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201214Jul12:03

Sci­en­tists slam Tele­graph blogger’s claims that cli­mate change will be good for the Amazon

Infor­ma­tion
pub­lished 14 July 2012 | mod­i­fied 05 Decem­ber 2012
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Recent blog posts on The Tele­graph and the Reg­is­ter claim­ing that trop­i­cal rain­forests like the Ama­zon are set to ben­e­fit from cli­mate change are “unin­formed” and “ridicu­lous” accord­ing to some of the world’s most emi­nent trop­i­cal for­est scientists.

The posts, pub­lished Sun­day and Mon­day by Tim Worstall, a Senior Fel­low at London’s Adam Smith Insti­tute, asserted that a new Nature study indi­cates that “cli­mate change will mean new and larger trop­i­cal forests.”

We’re told, end­lessly, that cli­mate change will mean the end of the Ama­zon, of the trop­i­cal forests, and the Earth will lose its lungs. It appears that this is not wholly and com­pletely true. Actu­ally, an increase in CO2 in the atmos­phere is likely to lead to the growth of huge, new, trop­i­cal forests
Tim Worstall »

In his col­umn, Worstall belit­tled the risks of defor­esta­tion to trop­i­cal forests, writ­ing “Good news for those of us who like our unsus­tain­able trop­i­cal hard­wood fur­ni­ture: it looks like there’s going to be a lot more of it to go around soon enough.” Worstall also exag­ger­ates pro­posed solu­tions for reduc­ing green­house gas emis­sions: “Of course what we’re told we have to do about it, clos­ing down indus­trial civ­i­liza­tion, is sim­ply crazed lunacy. Bet­ter to lose all the forests than have to return to rural peas­antry for all.”

The paper in ques­tion looks specif­i­cally at the poten­tial impacts of higher car­bon diox­ide lev­els on plant growth in the savan­nas of Africa. It found that ele­vated CO2 lev­els may favor so-​called C3 plants like trees over C4 plants like grasses, lead­ing to more trees sprout­ing up across Africa’s grass­lands and poten­tially more African woodlands.

Worstall extends the find­ings to argue that increased car­bon lev­els will sud­denly cause new rain­forests to emerge world­wide. “The major point of this paper is that far from cli­mate change being a threat to the trop­i­cal forests, it looks as if it will be the cause of more of them grow­ing,” he writes on The Reg­is­ter. “Burn­ing more fos­sil fuels there­fore seems likely to grow sev­eral new Ama­zon style forests across Africa and Latin Amer­ica,” he adds on The Telegraph’s finance blog.

But some of the world’s lead­ing trop­i­cal for­est experts took aim at Worstall’s logic, not­ing the lim­i­ta­tions of the study as well as the other fac­tors that are endan­ger­ing rainforests.

This is a typ­i­cally uni­formed piece by Tim Worstall. After con­fus­ing Ama­zon rain­forests and African savan­nas, he implies that sci­en­tists only report on what he calls neg­a­tives, such as the impacts of extreme droughts on trop­i­cal forests, and not on what he calls pos­i­tives, like car­bon diox­ide increas­ing plant growth. A sim­ple call to a sci­en­tist work­ing in the area could have pointed him to papers show­ing both things. Sim­pler still he could have read the news­pa­per web­site he writes for, where both drought and car­bon diox­ide impacts have been reported
(Simon Lewis, a trop­i­cal for­est expert at the Uni­ver­sity of Leeds)

Lewis, who led one of the most exten­sive stud­ies of car­bon uptake in trop­i­cal forests, explained that while there is evi­dence that more trees are grow­ing across the drier parts of Africa, it doesn’t mean rain­forests are poised to expand.

“Growth of new trop­i­cal forests depends on veg­e­ta­tion responses to mul­ti­ple changes in the envi­ron­ment and com­plex feed­backs. Increas­ing car­bon diox­ide amounts in the atmos­phere tends to increase tree growth, but higher air tem­per­a­tures tends to reduce growth. Droughts and asso­ci­ated fires kill trees,” he said, adding that the new sci­en­tific paper that Wor­tall cites ignored the effects of drought, which would reduce tree growth.

“A com­mon view within the sci­en­tific com­mu­nity is that at higher car­bon diox­ide con­cen­tra­tions, if busi­ness as usual emis­sions con­tinue, even­tu­ally trop­i­cal trees will become sat­u­rated with car­bon diox­ide, and at much higher tem­per­a­tures, pho­to­syn­the­sis may well decline, and there will be more fires and droughts which com­bined may reduce over­all tree growth and increase tree deaths. This net impact is not a panacea for trop­i­cal forests. Even a rudi­men­tary grasp of the sci­en­tific lit­er­a­ture would show that Tim Worstall’s dra­matic state­ment is a fairly wild extrap­o­la­tion from a sin­gle sci­en­tific paper.”

Greg Asner, an ecol­o­gist with the Carnegie Insti­tu­tion who has done advanced assess­ment of the impact of droughts across the Ama­zon, agreed with Lewis.

“Worstall has taken a sin­gle study on a sin­gle com­po­nent process (CO2 uptake) in a very dif­fer­ent ecosys­tem and extrap­o­lated it to a totally dif­fer­ent biome encom­pass­ing all processes at a global scale, and then he pro­ceeded to con­coct an inter­pre­ta­tion of that study that is incon­sis­tent with what is hap­pen­ing at the large scale in the trop­ics,” he told mongabay​.com.

