Press offices at institutions can either feed or help modulate this tendency driven by journalists’ normal hunger for “the front-page thought.”
Just today in a chat about another arena – social science work on human responses to disasters – Denis Mileti of the U. of Colorado gave the most important guidance for assessing trends in complex science: “A single study can produce ‘findings,’ but ‘knowledge’ only comes from reading across all the studies in a particular area of inquiry.”
.. Kind of what the IPCC tries to do. ; )
[Response: Andy, thanks for cogent comments. Well put.--eric]
So a drought gets the response from trees that restricted food intake gets from people? If it isn’t too bad, the organism fights harder to live and lives longer? If rain is plentiful, the tree gets a bit lazy? Interesting.
But Samanta couldn’t believe his eyes? Understandable.
More research into the genetics of the trees is called for.
Thanks for the link to the Amazon researcher’s statement.
The only thing the IPCC did wrong was to reference the review article rather than its original citations. Ok, so who hasn’t done this at least once please raise their hand.
Why didn’t Samanta and Saleska work more closely with tropical ecologists? These two articles seem to fall into the trap of reporting a new research method but then using their example data to draw conclusions about a different research question for which it is ill-suited.
The techies and plant press luggers need to get together here.
Sorry its a bit offtopipc:
Lindzen ans Choi have now an response to Trenberth et al. submitted to Journal of Geophysical Research
“On the observational determination of climate sensitivity and its implications” http://www.legnostorto.com/allegat /Lindzen_Choi_ERBE_JGR_v4.pdf
I think it would be of broder interest if you could cover this paper! Its a bit curious, although they state that most of Trenberth et al. points were correct, they raise exactly the same conclusions…
Thank you for writing this. I especially liked the summary points at the end which can be laid out as a quick response that most can easily understand. Nicely done with the take-home message. Perhaps more posts could have summary points to make it easier for journalists to pick up and print?
[Response: Thanks for that suggestion. I think we could do a better job of summarizing the essential points in our posts. I agree that Saleska did a particular good job of this.--eric]
Comment by Daniel J. Andrews — 20 Mar 2010 @ 4:21 PM
It might be helpful for nonscientist readers if someone could list the coauthors of the various papers in the last five years that all appear to be talking about the same area and using some of the same data sets. It’s normal in the sciences but likely to confuse the heck out of readers unfamiliar with how papers get extracted from data sets and how coauthors get involved.
@Daniel Andrews @8 and eric’s answer.
Coulnd’t agree more, summarizing essential points would be fantastic. Some of us have day jobs and families to prevent us from reading blogs 24/7 you know :) (Same goes for you guys I realize. Anyway thanks for the fine work you all do.
Good post!. I teach AP Chemistry in High School and am putting together a section on the scientific method and the literature. this type of feedback and demonstration of the method of debate in the published literature is a great example. I want to emphasize Andy’s point about findings and knowledge. Of course not all findings are confirmed, some are discarded.
There is a big error in Saleska’s comment, computing 10.8/33 has no meaning, 10.8 is already for the entire forest !
He is assuming that 10.8% is 10.8% of the 33% of the valid pixels, but in fact it is 10.8% of the entire forest !
[Response: This is fine isn't it? 10.8% of the total forest is definitely green -- but it could be much higher since 67% of the forest has invalid pixels. At least 10.8% of the forest is definitely green, and 10.8/33 provides an estimate of the likely total fraction of the forest that is green.--eric]
This is the kind of post I can reference to show people how science is done, seriously. Yet more proof that RealClimate is a treasure. It will be interesting to see the responses in comments/peer lit.
Comment by Marion Delgado — 21 Mar 2010 @ 12:09 AM
When I look at table S3 (Samanta et al. 2010, supplement) I conclude that the suggestion that these forests may be more tolerant of droughts than we previously thought isn’t wrong. Just look at the raindeficits and the green, brown and unchanged area’s. It looks to me that the 2005, 2006, 2007 and even the 2008 measured raindeficits are a bit more than a “light” reduction.
Surely more scientific work is needed to assess what is happening at the base of these forests.
Question for the writers and bloggers who read this: How do you approach the unscientific skepticism (versus useful scientific skepticism) and denialism that now surrounds every conversation available in the public discourse on climate change. Were well past the point where informed individuals accept anthropogenic interference is affecting earths climate cycles: How do you as a journalist/blogger/scientist whatever approach having meaningful conversation and debate on this subject, by which I mean, debate and conversation which we lead to action towards addressing those human caused factors which are making our climate less hospitable towards an advanced human civilization?
@Benjamin, #14 – You state that the 10.8% is for the entire forest. However, since the sum of green, brown and unchanged percentages equate to the ‘valid area’, it would appear that the calculation is correct although the statement in the text is misleading.
Where it says: “10.8% of the total area = 10.8/33.68 = 32% of the valid area) in 2005″ it probably should read: 10.8% of the total valid area = 10.8/33.68 = 32% of the valid area) in 2005.
(If the pixels cannot be read, then they cannot be read as ‘green’. Percentages do need to be clarified to what they refer to, I agree.)
@Ibrahim #18 – I also looked at the following years, particularly the still high reductions in rainfall, and the impact on the forest. Most definitely more analysis linking these observations to what is happening on the ground in the Amazon would be very helpful. I’m wondering how well these techniques for analysis can be validated on the ground in dense, multi-story forests. I understand a lot of work is being done in this regard and would be interested if anyone has any links to papers on same.
Let N = total number of pixels, V = number of valid pixels, G = # green pixels. According to the table, in 2005 G/N = 10.8% and V/N = 33.68%. Therefore, G/V = 10.8/33.68 = 0.32 (the N’s cancel). Saleska’s math is correct — 32% of the valid pixels are green. And, as Eric says in his response, it is reasonable to assume that a similar ratio holds for the invalid pixels.
Regarding comment #18 on precipitation deficit. A point of clarification might help. In all cases (whether for vegetation response as recorded by EVI or for precipitation as recoreded by TRMM), the columns represent the fraction of pixels in the drought region that experience anomalies more extreme than +1 (EVI green) or -1 (Precip, or EVI brown) standard deviations from the mean. On average (with a normal distribution) we expect this to be 16% of the valid pixels (16% more than +1 SD, and 16% less than -1 SD, with 68% in the middle). So years with values more extreme than ±16% are anomalously large, and values less extreme are anomalously small. So the the years in which the precip deficit is less than 16% (ie. 2000-2004) mean there is actually *more* precip than average.
Regarding comment 1 by Benjamin on the statistics: we used a different null hypothesis than assumed by Benjamin, but my post was obviously unclear on the details of the statistical analysis. The post might be amended to contain more detail as follows:
“Saleska et al. (2007): 34% (p<0.000001) (2.2 million km2 of valid pixels in drought region)
Samanta et al. (2010): 32% (p<0.004) (0.7 million km2 of valid pixels in drought region)
Note: Unlike our analysis in Saleska et al 2007, Samanta et al provided no objective criterion for distinguishing green-up from no green-up. So we quantified the statistical significance of observed EVI anomalies, for both their data and ours, by comparison to the null hypothesis that independent forest observations are as likely to exhibit positive (=greening) as negative (=browning) EVI anomalies. P-values are calculated from the binomial probability of seeing at least the observed fraction of positive anomalies by random chance, given the number of independent observations (seeing green vs brown is analogous to thinking of each observation as a coin flip with equal probability of getting heads vs tails).
