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Climate Hustle

What the IPCC and peer-reviewed science say about Amazonian forests

Posted on 4 February 2010 by John Cook

A recent 'scandal' being trumpeted around the blogosphere is an apparent error in the IPCC Fourth Assessment report. In this case, the IPCC's source on Amazonian forests came not from peer-review but from a WWF report. In one sense, this criticism has a degree of validity - one should always seek to use peer-reviewed science as their primary source of information. In fact, kudos to those championing peer-review! Ironically, the same critics who lambast the IPCC for not citing peer-review have shown little evidence of doing the same. To demonstrate, let's compare the IPCC statements and what the peer-review literature actually says.

First, let's examine the IPCC statement in Section 13.4.1 of the IPCC Fourth Assessment Report:

'Up to 40% of the Amazonian forests could react drastically to even a slight reduction in precipitation; this means that the tropical vegetation, hydrology and climate system in South America could change very rapidly to another steady state, not necessarily producing gradual changes between the current and the future situation (Rowell and Moore, 2000).'

The reference is Global review of forest fires (Rowell and Moore 2000), a non-peer-reviewed report by the WWF. The WWF report makes the following statement:

'Up to 40% of the Brazilian forest is extremely sensitive to small reductions in the amount of rainfall. In the 1998 dry season, some 270,000 sq. km of forest became vulnerable to fire, due to completely depleted plant-available water stored in the upper five metres of soil. A further 360,000 sq. km of forest had only 250 mm of plant-available soil water left. [Nepstad et al. 1999]'

The WWF correctly states that 630,000 km2 of forests were severely drought stressed in 1998 - this figure comes from Nepstad 1999. However, the 40% figure comes from several other papers by the same author that the WWF failed to cite. A 1994 paper estimated that around half of the Amazonian forests lost large portions of their available soil moisture during drought (Nepstad 1994). In 2004, new rainfall data showed that half of the forest area of the Amazon Basin had either fallen below, or was very close to, the critical level of soil moisture below which trees begin to die (Nepstad 2004). The results from these papers are consistent with the original statement that 'Up to 40% of the Brazilian forest is extremely sensitive to small reductions in the amount of rainfall'.

Subsequent research has provided additional confirmation of the Amazonian forest's vulnerability to drought. Field measurements of the soil moisture critical threshold found that tree mortality rates increase dramatically during drought (Nepstad 2007). Another study measured the effect of the intense 2005 drought on Amazonian biomass (Phillips 2009). The drought caused massive tree mortality leading to a fall in biomass. This turned the region from a large carbon sink to a carbon producer. The paper concluded that 'such events appear capable of strongly altering the regional carbon balance and thereby accelerating climate change'.

An investigation into the peer-review scientific literature shows the information presented by the IPCC on Amazonian forests is correct. The error is that the WWF erroneously omitted the citations supporting the 'up to 40% of the Brazilian forest is extremely sensitive...' statement. The lesson here is that the IPCC could have avoided this glitch if they'd quoted directly from the original peer-reviewed papers. Critics of the IPCC, if their goal is a clearer understanding of the science, would also do well to follow this advice.

UPDATE 5/2/2010: Thanks to Graham Wayne who reminds me that the IPCC don't claim to only source peer-reviewed science. They do source non-peer reviewed publications (otherwise known as grey literature which includes industry journals, internal organisational publications, non-peer reviewed reports or working papers of research institutions, proceedings of workshops etc), as stipulated in Appendix A to the Principles Governing IPCC Work. So I should clarify my words and say if presented the choice between peer-review and grey literature, one should always opt for peer-review. Or in the case of the Amazonian rain forests, if citing grey literature that cites peer-review, why not take that extra step and go straight to the source?

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Comments 1 to 50 out of 60:

  1. Blind Freddie knows forests, whether in the Amazon, or Australia, are stressed by drought and high temperatures (not to mention fires). From my window I can see Eucalypt forest which visibly changes appearance (I presume as leaves fall, or change orientation, or are reduced in size, or change colour) under extreme conditions. This rubbish about IPCC failures is again (like Himalayan glaciers) a piece of nonsense about the messenger while ignoring the message.

    "Peer Review" has become one of those terms which is just tossed around, contemptuously by deniers, with approval by those in the real world. I've always thought of the review process not as some magic bullet, removing all error, but as a way of getting your work looked at by someone familiar with the field, who can (a) have some chance, because of familiarity with the field and its literature, spot errors in references, or possible errors in tables, or see some error in logic, and (b) reassure you that you are not living in some alternative universe.

    Non-peer-reviewed material is the shock jock on the radio, Monckton at the press club, Plimer's book, most blogs (although in a sense the comments on a blog piece are a form of peer review, as long as your readers are not all raving lunatics). These are just statements made, out of someone's thought processes, or whacky experiment, which sees publication without anyone else getting to check it. Non-peer-reviewed papers may occasionally be right, of course, peer reviewed ones may retain errors (no one really knows the details of your subject as well as you do).

    It's all a bit like the difference between getting a PhD after being vetted by your supervisor and three hot shot examiners, and getting a PhD by filling in a form and sending money to an internet site in Uzbekhistan.
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  2. The first full explanation of this matter I've seen. Thanks!

