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Chapter 16:

Acid rain and forest death




Lomborg tries to give his reader the impression that acid rain and forest death are just myths that arose around 1983, but soon died out again. He recognizes that SO2 emissions may damage public health, but he nearly disregards all other damages, i.e. damages to buildings, monuments, lakes and forests. The method that he uses to belittle such damages, is linguistic manipulations, e.g. changing definitions from paragraph to paragraph. In trying to do so, he reveals to professionals that he lacks even basic knowledge on the subject, but he probably relies on that the lay reader will not detect this. Actually, after the first surge of worrying over forest death around 1983, research on the subject has continued in relative obscurity, and evidence for the actions of acidic depositions on the soil system, on tree roots, and on above-ground parts of the trees, is becoming ever stronger. In large parts of Europe, the critical load of acid deposition is still exceeded, which means that soil conditions still deteriorate. Recent evidence e.g. from Germany and Norway document that there are long-term downward trends in the health of forest trees.

Two general references that correct many of Lomborgīs claims:

P. Gundersen (2002): Air pollution and acid rain - myth and reality. Pp. 257-268 in "Sceptical questions and sustainable answers", to be downloaded here.

J. Puhe & B. Ulrich (2001): Global climate change and human impacts on forest ecosystems. 592 pp. Ecological studies no. 143. Springer Verlag.


P. 178 left: ERROR

"Apart from the fact that big-city pollution has nothing to do with acid rain . . ". Error: Nitrous gases from car exhaust (NOx) are an important source of acid rain, and not the least dangerous, because nitric acid, in contrast to sulfuric acid, can transform aluminium compounds in the soil into toxic, dissolved aluminium ions.


Lomborg starts on p. 178 to define acid rain as "a collective term for damage to forests, lakes and buildings believed to be caused by emissions of NOx or SO2." Inconsistency: On p. 180 left he changes this definition; now he writes that the forest death in Bavaria etc. was not due to acid rain but to local pollution. So now, it is only acid rain if the acidity comes from far away. Next, on p. 180 right, he refers to those effects that occur far from the source. But these, too, are not due to acid rain, he says, because "pollution does not directly cause damage to the trees (as was assumed by the acid rain theory) but . . it weakens the treesī resistance." So, his original definition, dealing with "damage caused by emissions . . " is gradually changed all through the text, so that it never applies to the actual cases. This change of definitions is deliberately misleading.

P. 178-179 and fig. 98: FLAW

Flaw: Figure 98 can be traced to a non-peer reviewed paper by Kulp that is printed in Julian Simonīs book, "The ultimate resource" (1995). As the stated purpose of Lomborgīs book is to check if Simon is right, he cannot use a chapter in Simonīs book to check this. The experiment referred to is called long-term, but lasted only 3 years. Furthermore, there could be problems with Pulpīs study. We are not told what acid was used to acidify the rain. If, for instance, sulfuric acid were used (which could easily be the case), then the aluminium buffer system would prevent soil pH from falling below 4.2, no matter how acidic the rain could be. In that case, the two right-most data points in each row would be irrelevant. This might explain why "even with precipitation almost ten times as acidic as the average rain in the eastern US (pH 4.2) the trees grew just as fast". The Danish specialist Gundersen asked Lomborg to procure a copy of Pulpīs original publication from the experiment, but Lomborg had no copy of the article and could not provide it. So it is impossible to check the source.

P. 179 left: (COMMENT)

"Some even longer controlled experiments were carried out in Norway, and here too the conclusion was that the predicted negative effects of acid rain `could not be demonstratedī ". Comment: The Norwegian study, by Abrahamsen et al., has many flaws. The trees were watered not with rain water, but with ground water, which had a high level of cations relative to what was in the very leached sandy soil used. The water was acidified with sulfuric acid which cannot dissolve aluminium, but, on the contrary, precipitates aluminium ions as insoluble aluminium sulfate. During the experiments, the soil pH of 3.5 did not change at all, and neither did the amount of exchangeable acidic protons on the soil colloids. In short, the soil chemistry did practically not change during the experiment, and therefore it is no wonder that no effect could be seen on the trees. Unfortunately, Abrahamsen believes that his own results are representative of other situations e.g. in Germany, which they are not, and thus the criticism that Abrahamsen has raised against other, e.g. German, scientists, is not justified.