What is the number of independent observations? The scale at which different patches of forest “greenness” can be treated as independent presumably corresponds to the scale of individual hydrological catchments – possibly larger than a MODIS pixel (1 km x 1 km), but almost certainly smaller than a 1deg x 1deg square (110 km on a side). Conservatively assuming that independence is achieved only as patch area approaches the larger of these, we analyzed the probability of observing the reported fraction %positive/(%positive+%negative) out of the total valid area exhibiting change. (This explains why p-value for the Samanta et al results above shows less statistical power: their method filters out a majority of the forest area, compared to ours, which keeps most of it.) "
I think Eric (and Sou’s comment at 21) probably already answered Benjamin’s question at #14 about how the fraction is calculated, but just to make sure it’s clear:
Samanta et al data show that 10.8% of the total forest area registers as green. That 10.8% is all in the valid area (as it must be, since by definition we can’t tell whether the area deemed “invalid” is brown or green), so this means that 10.8/33.7 = 32% of the valid area is green. What is the fraction green of the whole forest area? We don’t know, obviously, but logically it could range from 10.8% (if none of the invalid area is green) to 66.3%+10.8% = 77.1% (if all of the valid area is green). In the absence of further information, one estimate follows from assuming that the invalid area is like the valid area, in which case it would also be 32% green. In any case, the objective information we have is that, of the forest that we can observe in the 2005 drought region, almost three times more of it is green than brown, however you choose to calculate the separate percentages.
“A point of clarification might help. In all cases (whether for vegetation response as recorded by EVI or for precipitation as recoreded by TRMM), the columns represent the fraction of pixels in the drought region that experience anomalies more extreme than +1 (EVI green) or -1 (Precip, or EVI brown) standard deviations from the mean.”
Could you please clarify what period/area “mean” refers to? Is it the mean for an individual image, an individual year, or all images from all years? Something else?
Similar to the work by Huerte et al (2006 GRL 33: L06405), our earlier work on seasonal leaf phenotypes of tropical rainforest trees showed that greening occurs in several species during and in advance of an ensuing dry season (Graham et al. 2003. PNAS 100:572.) We have suggested that this greening response is the result of programming for two leaf types – a dry season and a wet season phenotype, each provisioned for photosynthesis under sunny and cloudy conditions, respectively. Our studies have shown that cloud cover limits the productivity of tropical rainforest during the rainy season, and it seems reasonable that carbon fixed during the early to mid dry season represents a substantial portion, possibly the majority, of annual carbon uptake. Optimal allocation of resources should result in the production of leaves with higher photosynthetic capacity for use during the dry season, and this is what we have found in trees and understory shrubs. Perhaps I am coming in on this discussion a little late, but it seems plausible that the greening you have observed is a community-level manifestation of programming for the dry-season leaf phenotype. This programming could result from either natural selection or developmental canalization, or both. This response would have limited meaning in the context of resistance to drought. Simply put, the greening may be unrelated to drought resistance, but is instead a response to maximize photosynthesis under clear skies.
Comment by Stephen Mulkey — 22 Mar 2010 @ 12:15 AM
It’s great that we are starting to see some real science debate on this site. A paper is publicised that raises some questions, then authors of the paper they were responding to rebut the paper. It’s all very well to insist that all of this should go through peer review but if the other side (a) doesn’t care if something could pass peer review or (b) that a flawed paper can get through the filter, you are in a losing position if you insist on playing the old way.
What I would very much like to see is a break away from the old model of publishing where a paper only sees the light of day after review and editorial corrections, at which point more flaws could be exposed but the fact that the paper is deemed published gives it a gravitas that is hard to shake especially if you insist that “peer reviewed” is a minimum standard.
In an electronic publishing era where versions don’t have to be frozen, as long as you have a way of citing the version you used as an authority, it should be possible for a paper to go through phases of draft for comment, formal review, revision and new revisions if fixable errors are discovered. Strangely enough this is not a new idea: network standards for example follow much this path.
I know that the period is far to short to really make any judgements, but I found the behavior around 2005 as interesting as 2005 itself. In particular, there are questions (in my mind) about when you might see more impact from a drought, in the same your or the subsequent year or two. There’s also a hint that the ongoing rain deficits, building on 2005, are causing problems down the road, as the green area drops below 2000-2003 levels, while the area brown increases. I suppose measurements aren’t available before 2000? Sorry, I don’t have easy access to your paper, so if this info is already there, forgive me for asking.
I’d also offer an alternative answer to the “green up” that would be interesting to consider. Not being a biologist, take this with a grain of salt and all that, but… when resources are depleted, I can think of three mitigation strategies; migration, hibernation, and competition.
Migration obviously means leave the area. On the surface, plants can’t do this. In actuality, however, as a species they can by producing more seeds that spread. I swear that the evil pine tree (pine cone city) and nasty oak trees (the litterbugs of the tree world, dropping volumes of leaves, branches and acorns) in my yard respond exactly this way after dry years. I’m definitely wasting more time cleaning up the mess after hot, dry summers.
My thought on migration would be that, to support the plant’s efforts to produce more seeds, the tree also greens up (more photosynthesis). The idea is basically “make kids before I die, so that if things get better, the children can carry on, and possibly farther from this spot, which doesn’t look so great right now.”
The second strategy, hibernation, would involve browning (less greening) in an effort to conserve resources and wait it out. This is what people seem to expect to happen.
The third strategy, competition, would involve trying to get as much of the diminishing resource for oneself as one can, right away, thus depriving competitors, driving them “out of business,” and so having less competition next year, which will be good whether the drought ends or not, but is best if the drought continues… less competition means “more for me.”
Of course, the problem with strategies one and three is that if the drought continues, the surviving trees are in trouble, having depleted a resource that does not replenish as needed. If this is the case, you’d see extreme browning and less greening in subsequent years, when the flaws in the strategies are exposed.
Has anyone performed a similar study, using the same technology, on other regions (rain forests, temperate forests, grasslands) to compare responses to varying precipitation conditions? It would be interesting to see and compare how a variety of environments react in terms of “greening/browning” to a variety of conditions (consistent rainfall, single drought, etc.).
Data filtering & Methodology
• Pixel reliability is based on a decision tree that uses the following information (Didan & Huete, 2005, White paper ‐ MODIS C5 planning)
– Pixel QA
– The VI values
– Viewing geometry
• Generates data reliability classes
– Ideal (No issues)
– Good data
– Marginal data
– No Data
I do repeat, there are far more papers and presentations online pulling information out of what I think is this same set of information than we’ve talked about, with overlapping authors — it’s not ‘camp A’ vs. ‘camp B’ and, like much of the climatology talked about at RC over the years, people contending on one issue may be coauthors on other issues.
Using a single year’s remote sensing data to draw conclusions about the forest ecology of a massive area with very different forest types and large regional and annual differences in rainfall is not science.
[Response: That's not what they did and wouldn't disqualify it as science if they had. Read the papers--Jim]
The authors of these studies have about as much a chance of drawing a correct conclusion as they would hitting a single cowbird with a stone flung at a flock of a million grackles.
[Response: Never trust anyone that says this or that study, published in a scientific journal, 'is not science.' I have colleagues that do this too; it's a petty put-down, and it's point-scoring, but its not an argument.--eric]
I think there is a major factor here that is being ignored: do these different authors even use the same definition of “the Amazon” i.e. regional area?
A guy at Discovery News has been writing some good commentary on climate issues:
Regional Rainfall in a Warming World
Analysis by John D. Cox
Fri Mar 5, 2010 05:15 PM ET
Slowly but surely, a picture of climate change at the regional scale — where it really matters — is beginning to take shape.