“The real prob­lem here is phys­i­ol­ogy, time and scale,” Asner con­tin­ued. “Sure, you can feed some­one more and more donuts and they might gain the weight, but cut off their water repeat­edly, and grad­u­ally increase the tem­per­a­ture in the room, and those poor souls will keel over, just more dra­mat­i­cally with all those extra donuts ingested. That’s exactly what is hap­pen­ing with cli­mate change in the humid trop­ics. Yes, the trees are get­ting more CO2 in the back­ground, but in the fore­ground are these repeated droughts and con­stantly increas­ing night­time tem­per­a­tures that pull the veg­e­ta­tion back, and to the ground. We are still try­ing to assess the longer-​term effects of the 2010 drought in the West­ern Ama­zon, but there’s no sign that the forests did ‘well’.”

In fact, drought and other fac­tors are trig­ger­ing the oppo­site of the pic­ture painted by Worstall, accord­ing to Eric David­son, Exec­u­tive Direc­tor and Senior Sci­en­tist at the Woods Hole Research Cen­ter in Mass­a­chu­setts. Ear­lier this year David­son led a review of 100 stud­ies look­ing at the effects of dis­tur­bance and cli­mate change on the func­tion­ing of the Ama­zon Basin. It con­cluded that the com­bi­na­tion of defor­esta­tion, for­est degra­da­tion, and the effects of cli­mate change are weak­en­ing the resilience of the Ama­zon ecosys­tem, poten­tially lead­ing to loss of car­bon stor­age and changes in rain­fall pat­terns and river dis­charge. Among the changes was a shift from rain­for­est to savanna.

“As our review paper in Nature ear­lier this year describes, the tran­si­tion for­est on the south­ern flank of the Ama­zon is show­ing a tran­si­tion from for­est to savanna. So, just the oppo­site from what he describes is cur­rently hap­pen­ing. The south­ern Ama­zon tran­si­tion for­est is expe­ri­enc­ing more drought, longer dry sea­sons, and more fire. Wet sea­son river flood­ing and sed­i­men­ta­tion has also increased in this region — another indi­ca­tor of for­est decline. While increas­ing CO2 con­cen­tra­tions can increase pro­duc­tiv­ity of many plants, drought and fire are the big deter­mi­nants of tree growth in the south­ern Ama­zon. Worstall’s rant about wide­spread Ama­zon for­est dieback rein­forces my view that this is a dis­trac­tion — let’s look at the evi­dence at hand where for­est meets savanna — it is mov­ing more towards savanna, not towards more forest.”

Dan Nep­stad, Direc­tor at the Ama­zon Envi­ron­men­tal Research Insti­tute (IPAM), agreed. “After study­ing the Ama­zon rain­for­est for 28 years, it is clear that one third or more of this mighty ecosys­tem is vul­ner­a­ble to severe degra­da­tion through the inter­act­ing influ­ences of dev­as­tat­ing droughts, fire, for­est con­ver­sion to crops and pas­tures, and log­ging. What is most wor­ri­some is that this process of degra­da­tion is self-​reinforcing — fire begets fire; drought begets drought. The severe weather episodes asso­ci­ated with cli­mate change may already be push­ing the forest-​climate-​fire sys­tem towards a tip­ping point of cas­cad­ing for­est degra­da­tion. These effects swamp the slightly faster growth rates that we are see­ing in some Ama­zon trees that may be the result of higher CO2 levels.”

Mr Worstall’s com­ments are a bit ridicu­lous, really. Yes, it’s true that, where dis­tur­bances are lim­ited, ris­ing CO2 lev­els might help give trees a com­pet­i­tive edge with grasses. And it’s also true that some trop­i­cal forests are slowly get­ting more mas­sive, quite pos­si­bly because of CO2 fer­til­iza­tion. But to sug­gest this means our wor­ries for rain­forests are over is patently silly. There are a whole con­stel­la­tion of fac­tors — such as bull­doz­ers, fires, chain­saws, and rapidly expand­ing road net­works — that are knock­ing down rain­forests every day. For­est destruc­tion is hap­pen­ing a whole lot faster than for­est expansion
(William F. Laurance)

William F. Lau­rance, an ecol­o­gist at James Cook Uni­ver­sity in Aus­tralia, told mongabay​.com that these other fac­tors make it far too soon to begin assum­ing trop­i­cal forests are set to expand. “We live in an era of rapidly shrink­ing rain­forests, and all signs sug­gest that is only going to con­tinue, espe­cially in a world with up to 9.5 bil­lion peo­ple in it.”

Worstall’s edi­to­ri­als come two years after Jonathan Leake, Sci­ence & Envi­ron­ment Edi­tor of the Sun­day Times, trig­gered the “Ama­zon­gate” scan­dal when he claimed that stud­ies fore­cast­ing a poten­tial die-​off of the Ama­zon rain­for­est were “bogus”. Sci­en­tists quickly refuted the story and a sub­se­quent inves­ti­ga­tion revealed the die-​off sce­nario was indeed backed by sci­en­tific research. The deba­cle led to Sun­day Times retract­ing the piece and issu­ing an apol­ogy, acknowl­edg­ing jour­nal­is­tic mis­con­duct in the han­dling of the story.

The above news item is reprinted from mate­ri­als avail­able at Mongabay. Orig­i­nal text may be edited for con­tent and lenght.

(Source: Mongabay, 12.07.2012)

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