Bishop Hill On rainforest sensitivity
Mar 29, 2010 Climate: WG2 A couple of days ago, I posted on the news that Dr Simon Lewis, a rainforest expert from the University of Leeds, has filed a complaint about an article written by Jonathan Leake at the Sunday Times. Leake's article concerned the IPCC's use of "grey" literature to support a claim that the Amazon is very sensitive to drops in rainfall and that as much as 40% was in danger of being wiped out by small reductions in precipitation.
The use of grey literature is not disputed, but Lewis has complained that the article's headline, presumably written by an editor rather than Leake himself, implied that the sensitivity claim was false. This, he says, is not the case, "there is a wealth of scientific evidence suggesting that the Amazon is vulnerable to reductions in rainfall". It is just that the citation was "bizarre".
In this second piece on the complaint, I'm going to take a look at the science supporting Dr Lewis's position.
Dr Lewis helpfully expands on his understanding here:
It is very well known that in Amazonia tropical forests exist when there is more than about 1.5 meters of rain a year, below that the system tends to ‘flip’ to savanna, so reductions in rainfall towards this threshold could lead to rapid shifts in vegetation. Indeed, some leading models of future climate change impacts show a die-off of more than 40% Amazon forests, due to projected decreases in rainfall. The most extreme die-back model predicted that a new type of drought should begin to impact Amazonia, and in 2005 it happened for the first time: a drought associated with Atlantic, not Pacific sea-surface temperatures. The effect on the forest was massive tree mortality, and the remaining Amazon forests changed from absorbing nearly 2 billion tonnes of CO2 from the atmosphere a year, to being a massive source of over 3 billion tonnes.
In support of his position, Lewis cites a number of authorities and I will look at these in turn.
Daniel Nepstad
When the Amazongate story first broke, Daniel Nepstad was one of the first to defend the accuracy of the claim (while again acknowledging the incorrect citation). Nepstad works at the Woods Hole Research Center, a green campaigning organisation and issued a statement declaring that 40% was the correct figure. Nepstad is slightly unclear about the true source of the figure, saying that the authors of the grey report used by the IPCC had got the information from "IPAM", which turns out to be another green NGO. He then talks about having found that 15% of the Amazon was severely drought stressed in 1998 and that in a later article he had shown that "half of the forests of the Amazon depleted large portions of their available soil moisture during seasonal or episodic drought".
Astute readers will notice that this is not the same thing as saying that 40% would be wiped out by small reductions in rainfall. Indeed, as Nepstad himself notes in a report published in 2007 (and one that was not cited by Dr Lewis)
One of the great ecological puzzles of the Amazon forests is their ability to withstand severe seasonal drought with no visible signs of drought stress.
As far as I can tell, it appears that the Amazon is quite able to deal with drought, even severe drought. For dieback to take place, it requires repeated drought.
Philips et al 2009 (PDF)
Oliver Philips is a colleague of Simon Lewis at Leeds University and indeed Lewis himself is among the 66 (!) authors. As far as I can tell, Lewis reckons this is among the key pieces of evidence to support his claim, but it is hard to see why. The study looks at the severe Amazonian drought in 2005 and found that in these circumstances the Amazon turns from a carbon sink into a net emitter of carbon. Philips et al seem to concur with Nepstad that it is prolonged drought that is the problem:
Prolonged tropical droughts can kill trees...and some models predict climate-induced Amazon dieback this century.
I see nothing in the paper that could support a claim that 40% of the Amazon could be wiped out by small changes in rainfall.
In fact this is a position that Dr Lewis himself seems to agree with. In a recent post at RealClimate he trenchantly sets forward his views on what matters regarding Amazon dieback. Discussing the findings in Philips et al he points out that trees were affected by the major drought, but that this is not the key point:
The evidence for the possibility of a major die-back of the Amazon rainforest is due to two factors,
1. That climate change induced decreases in rainfall in the dry season occur, and
2. The trees cannot tolerate these reductions in rainfall.
...
The critical question is how these forests respond to repeated droughts, not merely single-year droughts. The forests are of course able to withstand these single droughts (otherwise there would be no rainforest!) — it is their ability to survive an increased frequency of the most severe droughts that is critical to answer.
So, everyone agrees that dieback of the Amazon is predicated on repeated droughts. In order to justify the 40% claim of the IPCC we therefore need to see that small but repeated reductions in rainfall cause dieback.