Drought is indeed linked to precipitation changes, so you would think, rather than relying on a single source of data, the authors would have done the usual thing, looked at multiple types of data, not just satellite models. Since they didn’t do this essential ground-truthing, which would involve a lot of fieldwork all across the Amazon in fairly difficult conditions, this work is mostly schlock, on either side. Most people know you have to do satellite analysis of photosynthetic production very carefully to get anything like a reliable answer – “color green” alone doesn’t do it.
Furthermore, the short time period makes it even less likely that the study is applicable to climate change – RC authors know that year to year variability in temperatures is no indication of climate trends; neither is year-to-year variability in carbon fixation and respiration.
[Response: Pretty strong words there. First of all, the fact that these two papers use remote sensing methods to evaluate forest conditions is not in itself worthy of criticism. Satellite image analysis is an increasingly vital information source for monitoring the planet, including its vegetation. Other folks, such as Oliver Phillips and Simon Lewis (and others) are working on the ground- and biometrically-based methods of change detection, and still others are immersed in the flux tower and micro-meteorological work. Like the parable of the blind man and the elephant, each group is looking at a part of the whole picture, and reporting what they find with their approaches. Synthesizing a common understanding from the various, and sometimes contradictory data, that emerges, then follows, in the normal process of science. As for year to year variation, there is no one inherent temporal scale deserving all the attention at the expense of others--all are worthy of study.--Jim]
In other news, the British government has appointed a former Shell executive to head their “climate email science panel” – and this is another one of those who promote the fraudulent carbon capture schemes so heavily:
Ron Oxburgh trained as a geologist and has worked in academia, the civil service and in business. He has been chief scientific adviser to the Ministry of Defence (MoD) and was non-executive chairman of Shell Transport and Trading until the Company merged with Royal Dutch Petroleum to form Royal Dutch Shell in 2005. He is currently president of the Carbon Capture and Storage Association and chairman of wind energy firm Falck Renewables.
CCS boosters are appointed to investigate climate scientists for fraud over stolen emails related to tree ring data sets…
Will the also appoint a chemical engineering group to investigate CCS boosters for fraudulent scientific claims, which is a whole lot easier to demonstrate? Somehow, I doubt it.
After all, CCS is the #1 greenwashing propaganda line in the fossil fuel lobby’s arsenal – so why does RC boost it as well?
[Response: Do we? I certainly don't! Most of us at RC are pretty skeptical about these sorts of 'solutions'.--eric]
[Response: Baloney--I've seen no one here proposing that, and I've explicitly commented that I'm against it in relation to other C mgt strategies.--Jim]
Still hoping for an explanation on why 67% of the pixels are invalid.
[Response: Because the EVI data had to fall within areas defined as qualifying as both drought affected and undisturbed forest. Perhaps there were cloud and cloud shadow effects as well.--Jim]
Another question would be of the remaining 33%, unless the pixels are very carefully selected, how can the vaild pixels be a representation of the whole area? Perhaps it may be a good sample for parts of the Amazon, but are you telling us random chance gave a representive sample for the entire Amazon? Somone with a statistics background may wish to leap in at this point but I don’t see how the sample can be valid without knowing how the invaild/valid pixels are distributed, or that the data means anything at all. Soory to be a wet blanket but will be happy to educated.
[Response: The probability of sampling one third of your analysis area with imagery and getting a strong bias wrt to vegetation response to env. drivers is very low.--Jim]
Hmmmm, backtracking from the link I posted above, I find this pair of papers has been on an agenda. I wonder if there’s also a poster/PDF for Myneni in the same file somewhere? (Google searches happen on this kind of thing)
[Never trust anyone that says this or that study, published in a scientific journal, 'is not science.' I have colleagues that do this too; it's a petty put-down...not an argument.-eric]
Agreed – just say their timescale isn’t applicable to their conclusions, so it’s a bit schlocky.
[Response: To who's? Second time you've said this now. Saleska et al were studying the effect of severe drought in one year, using imagery and precip. station data. Their time scale is what it is.--Jim]
However, the study may still be useful if their datasets are of high quality, right? Often, science is really more about getting the data and/or material samples. The ice core archives produced by Lonnie Thompson’s expeditions to high altitudes & the many Vostok and Greenland cores – well, they have to write that up, submit grants for more research funding, but that’s almost incidental to the data collection effort. Notice here that data collection alone – without analysis – is also “not science”, but it’s a critical component. The same goes for satellite data. One good rule is never trust conclusions about complex systems like the Amazon based on a single type of data.
[Response: Nobody is, as I discussed in your previous comment. And the satellite data is extremely high quality data.--Jim]
This is also very true of any kind of paleoclimate reconstruction. The underlying problem? Well, one likely explanation why there’s only one dataset is that the others didn’t agree with the author’s bias/agenda/previously published work, etc.
[Response: Or maybe that they can't launch their own Terra/Aqua/Landsat with ETM or MODIS??--Jim]
Don’t fall into that trap – apparently, the entire “climategate inquiry” (run by Shell) rests on the tree ring dataset, which was truncated early as it deviated from the warming trend later on. It would have been far better to include all the data – then you could speculate as to why. Was there a CO2 fertilization effect? What tree species were you looking at? etc. If you brush the dirt under the rug, someone will come across it sooner or later.
The underlying issue, climate change forced by changes in atmospheric composition -> radiative forcing -> convective feedbacks -> cryosphere/ocean/precipitaion -> biosphere/agriculture feedbacks, is completely unaffected by the political wrangling and propaganda warfare, however.
I accidentally left out the precipitation projections – take a look – the lowland Amazon has the largest projected drop in rainfall, but the higland area indicates increased precipitation.
Here’s the reference for that figure:
Zheng et al. (2010) Indian Ocean Dipole Response to Global Warming: Analysis of Ocean–Atmospheric Feedbacks in a Coupled Model
Low-frequency modulation and change under global warming of the Indian Ocean dipole (IOD) mode are investigated with a pair of multicentury integrations of a coupled ocean–atmosphere general circulation model: one under constant climate forcing and one forced by increasing greenhouse gas concentrations.
In the unforced simulation, there is significant decadal and multidecadal modulation of the IOD variance. The mean thermocline depth in the eastern equatorial Indian Ocean (EEIO) is important for the slow modulation, skewness, and ENSO correlation of the IOD. With a shoaling (deepening) of the EEIO thermocline, the thermocline feedback strengthens, and this leads to an increase in IOD variance, a reduction of the negative skewness of the IOD, and a weakening of the IOD–ENSO correlation.
As the oceans warm, it seems the thermocline will deepen in the tropics.
In response to increasing greenhouse gases, a weakening of the Walker circulation leads to easterly wind anomalies in the equatorial Indian Ocean; the oceanic response to weakened circulation is a thermocline shoaling in the EEIO. Under greenhouse forcing, the thermocline feedback intensifies, but surprisingly IOD variance does not. The zonal wind anomalies associated with IOD are found to weaken, likely due to increased static stability of the troposphere from global warming. Linear model experiments confirm this stability effect to reduce circulation response to a sea surface temperature dipole. The opposing changes in thermocline and atmospheric feedbacks result in little change in IOD variance, but the shoaling thermocline weakens IOD skewness.
SO, even though the thermocline deepens, there are compensatory atmospheric feedbacks that even that out.
