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Drought in the Amazon: A death spiral? (part 1:seasons)

Posted on 15 May 2011 by Rob Painting

By and large, the mainstream media has a pretty dismal record in reporting about climate change, and a recent op-ed in the National Post, written by Lawrence Solomon, continues in this vein. In the piece, Solomon makes light of the dire threat global warming poses to the continued existence of the Amazon rainforest. After the IPCC Amazon non-controversy, it's probably time to look at the issue in a bit more depth, and debunk Solomon at the same time. 

Don't believe anyth...everything you read in the newspapers

In his article, Solomon highlights a sober assessment of the implications of the extreme 2005 and 2010 Amazonian droughts, from Simon Lewis, a leading Amazon researcher, based at the University of Leeds. To which Solomon writes:

"Today, just three months after that dire outlook, the doom and gloom is lifting. The Amazon and its species have made a dramatic comeback, so much so that the river populations of dolphins now exceed pre-drought levels, even in one of the hardest hit drought areas"

Is it really that simple?. Have scientists overstated the case? Can dead trees really spring back to life? And can river dolphins really breed so astonishingly quickly?. Well, leaving aside the dolphin issue, the answer is a resounding 'no'. Here's where a bit of background information is useful:

Seasons in the Amazon 

Like many tropical regions, a wet & dry season occurs in the Amazon, this seasonal variation is a consequence of the Earth's tilt, relative to its plane of orbit around the sun, and intense heating of the sea surface in the regions at the equator. See illustration below:

Figure 1 - Simple graphic of Earth's orbit around the sun. Left-hand side of image=southern hemisphere (austral) summer. Right-hand side=northern hemisphere (boreal) summer. North-South= Earth spin axis relative to orbital plane. Image from LASP

The Intertropical Convergence Zone (ITCZ), is a band of low pressure circling the equator, which is associated with strong rainfall. In the case of the Amazon, it brings moisture into the basin from the Atlantic sea surface. In the northern hemisphere (boreal) summer (June/July/Aug), the ITCZ travels north to the area of most intense heating, this deprives the Amazon of rainfall. In the southern hemisphere (austral) summer (Dec/Jan/Feb) the ITCZ is pulled south again, bringing the rains with it.

 

Figure 2 - relative position of the ITCZ for the northern (July) and southern (Jan) hemisphere summers. Image courtesy of Wikimedia Commons

This annual migration of the ITCZ, as it follows the sun, leads to the typical Amazon seasonal rainfall pattern we see below:

Figure 3 - Long-term mean (1979–2000) Climate Prediction Center Merged Analysis of Precipitation (CMAP, Xie and Arkin, 1997) seasonal precipitation totals (in mm) for December–February (left) and June–August (right). From Cruz Jr 2007. 

The Amazon & ENSO

On top of the seasonal cycle is the ENSO cycle, La Nina and El Nino. El Nino often brings drought because the warming sea surface in the eastern tropical Pacific pulls the Walker Circulation induced rain toward the Pacific Ocean, and the Amazon therefore dries out. The lack of moisture and evaporative cooling at the surface causes the land to heat up more than normal, amplifying the drought.   During La Nina, the Amazon typically sees higher-than-average rainfall and cooler-than-average surface temperatures (Foley 2002).

Figure 4 - Changes in the Walker Circulation during (a) La Nina and (b) El Nino periods. During La Nina, the Amazon region experiences higher-than-average precipitation. During El Nino, the main convection center shifts to the central Pacific, convection over Amazonia weakens, and the precipitation totals drop below average. From Foley 2002

This is a somewhat simplified version of the situation, for instance parts of the southern Amazon are drier than normal in both La Nina and El Nino phases (implications of which we'll discuss later), but it describes the general rainfall pattern for the majority of the Amazon.   

Context makes all the difference

With the benefit of background knowledge, we can see that Solomon's suggestion, that high CO2 levels ended the drought, is ridiculous. It's unsurprising, given we are still in a La Nina phase, and the Dec-Feb period is the Amazonian wet season, that the 2010 drought in the Amazon ended some months ago. Scientific concerns are not that drought would last forever, but that global warming might induce recurring and intensifying episodes of Amazonian drought, eventually resulting in die-back of the forest.

