Amazonian contradictions

Looks like the Amazon(non)gate wont die. And in keeping it alive the deniers are again showing their self-contradictions.

So what happened? It started in 2007, when a study (Saleska et al. 2007, Science) showed that the Amazon actually greened during the drought of 2005. This was an odd responses; no one expected a rainforest to green during a drought, though because the study conclusions were based on satellite imagery, rather than direct observations, there was less certainty in them.

Now, a new study (Samanta et al. 2010, GRL), also using satellite imagery, indicates that the 2005 drought did not cause a greening of the Amazon.  So how is this new study being spun by deniers? The same way the 2007 study was spun.

Or as Tim Lambert said “It’s always bad news for the IPCC”. Both studies can’t be bad news for the IPCC, but such contradictions are par for the course in denialist land.

Unfortunately those misrepresenting the story can point to a misleading press release, which claimed Samanta et al. disputed the IPCC claims of Amazonian sensitivity to drought:

New study debunks myths about Amazon rain forests

They may be more tolerant of droughts than previously thought

(Boston) — A new NASA-funded study has concluded that Amazon rain forests were remarkably unaffected in the face of once-in-a-century drought in 2005, neither dying nor thriving, contrary to a previously published report and claims by the Intergovernmental Panel on Climate Change…

“This new study brings some clarity to our muddled understanding of how these forests, with their rich source of biodiversity, would fare in the future in the face of twin pressures from logging and changing climate,” said Boston University Prof. Ranga Myneni, senior author of the new study.

The IPCC is under scrutiny for various data inaccuracies, including its claim – based on a flawed World Wildlife Fund study — that up to 40% of the Amazonian forests could react drastically and be replaced by savannas from even a slight reduction in rainfall.

“Our results certainly do not indicate such extreme sensitivity to reductions in rainfall,” said Sangram Ganguly, an author on the new study, from the Bay Area Environmental Research Institute affiliated with NASA Ames Research Center in California.

“The way that the WWF report calculated this 40% was totally wrong, while [the new] calculations are by far more reliable and correct,” said Dr. Jose Marengo, a Brazilian National Institute for Space Research climate scientist and member of the IPCC.

The only problem is that the IPCC was not referring to single year droughts like the one in 2005, which was the focus of Samanta et al., but rather to a change in the long term conditions of the Amazon. It is Intergovernmental Panel on Climate Change, not of Weather Change, after all.

Droughts happen, even without global warming, and if a single year of drought was enough to turn rainforest into savannah, then we wouldn’t expect rainforest. Samanta et al. didn’t address multi-year droughts, only the single year drought of 2005.

Unfortunately the study authors have implied that the IPCC was referring to single year drought, thus further obfuscating the issue:

The press release accompanying the GRL article disputed the following IPCC AR4 (2007) claim –

“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). It is more probable that forests will be replaced by ecosystems that have more resistance to multiple stresses caused by temperature increase, droughts and fires, such as tropical savannas.”

for two reasons: (1) this is presented as the consensus view by quoting Rowell and Moore, 2000. (2) There was more than a slight reduction in precipitation during the third quarter of 2005 and, most of the drought-impacted forest area for which we have uncorrupted satellite greenness data showed no enhanced or reduced greenness levels (third quarter average EVI values) as compared to non-drought years (between 2000 and 2008).

It is only in this context that the material in the press release and the GRL must be understood. We do not dispute any other results related to this theme in these two documents.

Arindam Samanta (on behalf of the authors of the GRL papers).

Simon Lewis’ response makes it clear that this is the wrong interpretation:

Dear Arindam,

Thanks for the response.

On the IPCC statement, as I have said it is not as well-worded as it ought to be. Strictly, perhaps it can be taken as having one of two different meanings,

1. That the IPCC mean that small reductions in precipitation at any given time cause a drastic response (of which your paper ably shows that for satellite-monitored ‘greenness’ there is no such drastic response, and is an important paper I will certainly cite), or

2. They mean responses of vegetation to mean climate regimes with differing precipitation (of which your paper says little).

It seems clear to me that the sentence is about responses to a shift from one climate regime, the recent past and present day, to another, with less precipitation, in the future (it is the IPCC climate change impacts report after all, and they do say ‘… not necessarily producing gradual changes between the current and the future situation’).

If meaning two of the sentence is taken, then what the IPCC say is reasonable, defensible, basic science: warm lower-rainfall environments tend to be dominated by savanna, while warm higher-rainfall environments tend to be dominated by rainforest, with a threshold amount of rainfall separating which vegetation type one finds. If substantial areas of the Amazon are in a climate regime close to the savanna-rainfall threshold, which diverse evidence suggests they are, then there may be a vegetation shift if rainfall consistently decreases in the future due to climate change.