    C&T legislation coming up here in the USA, maybe, and whether that happens will depend a lot on what sort of noise level can be generated by extracting "gotchas" out of IPCC as well as whatever other scat can be flung at climate science. Our legislators here seem to be going through a period of natural or forced variation where the "courage index" is at historical lows, so they'll take any excuse possible to remain sitting on their hands when it comes to serious attacks on carbon. So this is a year-- maybe the first of a few in a row-- where we'll see all the stops pulled out; fossil fuel interests have so much at stake in their battle to avoid us becoming accountable for C02.

    Readers here may not be aware that even as Dr. Mann is vindicated after Penn State managed to construct a coherent set of inquiry points from skeptic complaints, a new and massive round of FOIA requests are being volleyed by the "Competitive Enterprise Institute".* The very filing of these is eagerly reported by news outlets, regardless of merit, as they feed an air of scandal even where none exists. Some climate scientists are even being sued in connection with their right to free speech.**

    When it comes to "dragging politics into science", remember where the real political machinations are coming from: CEI, The Heartland Instute, those are the kind of entities projecting politics onto science. No need to imagine scientists engaged in conspiracies, you can read about the real plans in your newspaper, nearly every day.

    What we're seeing are a number of unwitting researchers blundering onto a stage while pursuing their inquiries, doing what has turned out to be the "wrong" kind of investigation. The stage is filled with actors armed with real swords. It's not a pretty scene, not at all.


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  3. Which raises the question of whether the Amazonian drought can be blamed on AGW. The last post on this site dealt with the connection between AGW and stratospheric water vapour. The question is – does increased water vapour lead to increased precipitation? If so, then the Amazonian drought may have its origins in more complex mechanisms. I am wary of attributing all environmental problems to AGW – this detracts from sober assessments of the issues and provides ammunition for those who might have an axe to grind.
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  4. chriscanaris at 18:24 PM on 4 February, 2010

    "I am wary of attributing all environmental problems to AGW"

    More really a matter of probabilities than definite assignment, and that's where error bars really help. Unfortunately error bars or the equivalent are the very first thing generally stripped away in communications styled for the general public, a shame because they're not at all hard to understand.

    I think journalists give too little credit to the average reader's ability to keep up. If you're sucked in by the headline and lede, you're probably going to stick around for the whole story as long as it is not egregiously dense.
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  5. Already professor S. Stanley in the "old" textbook: "Earth System History", 1999; for example, African gorillas, and another; reported by high climatic stability of the tropics ... It’s for this, also, in the process of evolution of the coral is not created to adapt to large changes in temperature.
    This tropical thermostat - it is obvious for climate students...
    but not for the IPCC ...?
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  6. Nevertheless, I really would love to know whether we're likely to be looking at a warm wet world or a warm dry world as it makes a world of difference - pardon the pun. I note the Phillips paper states, ‘Tropical droughts may intensify and become more frequent this century as a result of anthropogenic climate change...’ However, I wonder if this automatically follows if stratospheric water vapour increases. I certainly do have some understanding of probability - a very salient part of my professional field (psychiatry) but I am no climatalogist. However, I hope I can still ask a halfway sensible question. So might increased stratospheric water vapour lead to increased precipitation or does only tropospheric water vapour count? I ought to add that I spent my childhood years 5 degrees north of the equator in West Africa – very warm and very wet! Moreover, Freddy Norton might see dry stressed eucalypts outside assuming he’s living in southeastern Australia (as I do now) – he would encounter a very different environment if he travelled north to the Cape York Peninsula where lush tropical rainforest abounds.

    As an aside, I note the Phillips paper also says with appropriate caution: ‘We find that relative drought is indeed strongly implicated as the driver of the network-wide shift in forest behavior (Fig. 2) but that the absolute intensity of the 2005 dry period was only weakly related to biomass dynamics... Those forests experiencing the most elevated moisture stress relative to their long-term mean tended to lose the most biomass relative to their pre-2005 trend (Fig. 2). These losses were driven by occasionally large mortality increases and by widespread but small declines in growth. Our method may fail to capture growth impacts well because intervals were longer than the period of potential moisture constraint, thereby masking its effects (drought can kill trees but can only temporarily stop growth).’

    Incidentally, Phillips also states: ‘However, our findings do not translate simply into instantaneous flux estimates because carbon fluxes from necromass will lag the actual tree death events.’ This raises the further question of whether ‘necromass’ truly just ‘deadwood’ or is it in fact an intensely complex ecosystem made up of microscopic biomass with its own carbon dynamics and carbon sink properties?

    Given the exceptional nature of the 2005 drought, I wonder if we don’t run the risk of making long term forecasts based on a single event akin to popular assertions that the severity of the recent northern hemispheric winter ‘disproves’ AGW. It would be more pertinent to ask what is happening to the rainforest five years down the track.

    Quite a few questions, I know. Any ideas from anyone out there?
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  7. Since we're talking about the Amazon, here's a Brazilian paper (in English) on water vapour recycling in our rainforest.

    Climate change is projected to shift rainfall from Amazonia to the La Plata river basin, inducing a permanent El Niño-like behaviour.
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  8. Oh, sorry for the poor citation:

    Marengo 2006
    On the Hydrological Cycle of the Amazon Basin: A historical review and current State-of-the-art
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  9. Thank you, Alexandre - a fascinating paper. It's an amazingly complex system with many unknowns. Deforestation seems to be a major culprit and perhaps an amplifier of AGW impacts.
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  10. chriscanaris, it is fairly obvious that higher temperatures will lead to increased evaporation of surface water and greater quantities of atmospheric water vapor (since the amount of water air can hold increases with temperature). From there it also seems clear that increased atmospheric water vapor will lead to increased precipitation - though not necessarily in direct proportion.