The recent Amazonian drought, was not terminated by high levels of CO2 in the atmosphere, but by the onset of the wet season, amplified by La Nina. Increasing levels of CO2 present a danger to the future viability of the Amazon, but to understand why, we need to look at the mechanisms thought to be driving the changes. 

 

Next up: Climate model simulations of Amazonian 'die-back'

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Comments

Comments 1 to 41:

  1. Thanks Rob for an excellent article.
    Just over a year ago I was totally confused by all the contradictory arguments about AGW.
    I'd have read an article like Solomon's and found it compelling.
    After searching around for science based information free from from political sponsorship I found Skeptical Sceince.

    To be honest I think you guys can be a little harsh and scathingly rude when addressing comments from deniers but you keep to science based argument and cite your sources.(There again, I'd lose my cool quicker than most of you when debating crackpots who don't listen and think that debating is just repeating yourself louder each time.)

    Your adherence to scientific argument is laudable. Every argument is consistant with the big picture of AGW and free from the self contradictory mish-mash of evidence or political propoganda we get from the [ - snip - ]

    I look forward to the next installment in this series.
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  2. "the river populations of dolphins now exceed pre-drought levels, even in one of the hardest hit drought areas" - where does this stuff come from?
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  3. Hate to be nitpicky, but the map from Cruz jr 2007 is based on satillite data. It then is based on cloud color, which in SA is a very undependable source of ground recieved precipitation.
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  4. If you want to see current and somewhat historical images of the water vapor loop that affects the Amazon, here is a great link.

    http://www.ssec.wisc.edu/data/composites.html
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  5. The Cruz Jr 2007 rainfall map is meant to demonstrate the shift of the ITCZ (and associated rainfall) with seasons-- for that purpose the satellite data are more than sufficient.
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  6. From Solomon's article:
    The short version: It’s CO2 to the rescue. The more of it in the atmosphere, the better the Amazon’s chance of survival.
    From the paper on which he based his article:
    Meanwhile, carbon gains from photosynthesis cannot rise indefinitely and will almost certainly asymptote. Thus, ecophysiological principles alone suggest that the sink in intact tropical forests will diminish and may eventually reverse. The major uncertainty is when this will occur.
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  7. I'm hoping someone can help me by answering a question about the ENSO.
    I'm not a scientist and I work in the mining and energy sector so am surrounded by heavy resistance to the science of AGW.

    According to the Wikipedia link in the article the ENSO changes from el Nino to la Nina approximately every 5 years although this varies.
    In Australia our droughts are said to be becomming longer and the interdrought periods are getting shorter.

    Where can I find data to demonstrate this? And does this have a relationship to the ENSO or Walker Circulation?
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  8. Stevo - I'm not familiar with details of the Australian drought situation. I believe rainfall there is largely driven by changes in the Indian Ocean Dipole, a warming/cooling of surface waters in the tropical Indian Ocean, however changes in the Walker circulation with ENSO, do influence rainfall patterns in Australia as well.

    I don't know that we have a post specifically on Australia, but have a squizz at this post The Dai After Tomorrow and the paper that it references. Note the changes in rainfall projected for Australia, don't look too flash.
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  9. Some additional explanation of the connection between ITCZ and rainfall would be helpful.
    The position of the July band in the Old World looks very suspicious.
    I haven't heard about tropical rainfalls over Sahara or Saudi Arabia yet.
    That could have been several thousand years ago, but not recently for sure.
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  10. the ITCZ travels north to the area of most intense heating,

    This is a misleading statement with the obvious exceptions: In the Eastern Pacific, the ITCZ is ALWAYS in the Northern Hemisphere.

    The ITCZ is NOT driven by solar heating but, as its name implies, by CONVERGENCE of polar air masses from each hemisphere.

    It is the seasonal change in the relative intensity of each hemisphere's polar air masses that determines the location of the ITCZ.

    This is certainly consistent with the 'wet sahara' associated with the Holocene Climatic Optimum. Northern summers were warmer, Southern winters were colder and consequently the ITCZ was pushed north by the relatively pushier southern air masses.
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  11. Some context: Solmon's piece is not an article but an op ed. He's not a journalist nor did he interview anyone. He's a well-known denier who is a regular columnist for National Post, a right-wing rag in Canada that has never made money but somehow continues to be published and given away.

