2011-02-04 20:31:13The 2010 Amazon Drought
Andy S

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66.183.184.89

A short paper by Simon Lewis and four co-authors, just published in Science, reports on the 2010 drought in the Amazon Basin. The 2010 drought follows the 1-in-100-year drought of 2005. Lewis's paper compares the two droughts and finds that the 2010 drought was both more severe and more extensive than the 2005 drought.

 

From Lewis et al (2011) 

The comparison of the two droughts was made using satellite-derived anomalies of the dry-season rainfall (the red-blue maps in the figure) and by calculating the maximum climatological surface water deficit (MCWD) a measure that incorporates the most negative water input minus the estimated forest evapotranspiration (the brown maps). The MCWD is a measure of the water stress that the forest endures and correlates with tree mortality. The MWCD map shows for 2010 dry anomalies in Northern Bolivia and in Mato Grosso State, in addition to the dry zones in the SW Amazon Basin observed in both 2005 and 2010. 

Lewis and his co-workers used the comparative drought measures to estimate  changes in the biomass, due to trees not growing and to trees dying in the 2010 drought. They calculated that the impact to the biomass amounted to a loss of 2.2 Gt of carbon, with a 95% confidence range of 1.2 to 3.4 Gt. To put this figure into perspective, this is comparable to the emissions due to fuel combustion of India and China combined for 2008, according to the IEA. (India emitted 1.4 Gt and China 6.5 Gt of carbon dioxide, for a total of 7.9 Gt, which is equivalent to 2.2 Gt of carbon). The lungs of the world are breathing out carbon when we would prefer them to breath in.

Droughts in the Amazon are associated with sea surface temperature (SST) anomalies in the Pacific and the Atlantic. An increase in the frequency and severity of SST anomalies and droughts is predicted by several climate models. The two severe droughts, five years apart,  could, of course, just represent unusual weather years and a return to normal patterns could see the trees grow quickly back. But if the model predictions are correct and these two years point to an emerging trend, we could easily experience more such droughts over the coming decades. One of the slow positive feedbacks to climate change--the great Amazonian forests emitting, rather absorbing carbon dioxide--may be kicking in more quickly than we previously feared,

The BBC has a short video on this story. 

Hat-tip to Dorothy Cutting

2011-02-04 20:46:29
Andy S

skucea@telus...
66.183.184.89

I banged this out late at night and there may be typos and other problems that I can't see. John, you have free reign to change wahtever you like and publish this at will. It would be great if you could embed the BBC video.  

Please check the  numbers, If I've slipped an order of magnitude it would be rather embarrassing. The India and China emissions figures are read from graphs on pages 23 and 24.

2011-02-05 08:34:58Comment
John Cook

john@skepticalscience...
123.211.149.21
Andy, sorry to be a pain in the butt but could I offer one comment? It's quite technical and some readers will find it difficult to read. One of my hopes for 2011 is we regularly do what you've done here - take new research and explain its key results to the general public. But I think this will be more meaningful to people if explained in simpler language. Would you mind giving it a revision?
2011-02-05 10:21:44
Andy S

skucea@telus...
66.183.174.250

A short paper by Simon Lewis, Paul Brando and three co-authors, just published in Science Magazine, reports on the 2010 drought in the Amazon Basin. The 2010 drought has occurred only a few years after the exceptional drought of 2005. Lewis's paper compares the two droughts and finds that last year's drought was both more severe and more extensive than the earlier one.

 

Figure from Lewis et al (2011) 

A comparison of the two droughts was made using maps of the rainfall in the dry season, which were made from satellite data (the red-blue maps in the figure) and also by calculating the maximum climatological surface water deficit (MCWD), a measure that more accurately predicts the amount of stress that the trees endure (the brown maps). There was a dry zone observed in both droughts in the southwest of the Amazon basin, however, the 2010 drought showed two additional affected areas, one in the south of the Basin (Northern Bolivia) and another in the southeast (Mato Grosso State, Brazil).

By making comparisons with the effects of the 2005 drought, the researchers made an estimate of the damage to the forests in 2010 and the effect that this has on the ability of the Amazon Basin to absorb carbon . They calculated that the impact amounted to an effective net transfer of 2.2 gigatonnes of carbon from the biomass to the atmosphere. To put this into perspective, this figure is comparable to the emissions due to fuel burning in India and China combined togetherfor 2008, according to the IEA.  Last year, the lungs of the world were breathing out carbon when we would have preferred them to be breathing it in.