P. 179 left, note 1296: FLAW

Note 1296 has the text: "Ulrichīs hypotehses about aluminiumīs damaging properties were particularly in focus for these tests . ." Flaw: This formulation, in combination with the words that the predicted negative effects could not be demonstrated, will give the reader the false impression that the theories on the role played by aluminium ions have not been substantiated. The opposite is true, however. Many studies have demonstrated that the growth of tree roots is disturbed when the concentration of aluminium ions is increased relative to magnesium and calcium ions (e.g. Marschner (1991): Plant and soil 134: 1-20; Bennet & Breen (1991): Plant and soil 134: 153-166). Also, Ulrich (ref. cited at top of this web page) has demonstrated that Ca/Al and Mg/Al ratios have indeed decreased druing recent decades in German forest soils.



"For this reason NAPAPīs conclusion was . . " Flaw: Here, Lomborg quotes not a final conclusion from NAPAP, but an "external review draft" from August 1990, i.e. more than 10 years before Lomborg published his book. The NAPAP has continued their work, and Lomborg ought to have cited their more recent 1998 report to the US Congress. In doing so, he would not have been able to cite such positive conclusions.

P. 179 left: FLAW

" . . . NAPAPīs conclusion was that `the vast majority of forests in the U.S. and Canada are not affected by decline . . .". Flaw: This is a misleading citation. It seems to be Pulpīs interpretation, and it seems to originate from the executive summary of NAPAPīs 1990 report. However, US scientists and sources in the US-EPA say that this report was influenced by political judgements, and much emphasis was placed on the uncertainties. Furthermore, a range of important results from NAPAP studies was published at a later stage. In their 1998 report to Congress, the executive summary reads: "Sulphur and nitrogen deposition have caused adverse impacts on certain highly sensitive forest ecosystems in the United States . . . if deposition levels are not reduced in areas where they are presently high, adverse effects may develop in more forests due to chronic, multiple-decade exposure." (Gundersen 2002, cited on top of this web page).

P. 179 left: ERROR

" . . Moreover there is no case of forest decline in which acidic deposition is known to be a predominant cause." Flaw: This quote is from Simonīs book and thus cannot be used to check Simonīs postulates. Error: Cases of forest decline in North America caused by acid rain are indeed known. According to an EPA report to the US congress in 1995, one of the most thoroughly documented examples of manifest forest decline caused by the indirect effects of acidic precipitation is found in the plateaus in eastern USA (e.g. Great Smokey National Park). Lovejoy, in Scientific American Jan. 2002, writes: "Two clear-cut examples are red spruce in the Adirondacks and sugar maple in Pennsylvania." References to these latter cases are for spruce: C. Eagar & M. B. Adams (eds. 1992): Ecology and decline of red spruce in the Eastern United States, p. 385, synthesis by A.H. Johnson et al. And for sugar maple: C.T. Driscoll et al. (2001): Bioscience 51: 180.

P. 179 left: FLAW

"As far as lakes are concerned, it concluded that in even the most acid-sensitive regions, acidification problems affected only 4 percent of lakes and 8 percent of water courses." Flaw: This conclusion is cited from NAPAPīs 1990 report. If Lomborg had consulted EPAīs Acid rain environmental effects factsheet from 1995, he would have read that there are major problems with acid rain in the USA, especially regarding lakes and surface water. Moreover, pollutants from the USA are carried to eastern Canada, where i.a. 14,000 lakes have been acidified.

P. 179, figure 99: (COMMENT)

Comment: What the figure actually shows, is changes in alkalinity.