Your response implies you think meaning one is correct, which is mistaken (logically it can’t hold as a proposition). Had your paper cited the IPCC chapter and the sentence you object to and why – which it doesn’t – the misunderstanding could have likely been addressed at the review stage.

Details aside, it’s the ‘debunking Amazon myths’ headlines, and quotes about putting right ‘muddled understanding’, and, “The way that the WWF report calculated this 40% was totally wrong, while [the new] calculations are by far more reliable and correct,” that are problematic and have unnecessarily confused people. There are no calculations in the WWF report (it’s a review), nor are there any new calculated updates on the IPCC ‘up to 40%’ statement in the Samanta paper, and the ‘muddled understanding’ quote highlights the ‘twin pressures’ facing the Amazon, as logging and climate change, when outright deforestation is certainly the number one current pressure in the context of the quote.

I know the media regularly run out of control (its happened to me several times), but in my view it is critical to try and put things right. Most journalists and bloggers will help put things right once they know there is a problem, but you have to tell them.

With best wishes,


So what did happen in 2005? Real Climate has the answer:

Oliver Phillips, [Simon Lewis], and others, published a paper in Science last year, using ground observations [as opposed to satellite imagery] from across the Amazon, showing that while the 2005 drought did not dramatically change the growth of the trees compared to a normal year, as Samanta et al. also show, the deaths of trees did increase considerably. The new study of Samanta et al. does not contradict the Phillips et al. study, which itself shows the Amazon is vulnerable to drought via impacts on tree mortality. The Phillips et al. paper showed that remaining Amazon forest trees changed from absorbing nearly 2 billion tonnes of CO2 from the atmosphere annually over recent decades, as tree growth has been exceeding mortality, to being a large, but temporary, source of over 3 billion tonnes, from the elevated tree mortality associated with the 2005 drought event.

And if there is any doubt, 19 scientists who are quite familiar with the Amazon have written a statement confirming that the IPCC was correct:

Scientists’ statement on recent press release on Amazon susceptibility to reductions in rainfall: no Amazon rainforest “myths” have been debunked.

The scientists who signed this statement conduct research on Amazon forests, climate, and/or fire

The press release from Boston University describing a recent article in the journal Geophysical Research Letters by BU researchers on the response of Amazon forests to the 2005 drought is misleading and inaccurate. It claims that the study “debunks myths about Amazon rainforests”, which is simply not true. First, there is no myth. Rather, there are multiple, consistent lines of evidence from ground- ‐based studies published in the peer- ‐reviewed literature that Amazon forests are, indeed, very susceptible to drought stress. Second, nothing is debunked by the new study. The new study contributes to our understanding of interpretations of data retrieved from satellites, but it does not prove or disprove anything about what is really happening on the ground. The BU press release also claims that the new BU paper demonstrates that the IPCC statement about the sensitivity of Amazon forests to small reductions in rainfall is inaccurate, which is also not true. While the IPCC statement could be criticized for citing a review paper rather than original research papers, the main conclusion of the IPCC statement – that Amazonian forests are very susceptible to reductions in rainfall – remains our best understanding of the data available at the time of the IPCC report and also today.

The article published by the BU group (in contrast to the BU press release) makes a scientific contribution to our knowledge of Amazon forests. It presents new analyses of the forest canopy conducted using satellite data from the MODIS sensor. The article challenges the findings of a previous analysis of forest response to the 2005 drought using similar data from the MODIS sensor. This earlier study, published in Science in 2007, concluded that southwestern Amazon forests fared well during the severe drought of 2005, reporting that these forests were greener in 2005, not browner as would be expected if the forests were stressed by drought. The new study found that the forests fared neither better nor worse, as indicated by the color of the canopy as seen from satellite images during the 2005 drought. Scientists are likely to continue to debate the differences in their analyses of the satellite imagery, and the articles in question illustrate the scientific learning process as we explore the potential and the limitations of satellite- ‐based measurements to give us information about forest response to drought in the Amazon region.

Forest tree measurements made under the forest canopy following the 2005 drought provide a very different picture of the sensitivity of Amazon rainforests to drought. In tree inventories conducted in 55 long‐term forest plots scattered across the Amazon forest, the drought of 2005 was associated with a large surge in tree mortality and no gains in growth. These findings, published in the journal Science in 2009, are consistent with the results of two large- scale experiments, in which large canopy trees began to die after three years of experimentally reduced rainfall. The forest plot results are also consistent with studies of historical rainfall and soil water storage capacity and with simulation model analyses. These studies, published in some of the best peer- reviewed science journals, provide several consistent lines of evidence that the forests of the Amazon Basin are susceptible to small reductions in rainfall. We do not know why the drought stress and tree mortality documented in the field studies published in the 2009 Science article and predicted based upon rainfall patterns were not detected in the analyses of satellite images by the Saleska- and Samanta- led teams. It could be that tree deaths, which affect only a portion of the tree canopy, are hard to see in satellite images, especially if this tree death is accompanied by the growth of vines and plants on the forest floor. It could also be that the tree mortality induced by drought was sufficiently  delayed to be invisible in the imagery of 2005. This should be the topic of further research.

