Quantifying the negative feedback of vegetation

On another thread, John Michelmore has been telling us about an article by Lahouari Bounoua et al (behind the paywall) which finds that the enhanced effect of CO2 on plant growth provides a cooling feedback, so that doubling current CO2 to 780ppm would only cause a temperature increase of 1.64C. Hence we can all relax in relation to global warming mitigation. There’s no need to panic.

Here’s the Science Daily summary.

I haven’t read the article, but would make the following comments. First, it’s one study. Let’s wait to see what others say.

Secondly, it used one model only, and that at the bottom end of the scale. The model used says climate sensitivity is otherwise 1.94C as against the IPCC AR4 range of 2-4.5C. It would be interesting to know why they chose what looks like an outlier.

Third, it’s talking about shorter term “Charney” feedbacks only. An effect of -0.3C on climate sensitivity of 6C would make little difference. Furthermore, subtracting 0.3 from the IPCC range to leave 1.7C to 4.2C. That would not seem to alter the risk of dangerous climate change to any appreciable degree.

Fourth, I find the climate change emanating from the warming we’ve already got unacceptable.

Fifth, I have a bit of a worry that they didn’t take into account the extra warmth from the darker surfaces you’d get by vegetation growing on the Arctic Tundra.

Sixth, We are said to have about 0.6C of warming in the pipeline. It seems they have lost that little bit.

Seventh, in the first item of Climate clippings 6 we saw that the latest on clouds indicates that the cloud effect may raise estimates of climate sensitivity. We are some way from pinning this one down.

Eighth, I have a feeling their results don’t easily fit the paleoclimate record. Hansen reckons that the paleorecord indicates a shorter-term climate sensitivity of 3C, plus of minus 0.5C, with total climate sensitivity increasing as we warm from the current climate state.

It’s not time to put the cue in the rack and spend the next 30 years on business as usual, jawboning about what we might eventually do. There’s no reason for an outbreak of complacency just yet.

As far as I can see, none of the scientific blogs have picked up on this one yet. A pity.

18 thoughts on “Quantifying the negative feedback of vegetation”

  1. Ninth, plant growth isn’t CO2-limited, its generally N-limited. P-limited, in the ocean. I remember scanning plenty of older studies showing that the CO2 effect on plants only goes so far in light of those nutrient limitations.

    Still, even a little decrease in temp from a minimal CO2 growth boost is a strong argument to wind back deforestation.

  2. I am peeved by the simple listing of failed insights that apparently the “AGW Deniers” are being pinned with.And as for business as usual,there remains many well qualified scientists who are getting more pissed off by the hour,at a Steam Train approach to all countries and regions.

  3. Grumphy has hit the nail on the head.
    CO2 increases can only increase plant growth rates in the absence of any other limiting factors ( i.e. the only studies to demonstrate increased plant growth with regard to CO2 increases have been is cossetted greenhouse plants, it has never been demonstrated for non-controlled environments).
    The other major limiting factor I’d add in here would be water, if there’s a water shortfall stomates will be closed and therefore it would not matter what the external CO2 concentration is.

  4. And likewise we might add a note on morphology.

    Not the least of our concerns is the biodiversity of biomes. If it is the case that increasing CO2 changes the way plants produce and deploy sugars then this is going to change the composition of whole biomes in ways that we cannot model with confidence and which may well disrupt systems on whcih humans depend.

    As repeated FACE (Free air CO2 enrichment) studies have shown, not all plants that can take advantage of the kinds of change Bounoua describes are plants we’d want dominating ecosystems. Do we really want invasive and warm plant species creeping into diverse sub-temperate rainforests? And not all plants will respond mainly by growing large leaves. Some respond with greater masses of lignin (the woody biomass in stems).

    It’s also the case of course that human settlement will continue to put pressure on terrestrial vegetation so again, it’s doubtful one can simply extrapolate as Bounoua does.

    So really, while Grumphy’s point is very germane, its also far from clear one can extrapolate in the way one might if it were not.

  5. And as for business as usual,there remains many well qualified scientists who are getting more pissed off by the hour,at a Steam Train approach to all countries and regions.

    You been hanging around that very well informed, totally unbiased and not ever been sponsored by Exxon site. Next it will be millions of scientists. Marc Morano has a long history of making it up as he goes.