Droughts in the Amazon are commonly associated with sea surface temperature anomalies in the Pacific (El Niño) and in the Atlantic Oceans. Climate models predict an increase in the frequency and severity of ocean temerature anomalies and associated droughts in the Amazon. The two exceptional droughts that occurred in quick succession could, of course, just represent unusual weather years. If there were a return to normal rainfall and weather patterns, we might see the forests recover quickly. But if the climate model predictions are correct--and these two dry years do, in fact, point to an emerging trend--we could easily experience more droughts over the coming decades.

One of the slow positive feedbacks to climate change--the great Amazonian forests starting to emit, rather than continuing to absorb carbon--may be kicking in more quickly than we previously feared,

 

 

The BBC has a short video on this story. 

Hat-tip to Dorothy Cutting

2011-02-05 10:46:23OK done
Andy S

skucea@telus...
66.183.174.250

 I have tried to simplify the terminology and the language. Please check it for typos. When I rewrite an article my eyes glaze over and I can't see obvious errors.

I'm sometimes not sure who we are writing for. Many of our commenters seem to be very scientifically literate but they may not be representative of the general readership. When I wrote this, I had in mind as a reader an amateur like myself, but someone who did not have access to the text of the paper. I have found several of the recent SkS articles, for example by Dana, to be tough going (that's not a complaint, the subject matter isn't easy) and I didn't think that my original stab at this article was more difficult than those.

 But the customer is always right ;-)

2011-02-05 19:11:11
Rob Painting
Rob
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118.93.230.64

Andy, I know what you mean, but John is right. One only has to look at the comments thread to see the "game" the skeptic trolls engage in. Skeptics try to make matters so abstract and opaque, that casual readers are completely lost.

Some suggestions:

- Droughts in the Amazon are commonly associated with sea surface temperature anomalies in the Pacific (El Niño) and in the Atlantic Oceans. = Droughts in the Amazon happen when the sea surface temperatures in the Eastern Pacific (El-Nino - link to explanation) and the tropical Atlantic Oceans are warmer than normal.

- Maybe link to the Cox paper which suggested die-back of the Amazon by mid to late century?. http://www.nature.com/nature/journal/v408/n6809/abs/408184a0.html

 

 

2011-02-05 19:51:33Tone of the language
nealjking

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84.151.44.10

I think this article has been written as a summary presentation of the original paper in Science, and uses the same language as the original article. I don't think this is the right level for conveying the significance of the implications to the SkS audience.

I think the article should be more like what you would get from someone who heard the talk, and then was asked in the elevator, "What was that report all about?" The basic point is that the drought of 2010 was drier and more extensive: You can see this rainfall measurements and by measures of water loss for trees. This has led to a net loss of carbon from the rain forest to the atmosphere - which is not the role we were hoping the rain forest would play.

The graphic should play just a supporting role, to illustrate the point: You should not really expect that the reader would come to a conclusion without it being pointed out. 

"Short & sweet" would be more effective and more meaningful.

2011-02-06 06:36:19
Andy S

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66.183.174.250

Thanks for the comments, everyone.

If you search for  "simon lewis amazon drought 2010" in Google News you get 118 hits. My intention in writing this was to attempt to summarize the original paper at a science level a bit above that of the mainstream press and to liberate the diagram from behind the pay wall. I don't see much point in simply doing newspaper article #119, SkS is a science blog, after all. I included the link to the BBC video, which I thought did a very good job in explaining the story in layman's terms, so if anyone felt my explanation was too technical, they were just one click away from a simpler account of the story.

Having said that, I realize that my writing is not that clear and if people take the time to tell me that I should simplify it, I'm listening. So, I'll have another go at a rewrite. There's a blog entry in Nature that, I'm sure everyone would agree, succeeds in getting the story across without oversimplifying.

Rob: I think your wording is more clear but I worry that it goes too far. I don't want to imply that SST anomalies and Amazon droughts always go hand-in-hand because I don't know if that's true. The Nature blog used similar wording to mine (I didn't even see the Nature blog until just now, in case John Mashey is reading- wink): "Amazon droughts are often associated with unusually high sea surface temperatures in the tropical Pacific and/or Atlantic Ocean.  Climate models suggest that drought conditions will become more frequent in the region (and around the tropics), but whether the recent events can be attributed to global warming is unclear."

Thanks for the link to the Cox paper, I found a free copy here.

Neal: I have always tried to follow the presentation maxim "show, don't tell", which is why I included the maps and I think that they are more important than having just a supporting role. I don't like showing (or seeing) figures from articles divorced from their original captions. The caption however doesn't make sense without me explaining what MCWD stands for. I'll annotate the diagram to highlight the drought epicentres, which I hope will make the main point about the increased extent of the 2010 drought more immediate.