Little change under global warming in IOD variance in the model suggests that the apparent intensification of IOD activity during recent decades is likely part of natural, chaotic modulation of the ocean–atmosphere system or the response to nongreenhouse gas radiative changes
What this seems to mean is that as warming progresses, the frequency & amplitude of ENSO and other cycles will not undergo some kind of ‘tipping point’ bifurcation into a completely new mode, which is actually fairly good news. This also adds a bit more certainty to (precipitation-evaporation) projections for the tropics, subtropics, and mid latitude regions (wet-dry-wet, in the simplest take).
I think we’re seeing tip-of-the-iceberg still and that there are a whole lot of papers and presentations, public and private.
I think the real issue being discussed is the satellite imagery, how well it can be used, and whether it can eventually replace fieldwork on the ground.
So I think we’re seeing a little bit of what nonscientists often don’t see at all — typical scientific hard argument with much back-and-forth, and we’re seeing more of it than usual because, well, the world has changed and people can look stuff up.
And I’ll further speculate that someone lacking sufficient perspective on how back-and-forth happens over time as scientists work, possibly a new grad student, was (ahem) framing this in terms of “war” or “team sport” rather than being aware that over time what we have is usually “shifting alliances of fiercely individualistic scientists.”
I’d bet some such confused soul mistook the most recent paper for a heart’s desire final nail in the IPCC’s coffin, got in a position to draft the press release, blew that badly including the misquote that’s been silently disappeared from BU’s press release, and _maybe_ also hyped the original to Hannity and maybe others we don’t yet know about (tho’ the gmail address reeks of misdirection to me).
Whew. Okay, that’s all wild speculation on my part, no cite for any of it.
I have tried to make a summary of what I have been reading in the threads “Up is down, brown is green” (including the guest commentary from S. Lewis) and “Saleska responds”:
Recently, three articles have been published on the effect of short-term extreme drought (in 2005) on the Amazon forests. The conclusions from these articles appear to be rather contradictory, to say the least. Phillips et al (Science 2007) claimed a massive tree mortality that would temporary change the forest from a CO2 sink (2 billion tonnes absorbed yearly) to a CO2 source (3 billion tonnes released). Saleska et al. (Science 2007), however, found a large-scale green-up and concluded: “Coupled climate-carbon cycle models suggest that Amazon forests are vulnerable to both long- and short-term droughts, but satellite observations showed a large-scale photosynthetic green-up in intact evergreen forests of the Amazon in response to a short, intense drought in 2005. These findings suggest that Amazon forests, although threatened by human-caused deforestation and fire and possibly by more severe long-term droughts, may be more resilient to climate changes than ecosystem models assume.” And recently Samanta et al. (GRL, 2010) disagreed with Saleska’s conclusion because they found “no evidence of large-scale greening of intact Amazon forests during the 2005 drought” and they added that the changes that they found “are also not unique – approximately similar changes are observed in non-drought years as well.” In other words, nothing much had been changing.
To make things even more complicated, Saleska now comments that in his view the results from Samanta are NOT different from his own earlier conclusions on the increased greenness in 2005. But regardless of whether there was an increase in greenness or no change at all, it seems to me that in both cases this is very difficult to reconcile with the claim made by Phillips et al. about massive tree mortality and strongly decreased CO2 consumption
It is therefore hard enough to bring together the conclusions of these three publications. But Simon Lewis wants us even to believe with respect to all three articles that “Overall the conclusions in the IPCC 2007 Fourth Assessment Report are strengthened”. Apart from the fact that the IPCC report was dealing with possible effects of LONG-TERM droughts, how can an increased greenness support a projection of strong deterioration ??
[Response: Couple of points. First, you are looking at the normal process of earth/ecological science--different research groups approaching complex, large scale phenomena with different data, tools, approaches and specific questions. Sometimes the results are disparate and thus require either more evaluation or new explanations. Read Stephen Mulkey's post #31 here, and also the work of Nepstad and others that forms the basis of the IPCC AR4 statements, and also the recent statement made by Nepstad and others regarding this whole topic, the link to which now escapes me.--Jim]
Orwell would probably have used the following Newspeak line: Brown or Green, the IPCC is always right!
Ok, my comment was trash, I admit that. Definitely not the first time I’ve gobbed up a blog post and probably not the last.
Here is my criticism of the work. I read the Saleska paper when it was first published, so it’s been a while:
The paper proposes an effect based on a single occurrence of drought. This is problematic because vegetation response to rainfall differs dependent upon actual soil moisture conditions which are not always cleanly predicted by rainfall amount.
[Response: Saleska et al. discuss this, with reference to a site where the seasonal course of the soil water potential at depth was monitored in relation to the seasonal precipitation.--Jim]
They are further complicated by the effect of temperature, prior moisture conditions, and prior seasonal growth conditions (overall plant condition going into the drought) on the observed plant response. In other words, there is a lot of natural variability to take into account and drawing conclusions with such a short data set is may provide an answer totally at odds with reality.
[Response: The only conclusions they are really drawing is that there is an apparently enhanced chlorophyll ("green-ness") signal associated with a drought event, which is counter-intuitive.--Jim]
I see a lot of criticism from climate scientists to those who would make future predictions based on short temperature, rainfall, etc. records due to natural variability. The same standard should have been applied to this paper.
The authors propose some mechanisms for the effect based on the site’s characteristics. These do not include an ecological mechanism, yet the conclusions suppose to report an ecological response of the forest to drought.
What would I have done differently?
I’d have included more data or at least more supporting ground information that related the remotely sensed data to observed plant growth responses so that a cause and effect was elucidated (ie. what caused the green-up observed – vine growth, more leaves, more chlorophyll, what?). I’d have included more background information regarding the targeted forest community types and what was known about climate constraints on plant growth, survival and reproduction.
[Response: People need to understand that these are big, complex topics and no one group or person can do more than a part of what's required for a coherent picture to emerge. This is hard work--Jim]
I very much appreciate this guest post which provides a viewpoint from an ecologist, but I don’t think his conclusions or criticisms of the papers are being addressed in the comments or replies to comments.
Maybe it an overzealous grad student was involved – for instance, that appears to explain the Marengo quote which was a surprise to everyone, including Marengo.
But none of the authors have done anything to correct misimpressions. In particular, senior author Myneni apparently told the National Post’s Terence Corcoran that the IPCC Amazon statement was “alarmist”, and hasn’t bothered to correct any of Corcoran’s other misinterpretations as far as I know.
So your explanation may be valid in part, but appears incomplete.
I feel like i am missing something with respect to the claims that the new paper by Samanta et al contradicts IPCC claims about the vulnerability of the Amazon to drought. In fact, it would seem to me that their results are *more* supportive of the IPCC report statement that the Amazon may be highly sensitive to drought.
Saleska et al (207) were the ones whose results hinted that the forest could be more resilient to extreme (if short-lived) drying than many ecosystem models suggested. IF anyone’s results were to be used to wag fingers at the IPCC, it seems like it should have been theirs. If Samanta et al’s results show that the forest did not green up during the 2005 drought, then their results tip the balance back toward the Amazon being very sensitive to rainfall and, as the IPCC report indicated, prone to conversion to savanna in a warmer, drier tropics. I really don’t understand why they (or their press department) think that their results undermine the IPCC statements.
The other question I have (perhaps RC could solicit a post from the Samanta, et al authors?) is, if they believe the Amazon didn’t green up during the 2005 drought, do they have similar uncertainties about the seasonal patterns of enhanced greenness that were described in the even earlier paper (Huete, A.R., Didan, K., Shimabukuro, Y.E., Ratana, P., Saleska, S. R., Hutyra, L.R., Yang, W., Nemani, R.R., and Myneni, R.(2006) Amazon rainforests green-up with sunlight in dry season. Geophysical Research Letters, 33, L06405, doi:10.1029/2005GL025583)?