    When you post me links from Sandstone establishments or major independent international bodies changing their minds, instead of non existing imaginary steamtrains, I may consider to adjust my risk assessment on this matter.

    Thanks for the laugh in this rather serious subject.

  6. Sorry about biting above, that spin crap has been dished out to me repetitiously and I could not take it anymore.

    From a post in arstechnica re Bounoua et al study

    There’s a tip-off right off the bat to problems in this paper in that it is published in GRL. GRL is a highly-respected journal, but it is a “Letters” Journal; submissions are required to be short, stringent page limits apply, and the purpose of the Journal is to provide rapid publication for results which can be communicated this way.

    Personally I don’t believe a modeling study of this kind CAN be responsibly presented within the GRL format, and when a reviewer is presented as little information as this paper provides, the review cannot be thorough, nor can a reader’s understanding more generally. A reviewer cannot say “you must provide far more detail AND demonstration of impacts of various parameterizations you are employing vs others,” without the consequence being “this paper is unsuitable for GRL,” … which reviewers can say, and I think is what they should have said … but obviously didn’t.

    How climate myths are created here

    There has been some discussion of the Bounoua et al study on sceptical science, specifically comments 15-24 located here as well as from 21 here. Sorry too hot atm to concentrate to comment on these.

  7. If you want to know the real story on this watch this

    Short version: Some blogger caught a NASA press release describing a study saying that evaporation from trees etc. would lower climate sensitivity by 0.26.

    He then miscalculated by a.) using a low base figure and b.) rounding to come up with 1.64

    He then further compounds the error by miscalculating the rate of CO2 increase to come up with 200 years.

    It’s a crock.

  8. Brian’s Point 7,
    I think it a bit early conclude (or even say “may”) what effects clouds really have on temperatures.

    Dr. Roy Spencer has mentioned that it doesn’t take much in the way of cloud cover changes to add up to the “global warming signal” that has been observed.
    “The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling.”

    Jasper Kirkby of CERN explained the Centre’s CLOUD experiment, which is moving forward:
    “The current understanding of climate change in the industrial age is that it is predominantly caused by anthropogenic greenhouse gases, with relatively small natural contributions due to solar irradiance and volcanoes. However, palaeoclimatic reconstructions show that the climate has frequently varied on 100-year time scales during the Holocene (last 10 kyr) by amounts comparable to the present warming – and yet the mechanism or mechanisms are not understood. Some of these reconstructions show clear associations with solar variability, which is recorded in the light radio-isotope archives that measure past variations of cosmic ray intensity. However, despite the increasing evidence of its importance, solar-climate variability is likely to remain controversial until a physical mechanism is established.”

  9. Brian,
    It is impotant to remember, models are just that MODELS and they (any or all of them may be incorrect).
    Also some may be close to reality, nobody is in a position to say which.

  10. Thanks JM for that link, yeh what do you say to that?

    This sort of lunatic crap is so ubiquitous nowadays. It really shows how these political spinmasters have released a viral anti science campaign. Anything goes, no method, no ethics, no morals and no responsibility.

    The hide to call themselves Skeptics, they would not know of it, if it bit their bum! Do these sort of skepticbots actually do know the role of scepticism (I prefer the original spelling) in science, indeed do they understand the method of science? And @7, at least the Lancet did and that is why we do have now solid critique of the critique.
    (end of rant)

    Fortunately there are now more sources, such as JMs link, which distribute rebuttals. Another one I came across is wottsupwiththat. However, it is time consuming to check the rebuttals, so it is not easy being a true sceptic. This is something these narrow or single minded people will not understand and gullible swallow and distribute such crock!

  11. Anything goes, no method, no ethics, no morals and no responsibility.

    Yeah, but the mainstream parties still have some sembance of integrity:)

  12. Ootz – I think you are missing the point and then extending miscomprehension into a rant about skeptics.
    The original article is describing a possibly useful model which is looking at feedbacks.
    The fact some other people eg The Blogger linked to via the Register,don’t understand the article or misinterpreted the results is hardly something to see a conspiracy within.
    There are plenty of ignorant people who are perhaps just trying to develop their own understanding of very complex matters.
    Many more climate models are going to be developed in the near future and one area they look to be focused on is the positive and negative feedbacks.
    Look at the original research and forget about the commentaries trying to explain them.
    The original research works will all be making a contribution to knowledge and it is unnecessary to dismiss them all as being motivated by a desire to muddy the waters.
    And JM isn’t discussing the real story – he is talking about someone making a mistake.