    Solmon's speciality is the cherry pick.

    I actually interviewed Lewis, as well as a tropical biologist in the Amazon and Thomas Lovejoy who headed a huge metastudy last year for this article published by IPS - a global news wire. One of the warnings: 'forests are also shifting from absorbing CO2 to emitting the global warming gas'

    Amazon Drought Accelerating Climate Change
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  12. Pohjos - Some additional explanation of the connection between ITCZ and rainfall would be helpful

    Thks, will be discussed in a later chapter focusing on the ITCZ & Amazonian rainfall.

    Climatewatcher - as above.

    Stephen Leahy - will correct, thks.
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  13. Stevo, the situation on rainfall in Australia is complicated:

    1. Some models predict less rain, and some models predict more rain. There are more models predicting less rain, which suggests it is more likely that one of the less rain models is correct, but there is no reason one of the models showing more rain might not be correct.
    2. Uniform dyring is not predicted. The average case of all models is for drying in the south, particularly during winter, and more rain in the north, particularly during summer. The reflect the processes of a strenthening monsoon driven by increased water vapour supply, and a strengthening high pressure belt in the subtropics, which seem both to be robust and common features of all climate models and are both being observed. What other processes may change is a mystery.
    3. One of the key mystery processes is ENSO. During the 80s and 90s ENSO was the warmest (dry for Australia) it has ever been in over 100 years. This led to much speculation that Co2 was to blame, as the average SOI index during the 80s and 90s reached unprecedented dry values. Since then it has recovered, and the La Nina just ending has the wettest SOI value ever recorded over a 6 month wet season period. Climate scientists are divided over whether warming should lead to a cooling or warming of the ENSO.
    4. The recent Australia drought is not unprecedented (in rainfall terms), unless you narrow the rainfall defencies down quite a lot, to SE Australia during April and May, and SW Australia during the entire year. Choosing only specific regions and times is cherry picking, so the results may still be valid, but you can't claim that the results are a significant proof of anything.
    5. Although the low level of rain is not unprecedented, the combination of low rain and high temperatures is. The high temperatures make the drought worse. Also last time we had a drought as strong as what we recently experienced the tropics were also in drought. This time the tropics are quite wet during summer, which lines up with the general pattern predicted by models.

    To summarise the models predict wet in the north and dry in the south. We don't have clear cut evidence that this is definitely the entire story for Australia rainfall, but the trends we do see are certainly in the right direction.
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  14. "Today, just three months after that dire outlook, the doom and gloom is lifting. The Amazon and its species have made a dramatic comeback, so much so that the river populations of dolphins now exceed pre-drought levels, even in one of the hardest hit drought areas"

    I'm not allowed to say where Solomon pulls his information from but I can tell you that Amazon dolphins have a gestation period of 9-12 months.
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  15. Michael Hauber,
    Thankyou for the explanation. I guess I'll just have to keep watching to see how weather patterns match up to the model projections. Also glad you helped me to identify what are real trends and what are cherry picks.

    Wet in the North and dry in the South certainly fits the current weather patterns. (Now I know to wait some more years in order to determine if it is just weather or a real change in climate, but if I was a gambling man I'd put my money on climate change.)
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  16. CW @10,

    "The ITCZ is NOT driven by solar heating but, as its name implies, by CONVERGENCE of polar air masses from each hemisphere."

    No. From Wang and Wang (1999):

    "The antisymmetric solar forcing due to annual variation of the solar declination angle can convert a stable latitudinal symmetric climate into a bistable-state latitudinal asymmetric climate by changing trade winds, which in turn control annual variations of the ECT. The ECT then interacts with ITCZ, providing a self-maintenance mechanism for ITCZ to linger in one hemisphere, either the northern or southern, depending on initial conditions. The establishment of the bistable-state asymmetry requires a delicate balance between counter effects of the antisymmetric solar forcing and self-maintenance."
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  17. #14 villabolo Yes, and in any case I may be wrong but my impression was that there is little if any population ecology data available, and certainly none in the kind of time frame he is talking about, but that these are very rare animals. So how does he come to make a statement like that which will almost certainly be repeated on denialist blogs, become established as "fact"?
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  18. Michael Hauber - Climate scientists are divided over whether warming should lead to a cooling or warming of the ENSO

    ENSO will be covered. There's a fair amount of evidence that ENSO frequency/intensity increases as the tropics warm.
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  19. Mr. Solomon invents generals from exceptions.

