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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 51 to 60 out of 60:

  1. Just to clarify, it's fairly obvious that IPCC agricultural projections were not produced "without any supporting data", unless one is prepared to say that agronomists producing reports for governments are no different than cursory speculations driven by newspaper articles.
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  2. One more (I doubt it, actually) thought about peer reviewed research versus "grey literature." Discussion around climate science per se is dominated by peer reviewed research publications. That's as it should be; this is scientific research and publication via peer scrutiny has proven to be a generally robust and productive way of eliminating weak bricks from the ever growing tower of knowledge. However, when it comes to impacts of climate change we begin to see a transition from pure research into operational activities. For instance, predictions of hydrological changes are or at least should be rooted in scientific research, but those findings are handed off for application into the purview of people practicing engineering and agronomy. Although pure research on climate change impacts is and will continue to be conducted in those arenas, at some point research gives way to practicum and there's where the system of peer review will disappear. Scientists doing research are not engineers and farmers; they will not and should not be people plugging numbers into known equations and producing answers. Just so, practicing engineers and agricultural extension experts will be concerned with processing integrations of climate change impacts into products for their customers; practicing experts do and can not resort to peer review before responding to solicitations for bids or requests for crop planting advice. Yet engineers and farmers will have much that is valuable to say about climate change impacts. Indeed, it is not going to be possible to assign numerical values to the costs or opportunities of climate change without tapping these people and their practical experience. For that matter, this is true of many conservation organizations, even including the hapless WWF. Many of these are project oriented organizations concerned with practical results yet they have valuable observations to contribute. Clearly the exact process of integrating disparate sources of information into IPCC reports was not perfected prior to the 2007 report. As a wag here on Skeptical Science elliptically pointed out, the WG2 report included "grey literature" which has leaked into peer reviewed literature because not everybody received the memo that WG2 explicitly permitted grey literature. Allowing grey literature means that material intended for popular audiences found its way into the WG2 report, and some of this has experienced what IT security folks call "privilege escalation"; popularized and what one must admit may even be sensationalized descriptions of scientific findings have found themselves blinking in the harsh light of scientific literature where they are found damaging to precious credibility. I don't think they are a hazard to actual science itself, as attempting to use this material for conceptual underpinnings would quickly reveal the shoddy nature of the material. I hope when IPCC tweaks its inputs it does not commit the mistake of disallowing all so-called "grey literature". To do so would be throwing out the baby with the bathwater; there is too much useful expertise outside of the academic arena to ignore. At the same time the material that does get in is going to need passing through a very fine and particular sieve. And somehow IPCC must clearly telegraph what is suitable for citations lest we have more embarrassments such as the unfortunate Kehrwald et al, where decent research is dulled by duff citations.
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  3. Doug_Bostrom, I agree with most of your last comment but there is no need to make it more complicated than necessary. The IPCC could have avoided most of the mentioned problems with a couple interns or grad students working as "fact checkers". The fact checker job is simply to see that each statement is supported by original source material. The problems have been that the IPCC assessment and synthesis document has too often relied upon other synthesis and assessment documents -- whether or not those were peer reviewed, or papers from conservation groups, or by environmentalist activist groups. When we trace back from IPCC to a WWF assessment paper to another assessment paper and through one or more steps before finally getting back to the orignal source, we find that the final statements in IPCC don't correspond to that of the original source. In other words, I don't see it as a grey vs peer reviewed problem, but as original vs hearsay.
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  4. My job is agro-meteorology. I think warming it’s positive - in sum, for agriculture - in global. Let's do the simplest analysis of the older "warm-up’s", for example, based on the (above-mentioned) book by Stanley: 1. The higher the temperature (f. e. more than 2 deg more than now) that the greater part of the Earth's surface, are similar ecosystems. 2. The higher the temperature - the weaker zoning plant. 3. The higher the temperature - the less the deserts ... 4. Conclusion: The higher the temperature the more anticyclones (smaller pressure gradient?); increasing the area covered by a thick layer of cirrocumulus - tropical and maybe subtropical thermostat? Warming Climate is simpler in operation? P.S. Important observation: Changes are not linear: my "avorite" example - Mongolia - current warming: It takes 60-80 years there is drought, when the former was about 1 deg warmer than now, reaching there monsoons ...
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  5. "avorite" - favorite obvious
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  6. Charlie A at 19:31 PM on 8 February, 2010 "The IPCC could have avoided most of the mentioned problems with a couple interns or grad students working as "fact checkers". The fact checker job is simply to see that each statement is supported by original source material." Perhaps a bit more than a couple of interns. This is a critical document and really does need to be reliable. I've not gone over the review process in detail so I'm speculating just a bit here, but from what I've learned of the Himalaya glacier business it seems that the chain of command on the review process petered out, not leading to an editor with sole focus on quality control but instead to a multi-tasking professional with primary responsibilities in another arena. I'm acquainted as the proverbial fly on the wall with the role of volunteer peer editors (where the scientifically important editing is done) in the academic publication process. That duty is very demanding and picky, requires a lot of time to be done right and yet is shoehorned into the middle of an active career ipso facto. People asked to be editors are generally productive researchers so it's almost axiomatic they are overcommitted individuals. So (harumph) if -I- were running the process I'd make sure there was a single person for each domain section of the report with an existential interest in making sure the quality control you mention was completed properly. A bit of a conundrum, because that person is going to need a good general grasp of the field in question yet will need to devote slavish attention to the task at hand. Perhaps this could be a career candle for emeritus professors? Unfortunately many of those tend to continue publishing until they drop dead, but after all this is a distinguished publication, akin to a literature review or compendium book.
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  7. What about other science organizations that make predictions not directly affiliated with the IPCC that I would expect have high standards of peer review? Or has the public forgotten about them (hopefully policy makers haven't) In the blog sphere on articles to do with climate change, people seem to jump right on criticizing the IPCC's credential in such a way that even if something is only slightly sketchy in one particular report then the IPCC then the whole of climate science is wrong. I remember reading about the physicist Richard Feynman defending an adult bar in court (which he attended regularly) and nobody attacked his science, now one man writes a raunchy novel and it makes headlines and suddenly the IPCC is perceived as a fraud. Mistakes are inevitable in science and happen all the time. I think, unfortunately that the major drawback with the IPCC is that in the public's point of view, the validity of climate science is tied so closely to any mistake, error or scandal (or even on people's characters). I think the number one thing for the next report the IPCC needs is PR training.
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  8. is an article with lots of details on the IPCC claim of 50% reduction in rain-fed agriculture in Africa by 2020. It includes info on how the lead author had a company that accepted government money to study potential problems and came up with conclusion that there were no significant potential problems. Then that same lead author wrote the alarmist claims that don't jibe with his own company's studies.
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  9. Charlie A at 13:41 PM on 14 February, 2010 Telegraph: "Yet it has now come to light that the IPCC, ignoring the evidence of its own experts, deliberately published the claim for propaganda purposes." An opinion piece, apparently, and odd that the Telegraph should consider unsubstantiated claims by the IPCC worse than what they themselves publish.
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  10. This recent research is being quoted on a few skeptic blogs as further evidence of sloppy work by the IPCC A recent study that seems to indicate that the rain forest is resistant to short term drought
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