  13. John Michelmore, back @ 9 you said:

    Dr. Roy Spencer has mentioned that it doesn’t take much in the way of cloud cover changes to add up to the “global warming signal” that has been observed.

    “The most obvious way for warming to be caused naturally is for small, natural fluctuations in the circulation patterns of the atmosphere and ocean to result in a 1% or 2% decrease in global cloud cover. Clouds are the Earth’s sunshade, and if cloud cover changes for any reason, you have global warming — or global cooling.”

    I wish you wouldn’t quote Roy Spencer on this blog, quite frankly. His views are a waste of brain-space.

    Check out this on Climate Progress:

    Because this is such an important issue — and because this study should be the final nail in the coffin of the central denier myth that the climate has a low sensitivity to CO2 — this post includes two videos explaining the study, an exclusive comment on the study by one of the leading experts on the cloud feedback (NCAR’s Kevin Trenberth), and Dessler’s debunking of the laughable conspiracy-laden response by a discredited disinformer (Roy Spencer). (Emphasis added)

    There are plenty more juicy quotes in the post, but if you follow the link to the second video you’ll get the low-down on the Dessler study and clouds.

    Clouds shade the earth from incoming radiation, but they also trap the upwelling radiation from earth. Dessler found the second effect to be stronger than the first by actual observations, supporting the models.

    There is an error bar and it dips below zero, but you can say the feedback is likely positive to use IPCC terminology.

    Also the whole effect is small, about 0.5 watts per degree Kelvin compared with the water vapour feedback which is about 2 watts. So, he says, clouds are not going to save the day. Nevertheless, he says his study is only one study, but he thinks that the cloud bogey from the skeptics/denialists/disinformers is going to be laid to rest in the next few years.

  14. That’s a seriously dodgy model they’ve got working there. How can trees increase their LAI, just magically within one generation?

    Trees can’t just grow bigger leaves (increasing water stress) due to more CO2, even if it was good for them. Maybe if you chopped down all the original trees and replaced them magically with some geneteically engineered monstrosity? hmmmm.

    Simple summary – don’t ask NASA about trees!

  15. Brian,
    When it comes to the influence of clouds on the worlds climate and whether it was the chicken before the egg or vice versa, I don’t think anybody has the final answer; maybe in a few years I’ll have to agree with you, who knows.
    What is interesting is that in AR4 2007, cloud feed back represents the largest souce of uncertainty, and water vapour is the most important greenhouse gas. It is unlikely in three years that the human race actually knows much more than it did then. Again how much of the impact of water on the worlds climate is the result of human activity. A difficult question I think, but hell, lets jump in and try and control the worlds climate anyway.
    It is probable that neither Dressler or Spencer are correct. However just because you consider one scientist (Dr.) to be a waste of brain space, doesn’t actually carry much weight when you repeatedly say you will leave the science to the scientists. Is this only if the scientist agrees with your views?

  16. John M, you have to decide what sources are credible and which are not. Joe Romm at Climate Progress is what I would term a science journalist who I find consistently reliable and well-respected by climate scientists. From his post:

    Few of the climate science disinformers have been as wrong — dead wrong — as Spencer for as long. He famously made a bunch of analytical blunders and spent years pushing the now long-overturned notion that the satellite data didn’t show significant warming

    So for me the process would be this. First I read Roy Spencer. Then I wait around for real scientists to debunk what he says. And they do debunk him and people like Richard Lindzen because they are working climate scientists. Usually they don’t bother with Ian Plimer or Bob Carter. (Carter can claim to be a climate scientist, but in a very specialised area.)

    So if I do that I’ve wasted time and had my head full of rubbish in the meantime. It’s a waste of brain space, or worse.

    He’s a serial offender who actively misinforms, hence a disinformer. To be actively avoided if possible.

  17. BTW, John M, as far as I can see you get that chicken and egg thing about clouds from Spencer. Nuff said.

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