    However, it needs to be understood that these are localized phenomenon. Increased evaporation drying out scrub-lands is helping the Sahara desert to grow... because that extra evaporation is not offset by equally increased rainfall in northern Africa. The same is true of glacier loss all over the world... higher temperatures are leading to increased melt rate. That extra flowing water does mean increased precipitation, but it is spread out around the world rather than all falling back onto the glacier to replace the mass lost to melting.

    So your question of whether global warming will lead to a 'wet world' or a 'dry world' isn't really on point... the hydrologic cycle will certainly continue to intensify, but that will result in some areas becoming drier and others wetter... rather than increased evaporation and melt being perfectly offset by increased precipitation in each region.
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  11. chriscanaris, this is a pertinent paper (see below). It addresses the latitude-dependence of expected changes in precipitation in a warming world, and compares this with the observational evidence. The observations and predictins are that the central latitudes experience increased drought in a warming world, whereas the higher latitudes will experience increased precipitation. The region from the equator to ~30 oN is the particularly vulnerable region that is expected to dry fastest, and this has already been observed during the observational period (1925-1999).

    X. Zhang et al. (2007) Detection of human influence on twentieth-century precipitation trends Nature 448, 461-465
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  12. Isn't this a bit of a tautology.

    Surely by its nature a rainforest ecology is going to be affected by reduction in rain. Just like a saltwater marsh would be affected if its no longer inundated by seawater or a lake system is affected by in flow from rivers. The question is what is the relevance to climate change, what's causing the drying?

    The 1999 paper specifically links the drought to the 1998 El Nino.

    There are papers which show that fire has played an important part in amazonian rainforest for over 6000 years.

    Holocene fires in the northern Amazon basin.
    Saldarriaga, JG | West, DC
    Quaternary Research [QUATERN. RES.]. Vol. 26, no. 3, pp. 358-366. 1986.

    The paper puts forward the hypothesis that there have been "unstable environmental conditions" for >6000years in the Upper Rio Nagro region as evidenced by dated charcoal in the soil.

    Do you see a trend or fluctuation?

    Peer-review or WWF is a red herring. The question is relevance.
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  13. And this for a historical view of rainfall in the amazon basin.
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  14. It's my understanding that the IPCC reports themselves are reviewed. Each of the 2007 reports lists a very large number of reviewers.

    I also thought I saw written on that for at least some of the WG docs the guidelines do not stipulate that all references must only come from peer reviewed journals. I don't have a problem with that provided the IPCC review process works well.

    The current kerfuffle is likely to result in one of two things: either relevant material will be omitted because, while known, it has not been published in a peer reviewed journal; or material such as potential impacts will be included that are not referenced at all but simply checked by IPCC reviewers for accuracy and relevance, based on their personal knowledge. Neither of these is satisfactory to my mind.

    I hope that any review of drafting and review processes does not result in important information and likely impacts under specific scenarios being omitted from future reports.
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  15. You could also add Hutyra 2005 “Climatic variability and vegetation vulnerability in Amazonia” to your list too.
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  16. Arno Arrak at 02:50 AM on 5 February, 2010:
    "That the Brazilian forest is sensitive to drought is not a world-changing revelation. [...] idiotic policies that have no effect on climate but [...]"

    My understanding is that there is not much trend in rainfall over the Amazon basin during the last 60-80 years. If anything, it is increasing slightly. And draught is draught, it just happens every now and then.

    It is not even true, that biomass decreased there in 2005 tremendously. In most parts of the basin phosynthesis even inreased due to more light from cloudless skies. That is, water availability was not a limiting factor.

    Deforestration and wildfires is clearly a problem and it is a man-made one. Not through global warming though, but irresponsible land use practices by large corporations whose business is government subsidized biofuel production (soy bean diesel & sugar cane methanol).

    It is not that Amazon should be left alone. In fact it could support a large population, just some ancient practices are to be picked up again. About 10% of the basin is covered by terra preta, an up to 2 m deep, tremendously fertile black anthropogenic soil, made by a large population between 450 & 1500 AD. Five hundred yers ago most of the people were exterminated by plagues brought in by conquistadors. The rest were hunted by slavers, escaped to forest. Most of the so called primitive tribes there are in fact offsprings of refugees, deprived remnants of a higher civilisation.

    Considerable part of the basin is not native forest, but an abandoned garden. Terra preta, even after five hundred years with no further care, turned out to be self regenerating. It keeps growing into the barren clay below.

    The long forgotten technology to create terra preta do indio is already rediscovered, it could also be reimplemented.
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  17. I'm always surprised when the "argument", "that it's all a lie" comes in to the discussion.

    But to adress the problem at hand. My view of these matters is that the world is warming up, as the science is making clearer to us by various studies. In the future (even now) there will be climate changes as a result of this warming. Of course there are some uncertanties about how these changes will be in the future, expecially if we are talking about some specific areas (like the Amazonas). But also these changes in climate will have some consequence in the future and science is trying to adress those questions as well as possible, with scientific studys. Of course there will be some mistakes made, but overall I don't think the mistake is the big issue (and of course we'll have to learn from them).

    With all this noise beeing produced by some "critics" it's going to take more time then it should, but if that's the process we have to go through, well then thats what we'll do. It's amazing how some arguments do evolve and how the small issues are sometimes made to look like as they are the whole picture.