Models
The evidence that repeated droughts will take place appear to be largely based on application of models. In his PCC complaint, Dr Lewis cites Huntingford et al and Nepstad et al, but in his RealClimate article he points to a paper by Bett et al as well. Before looking at these I want to discuss a couple of points made in the RC article.
Firstly, there is considerable doubt over the model output, in particular with respect to the idea that Amazonian rainfall will decrease in a warming world:
I should add that there is considerable uncertainty associated with the models suggesting decreases in rainfall, and uncertainty as to how Amazon forests may react (especially when one considers the impacts of deforestation, logging, and fire combined with climate change impacts). But this uncertainty is being chipped away at by scientists, a task in which the Samanta et al. paper assists.
But he also sets out the IPCC view on these models. Mostly, he says, the modelling work has been ignored by the IPCC, who cite Betts and Huntingford and make the infamous 40% claim. But, he reiterates, this claim is correct:
Rainforest persists above a threshold of rainfall, below which one finds savanna. If this threshold is crossed a landscape dominated by rainforest can ‘flip’ to savanna. Therefore a ’slight’ reduction can lead to a ‘dramatic’ reaction. Of course, evidence of a shift to a new lower rainfall climate regime is needed, and evidence of large areas of forest close to that rainfall threshold would be required for the IPCC statement to be reasonable; there is ample published evidence for both.
You will note that what he states as the preconditions for Amazon dieback here are slightly different to those he gives in the complaint. Putting these together we really have three conditions
- that the Amazon will move to a new, lower rainfall regime (repeated drought)
- that trees are sensitive to repeated drought
- that 40% of the Amazon is close to this threshhold.
The second point seems undeniable, so I don't propose to look into it any further. I will accept Dr Lewis's figure of 1.5m of rainfall per annum as the correct one. However the question of whether the Amazon will move to a regime of repeated droughts looks more interesting.
Will the Amazon dry up?
I am grateful to Professor Hector Maletta of the Universidad del Salvador in Buenos Aires, who left a link to his draft paper on the science of Amazon deforestation. I would urge readers to get hold of this paper themselves, because it is remarkable stuff, much of which bears directly on the question of the IPCC's 40% statement.
The dieback sections of Professor Maletta's paper examine four different modelling studies - Cox, Nepstad, Betts and Lenton all of whom predict rapid large-scale dieback and replacement of rainforest by savannah. I think we can say with some confidence that these papers are the ample evidence referred to by Dr Lewis.
However, the evidence seems highly questionable at best. For example Nepstad suggests that more than half of the rainforest could be gone by 2030. As Maletta puts it:
These dire predictions (mostly inspired by the Amazon 2005 drought and recent El Niño episodes) emerge not from a global or regional model, but as a possible result of the hypothetical persistence of then-recent events (up to the early 2000s) plus the purely theoretical hypothesis of a 'tipping point' to be hypothetically reached if deforestation advances past some unknown percentage of tree cover, thus possibly triggering an 'abrupt change' process of unknown duration. The critical percentage of tree cover that would trigger the dieback process, if it exists, is unknown, though hypothesized to be 30%.
Nepstad's findings, says Prof Maletta, should be treated with caution in view of...
- the lower rates of deforestation observed in recent years
- improved protection of fragile areas
- increasing establishment of protected areas in the frontier of deforestation
- lack of data on crucial issues such as the very existence of a tipping point, and parameters such as the critical value for the tipping point in case it exists, the time it would take for the subsequent process to complete, and the reversibility or irreversibility of the process.
And as Maletta point out, even those who have been the main proponents of the idea of Amazon dieback say that "it remains just a theoretical possibility without much in the way of empirical evidence". This is a long way from Dr Lewis's "ample published evidence".
Both the Cox and Lenton studies predicate the idea of Amazon dieback on the idea of the development of persistent El Nino conditions, another point discussed by Maletta. The problem with this hypothesis is that according to the IPCC,
there there is no consistent indication at this time of discernible future changes in ENSO amplitude or frequency"
As readers will note, this is a serious blow to the idea of a persistent El Nino if this is really required to bring about persistent drought and therefore dieback in the Amazon. However, Lenton at least, choose to differ from this finding, saying, without providing supporting evidence, that a transition towards a higher ENSO amplitude will happen within a millennium. So even Lenton, who is out of kilter with the IPCC consensus, thinks that global warming will only affect amplitude (which will not make El Ninos more persistent or permanent, as required by the dieback hypothesis) and moreover that it will only do this on rather long timescales. This makes Nepstad's claims of Amazonian dieback in the next twenty years look, well, interesting.