    The 'rebounding' dolphin population probably came from this report:

    http://www.earthweek.com/2011/ew110513/ew110513c.html

    Connecting two Amazon studies published years apart, and covering the drought-impact in two very different contexts, probably came from the ScienceDaily article on the second study:

    http://www.sciencedaily.com/releases/2009/03/090305141625.htm

    The sidebar to other articles features the 2007 study.

    The easiest way to kick out the chair is to challenge the relationship - the response correlated to precipitation levels, not CO2 levels.

    From the ScienceDaily report on the 2007 study:

    "The UA scientists and their Brazilian colleague already knew the Amazon forest took advantage of the annual dry season's relatively cloudless skies to soak up the sun and grow."

    Who would have thought that the canopy cover would grow during warm, sunny periods? Well, apparently everyone but Mr. Solomon.

    However, this 'Joy of CO2' isn't even his best square dance; four days earlier, he claimed that record tornado levels in the Midwest are part of a global-cooling onset:

    http://www.financialpost.com/news/Global+cooling+wind/4722245/story.html
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  20. Rob Painting - ENSO will be covered. There's a fair amount of evidence that ENSO frequency/intensity increases as the tropics warm.

    Do you mean more frequent and severe events in both the warm and cool direction with little overall trend towards warming of cooling? That is currently my gut feel. Is there any of the fair amount of evidence you can easily refer me to? Of the top of my head IPCC says nothing much more than ENSO impacts are uncertain.
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  21. Michael Hauber- it's now 4 years since the IPCC AR4 was published. Although by no means definitive, La Nina & El Nino (cool/warm) episodes are now happening more frequently and with greater intensity, within the last millenium at least. Although there is no trend toward greater La Nina, or El-Nino frequency, this still has serious implications (the drying of Southern Amazonia I alluded to in the post).

    I'll try to get that post knocked out tomorrow or the following night, depends how long it lingers in forum-review before it gets published. I don't want to go over it, in the comments section, before I'm able to provide some further background and context.
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  22. "The antisymmetric solar forcing due to annual variation of the solar declination angle can convert a stable latitudinal symmetric climate into a bistable-state latitudinal asymmetric climate by changing trade winds, which in turn control annual variations of the ECT. The ECT then interacts with ITCZ, providing a self-maintenance mechanism for ITCZ to linger in one hemisphere, either the northern or southern, depending on initial conditions. The establishment of the bistable-state asymmetry requires a delicate balance between counter effects of the antisymmetric solar forcing and self-maintenance."

    They're arguing that ocean temperatures drive convection and convection drives the ITCZ which controls ocean temperature.

    My perspective is this:

    Dynamics seem to account for this pretty well when you consider the orientation of the Andes. They run sharply and close to uniformly from south to north. This channels Antarctic air masses nearly due north, all the way past the equator,

    In the Northern Hemisphere, Eastern Pacific, however, Arctic air masses tend to encounter the North American continent. From Baja California to Panama, the Pacific is sheltered from Arctic air masses, allowing the channeled Antarctic air masses to penetrate into the Northern Hemisphere, even in the Northern winter.

    This is driven by asymmetric insolation because the cooling of the winter hemisphere creates denser air masses which push harder into the summer hemisphere.
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  23. This is what he writes Michael Hauber be supplemented by the recent paper: Influence of El Nino and ITCZ on Brazilian River Streamflows, Lopes & Dracup, 2010.:

    “At the Amazon river basin, almost all dry years occurred when NINO3.4 was above average (El Nino years). Moreover, in almost every year when NINO3.4 was below average (La Nina) the streamflows were above average. Thus, it seems that La Nina have strong effects in floods in Amazon river. Moreover, El Nino events seem to be a necessary, but not sufficient condition for low streamflows at Amazon river.”