Some of the authors who are now disagreeing about the impact of the 2005 drought were co-authors on the seasonal cycle study, which seems to be based on the same/similar data. How does the current disagreement affect the interpretations of that paper?
[Response: I had the same initial response as you. It's all pretty confusing frankly.--Jim]
“These findings suggest that Amazon forests, although threatened by human-caused deforestation and fire and possibly by more severe long-term droughts, may be more resilient to climate changes than ecosystem models assume.”
This statement directly conflicts with Dr. Lewis’ findings and those of the scientists who recently signed a statement disagreeing with reporting that the IPCC was flawed (i.e. Amazongate). Doesn’t it? Or am I missing something (totally possible – not a rhetorical question)?
The study uses green up as an indicator of health. I believe that it may supply data that backs up the hypothesis that the forest is sensitive to variations in rainfall. But I don’t believe the observed sensitivity indicates the forest is or isn’t resilient against changes in species composition (forest health) caused by climate change.
[Response: It's not attempting to do that (certainly not addressing compositional changes, which at any rate do not equate to "forest health"). It's simply describing green-ness with respect to drought--throwing some observations out there if you will.--Jim]
For example, the rainfall deficits continue past 2005 and the amount of greening steadily drops in response. What is going on here? I can’t tell without a lot more data, but it doesn’t seem like a simple relationship.
I have experience conducting vegetation studies in seasonal, deciduous swamps (subtropical). These areas respond very differently to changes in rainfall, often in complex ways. For example, if we have a dry winter and the swamp dries down early, leaf flush occurs earlier as leaf growth is positively affected by the lack of soil anoxia. If we get enough rain to keep the soil moist during the summer and fall, then the swamp will stay green (I have no idea what the leaf color signature MODIS would see, but I assume at least green for longer). But is this good for the swamp forest? If moist but less inundation persisted, the forest would obviously change to become dominated by a drier plant community as these exist just slightly uplope of the swamp. A very fine gradient from swamp to dry forest is observed and is driven by average inundation period (soil conditions change little in permeability and moisture retention and are probably not a factor).
Your example is exactly why the ground-based demography work of Phillips and others, in relation to climatic monitoring, is critical. Neither of the remote sensing papers are attempting to address these longer term questions you discuss.--Jim]
Also rainfall wouldn’t be the best climactic factor to use to correlate forest change with, rather duration and intensity of soil anoxia and moisture deficit are.
[Response: I already mentioned that Saleska et al provide evidence of the relationship between gauge data and soil water (and satellite data)--in their supplemental naterial, which should be available.--Jim]
In drier climates just to the south, such swamp forests don’t exist. In these areas similar landforms (large depressions with impermeable soils that are inundated by rainfall) contain marshes with shrubs instead of forest as the extreme swings between long inundation during wet periods and multi-year dry periods (which don’t occur to the north in the swamp forests) preclude tree growth.
At least where I work I can make a prediction that less annual rainfall or longer drought periods will equal less swamp forest. I would question anyone using remotely sensed greeness data to say otherwise regardless of whether it was publised in Science.
[Response: Again, they're not addressing long term type conversion.--Jim]
Ecology is the dominant journal in my field. Tropical Ecology is another. Science – not so much.
Comment from Jim (#44)”.. you are looking at the normal process of earth/ecological science–different research groups approaching complex, large scale phenomena with different data, tools, approaches and specific questions. Sometimes the results are disparate and thus require either more evaluation or new explanations.” I agree completely, but if the results are completely contradictory then it is not easily understood that they are assumed to fit in one pattern, and together would support the IPCC projection. Green IS green, and is not the same as dead trees.
[Response: I agree--that's why the public statement linked to in the post discusses the primacy of ground-based demographic census data in relation to the effects of drought on tree mortality.--Jim]
> using remotely sensed greenness
Not only remote data, they also report field results that matched it.
Here’s another verision of the recent press release (basically same text as the first version, not the current version now at the BU press site):
(hat tip to Eli, who said these easter eggs were out there to find)
This one includes this comment about the Editors of Science:
“We actually submitted our evidence to the Editors at Science, but they decided not to seek peer-review, perhaps afraid of a controversy given all the hoopla surrounding IPCC” said Ranga Myneni, the senior author from Boston University.
I am puzzled by the amount of commentary on a single paper, well, pair of papers. It seems to me reminiscent of the media hype about some single fossil discovery which “proves Darwin wrong” or “completely rewrites the theory of evolution”.
Surely what is going on here is that studies are looking at whether you can use satellite imagery to analyse what is going on in forests as climate changes. Obviously if you can this will produce a lot more data than could be generated by lonely ecologists trudging around the Amazon measuring individual trees. But in order to use satellite imagery there has to be a correlation between climate/ecology interaction and what can be seen from space. There will obviously need to be a lot of satellite imagery, covering a range of different climatic events and forest types, and a lot of ground proofing to refine the correlation (if there is one). Surely the papers being discussed here are just a couple of early examples of the process, and have little if any direct information to offer on climate change in themselves?
[Response: Not a couple of the "early" ones. The relationship between directly sensed and remotely sensed data in ecological and earth system science is a very active research area with a nearly 40 year history dating to LANDSAT 1. The integration of biometrical, meteorological and remotely sensed information is absolutely crucial to the development of a mechanistic understanding of global change, and will only grow with time. An outstanding example of this integration is the North American Carbon Program.--Jim. correction--actually dating to much earlier than this if one includes aerial imagery--jb]
> David Horton
> surely …. Surely … little if any direct information ….
It’s not so much the paper, it’s the at least four different versions of the press release (old at EurekAlert; revised at BU; variations at Hannity and PRLog, all linked and noted above).
We’ve turned up _lots_ of papers on the subject using this same data set, by many of the same authors, in various combinations. This last one stands out to nonscientist readers I think because the PR done for it seems so out of line.
David Horton is “puzzled by the amount of commentary on a single paper, well, pair of papers”.
But there’s nothing puzzling about it at all. Any paper issued with a press release that viciously attacks the IPCC is going to get a lot of right-wing media coverage, especially if the authors are available to support that message.
Well, colour me puzzled. I know satellite imagery per se has been used a long time in ecology. I thought we were into some brave new world method of analysing leaf colour or such like. What is the actual question here? It can’t just be whether forests get more green during a year of drought can it? I mean, that would be just silly, wouldn’t it? And it certainly can’t be that one forest got more green (apparently) during one year of one drought in one place therefore global warming isn’t going to be a problem for the Amazon forests can it? That would be really silly.
Ike’s ire is fully warranted: While the Samanta et al paper and research is science, the sweeping, unsubstantiated claims in the press release and Myneni’s hobnobbing with the conspiratorial radical right is anything but. I can think of no more egregious example of inappropriate politicization of science. Myneni makes Greenpeace appear downright objective in comparison.
It can’t just be whether forests get more green during a year of drought can it?
Why not? The obvious conjecture that the forest would brown turned out to be not only false, but reversed, because it greened. At a minimum, the experiment would have somewhat validated the use of satellite imagery as a tool to quickly, quantitatively measure drought effects, and instead it presents an unexpected new thing to study. It’s Science at it’s very best, where the Unexpected begs for further Investigation.