John said that he hoped that we could make this kind of article more common on SkS and it's worthwhile taking the time with this one to get the language level  right. Rebutting deniers is the very important (and the original point of the blog) but I think that too much focus on that perpetuates the idea that climate science is a kind of boxing match, whereas the reality is that it's more like an incomplete jigsaw puzzle with a clearer picture emerging as pieces are constantly being added. 

 

2011-02-06 07:38:29Second revision
Andy S

skucea@telus...
66.183.174.250

A short paper by Simon Lewis, Paulo Brando and three co-authors, just published in Science Magazine, reports on the 2010 drought in the Amazon Basin. This drought occurred only a few years after the exceptional drought of 2005, which was supposed to have been a one-in-a-hundred-year event. The paper presents evidence that last year's drought was both more severe and more extensive than the earlier one.

Figure from Lewis (2010) with annotation added.

Using data from satellites, the red-blue maps compare the rainfall in the dry seasons of 2005 and 2010. The "maximum climatological surface water deficit" (MCWD) is a factor that more accurately predicts the amount of stress that the trees endure in a drought and is shown in the lower, brown-colored couple of maps. The zones with the most severe expected drought damage are highlighted by green circles, added here to the orignal published figure. There was a dry zone observed in both droughts in the southwest of the Amazon basin. The 2010 drought affected two additional affected areas, one in the south of the Basin, in Northern Bolivia and another in the southeast, in Mato Grosso State, Brazil.

Droughts reduce the rate of tree growth and repeated droughts may cause trees to die off altogether. Forest fires are also more likely during unusually dry periods and in 2010 extensive fires were reported in Northern Bolivia . All these effects combine to make the Amazon basin in 2010 into a source of carbon rather than a net sink  Simon Lewis and his co-workers calculated that the impact of the 2010 drought amounted to an effective net transfer of 2.2 gigatonnes (billion tonnes) of carbon from the biomass to the atmosphere.

To put this into perspective, 2.2 gigatonnes is comparable to the emissions resulting from fuel burning in 2008 from India and China combined, according to the IEA. One dry year in the Amazon, therefore, may have made as big a contribution to greenhouse gasses as the annual contribution of the two largest developing economies. Last year, the lungs of the world were breathing out carbon when we would have preferred them to be breathing it in.

Droughts in the Amazon tend to occur at the same time as sea surface temperature anomalies in the Pacific (El Niño) and in the Atlantic Oceans. Climate models predict an increase in the frequency and severity of both ocean temperature anomalies and droughts in the Amazon. On the other hand, the two exceptional droughts that occurred in quick succession might just represent unusual weather years and, if there were a return to normal rainfall patterns, the forests might recover quickly. But if the climate model predictions are correct, we should expect additional severe Amazon Basin droughts over the coming decades.

One of the slow positive feedbacks to climate change--the great Amazonian forests starting to emit, rather than continuing to absorb carbon--may be kicking in more quickly than we previously feared (for example, see Cox et al 2000}.

The BBC has produced an excellent short video report on this story. 

Hat-tip to Dorothy Cutting.

2011-02-06 18:08:51
Rob Painting
Rob
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118.93.194.164


2011-02-06 18:29:22
Rob Painting
Rob
paintingskeri@vodafone.co...
118.93.194.164

Andy, the association between ENSO and Amazonian rainfall is remarkably persistent throughout the 20th century. 16 out of 17 El-Nino are tied to Amazonian drought & 14 out of 16 La Nina are associated with wet episodes in the Amazon. See Ropelewski & Halpert 1987 http://www.icess.ucsb.edu/gem/Ropelewski.and.Halpert.1987.patterns.precip.enso.pdf.  

El-Nino perturbs the Walker Circulation shifting the rainfall westwards of the Amazon, whereas the warm tropical Atlantic shunts the ITCZ further northwest during the Northern Hemisphere summer (Amazonian dry season). Unless something shunts that "convective engine" south again during warm SST episodes in the tropical Atlantic, then drought is going to become a familiar feature in the Amazon. As Peter Cox (2008) and his colleagues point out here: http://nora.nerc.ac.uk/2985/1/CoxNaturePostP.pdf

I just point this out for your info, not expecting you to incorporate it into your post.  

2011-02-06 21:38:44Published
John Cook

john@skepticalscience...
123.211.149.21
Just published this. Many thanks Andy for writing this and being patient with all our feedback :-)