    Add to ENSO North Tropical Atlantic SST indexes (NTA).

    During El Nino in the atmosphere also are adding even more than 5 ppmv CO 2 (average of many years - since 1980 - 2-2.5 ppmv).

    Is CO2 affects the formation of drought in the Amazon?

    First you have to prove the impact of CO2 on ENSO and the NTA ...

    I hope that proves to the next post on this topic.

    I recommend to analyze the sentence: „...on the ITCZ moving north from the Little Ice Age to the Modern Warm Period, correlated to solar-modulated cosmic ray variation ...”
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  24. #20 ENSO is complicated and difficult to ascertain impacts of CC over short period of time. Here's what some experts said in my recent article published for a Latin American news service:

    “It would be surprising if there wasn’t an effect,” Trenberth said..... latest research seems to show “that we may even see new ‘flavours’ of ENSO emerge as we move into the future,

    Climate Change Could Be Worsening Effects of El Niño, La Niña
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  25. CW,

    I am not going to argue with you about your misguided "perspective". You seem reticent to concede error, a common trait amongst "skeptics". So it is pointless trying to inform you.

    To CW and Arkadiusz:
    You seem intent on missing the point of Rob's post. Instead, happy to argue and nit pick at Rob's piece. Can I assume then that you support Solomon misinforming, misrepresenting the work of scientists and using the science as a political tool? Because that is what he is doing. As Stephan Leahy noted, Solomon is essentially a professional misinformer. Please let readers know where you stand on Solomon's propaganda. Thanks.
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  26. Owl905 @19,

    Thanks for that link about Solomon claiming the tornadoes in the southern States are a sign of global cooling-- I think it is relevant here, becasue it speaks to his lack of credibility and propeonsity to mangle and distort the facts.

    Forgetting for the moment the ridiculous notion of using regional temperatures for one month to infer global temperature trends. Let us look at the April temperatures for the southern USA for April from 1980-2011. Trend is 0.5 F per decade. Worse yet for Solomon, air temperatures in April 2011 for that region were 3 F above the 1980-2011 average, and ranked the 13th warmest April since 1895.
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  27. Mr. Solomon seems to have missed this Ecology Letters paper's findings (Feeley et al. 2007):

    "The impacts of global change on tropical forests remain poorly understood. We examined changes in tree growth rates over the past two decades for all species occurring in large (50-ha) forest dynamics plots in Panama and Malaysia. Stem growth rates declined significantly at both forests regardless of initial size or organizational level (species, community or stand). Decreasing growth rates were widespread, occurring in 24–71% of species at Barro Colorado Island, Panama (BCI) and in 58–95% of species at Pasoh, Malaysia (depending on the sizes of stems included). Changes in growth were not consistently associated with initial growth rate, adult stature, or wood density. Changes in growth were significantly associated with regional climate changes: at both sites growth was negatively correlated with annual mean daily minimum temperatures, and at BCI growth was positively correlated with annual precipitation and number of rainfree days (a measure of relative insolation). While the underlying cause(s) of decelerating growth is still unresolved, these patterns strongly contradict the hypothesized pantropical increase in tree growth rates caused by carbon fertilization. Decelerating tree growth will have important economic and environmental implications."
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  28. Albatross - thanks, but I don't have time to correct every misguided "skeptic" notion. The following installments will rectify that.

    Stephen Leahy - thanks once again. A paper published two weeks ago indicates (based on paleodata) that ENSO will only intensify as the tropical Pacific warms.
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  29. On the California coast, La Nina brought us a wet winter and huge snowpack in the Sierra mountains this year. Not a typical La Nina year here, which are usually dryer than normal. Last year, we saw a fairly typical El Nino winter, with plenty of rain, but an unusually cool summer followed. Any ideas as to why?
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  30. Solomon is essentially a professional misinformer.

    Maybe ...

    Sometimes he is too biased - use "cherry picking". Only that this case shows that - here - he's right. Like Idso who cites many articles of the late twentieth century, for example:
    “In the relatively short-term study of Lovelock et al. (1999a), for example, seedlings of the tropical tree Copaifera aromatica that were grown for two months at an atmospheric CO2 concentration of 860 ppm exhibited photosynthetic rates that were consistently 50-100% greater than those displayed by control seedlings fumigated with air containing 390 ppm CO2.”