I previously (post #34) offered three scenarios as purposeful strategies for plants against drought (migration, hibernation, competition), of which the first and last might cause extra greening, but I’ll offer an idea for another explanation:
Drought stress kills off the older, weaker trees, which gives more room in the overstory and canopy for the younger, healthier trees, and also leaves them more of the scarce water to work with. These young, healthy trees are better at producing foliage even in a drought than the older trees were in a good year, so the drought (like natural forest fires) has just helped things along by finishing off the weaker competition. Their extra greening quickly covers the browning of the dying trees, as well as areas where the dead trees were already sparse. This process also lets slightly more mature, taller trees crowd out and shade shorter ones, which under the stress of the drought also die. As such, tree mortality is up but so is greening. So one drought every once in a while could be a good thing for a forest, by culling the herd.
FYI, this happens in the tiny forest beside my yard every year, as the oaks battle each other to see who can get taller first, while their older, lower branches die and drop off to litter my yard, and every year or two another short, loser tree just gives up and dies.
The point being… looking at the satellite imagery and color is a perfectly logical, simple experiment to perform. It was never meant to answer the ultimate question to life, the universe, and everything. It was just meant to confirm the conjecture that forests would brown in a drought and that satellites could detect this. Nothing more, nothing less, and as often happens, the answer didn’t match the hypothesis, which is exactly why experiments must actually be performed.
The only mistake here involves any scientist that chose to over reach with his conclusions, and to needlessly politicize a single, useful experiment in an already volatile environment.
[Response: Do we? I certainly don't! Most of us at RC are pretty skeptical about these sorts of 'solutions'.--eric]
[Response: Baloney--I've seen no one here proposing that, and I've explicitly commented that I'm against it in relation to other C mgt strategies.--Jim]
Ah, I think you need to sit down with Gavin’s book, my friends, which has several chapters explicitly boosting ludicrous CCS strategies. It’s called “climate change: picturing the science” – by Gavin Schmidt, Joshua Wolfe, Jeffrey D. Sachs. If that’s not explicit promotion of CCS, what is?
Why doesn’t RC resolve this issue and publish a post reviewing the technical issues involved in CCS? You did something similar with solar energy issues, correct?
[Response: Oh please. Now merely mentioning CCS is 'explicit promotion'? How about you quote me 'explicitly promoting' anything of the sort? If you'd rather just pretend the concept or technology doesn't exist, go ahead. - gavin]
> Drought stress kills off the older, weaker trees, which gives more
> room in the overstory and canopy for the younger, healthier trees
Depends on your specific situation. One of my hobbies is a forest fire restoration site that gets almost all its water as snowfall. Drought there hits the shallow-rooted younger trees while the older trees with deeper roots will survive a few dry years much better.
One of the papers you’re talking about mentions the lag time at their study site between precipitation and changes in groundwater as about a month, I recall.
Agreed, and I’m speaking from relative ignorance, but recognizing that a rain forest is very, very different from a temperate forest. Mostly, I’m just offering a possible scenario that would account for both increased tree mortality and increased greening. I do remember reading that roots in rain forests aren’t that deep, however, because they don’t need to be, and that’s one reason that rain forests are very susceptible to flipping to savanna.
It will be interesting to see, in future years, when they combine a study of more specific ground observations tied to corresponding satellite observations. I wonder if the data for that exists now (i.e. measured tree mortality rate vs. moisture level vs. greening rate for a set of pixels) so that someone just has to do the collating and thinking, or if a study needs to be designed from the ground up (so to speak).
I could also see looking at it from another perspective and comparing greening with “bluing” (i.e. “blue sky” measurements from the ground up over time). Each week, use a camera or light sensor to take pictures from the same spots, straight up, to determine the amount of blue sky visible (versus bright green, i.e. leaves with strong light passing through vs. dark green leaves which are shielded by higher leaves). I could also see this being done with cameras established above the canopy looking up into the overstory.
In a perfect world, I could even see a remote controlled or robot helicopter designed to cover a very wide area taking such measurements (predator drone and shopping mall toy RC helicopter technology put to good use).
Oh, well… it’s all just amateur musings. I do think there’s merit in the further pursuit of their “greening/browning” evaluation strategy, however. It doesn’t seem “silly” at all to me.
I response to my remark (#44): “Orwell would probably have used the following Newspeak line: Brown or Green, the IPCC is always right!”, Barton Paul Levenson wrote: “No, he wouldn’t. Orwell was very concerned with telling the truth.”
So I suppose he would have written: Brown or Green, the IPCC is always wrong ?!
[Response: The probability of sampling one third of your analysis area with imagery and getting a strong bias wrt to vegetation response to env. drivers is very low.--Jim]
Um, not trying to pick a fight or anything but this isn’t right, or at least it doesn’t apply to the case at hand. The 33/35% of valid pixels aren’t just a random sample. (Or at least, that’s not my understanding of what “valid pixels” means.) The key question is: is this 32% a *representative* sample of the total area? Is there some possible reason that, say, areas that react strongly to drought conditions might be less (or more) likely to turn out valid pixels (say by being situated on flat ground etc.)? This seems to me to be a fairly important question – apologies if it has already been dealt with in the comments.
[Response: I hope Scott responds, but my reading of it is that the 33.7% of the area with valid pixels in 2005 represents those locations that both fell within the drought-defined area and also were considered to be "intact" forest. 32% of that area (=10.8% of the total area) showed EVI-based greening. Some other (unstated) % of the entire area was also intact forest but did not fall within the drought-defined area, which was defined with relation to precipitation alone, not topography, vegetation condition etc. I see no evidence or reason to expect that this latter area would have a different % of it's pixels showing greening--but it seems this could be easily checked by the authors.--Jim.
p.s.--correction, that last clause is wrong. Such a check wouldn't address what we are discussing--any check would have to involve an analysis of the hydrological or vegetation characteristics of that area in relation to the drought affected area.]
> what “valid pixels” means
This information is available; try some of the links posted earlier.
There are a _lot_ of discussions and papers on this data set with much effort put into distinguishing pixels covering original forest, from those showing smoke, clouds, agriculture, etc. or those taken at too great an angle rather than from closer to straight down. They put a lot of work into explaining this, and different studies do it differently trying to get better information.
It also shows effects on the Amazon region, though it looks to be more of a macro-study than the topic here.
Comment by Lynn Vincentnathan — 24 Mar 2010 @ 10:45 AM
#33 (OT but that comment needs a reply)
Brian Cox (and spouse?) on the atmosphere. Super photography,very interesting on Titan, some good teaching, but …..
The narrative missed yet another opportunity for the BBC to explain the CO2 mechanism properly. He ran at least three themes simultaneosly, the role of gravity in retaining (or not) the atmospheres of the planets, the roles of the atmosphere in protecting the surface from meteors and in creating the greenhouse (gh) effect.
For the gh effect he started by going to a desert in Mamibia where the temperature falls by about 30K after dark. This was attributed to the lack of water vapour; this is fair enough. His next example was Mercury which has no atmosphere at all and has a much bigger diurnal effect. Did he ask whether this might be caused by the fact that it had neither water vapour nor CO2.?. No. Perhaps that would have been too advanced (our Moon might have been simpler) Instead he switched abruptly to the other two themes mentioned above. Later he quoted the well known (rough) result that the globe would be about 30K colder without an atmosphere. The same 30 K as for the desert. The alert beginner might recognise this quantity from the earlier discussion and deduce that water vapour is the only gh gas that matters. (Sounds familar?)