In conclusion
A few days reading of the literature is not enough to draw definitive conclusions, but it appears to me that Dr Lewis's position - that there is "ample evidence" that the Amazon will move to a lower rainfall regime is one that is at best debatable and may in fact not be a fair representation of the literature. If any readers want to investigate this claim further, or indeed if anyone wants to dig into the other aspects of Lewis's claims - that large areas of the Amazon receive rainfall close to the 1.5m threshold and that there is the possibility of Atlantic-driven drought as well as El Ninos - I'd be interested to hear from you.
Reader Comments (67)
My dear Frankie
Before I get into your claims, what credentials have you got to interpret my blog?
Perhaps you would like to advise us of the nature of your PhD?
With love
Northie (Dr)
Richard North,
I already told you I am 100% persuaded by your argument that it is a grave mistake to rely on 'grey literature' such as your blog for information on the Amazon. I have therefore stopped reading it. Sadly therefore I have to report your question is based on a false premise.
Now you may feel free to 'get into my claims' but can you please answer my questions first? I imagine that as an expert in so many disparate disciplines you must be a very busy guy, and you probably don't get great broadband service out there in the Amazon, so I really appreciate your taking the time to tell me where I can read your peer reviewed material on the rainforest and that. Thanks a bunch.
Mr O'Dwyer
In case it had escaped your attention, the blog you are reading (Bishop Hill) is not peer reviewed, and neither are the comments that you have been reading and on which hitherto selectively commenting. To be consistent, it would appear that you need to stop reading this material immediately.
On the other hand, if you can escape your fixation with "peer review", you might learn that the process is not a measure of veracity or even quality. It simply means that a paper is suitable for publication, in the opinion of the reviewers. But it is a mark of the unqualified, like yourself, that they set such great store by the process, which absolves them having to think and apply their own judgement - assuming they are capable of such endeavours.
Further, your limited intellect (and qualifications) seem to render you incapable of distinguishing between the role of papers which make assertions, and are peer reviewed, and criticism. The purpose of publishing a paper in a scientific mileau is to invite criticism (i.e., debate).
If you are going to restrict debate to peer-reviewed comment in scientifc journals, then you have no business on this (or any) comments section, and neither should you be commenting on any blog post here. For that matter, since your own comments are not peer reviewed, by your own standards, they can have no value and, thus, we should not be reading them.
Aside from your intellectual contortions on this, if you still insist that comment (and judgement) on matters of fact - or claims which purport to be fact - are only valid amongst peers with common qualifications and experience then you deny, for instance, the right of a judge and jury to pass a verdict on a suspect criminal brought before them.
By the same token, you would deny the right of a coroner to pronounce - by way of another instance - on the cause of death of a soldier in Iraq, by virtue of the fact that the coroner had no military experience or expertise, had not been there and had no first-hand experience of the circumstances.
By your logic, you would also have rejected the WWII study on the effectiveness of the RAF's early strategic bombing effort, as it was carried out by civilian intelligence officers with no military experience, who were not aircrew and who had not flown over enemy territory - and whose findings were in direct conflict with senior officers who were asserting that the programme was successful.
In contemporary situations, you would even deny the right of politicians to pass laws on climate change because that would require them to debate and pass judgement on competing claims, and to have assessed conflicting information, is areas where they are neither qualified nor experienced.
In short, your propositions are absurd - intellectually convoluted and inconsistent. You are confronted with an easily verifiable situation where the IPCC has made an unsubstantiated assertion, for which none of its advocates have been able to find support. Instead of recognising that, you tie yourself up in knots, trying to deny the obvious, retreating behind an elaborate smokescreen in an attempt to conceal your own discomfort and inadequacies.
Sincerely
Richard North (Dr)
Richard North,
Oh I certainly don't think people should be getting their information on the rainforest from this blog either. That's the kind of mistake that Jonathan Leake would make - and look how often he gets things wrong! They could try asking people who are experts and who have actually worked on the topic perhaps.
Can you tell me whose name appears under this comment (I'll start you off - it isn't mine):
I urge you to contact the man who wrote that and ask him why he thinks that relying on a non peer-reviewed source was a serious mistake. Maybe he will change his mind and 'escape his fixation with peer review' if an expert such as yourself explains things to him. Or maybe he will simply change his position from one comment to the next.
Anyway it is worth a try. Let me know how it goes.