Reductions in rainfall can affect Amazon forests by increasing tree mortality, but also by increasing their susceptibility to fire. The initial fire kills trees, increasing the likelihood of subsequent fires for years afterwards in a vicious positive feedback loop. In 2005, more than 2000 km2 of forest caught fire in the tiny state of Acre alone. During the severe drought of 1998, approximately 40,000 km2 of forest caught fire. These are indisputable facts. It is important to remember that these droughts are part of the current Amazon climate regime. If climate change increases the frequency, severity or duration of these episodic droughts, then increased forest fire and tree mortality and reduced river flow are the likely results.

The IPCC must be held accountable for the best scientific information that is available in the peer- review literature at the time of its writing. The passage in the IPCC that refers to the susceptibility of the Amazon forest to drought cites a World Wildlife Fund review report which, in turn, cites an article in the journal Nature. Ideally, the IPCC should have cited the Nature article as well as several other existing articles in support of its statement, and not a WWF report. The point is, however, that the statement made by the IPCC about the sensitivity of Amazon forests drought was consistent with our knowledge at that time, and has been reinforced by new studies.

It doesn’t get any clearer than this. This was a good study, followed by a bad press release and some obfuscation by the authors. But that doesn’t give anyone an excuse to misrepresent this study and baselessly attack the IPCC, especially when previously they wee championing the greening study that has no been shown to be flawed.

UPDATE: Saleska (the author of the greening study) has responded to the claims made by both the Samanta et al. and the press release. Saying that the Samanta et al. paper does not actually contradict the greening claims:

The bottom line is that their observed 2005 result (32% greenness) is indistinguishable from ours (34%). I.e. Samanta et al effectively reproduce the results of Saleska et al.

The greening response is still puzzling, but jumping to the conclusion that it demonstrates Amazonian resistance to multi-year droughts and long term changes in precipitation levels, thus contradicting the IPCC, is incorrect:

This summary response, of course, begs some very interesting questions about tropical forest function under climatic variability and change (indeed the most interesting questions of all!): what caused the anomalously disproportionate green-up in the drought region? And, even if satellite “green up” does in fact represent an increase in photosynthesis (as we think), could this in fact be a symptom of the trees compensating for the increased stress of the drought? The bottom line “carbon balance” of a tree depends on both photosynthetic uptake and respiratory losses, and it is almost certainly the case that those losses (which were not seen by the satellite) increased under the hotter and drier conditions of the drought as well.

Thus, the most intriguing idea to me is that the short-term satellite-detected green-up, and the longer term increase in net carbon loss reported in the Phillips et al paper (discussed by Simon Lewis) are not in conflict at all. It might well be that they represent different parts of a coherent forest response to drought, in which the longer term losses are larger than the satellite-detected attempt to compensate for them by increasing photosynthesis, and in the end, increased tree mortality is the result.

The greening response is still not well understood, it could indicate drought resistance, or it could be consistent with drought sensitivity.

And finally Saleska reiterates that it is absurd to think that either of these papers demonstrate that the IPCC was in error:

In conclusion I would like to reinforce Simon’s point about Samanta et al and the IPCC. More important than whatever they say about our one short paper, Samanta et al. truly and egregiously misrepresent the implications, of both their work and ours, when they claim that a single paper on short term vegetation response somehow rebuts the IPCC’s review of the large scientific literature on how Amazonia might respond to long-term shifts in the mean climate state. It is an illogical and misguided claim on many levels, one that is already and deservedly attracting the opprobrium of many of my colleagues, talented scientists who study Amazon forests and climate (see Scientists speak: Amazon “myths” are not debunked).

Jumping to the conclusion that any study, that on the surface appears to contradict the IPCC, automatically proves that the IPCC is wrong is not proper skeptisism, it is denialism.

2 thoughts on “Amazonian contradictions

Add yours

  1. I’ve heard someone, Dr. Rong Fu IIRC, talk about the greening thing.

    The prevailing idea is that water-stressed trees die in a drought, but less water stressed trees get more sunlight and can afford to take advantage of it with a growth spurt.

    Of course, long term drought is bad for rain forests. Sort of obvious. That’s why they are called “rain” forests. They don’t grow in the arid regions, do they? I wouldn’t think you;d need thousands of scientists to figure that out, actually.

  2. The trick is finding exactly where that threshold lies, and how much of the forest is is close to it. Forest ecology has way more complexity than most people think.

    I had a prof in university that used to say “Ecology is not rocket science, it’s harder“.

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