    The big picture in my mind is that the climate is changing because of human emission of CO2, there will be consequences of these changes, but how severe is up to us, because we are starting to get the pieces together to make the big picture even better.
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  18. The Amazon rainforest was severely reduced in size during any of the geologically recent ice ages. This is well-known in the peer reviwed literature. Since these drastic reductions occur naturally, there is no reason to be overly concerned with the forest shrinking/expanding in the first place, (which isn't even mentioned above).

    The supposed 'lungs of the earth'(a ridiculous term, seeing as northern termperate forests dwarf the size, and effect, on C02 of the Amazon forests) have expanded and receeded markedly during recent glacials/interglacials, meaning all this nonsense about species-area vulneribility with regards to the Amazon is rubbish. There is obviously a high natural species turnover within the Amazon durng glacials/interglacials. Sepcies adapt to this. I the Amazon reduces in size with warming, (which is opposite to what it shoudl do, since it reduces in size with cooling in glacials) its nobig deal.

    What the WWF fund and other green groups fail to appreciate is that if the forest size reduces/expands quite naturally, why is there so much concern from human activities? It's is a fair question, depsite all the rhetoric.
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  19. thingadonta, "a high natural species turnover" contradicts "species adapt to this."
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  20. Thingadonta:

    "What the WWF fund and other green groups fail to appreciate is that if the forest size reduces/expands quite naturally, why is there so much concern from human activities?"

    The concern is that human activities alter forest cover far more rapidly than the changes experienced during glacials/inter-glacials. Species adaptation is much easier when a habitat change occurs gradually.

    A species, particularly an endemic with a narrow range, will struggle to adapt if a large portion (or all) of its habitat is clear-felled within the course of a few months or years.
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  21. thingadonta at 13:51 PM on 5 February, 2010

    Your examples of previous instances of natural variability are poor analogies to the situation we are now creating.

    From various historic examples it appears uncontroversial that we have the ability to exert significant power over various ecological systems, as exhibited by extinctions of various species we've accomplished.

    The scope of our ability to modify planetary systems also appears rather uncontroversially to have been steadily increasing, as demonstrated by CFC emissions and our subsequent successful initiation of reversal of CFC impacts on the upper atmosphere, or for that matter acidic emissions from industrial sources.

    These events and the story they tell of our growing capability to harm ourselves beg a couple of questions. Should we continue doing so even after we've developed the skills to perform in a more competent way? Are we in control of ourselves sufficiently to choose the changes we impose? The answers will not come from nature, the responses must come from us.
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  22. Peer reviewed literature is not the holy grail many assume.

    For example, in the 5th assessment report, IPCC can use peer reviewed literature to make essentially the same claims about glacier melting that were made in AR4.

    A 2008 article published in Geophysical Research Letters states that "“The surface area of glaciers across the TP is projected to decrease from 500,000 km2 measured in 1995
    to 100,000 km2 in 2030 [Cruz et al., 2007],”

    It's right there in peer reviewed literature --- most of the glaciers in the Tibetan Plateau will be gone by 2030!

    Ref: “Mass loss on Himalayan glacier endangers water resources”, Kehrwald, etal Geophysical Research Letters Vol 35.

    This article has very many other "interesting" statements. All in a peer reviewed journal. All available for the IPCC to cite in the next assessment report.
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  23. Charlie,

    we have already done with this issue. The "Cruz et al., 2007" reference in the Kehrwald et al. paper is to IPCC AR4, WG II Report, chapter 10. Figure 10.4, letter "s" omitted.

    Basic circular reinforcement technique of new age science at work.
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  24. Charlie and Berényi, I don't think anyone is suggesting that the process of peer review magically transforms humans into infallible beings. To be human is to err. Scientific peer review can help to reduce the frequency and severity of errors, but not to eliminate them.

    That said, there actually has been quite a bit of research on Himalayan glaciers which the IPCC will be able to draw on for AR5. Not enough to make definitive projections, but estimates have been made based on a few different methodologies. They won't be saying 'all gone by 2035' again, but don't be surprised if it is along the lines of '66% gone by 2050'.
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  25. Charlie A at 18:47 PM on 5 February, 2010

    "A 2008 article published in Geophysical Research Letters states that "�The surface area of glaciers across the TP is projected to decrease from 500,000 km2 measured in 1995
    to 100,000 km2 in 2030 [Cruz et al., 2007],�

    It's right there in peer reviewed literature --- most of the glaciers in the Tibetan Plateau will be gone by 2030!

    Perhaps you'd better read the article and discover where are the errors, then mention them here specifically?

    For instance, one might find that ice will retreat with a steep initial slope over time, with a flattening of the slope as time passes, meaning that the ice will never actually disappear as you imply but the authors apparently do not. It's impossible to tell from the little you write, you'll need to provide much more detail before anybody will find your suspicions credible.
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  26. Stop apologizing for the IPCC - the latest is the claim that 55% of the Netherlands was below sea level. The Dutch government says 26%.

    Now this is not a hard figure to check. Any wonder why folks suspect the rest of the report is equally sloppy?
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  27. oracle2world,
    could you please quote where in the report it is written?
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  28. Seems to be quite a fad, picking over the IPCC report, but all that seems to be coming off is a bit of gristle. No meat? Nothing about the physics?
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  29. Doug_bostrom, this sudden switch from attacking the science of global warming to attacking the predicted impacts of global warming-as suggested by the IPCC-seems indicative of a rear-guard action by the so-called skeptics. Unless I'm wrong, rear-guard actions are only performed by the side which is *losing* the war-which suggests to me that, for all their bluster & bravado, the skeptics *know* they're losing the war over the science, so are desperately trying to nit-pick the predictions of the IPCC in some desperate bid to save some face.
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  30. Predictions are key to testing a hypothesis.