So Frank, as I read your brilliant insights, I wonder about your "credentials". You appear to have a background in computer security software, iPhone aps and riding bicycles. That is all a quick google found. Which of these makes you a scientist?
Perhaps you can list your advanced degrees and where you obtained them?
Fair is fair. I have listed mine in the past and you called Dr North out on his. Where are yours?
Mr O'Dwyer
Once again, your intellectual limitations betray you. You continue with your inability to distinguish between assertions, which claim the authority of fact, and subsequent criticism of those assertions. There is value in arguing that the IPCC should rely, where possible, on peer reviewed documentation, as indeed it does. There is also validity in arguing that, where the IPCC relied on non peer-reviewed documents, when there was a substantial volume of peer reviewed material available, was a mistake, in its own terms.
The fact nevertheless remains that peer reviewed work might be erroneous ... it often is ... but that does not absolve the IPCC from taking at least the very basic step in seeking to use material that had passed at least the very basic hurdle of peer review.
That notwithstanding there is no value then in arguing that subsequent criticisms should likewise be peer reviewed - which is what you appear to be claiming, in and amongst your facile word games.
Likewise, you continue with your smokescreen, having now completely abandoned any efforts to address the substantive points, which are left unaddressed. The verifiable facts are that the IPCC got it wrong and neither the case made by its advocates nor yourself, to the contrary, stands up. The IPCC was wrong. Your inability to argue otherwise, and your determination instead to throw up a smokescreen, is more than adequate testimony to that fact.
Sincerely
Richard North (Dr)
Don Pablo,
You have not even provided your name. Perhaps the irony of posting anonymously and doing the equivalent of 'Don't you know who I am?' is lost on you, but I'm sure with all your claimed credentials you'll be able to figure it out.
I am as much of an amateur at this as you or Dr North, and so no special credentials are needed to spot the errors in your output any more than they should be needed to spot errors in mine. But then I'm not the one arguing that most of the experts are dishonest fools, so you better be an expert if you want to do that. In fact I prefer that people would listen to the experts (all of them, not just the ones that tell them what they want to hear), especially in the peer reviewed venues where they are invariably more conservative and less excitable in their claims, as they need to convince other experts.
Richard North,
You're projecting. You wrote that you thought it was a terrible mistake for the IPCC to rely on sources that weren't peer reviewed and then you took me to task for a 'fixation' with peer review. Which is it? Is not relying on peer review a mistake or isn't it? Can't have it both ways.
Nobody with relevant expertise has said so yet, to my knowledge, while people with relevant expertise - and who have even been to the Amazon - contradict you. Your quote mining of the literature doesn't change that.
I am as much of an amateur at this as you or Dr North, and so no special credentials are needed to spot the errors in your output any more than they should be needed to spot errors in mine.
Ah, a dilettante! Frank, I have an excellent background in the scientific method and statistics, and so does Dr. North. I am wondering if you even have a university degree or did you buy a "Science for Dummies" book from Amazon?
And if what you say is so, why did you demand Dr North to give his credentials? That is not logically consistent. Or do I need to explain that to you?
As for keeping my name to myself, it is hard earned. There are crazy people out there. I have run into a couple in my many years. Hopefully you are spared that.
Mr O'Dwyer
QED. You would hold on to nanny and listen to what she tells you, rather than use your own brain and work out the truth for yourself. Thus, you are a slave to the cult of the "expert", so much so that you revere even their droppings, seeking to prove (to yourself) that they are always right.
Your need for reassurance might in part be explained by your inability to understand the logical distinction between expecting the IPCC to rely on peer reviewed literature (where it is available) and the rejection of your facile argument that everything else should be peer reviewed.
Either way, the only thing you can now offer is "the experts are right 'cos they haven't said they are wrong." As an argument, that is truly pathetic.
Sincerely
Richard North (Dr)
Don Pablo,
So you claim. I bet you're a terrific dancer and a big hit with the ladies too. Anyone could post as Don Franco or Mickey Mouse and say as much.
Maybe you have a Nobel prize, maybe you work at MacDonalds, maybe you are one page behind VS in your 'statistics for idiots' book, or maybe you are posting from a mental institution. That's the price of anonymity - you leave your credentials at the door with your name.
If you have the qualifications and skills you claim to have, why don't you do something useful with them like address the topic instead of your constant ad homs and trolling? Just a suggestion. A serious one, by the way.