    Co2 favors the development of tropical forests and these buffering - the hydrological cycle - is less periods of extreme drought.

    And what says - cited by Solomon - Phillips et al., 2008., in: The changing Amazon forest : “Because growth on average exceeded mortality, intact Amazonian forests have been a carbon sink. In the late twentieth century, biomass of trees of more than 10 cm diameter increased by 0.62 +/- 0.23 t C ha-1 yr-1 averaged across the basin. This implies a carbon sink in Neotropical old-growth forest of at least 0.49 +/- 18 Pg C yr-1. If other biomass and necromass components are also increased proportionally, then the old-growth forest sink here has been 0.79 +/- 29 Pg C yr-1, even before allowing for any gains in soil carbon stocks. This is approximately equal to the carbon emissions to the atmosphere by Amazon deforestation.”

    And what speaks - on this topic - Greenpeace?: “ Rafael Cruz, a Greenpeace activist in Manaus who has been monitoring the drought, said that while the rise and fall of the Amazon's rivers was a normal process, recent years had seen both extreme droughts and flooding become worryingly frequent.
    Although it was too early to directly link the droughts to global warming, Cruz said such events were an alert about what could happen if action was not taken.”

    Of course it is. Historically, droughts have been even greater and the smaller population of Amazonia. So We must - firstly - to increase the possibility of water retention in periods of drought - of course ...
    It is always useful.

    Will Amazon drought significantly affected the photosynthesis?:
    We found no big differences in the greenness level [!] of these forests between drought and non-drought years, which suggests that these forests may be more tolerant of droughts than we previously thought,” said Arindam Samanta, the study's lead author from Boston University.
    The comprehensive study published in the current issue of the scientific journal Geophysical Research Letters used the latest version of the NASA MODIS satellite data to measure the greenness of these vast pristine forests over the past decade.
    A study published in the journal Science in 2007 claimed that these forests actually thrive from drought because of more sunshine under cloud-less skies typical of drought conditions. The new study found that those results were flawed and not reproducible.

    “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.”

    A significant mistake of catastrophic forecasts (the reaction of global ecosystems to extreme phenomena - were found to be greater resistance - a significant reduction of "tipping points") speaks this paper:
    The ecological role of climate extremes: current understanding and future prospects, Smith, 2011.:

    “For example, above- and below-ground productivity remained unchanged across all years of the study ...”
    Meanwhile in: The 2010 Amazon Drought Lewis et al, 2011.,

    they are frighten us ...


    Lewis also threatens us with fire

    But here (SH - Southern Hemisphere) has recently seen something quite different - a surprising ... Large Variations in Southern Hemisphere Biomass Burning During the Last 650 Years, Wang et al. 2010.:
    “ These observations and isotope mass balance model results imply that large variations in the degree of biomass burning in the Southern Hemisphere occurred during the last 650 years, with a decrease by about 50% in the 1600s, an increase of about 100% by the late 1800s, and another decrease by about 70% from the late 1800s to present day.
    And so it looks like ...

    I recommend also comments (not the same "very incomplete" text post) - here - to this post.
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  31. Re #30,

    Really, it is not clear what you are trying to say. But you seem to think that more than doubling CO2 and associated climate disruption will more than be compensated for by CO2 enrichment. Recent research has found that the ITCZ can migrate up to 5 degrees latitude when the planet warms-- think of the consequences that would have.

    You ignored the results from field studies by Feeley. And you forget that this is not so much as to what has happened but where we are heading.

    And really, citing cherry-picked studies from ideologues like Idso does not help you case. And what has below ground productivity got to do with things, or how is that related to this post? Oh, it is strawman, of course. We are talking about the canopy and transpiration, and die back of the canopy.

    And talking of strawmen, you are also making a arguing a strawman about fires. Making the argument that there have been periods of greater fire activity in the southern hemisphere before so there is nothing to worry about in the future is nonsense. All you have demonstrated is that large variations in the degree of biomass burning in the Southern Hemisphere (not the Amazon per se, the authors do not mention specifically the Amazon that I could see), and that it is possible to burn a lot more biomass than has been of late. Hardly reassuring.