To be fair he did assert that CO2 was another gh gas and that it was helping to warm Venus. But he never mentioned that much of the water vapour would condense or turn into ice without the CO2. So this version would not upset most contrarians like Lindzen, perhaps not his wife either, who comes to this ‘balanced’ if vague conclusion:
I can’t say for sure that it has anything to do with burning fossil fuels, but I strongly lean towards thinking that it does. That’s merely a ‘gut feeling’ though. There’s been fairly convincing research that states that we don’t have that much of an effect, but it’s best to err on the side of caution… so, you know, just boil enough water in your kettle
[I don't oppose everything in her article, but I draw the line when it comes to adding a link to Patrick Moore from the Great Global Swindle who uses his early association with Greenpeace to act as an extreme lobbyist for almost every anti-environmentalist campaign going.]
I remember some 40 years ago going to Seattle from California for a summer course, and being stunned by how lush and green it was. There didn’t seem to be much rain, and the summer was very sunny until very late in the day/early in the evening. (So why is Calif brown and this place green, I wondered). So I said to a resident, “There must be a lot of rain here during the winter,” and the person responded in the extreme affirmative. Later I learned that the Pacific NW Coast is a temperate rainforest area.
[Response: It has much more to do with the intensity of the summer drought and the vegetation types in the two places, than the winter precip, which can be enormous in parts of CA as well as WA (e.g. the winter snowfall record was in the central Sierra for many years before broken on Mt Baker (WA) ~10 yrs ago).--Jim]
So I can believe that there could be a greening during a higher drought summer in a tropical rainforest.
I’m also thinking that droughtish summers are going to “stress” the roots by forcing them to go deeper (a slow process over many years) — and such droughtish conditions would select for trees and plants with deeper roots. Maybe plant “stress” might be like animal exercise — and no pain, no gain.
There was an anthropological study that showed minor stress/pain on babies and children (such as bathing them in water a bit too hot for them, or other stresses/pain) makes them grow taller. Very counter intuitive. I know people are different from trees, but maybe some similar principles are at work.
Comment by Lynn Vincentnathan — 25 Mar 2010 @ 11:13 AM
Lynn Vincentnathan “I remember some 40 years ago going to Seattle from California for a summer course, and being stunned by how lush and green it was. There didn’t seem to be much rain, and the summer was very sunny until very late in the day/early in the evening.”
hahaha – That must have been the same year I moved to the PNW [from AZ], thought I’d died and gone to heaven. It rained every week or so, but only at night for about 4 months that summer, and while it’s still pretty common for summer rain to happen at night, the frequency and intensity seems much less. The change I’ve watched in this area of temperate rain forest is the western red cedars dying while the various species of fir carry on – the cedars require a more consistent high level of soil moisture and summers are getting drier. Not sure the change would be detectable from space with the mix of species, and part of the color effect would be due to increased cone production by some species when drought stressed.
It would seem to me that the Rainforests – and, perhaps, other types of vegetation – are saving water for the dry times; probably in both their own Roots, as well as in the various soil fungi and bacilli around them; and then taking advantage of the increased insolation of the (assumedly cloudless/reduced) drought time to do some real growing.
This would account for the seeming paradox of a ‘Rain’ Forest ‘greening up’ during a ‘drought’, nicely.
It’s not just rain that falls from the sky – not to a Tree.
James Staples (#72), I think you are right, this could nicely explain the paradox. In addition to the increased temperature that goes with the increased insolation, the increase of light intensity is probably at least as important (after all it’s called photosynthesis for a good reason!)
Thanks for the information — I always like to learn more.
Another thing I was thinking is that the harms we are doing to the rainforests and earth in general — to all the myriad of species that live in those habitats — is very very sad. How can we explain to the animals, for instance, what we are doing and why.
We have this standard of “pick on someone your own size [and I would add 'your own intellect'].” I’m not suggesting that we should not use the biota of the world for our own sustanence and well-being, and spiritual uplift (of enjoying the beauty of nature). However, simply destroying it because we have to blow-dry our hair instead of let it dry naturally and a myriad of other frivolous actions, makes it all the sadder. How do we tell the animals as they die and go extinct at our hands? How do we tell the plants?
Comment by Lynn Vincentnathan — 26 Mar 2010 @ 8:55 AM
Pixel-based image analysis is the past, GEOBIA (geographic object-based image analysis) is the future.
[Response: I never said that image analysis had to be pixel based--but I very much agree with your statement as a broad generalization, and am very interested in object-based analysis, particularly w.r.t. image segmentation employing textural information and high spatial resolution (< = 5m) imagery, for structural analyses. R seems to be very lacking in existing methods although SciLab seems promising at first glance. GEOBIA looks interesting--thanks for the info.--Jim]
I must say, am truly impressed with the level of commentary here at RealClimate, there is a real engagement with the issues, including by Robert Simmon of NASA who generously refers Real Climate readers (in comment 51) to a rather nice piece he put together reporting on the work of my collaborator Alfredo Huete and I (http://earthobservatory.nasa.gov/Features/AmazonEVI/amazon_evi.php), and some of our prominent tropical ecologists like Steve Mulkey (comment 31), who cites his group’s important high-profile Graham et al 2003 paper in PNAS about how tropical trees are light-limited during the wet season. Incidentally, 2003 was a good year for advancing our understanding of controls on tropical forest productivity, seeing the publication not only of the just-mentioned Graham et al study, but of Nemani et al in Science (a remote sensing-based modeling study suggesting the Amazon was light llmited) and our previous Saleska et al, also in Science (an observational study that saw unexpected seasonality of CO2 fluxes in an Amazon forest). Of these, I would say the Graham et al was perhaps the most compelling, as it was based on actual experimental manipulation (they installed high-intensity lamps above the forest to augment the incoming radiation).
It would be difficult to address all the questions that have arisen here, so maybe the best thing would be if posted more of the details about this “controversy” (more like a tempest in a teapot) on my website, which I should be able to do in the next few days. In the meantime, let me just quickly say:
1. About “valid” v. “invalid” pixels, asked about by many: this is indeed one of the technical disputes between Samanta et al and Saleska et al. They say you have to throw out 60%, whereas we think you can actually keep a much larger fraction of the drought area (something like 90+%) than they do. There will be more details about this in our response paper, but as I indicated in my original post: it doesn’t make much difference in the results, because whatever you use as a criteria for “valid” pixels, you still see an anomalously green drought region.
2. About Ranga Myneni’s comment that “perhaps” Science didn’t publish their critique because Science was afraid of a controversy” about the IPCC (comment 52). We need not speculate about Science’s motives, because they told Ranga and me why they declined to publish his comment critical of our work. In the words of the Associate Editor who handled it: “the arguments presented in the comment, which were well addressed in [the Saleska et al] response, in the end did not pose a sufficiently robust challenge to the main conclusions of the original report.”
3. About what is perhaps the crux of the issue, highlighted in a colloquy (comment 49) between commenter Andy and RealClimate contributor Jim, where Andy quotes are 207 Science paper conclusions: “These findings suggest that Amazon forests, although threatened by human-caused deforestation and fire and possibly by more severe long-term droughts, may be more resilient to climate changes than ecosystem models assume.” The context to this conclusion is the Hadley Center model in particular, which has been used to make both short-term and long-term predictions, and made famous the now widely-replicated prediction of Amazon-forest die-off under climate change. The motivation and purpose of our 2007 Science paper was to test the short-term prediction of prompt slow-down in forest photosynthesis following drought. Our observations tended to falsify that short-term prediction (at least if you accept that satellite EVI correlates with photosynthesis, for which I think there is pretty good evidence).