Because he is pontificating that the experts are wrong while apparently having no relevant expertise himself. It is more likely that any mistakes will be his than theirs. If he wants to take on the experts then let's see some evidence he knows what he's talking about first. Indeed maybe, just maybe, we should let North practice for say 20 years with a small woods before we trust him with future of the freaking amazon rainforest, eh? We only have one of those.
I have read some of the references North provides and while it is always interesting to get pointers to such articles, the issue is that the argument doesn't lie in the articles but in his narrative. I can plainly see that he is quote mining his references and overall he is actively cherry picking. He's not doing a review of the literature, he's telling a story and selectively supporting it.
He's also pontificating against grey literature, while writing grey literature himself.
I don't think he has really been to the Amazon, do you?
Mr O'Dwyer
I can plainly see that this is an unsupported assertion, in a non-peer reviewed comment section of a non-peer reviewed blog. You may feel the need to believe that your assertion is true, but have you any evidence to back it up? Or is this merely the opinion of an unqualified commentator who is not even willing to claim he has a first degree?
Sincerely
Richard North (Dr)
Richard,
Frank is clearly a self-appointed expert with admittedly no credentials, nor demonstrative knowledge of the scientific method. He once accused me of ad hominem attacks but he uses them himself. While he insists that you haven't the credentials to comment on the topic, he feels that he is an expert. Just where he got that expertise is not apparent to me nor will he state where he got it. He clearly has a double standard when it comes to science.
I once pointed him to the Kübler-Ross Grief cycle, which while originally postulated for grief over loss of a loved one, it has been extended to other causes.
http://changingminds.org/disciplines/change_management/kubler_ross/kubler_ross.htm
He is Angry now. Next he will Bargain, or at least become more civil. We can pray that it is soon.
I suggest you follow the advice of others as I have and ignore him. The only reason I hopped in on this diatribe of his is he insisted you were unqualified and wanted to know your credentials. I consider that a hypocritical, given he still hasn't claimed a university undergraduate degree, so I called him on it. As for the future, Frank can whistle in the wind, global warming or whatever all he cares to. I will not hear it. Time to move on and leave Frank behind us.
"Don Pablo",
Why do you lie about easily checked facts?
I posted that I am as much an amateur when it comes to climate and the rainforest as are you and as is Richard North. You, since you post anonymously, have zero verifiable credentials on any matter at all, and North says he has a Ph.D in an unrelated discipline.
I too have qualifications in unrelated disciplines, but I also have more sense than to post them as if they mattered. I certainly don't need any special credentials to rebut some blog comments of non-experts such as yourself and North. Nobody does.
Another obvious falsehood, since you not only repeatedly attack me you have (like North) just today chased me on an unrelated thread if I haven't answered your comment within 20 minutes. And though I have often read your reminiscences about your alleged and rather peculiar CV, I have yet to read you provide a substantial argument or rebuttal on any matter at all.
I say that you provide ad hominem, as a substitute for a rational argument, nothing else. I don't. I offer both.
Richard North,
[ about my statement that you are quote mining and cherry picking ]
Yes. Before I post it - are you claiming that you have not ignored quotes from your references, as well as other literature, that is unfavorable to your argument? Do you claim that your linked blog post is a full and fair discussion of the literature and your references, and you have disclosed everything unfavorable to your narrative? Let's see you own that claim before I prove it false.
Mr O'Dwyer
I make no claims as to my posts - you or anyone else takes them as they find them, in their entirety. Few of them stand entirely alone, as they represent a progression of thought.
The only one making claims, in this respect, is yourself. What you care to "prove" or "disprove", is a matter of indifference to me. In the unlikely event that you have an intelligent comment to make, post it on my forum and I will look at it there.
As it is, I simply enjoyed tweaking your tail as you made a fool of yourself. Now, I have wasted enough time on you ... I will take Don Pablo's advice - you are a troublesome nuisance, who cannot prove your point, or even argue coherently, but simply resorts to bluster.
You may reply if you wish - and you are vain and insecure enough not to be able to resist the temptation so to do - but you will be talking to yourself. I will not be revisiting this thread.
Sincerely
Richard North (Dr)
Richard North, asked to confirm that he had disclosed everything unfavorable to his narrative and hadn't overlooked unfavorable quotes from his selected references (aka quote mining), demurs:
QED. North has gone down the quote mine and he is none too sure whether he's missed anything that doesn't fit his story.
But I am sure that he has.
[snip ad homs]
OK, let's call it a day.