    Of course, if one puts forth a hypothesis of Anthropogenic global warming in such an unclear fashion that the actual hypothesis is unclear and any predictions (ooops, I mean projections) made are also unclear, then it is impossible to falsify the hypothesis.

    A untestable, unfalsifiable hypothesis is more akin to a faith. One may or may not believe in God, but God's existence is an untestable, unfalsifiable hypothesis.

    It is best to avoid such types of hypotheses in true science.
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  31. Doug_bostrom at 04:23 AM on 6 February, 2010 "Perhaps you'd better read the article and discover where are the errors, then mention them here specifically? "

    I would prefer to engage the authors in discussion, but they have failed to respond to repeated inquiries.

    Even better, I would expect the authors to proactively correct errors in their article to keep others from further propagating the errors.

    Typical misstatements:

    Section 6, para 17 has multiple errors ---
    1) "TP ice riled are a critical resource for 1/6 of the world's population becuase they provide dry season runoff" This is incorrect for most of the TP. The dry season corresponds to the winter, near zero melt season. The melt season occurs during the summer, which is also peak monsoon season.

    2. "The surface area of glaciers across the TP is projected to decrease from 500,000 sq km measured in 1995 to 100,000 sq km in 2030." There are multiple estimates of total glacier area in the TP that range from around 100,000 sq km to 110,000 sq km. None are anywhere near 500,000 sq km. (References are available upon request).

    Considering that these are the two major conclusions of the paper, these two errors alone are significant enough to warrant a corrigendum or errata.

    A couple of other errors:

    3. "Himalayan glaciers have been retreating more rapidly than glaciers elsewhere in the world". There is no scientific basis for this statement.


    Both this paper and Barnett et al, 2005 conflate glacier melt and snowmelt. There are many areas in the world that have no glaciers, but do depend upon snowmelt to even out seasonal variations in streamflow. Some alarmists seem to confuse glacial melt and snowmelt. O

    On the other hand, hydrologists at the Indian Institute of Hydrology clearly distinguish between them. See for example, Figure 3 of "Role of glaciers in watershed hydrology: “Himalayan catchment” perspective" by R. J. Thayyen12 and J. T. Gergan. Or look at Figure 8 which has monthly variations in discharge and percentage contribution from the glacier catchment in the stream flow.
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  32. Charlie A at 13:13 PM on 6 February, 2010

    "Section 6, para 17 has multiple errors ---"

    There is no such paragraph in the article. You actually were referring to section 6, paragraph 18. Anyway...

    "The dry season corresponds to the winter, near zero melt season. The melt season occurs during the summer, which is also peak monsoon season."

    Wrong, or at least your generalization is much worse than what you're accusing this paper of committing. For the Ganges, about 70% of flow is glacial meltwater during summer, for many other rivers serving the enormous concentration of population in the northern portion of India, between 50 and 60%. How about the other side, China? 23% of China's population receives most water from glacial melt during the dry season. *

    "The surface area of glaciers across the TP is projected ...

    (References are available upon request)."

    Based on the accuracy of your claim #1, it would indeed be helpful to see those references.

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  33. Charlie A at 13:13 PM on 6 February, 2010

    And belatedly I see your distinction between snow melt and glacial melt, something I have somewhat personal experience with as here where I live we depend to some extent on snow melt. I find it astonishing that you dismiss the findings of researchers in this field with casual references to conflation and "alarmism".

    The Thayyee and Gergan paper is very interesting indeed. It looks at the IPCC roll up of the general contribution of glaciers to stream flow and points out that the Himalaya should be examined more closely in distinction from the IPCC's generalized conclusions.

    The paper hardly seems to dismiss the role of ice and snow as an important source of water for major river systems:

    "River Ganga is being replenishedby the melt water from around 4000 glaciers spread over India and Nepal and the River Indus is being fed by more than 3300 glaciers. Snow and glacier melt together 5 with monsoonal precipitation determines the headwater flow regimes of large parts of the Himalayas, including central and eastern Himalayan tributaries of River Ganga and Brahmaputra. Snow and glacier melt contribution is very significant in many of these Himalayan Rivers. On an average, annual snow and glacier melt contribution is estimated to be 60% in Satluj river at Bhakra dam (Singh and Jain, 2002), 49% in 10 Chenab river at Akhnoor (Singh et al., 1997) and 35% in Beas river at Pandoh (Ku-mar et al., 2007). "

    Now, if you read this paper carefully, you'll see that much of the snow the authors are speaking of is that which is lying on top of glaciers. So while it is technically true that the particular portion of the Himalayan catchment they are looking at is dominated by snow melt, if the glacier this snow melt sits on vanishes clearly the hydrological picture is going to change.