    So your long post ultimately does not support Solomon's propaganda. In fact, it is just a fine example of the lengths people will go to to delude themselves.
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  32. I think it is very safe to say that there are published papers showing a large climatic variation in the Amazon in times past.

    The below ground productivity is very important to this topic. I will say it simply, you can have nothing of consequence above ground unless supported by solid root structures.
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  33. Camburn - "...you can have nothing of consequence above ground unless supported by solid root structures."

    But I thought the big issue with tropical forests was that there is little to no 'solid root structure' below ground. Practically the whole of the growth, carbon, nutrient cycles occur above ground which is why clear felling and/ or burning such forests depletes those soils so much more quickly and completely than soils in other regions.
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  34. Adelady - a vast amount of carbon is stored underground. A multitude of factors lead to drying of the forest. I'll get to that eventually.

    Camburn- I think it is very safe to say that there are published papers showing a large climatic variation in the Amazon in times past

    Perhaps not as large as many readers may think. IIRC, during the ice ages for instance, mean annual temperature in the Amazon is thought to have fallen only 1-2°C, and this was mainly due to frequent outbursts of friagems being channeled up the Andes into the Amazon. Were it not for that, temps would have been closer to modern day. And, of course, when it was too dry in South America in the deep past, the Amazon didn't exist at all
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  35. @Camburn 32

    "you can have nothing of consequence above ground unless supported by solid root structures. "

    Of course the same could be said in reverse as well, no roots without shoots. Moreover, under a given set of conditions, a plant which apportions a larger fraction of their biomass to root structures must, by necessity, grow slower because their metabolic costs increase relative to their photosynthetic rates.

    Because of this tradeoff, the root to shoot ratio is pretty constrained for a given biome. In the Amazon (and most wet tropical forests), belowground typically is 25% of above ground, roughly speaking. And there isn't a lot of dead soil carbon as it is quickly decomposed, except in consistently saturated soils.

    Of course if it gets drier, the root to shoot ratio will increase as plants try to access more water, but that will only happen because root biomass will decrease a little less than above ground biomass. IOW, the below ground biomass will not compensate for the loss of above ground biomass as climate dries in the Amazon.
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  36. @Albatros

    Recent research has found that the ITCZ can migrate up to 5 degrees

    - were doing it, and past from natural causes . One of the most recent works says: “Specifically, our data indicate that the ITCZ was 500 km closer to the equator during the LIA than it is today and that it was south of its present position (7 degN) for the last 1,000 years.”

    You ignored the results from field studies by Feeley ...

    Ppaper by Feeley, it is typical of Chery Picking - typical, because it is "not reproducible."

    Paper Smith, 2011. - an analysis recently published a large number of papers - on the impact of extreme climatic phenomena on productivity and 37 other parameters of the ecosystems - in the world. It is “off topic”?

    All you have demonstrated is that large variations in the degree of biomass burning ...

    - No. I just wanted to say that biomass burning - SH - is definitely - a record - the lowest in 650 years ...
    ... of the poor in the reference - the paper Lewis et al., 2011., does not speak.

    Furthermore, please do not ignore the most important sentences - with my commentary: “... no big differences in the greenness level [!] of these forests between drought and non-drought years ...”
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  37. Arkadiusz @36,

    "Furthermore, please do not ignore the most important sentences - with my commentary: “... no big differences in the greenness level [!] of these forests between drought and non-drought years ...”

    I will address this confusion when I have some time. You are ignoring the die back issue....more later.

    Feeley was a field study, real world data-- so I have no idea what you are trying to say.
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    Moderator Response: Fixed unclosed HTML tag
  38. Arkadiusz @36,

    "Furthermore, please do not ignore the most important sentences - with my commentary: “... no big differences in the greenness level [!] of these forests between drought and non-drought years ...”

    I will address this confusion when I have some time. You are ignoring the die back issue....more later.

