying to recruit more people from the evidence-based community to comment on El Reg’s climate articles.

    A futile endeavour, in my experience. They simply don’t publish comments that point out when one of their pet septics (Page, Orlowski) is talking absolute rubbish, no matter how polite, well-reasoned, or referenced. All I can conclude is that they’ve decided on what their readership (or at least a vocal subset thereof) wants to hear, and intend to give them it. I would hope that anybody with half a brain doesn’t read the comments anyway, as they’re almost pure nonsense. El Reg may be read by IT professionals, but it’s commented on by teenaged Slashdot rejects.


  25. I emailed David Lawrence, author of the permafrost projections Romm cites, to ask about resultant GHG emissions from those projections here is his response:

    This is an active area of research by myself and many other groups. The
    reality is that there are not any robust estimates of what the CO2
    emissions or the CH4 emissions might be. I attach an observationally
    based paper that includes some speculation towards the end at the
    potential magnitude of the CO2 emissions, but I would not consider this
    a robust estimate, more of a back of the envelope calculation. CH4
    emissions is even harder as it is extremely highly dependent on what
    happens to local hydrology as permafrost thaws, which is extremely
    difficult to model.

    The article he sent me ( The effect of permafrost thaw on old carbon release
    and net carbon exchange from tundra
    ) estimates about 1 Pg/yr of carbon released. Sounds to me like nothing to sneeze at.


  26. I took the radical step of writing to Mahechca and asking for a copy of the paper. He is on limited connectivity until the 26th, so it took a couple of days.

    They are looking at overall ecosystem respiratory response here not isolated values. They use a new method of analysis of the data to remove confounding factors in the data and feel that this is a better method than those used in the past. If their results hold up it seems to answer a problem which the modelers had been having in which they had to use a value of Q10 less than two to achieve realistic responses, yet the experimental evidence had all suggested a value greater than 2. Looks like another case of the models being right!

    So overall, I couldn’t find anything fishy here, it looks like good work.


  27. > cutoff

    Ah, Brian has collected the cutoff dates and promises to keep his list updated. Linkworthy far’n’wide:

    “AR5 Timetable
    I keep having to resort to web pages all over the place as well as email to find the AR5 timetable, which has changed a few times. So I’m going to put it here, and update it as necessary (via trackbacks and/or direct editing). …”

    [Thanks (and to Brian). So papers have till mid-2012 to be submitted -W]


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s