    This portion highlights that:

    Figure 6 explains the role of glaciers and precipitation in controlling the river flow variations in a Himalayan catchment. While discharge at Tela and Gujjar Hut stations were reduced by 58 and 50 percentage, respectively from 1998 to 2004, discharge
    from the glacier catchment showed comparatively steadied response. Analysis of specific runoff from each sub-catchment showed that the contributions from Tela catchment (41.8km) reduced from 25mm/day in 1998 to 9mm/day in 2004 (Table 1). Similarly, runoff contributions from the Gujjar Hut sub-catchment (20.3km
    2) reduced from 18 mm/day to 4 mm/day during the same period, whereas runoff from the glacier catchment (15.7km2) varied between 29 to 15mm/day. Variations observed in the summer specific runoff from the non-glacierised part of the catchment covering 62 km
    2 are obviously driven by the variations in the precipitation. The lowest specific runoff of the glacier catchment observed during the study period was 15mm/day, which is much higher than the lowest specific runoff of 9mm/day and 4mm/day of the non-
    glacierised Tela and Gujjar hut sub-catchments, respectively. This highlights the buffering role of the glaciers during the years of low summer flow in the glacier fed rivers of the “Himalayan catchment”.

    I'm wondering if all this confusion about glacial melt versus snow melt is because amateurs are scrutinizing papers without the training needed to properly deal with terminology. I couldn't say for sure; I'm an amateur.
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  34. I said "The dry season corresponds to the winter, near zero melt season. The melt season occurs during the summer, which is also peak monsoon season."

    You say "For the Ganges, about 70% of flow is glacial meltwater during summer, for many other rivers serving the enormous concentration of population in the northern portion of India, between 50 and 60%. How about the other side, China? 23% of China's population receives most water from glacial melt during the dry season. *

    I'm glad to see that your references agree with me.

    The peak melt coincides with the peak precipitation. When the monsoon is dumping lots of water on the region, the addition of a bit of glacial melt doesn't benefit the river users much, and might actually be counterproductive if it causes flooding. And the low flow periods are during the winter, when glacial melt is negligible. In other words, glaciers don't do the sort of seasonal smoothing that is so important in some other areas of the world. Rather than take Barnett 2005 as gospel, you should click on through to his references for the related statements ... his refs 40,41, and 43. All are papers where the lead author is Pratap Sing of the National Institute of Hydrology.

    You will find the Barnett is confusing discharge from a glacial basin with glacial melt. In other words, he adds snowmelt to glacier melt.

    Again, I suggest you look at figures 3 and 8 of

    Note how during the dry season that glacial melt is an insignificant percentage of the flow.

    Or look at Table 1 which shows that glacier melt supplies approximately 9% of total annual flow of the Ganges.


    Regarding the area of glaciers in TP, you can look at the joint report by United Nations Environment
    Programme (UNEP) and the World Glacier Monitoring Service (WGMS). See
    and in particular section 6.9 Regional Glacier Changes, Central Asia. "Central Asia with an estimated total ice cover of 114 800 km2 has as its dominant mountain range 0the Himalaya, where most of the glaciers occur (33 050 km2). That is consistent with other estimates I've seen.

    And table 3.1 from shows global estimates of ALL glaciers excepting those in Greenland, Antartic and Artic as ranging from 510,000 sq km to 540,000 sq km.

    Now compare that estimate to Kehrwald 2008 which says that the measured area of Tibetan Plateau glaciers was 500,000 sq km in 1995.

    Perhaps Kehrwald 2008 has an error ????
    0 0
  35. It is often difficult to determine whether a specific change is happening due to 1) the natural warming of coming out of an ice age 2) natural variability (google Hurst Phenomena for some interesting reading. Those hydrologists at work again) 3) global warming or climate change due to well mixed greenhouse gases such as CO2 and methane, 4) other anthropogenic causes.

    In the case of Himalayan Glaciers, it appears that CO2 is not the culprit.

    Full paper is at
    for a change, it isn't behind a paywall.
    0 0
  36. Charlie A at 17:14 PM on 6 February, 2010

    "I said "The dry season corresponds to the winter, near zero melt season. The melt season occurs during the summer, which is also peak monsoon season."

    You say "For the Ganges, about 70% of flow is glacial meltwater during summer, for many other rivers serving the enormous concentration of population in the northern portion of India, between 50 and 60%. How about the other side, China? 23% of China's population receives most water from glacial melt during the dry season. *

    I'm glad to see that your references agree with me."

    They do?

    "In other words, glaciers don't do the sort of seasonal smoothing that is so important in some other areas of the world."

    Really, did you read Thayyee and Gergan? That's not what they say.

    "You will find the Barnett is confusing discharge from a glacial basin with glacial melt. In other words, he adds snowmelt to glacier melt."

    No, what you've failed to pick up is that much snow melt is derived from glaciers. Again, I think our lack of training here is a problem. Read Thayyee and Gergan, carefully.

    "Perhaps Kehrwald 2008 has an error ???? "

    Going straight back to the WWF, if you follow his cite. Ouch.
    0 0
  37. thingadonta at 18:36 PM on 6 February, 2010

    It all sounded so reasonable, sort of, until you got to this part:

    "I suspect, your comments about the CFC are also misguided. I suspect most of the rise /declne in ozone is probably natural, and unrelated to human activities. Academia is stuffed and stacked with people searching everywhere for human effects on natural systems- its the very reason for their academic existance, so they sometimes see human effects which are simply not there, and/ or natural (global warming). "

    A neat trick, sort of a deck of jokers. Any findings having to do with humans interacting with their environment with which you disagree, you can put down to lying academics, without a scintilla of actual evidence, data? How credible do you think that is?
    0 0
  38. By the way, the little "gotcha" on the Kehrwald paper does not affect the actual significance of the work, which has to do with ice cores revealing a long term mass imbalance:

    "Ice cores drilled from glaciers around the world
    generally contain horizons with elevated levels of beta
    radioactivity including 36Cl and 3H associated with
    atmospheric thermonuclear bomb testing in the 1950s and
    1960s. Ice cores collected in 2006 from Naimona’nyi
    Glacier in the Himalaya (Tibet) lack these distinctive marker horizons suggesting no net accumulation of mass (ice)since at least 1950. Naimona’nyi is the highest glacier (6050 masl) documented to be losing mass annually suggesting the possibility of similar mass loss on other high-elevation glaciers in low and mid-latitudes under a warmer Earth scenario. If climatic conditions dominating the mass balance of Naimona’nyi extend to other glaciers in the region, the implications for water resources could be serious as these glaciers feed the headwaters of the Indus, Ganges, and Brahmaputra Rivers that sustain one of the world’s most populous regions.

    As Charlie A so helpfully demonstrated by pointing out Thayyen and Gergan's paper, losing significant ice in the general region concerned will have significant hydrological impacts.

    So at the end of the day, the bloody WWF imbroglio once again affects nothing in actual physics, but this was sure an object lesson on how much irritation it must be causing in academic circles.
    0 0
  39. The "physics" as you like to call it tells us that melting snow delivers the same amount of water to a river whether it melts on top of a glacier or on top of rock. The long term average outflow from a basin is simply the precipitation minus the evaporation/sublimation. Mass loss of glaciers adds fossil water, much like pumping or mining water from an underground aquifer. Ignoring the fossil water, the presence or absence of a glacier simply affects the timing of when the precipitation shows up as basin discharge.

    The critical period for most water users is the low flow period during winter. Winter river flow is mostly base flow, some from precipitation, and very little if any from snow and glacial melt.

    I figured that somebody must have done the more detailed calculations/modeling to see the effect of glacier disappearance. It turns out that there is a relatively comprehensive report that was funded by the UK Department for International Development, titled "An assessment of the impacts of deglaciation on the water resources of the Himalaya; by Gwynn Rees and David N. Collins, June 2004. aka "Sagarmatha report"

    They ran simulations of what might happen with global average increases in temperature of 3C/century, 6C/century, and 15C/century.

    Page 44 of the report (56 of pdf) reports:

    "Changes in decadal mean winter flows, observed at two selected sites, are similar to the mean flow behaviour. Winter flows of the Indus at Partab Bridge mostly peak between 5% and 10% higher than the baseline winter flow in the first decade and then reduce to around -13% of baseline by decade 10, according to both the +0.03 and +0.06 C/year incremental temperature scenarios (Figure 4.9). For the Modi Khola at Kusma (Figure 4.15), decadal mean winter flows increase gradually throughout the 100-year model run, to a maximum of over +10% versus the baseline winter flow by decade 10, according to the +0.06 C/year scenario. While the relative changes are less in winter, any variation in water availability during this traditionally dry period could have serious impacts for water users".

    0 0
  40. Whoever the authors of WG2 were (the list doesn't have familiar names), some of them seem to have been rather lazy.
    0 0
  41. Carrot eater says " .... authors of WG2 ..... lazy".

    Not just the WG2. Here's the latest blooper, which appeared in the synthesis report, and has been quoted by the IPCC Chair and UN Secretary General Ban:

    "By 2020, in some countries, yields from rain-fed agriculture could be reduced by up to 50%. Agricultural production, including access to food, in many African countries is projected to be severely compromised."

    I haven't done the literature search myself, but it appears that there isn't any scientific backup for the rather dramatic conclusion.
    0 0
  42. I don't know about the year being right, but the basic problem is quite real. Here's some papers about problems with food crops around the world

    The first one shows that the mean losses in protein content were 13.9%, 15.3%, 9.9%, and 9.8% for potatoes, barley, rice, and wheat respectively. That means that these four staple crops all got less nutritious as a result of higher CO2 concentrations (never mind drought)

    The second paper shows that African staples cassava and sorghum didn’t technically become less nutritious and lose protein content, they did became poisonous as a result of higher CO2 and the crop yields plummeted – at less than double current CO2 concentrations, crop yield for cassava fell by 90%.

    Another paper by the same group found that white clover, an important pasture food for domesticated animals, will become more poisonous at higher CO2 concentrations too.

    And let's not forget that plants in general aren't going to grow as much as most current models expect, because there's not enough fixed nitrogen globally for plants to absorb even the percentage that GCMs are anticipating. Here's the original paper, followed by my blog about said paper

    So the 2020 date is probably messed up. But the overall sentiment - that staple food crops will become scarce and/or less nutritious, leading to large parts of the world having food shortages - is right on.
    0 0
  43. Charlie A at 14:05 PM on 7 February, 2010

    "I haven't done the literature search myself, but it appears that there isn't any scientific backup for the rather dramatic conclusion."

    Come now, you've shown you can do better that that! How "appears", if you've not looked the literature?
    0 0
  44. Ah, Charlie A. "By 2020, in some countries, yields from rain-fed agriculture could be reduced by up to 50%.". Mmmm, let's check out the logic of that statement shall we? I know you don't like to do the research yourself.

    OK "By 2020" - well that's ten years away. And since we know that agriculture in some countries (Australia is the one I am intimately equated with) is already under strain, and the forecast is for worsening conditions in the part of Australia (and therefore other similar countries, certainly in the southern hemisphere) that has the most agriculture, I suggest that 2020 as a date for big reductions in crops is not unreasonable.