    Feeley was a field study, real world data-- so I have no idea what you are trying to say.
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  39. "you can have nothing of consequence above ground unless supported by solid root structures"

    What in the world is this supposed to mean and what is the relevance? The soils in tropical forests are thin and severely limit how deep the roots can go. Tropical trees have horizontally spread root structures and extensive butresses to account for that.
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  40. Regarding the following (fallacious) claim made by a 'skeptic' on this thread:

    "no big differences in the greenness level [!] of these forests between drought and non-drought years."

    It seems the misguided commentator is referring to this 2007 Science paper by Saleska et al.. However, what the resident 'skeptic' forgot to tell people here is that the findings form that 2007 paper were based on contaminated satellite data. The paper they should be referring to, Samanta et al. (2010), paints a very different picture.

    "We find no evidence of large-scale greening of intact Amazon forests during the 2005 drought - approximately 11%–12% of these drought-stricken forests display greening, while, 28%–29% show browning or no-change, and for the rest, the data are not of sufficient quality to characterize any changes. These changes are also not unique - approximately similar changes are observed in non-drought years as well. Changes in surface solar irradiance are contrary to the speculation in the previously published report of enhanced sunlight availability during the 2005 drought. There was no co-relation between drought severity and greenness changes, which is contrary to the idea of drought-induced greening. Thus, we conclude that Amazon forests did not green-up during the 2005 drought."

    The opposite of what the "skeptics" are trying to trick you into believing.

    Interestingly, Terence Corcoran from the National Post (Solomon's colleague) decided to distort the science from the Samanta et al. paper. The National Post are quite the disinformers it seems.

    Here is what Dr. Simon Lewis had to say about the Saleska et al. (2007) and the Samanta et al. (2010) papers:

    "This is important new information, as in 2007, a paper using the satellite-based same method showed a strong 'greening-up' of the Amazon in 2005, suggesting tolerance to drought. The new study shows that those results were not reproducible, but also highlight the extreme caution that should be attached to satellite studies generally in this field, with instruments in space collecting data which is then used to infer subtle changes in the ecology of tropical forests.

    In contrast to the 2007 paper, Oliver Phillips, myself and others, published a paper in Science, using ground observations from across the Amazon, that while the 2005 drought did not dramatically change the growth of the trees compared to a normal year, as Samanta also show, but the deaths of trees did increase considerably. The new study of Samanta et al., supports the Phillips et al. study, which itself shows the Amazon is vulnerable to drought. The Phillips paper showed that remaining Amazon forests changed from absorbing nearly 2 billion tonnes of CO2 from the atmosphere a year, to being a massive committed source of over 3 billion tonnes, from tree mortality.

    The evidence for the possibility of a major die-back of the Amazon rainforest is due to two factors,

    1) That climate change induced decreases in rainfall in the dry season occur, and

    2) The trees cannot tolerate these reductions in rainfall.

    The Samanta paper does not directly address the first point, this is addressed using modelling. The second point is only addressed in a limited way. The critical question is how these forests respond to repeated droughts, not merely single-year droughts. The forests are of course able to withstand these single droughts (otherwise there would be no rainforest!) - it is their ability to survive an increased frequency of the most severe droughts that is critical to answer. Drought experiments, where a roof is built under the forest canopy, show that most forest trees survive a single year's intense drought, but can't persist with repeated years of drought. The Samanta study does not address this point at all.

    In conclusion the new study lends further weight to the emerging picture of the 2005 drought, that tree growth was relatively unaffected, but tree mortality increased, contributing to temporarily accelerating the rate of climate change, rather than as usual reducing it via additions of carbon to the atmosphere from the dead trees. Furthermore, the climate change model results suggesting decreasing rainfall in the dry season over Amazonia in the coming decades are unaffected by the new study, thus overall the conclusions in the IPCC 2007 Fourth Assessment Report are strengthened (because the anomalous result of the Saleska 2007 science paper appear to be at fault), not weakened, by the new study as the press release implies."


    And this is just one reason why the "skeptics" have no credibility.
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  41. With regards to the pink dolphin issue. The latest report from the research is here (pdf), it is unclear when the project started but from this document (pdf) it appears the methodology is from 2005 (Alfonso, Titled Thesis) though the PI on the project has been working in the area since 1984.

    David Horton states "there is little if any population ecology data available" this may be correct but this research looks pretty sound.
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