Our observations implied to me that forests were more resilient than the model assumed, at least in the short term. But what does that imply about the long-term prediction? That’s a more complicated question. In the model world, the same mechanism (strong water limitation of forest productivity) is implicated in *both* the short-term prediction of photosynthetic slow-down and long-term die-off. In the model world, greater short-term resiliency also implied greater long-term resiliency. But it could be that in the real world (as opposed to the model world) that forests are more resilient in the short term but still vulnerable in the longer-term. In fact, I think the accumulating evidence from observations and experiments is consistent with this interpretation. Results from forest drying experiments (e.g. Nepstad et al 2007, cited in our Science paper) showed that forests did start to experience big mortality increases following drought – but it took several *years* of drought, not just a few weeks or months as suggested by the models. Likewise, the Phillips et al results discussed by Simon show elevated mortality during a several-year interval – not inconsistent with our observed 3-month green-up. Since several years is still very short compared to long-term climate changes, it seems that the balance of evidence now is that forests are more resilient in the very short-term, but still vulnerable on the timescale of years to decades that is relevant to global climate change.
[Response: Scott, many thanks for your contribution and detailed responses to questions/comments, as well as those by Simon and Steve (and also many good reader comments/questions). Topics like this really help educate everyone on the research process, as well as important results, of highly important investigations--exactly what we want to do here--Jim
p.s. this is not to be taken to mean the discussion is now over!]
“the increase of light intensity is probably at least as important (after all it’s called photosynthesis for a good reason!)”
Not necessarily. Plants have in general evolved to optimize their photosynthetic efficiency at some optimum, not peak, intensity that they experience in their particular ecological niche. I know more about algae and duckweed, not rain forests, which I am interested in for biofuels. Many species of biofuel useful algae saturate the photosynthetic mechanism at about 20-30% full sun. Stirring a raceway so that the algae move vertically in a water column or distributing them vertically in tubes in greenhouses so that they self shade is how 200 tonne dry matter yield per hectare can be achieved. See http://www.ncbi.nlm.nih.gov/pmc/articles/PMC541035/pdf/plntphys00359-0031.pdf for groth curves.
Duckweed has to float on the surface, so it is harder to manage for maximum yield. Frequently companion crops that partially shade the pond surface are grown to productively use otherwise excess photons.
“Bamboo, for example, grows well in a wet environment
and has market value as a structural material. Planted along the
perimeter of a duckweed culture plot, bamboo will diffuse the
wind and filter sunlight during hot, dry weather. When the more
moderate and cloudy monsoon season begins, the bamboo crop
can be thinned to allow more light on the duckweed crop and sold
to increase cash flow.” http://www-wds.worldbank.org/external/default/WDSContentServer/WDSP/IB/1993/03/01/000009265_3970128103342/Rendered/PDF/multi_page.pdf
Brian Dodge (#77), thank you for your interesting remarks. But wouldn’t you agree that when as a result of dying trees holes would form in the canopy this would provide more sunlight to the area below and bring sunlight intensity closer to the optimum for several plants and small trees? In other words some trees may die but overall the greening may remain more or less the same?
“In other words some trees may die but overall the greening may remain more or less the same?”
Sure, especially if the ecosystem is complex, and the changes are small. A shift in rainfall just large enough to kill a few susceptible members of the most sensitive species won’t (by definition) be large enough to disrupt the ecosystem; tolerant organisms will increase their growth in response to the removed competition. An ecosystem evolves to optimize resource utilization in response to both the average conditions and normal variability, just like a species evolves to the conditions in its niche. The ecosystem in my part of NC, where we get about 1 meter of rain per year, but only a 2:1 monthly variation, is very different from places in Northern CA with similar annual rainfall, but very dry summers. The change that I’ve seen in the climate in the 40 years I’ve lived here towards drier summers have shifted the forest balance towards more pines and fewer oaks and magnolias. In the clay soils here pines typically have more robust root systems, so they are more drought tolerant, and More evergreens might give a “greener” yearly average satellite image. There is a very diverse forest in my neck of the woods – 14 species native on my 2 acre lot – which limits the spread of pests like pine borers. In western NC and the sandhills, where there are larger percentages of pines, drought stress plus easy spread of the pine borer has resulted in larger mortalities in pines. In oak dominated woodlands (typically deep unsaturated loamy-sandy soils) drought has increased the effect of “oak decline” from a complex interaction between weather, insects, and fungus. One drought year is going to have a small effect on a robust, complex ecosystem that experiences occasional drought, and may have counterintuitive effects on the chlorophyll measured by satellite. 5 years of drought will have a much larger effect, and if 5 year droughts occur every 20 years instead of every 100 years, the effect will be greater still. If the droughts become severe and frequent enough civilization collapses – google anasazi+hopewell+drought; it’s never just the drought, because the drought doesn’t occur in a vacuum. There are always pine beetles, and fungi, and soil type, and warfare, and dependence on corn, and so on that vary spatially (the realtors are right – location, location, location!). Arguing about which is most important in an attempt to discredit the importance of something you like (burning fossil fuels) is as ridiculous as arguing “which is more important if you get shot in the head, the gunpowder or the lead?”
Brian Dodge (#77), thanks again, it’s a pity that your contributions did not appear earlier during the discussion because in my view your observations make sense. I had underestimated the ability of the ecosystem to adapt, certainly when the drought is short-lasting like in 2005. It suggests to me that none of the articles that try to extrapolate from the 2005 obeservations make much sense in relation to projections of long-term droughts, and the discussion in this thread about increase or decrease (or no change) in photosynthesis in 2005 is largely academic.
The “holes in the canopy” discussion triggered my memory from Ecological Anthropology. Swidden horticulture (also called “shifting,” and in some cases “slash & burn,” with the ash putting nutrients into the soil) is adapted to rainforests because apparently the soil is very poor, and the nutrients are in the plants & canopy. I can’t remember if it’s due to the heavy rain washing out the soil’s nutrients, or lack of decomposition. Anyway, to grow crops in one spot more than 1 or 2 seasons would degrade the soil, and continuous agriculture could turn it into moonscape. At least that’s what I learned.
Well, when tribal peoples practicing swidden plant a crop they cut down the trees in that area so sunlight can come through to let their crops grow (also to clear space). After the harvest, they then move on to another spot, and the rainforest in the original spot then takes from 6 to 25 years to grow back to how it was, after which they can again grow crops there. Also, I’ve seen films on how they plant — they do so without disturbing the soil and leaf litter very much.
The point is, from what I learned, rainforest soil is poor, and if some trees die out, then my guess is that the area there would not thrive for long. When the rains do come the soil would probably get degraded in those areas so that the rainforest there would not easily “pop back” to life. So perhaps (I’m no expert), that type of situation in which increasingly more dire and more frequent droughts (which might happen with global warming) would slowly kill off small stands of trees here & there in the rainforest, causing it to shrink and shrink in total area, and be replaced by savanah or something else less rich in life.
I also understand from someone who lives in the arctic that the soil there is also poor. So the idea that agriculture will just shift north with the onslaught of global warming may not be as rosy a picture as some make it out to be.
Now if you add all the other assaults on the soil and growing conditions in rainforests and elsewhere (I understand we Americans have used up over half of our rich, very deep topsoil in 200+ years), then the situation for the future looks still bleaker.
Comment by Lynn Vincentnathan — 29 Mar 2010 @ 12:15 PM
“I can’t remember if it’s due to the heavy rain washing out the soil’s nutrients, or lack of decomposition.”
From what I remember of physical geography, it’s the rainfall leeching.
Comment by Completely Fed Up — 30 Mar 2010 @ 5:29 AM