    "Some countries" - see they are being very cautious here to avoid the "alarmist" stuff that the denierindustry loves to accuse them of. Just "some countries", not all, because circumstances will differ across Africa, "some countries". So what are you saying Charlie - you think NO African countries are going to have agriculture under threat in ten years? Hmmm, I have a house to mortgage if you want to bet your shirt on that.

    "Could be" - again, you see, cautious. I would say "will be" but then I've read a lot of literature and I'm living through the global warming of Australia on a farm.

    "Up to 50%" - enough caution already. But what do you think would be a fair figure Charlie - 10%, 20%, 30%, 40%? Well, I don't know, either, precisely, no one does, but those figures are all "up to 50%". You think none of them are right Charlie?

    "appears that there isn't any scientific backup for the rather dramatic conclusion" - you reckon Charlie? We've already seen that it isn't a "dramatic conclusion", in fact it's rather wimpy, really. But CSIRO and other agencies in Australia have undertaken studies here showing the real (and already developing) threats to agriculture in what was once one of the breadbaskets of the world. Threats so real that even our former prime minister, a notorious climate change denier, set in train 5 years ago an investigation to see whether Australian agriculture could be moved from the southern half of the continent, where it has flourished for 220 years, to the tropical north (it can't in any meaningful way).

    Southern Africa is in a similar geographical situation to Australia, and I'm betting science bodies there are making the same grim projections.

    My apologies for the lengthy response, I grow weary of this glib denialism ("So the 2020 date is probably messed up") that thinks nothing bad is going to happen, or indeed could happen, to this planet as a result of human activities. Try doing the literature search Charlie, it ain't that hard. Come back when you are ready to discuss things sensibly.
    0 0
  45. I fail to see how the papers regarding clover grown in 700ppm CO2 relates to the UN assertion of 50% reduction in yield by 2020 in rain-fed agriculture in Africa.

    Chris Field, the current co-chair of IPCC WG2 fails to find any evidence to support those claims either.
    0 0
  46. For those interested, the report on shifting agriculture to northern Australia has just appeared. No go, says the committee.
    0 0
  47. David, clearly you don't know who your friends are, given I was supporting you 99%. Way to focus on that 1%.

    Charlie, try "90% reduction in cassava yields." Try cassava becoming poisonous due to increased cyanogen compounds (yes, those are compounds that your digestive system turns into the poison cyanide).

    Agriculture includes raising livestock, Charlie. From the M-W definition here:

    agriculture is "the science, art, or practice of cultivating the soil, producing crops, and raising livestock and in varying degrees the preparation and marketing of the resulting products"

    So if you make all that white clover poisonous and kill the livestock, then that is a "reduction in yield."

    Maybe the 2020 year is indefensible - I don't know, although the current projections for CO2 emissions are high enough that it could be. But focusing on a single date instead of the underlying science is a straw man. Try something serious next time.
    0 0
  48. 99% is good angliss, but my point was that there was, is, no reason to say "So the 2020 date is probably messed up". It might be spot on, it might not be, there is no way of knowing, and in any case a particular year isn't the point. But saying it is "probably messed up" without evidence for (or against) this statement is just giving credence to the hordes of deniers who are pushing the idea that all IPCC projections are "messed up".
    0 0
  49. The IPCC, on page 50, section 3.3.2 of the AR4 Synthesis report has a bulleted item that reads "By 2020, in some countries, yields from rain-fed agriculture
    could be reduced by up to 50%. Agricultural production, including access to food, in many African countries is projected to be severely compromised."

    As this is in the section about the effects of climate change on regions, one must assume that this is an IPCC claim about climate change and/or anthropogenically triggered climate change.

    The current chairman of the IPCC Working Group 2 has reviewed the documentation and says that this finding is not supported in any IPCC documentation or references.

    Making of such unsupported statements is, in itself, a problem. It is even more so if there are no reliable studies that support such findings. None of the studies posted in comments in this blog are relevant to the IPCC statement.

    It would be helpful is someone could point to some studies that actually support the IPCC statement. These may, or may not exist.


    The cassava study and the clover study are not relevant to the 50% reduction in crop yield in Africa by 2020.

    David Horton says "Southern Africa is in a similar geographical situation to Australia, and I'm betting science bodies there are making the same grim projections." IPCC seems to also have been "betting" that the grim projections would be accepted without any supporting data. Until recently, they were.
    0 0
  50. From the Times article:

    "The claims in the Synthesis Report go back to the IPCC’s report on the global impacts of climate change. It warns that all Africa faces a long-term threat from farmland turning to desert and then says of north Africa, “additional risks that could be exacerbated by climate change include greater erosion, deficiencies in yields from rain-fed agriculture of up to 50% during the 2000-20 period, and reductions in crop growth period (Agoumi, 2003)”."

    The Times goes on to point out that estimates of future crop yields are derived from governmental assessments, which are not peer reviewed.

    I think one of the challenges for upcoming improvements to IPCC reports will be figuring out what non-peer reviewed material will acceptable for inclusion. Clearly much important work is done by governments that is not peer reviewed yet found generally acceptable for planning purposes. To exclude all such material does not seem very wise.

    This seems particularly true of impact assessments.

    As to the fundamentals of climate change, a different matter; any projections of impacts etc. ought be driven by the best science possible, even where academic resources are insufficient to supplant the rather enormous amount of technical expertise to be found in governmental agricultural ministries and the like.
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