P. 179 right: (COMMENT)

"In 27 percent of all lakes in Norway the sulfur deposition exceeds the critical load". Comment: Out of 5643 lakes in Norway with trout, the trout populations have disappeared in 820, and become reduced in additional 1069. Thus, altogether, 33 % of all trout lakes have become affected (B.L. Skjelkvåle, rapport 671/96, Statens forurensningstilsyn, Oslo). When Lomborg is able to find a slightly smaller figure (27 %), this must be because this figure deals not with reported effects, but with critical load. And there may be some lakes which were acidified earlier, but in which the continued acidification is now below the critical load, i. e. where no further deterioration will happen.

P. 179 bottom right: ERROR

On damage to buildings and monuments: "It turned out that if the acid content was increased by 20 percent, the time at which restoration would be necessary was only brought forward by 2-5 percent. . . " Error: This paragraph is based on the executive summary of the NAPAP 1990 report. The conclusion is very misleading and at variance with what is stated in other sources to which Lomborg has had access. Thus, in an overview paper on this subject (Kucera & Fitz (1995): Water, air and soil pollution 85: 153-165), printed in a volume which Lomborg has held in his hand, we read: "At numerous sites where the SO2 levels have decreased between the 1987/88 exposure and the 1992/93 exposure, a pronounced decrease has been found of the corrosion rate of especially carbon steel. . . The decreasing trend in SO2-concentrations has for some materials led to a substantial reduction in deterioration rates . . Studies of cost of air pollution damage to materials show that the savings may balance a considerable part of the total abatement costs." This paper also gives formulae to calculate the rate of erosion of various materials. If, for instance, we take sand stone, the formula tells us that if we reduce the acid load by 50 %, the rate of erosion will be reduced by 48.4 %, not 10-15 % as stated by Lomborg. Indeed, Lomborgīs text is completely against the general knowledge that antique monuments that have been standing for thousands of years are now nearly mouldering before our eyes. Lomborg has read a text by Gundersen in 1999, as well as a conference summary statement from 1995, according to which the reduction of sulfur emissions in Europe will lead to a saving of damages to buildings of 14,000 mio. DM a year, at a cost of 26,000 DM a year. So, Lomborg knows that costs on buildings are large, but he leaves out this information. Thus, his text is deliberately misleading.

P. 180 left: ERROR

" . . that smoke directly from the sources of pollution damaged the trees." Error: This is not correct. Apparently, Lomborg does not know the difference between smoke (which is fine particles suspended in the air) and compounds such as SO2, which are gases, not particles. Lomborg makes this unjustified distinction between smoke and gaseous pollution, which was not made in the source referred to, and furthermore he fails to understand that, when brought into contact with water, SO2 is transformed into an acid (hyposulfuric acid), and, when it is also oxygenated, is transformed into sulfuric acid. Thus, he does not have even the most fundamental chemical knowledge necessary to write about this subject. His misunderstanding leads him to write that SO2 pollution ("smoke" in his terminology) can be reduced locally, whereas acid rain cannot, although reduction of SO2 and reduction of air pollution with sulfuric acid is the same process. Remarkably, precisely these misunderstandings happen to lead him to postulate that the clear-cut effects seen near to the sources of sulfur emission are not relevant to the acid rain phenomenon, and thus, that there exist no clear-cut effects of acid rain at all.

P. 180 left, note 306: FLAW IN REFERENCE

Flaw: When Lomborgīs students in 1998 had a newspaper article printed with the claim that "acid rain is a myth", 4 of the most prominent Danish experts in this field wrote a counter-article. However, the newsapaper did not want to print this article which explained why Lomborgīs students were not right. Only an abbreviated version was printed later. As a studied insult, Lomborg repeatedly uses this never published article as one of his prime sources on the subject of acid rain, and uses it as a reference for claims contrary to what was actually said. As the article has never been published, and is in Danish, English readers have absolutely no chance to read it and to find that this source is being misused. So, this again is a case of deliberate misleading.

P. 180 left: FLAW

"If we look at the growth of European forest, it has not been reduced . . " Flaw: This is not correct everywhere. Thus, it may be seen from Puhe & Ulrich (2001 - referred to on top of the web page) on their pp. 171-173 that the growth of many trees has been reduced in the Harz, and the growth of many trees in Bavaria was stimulated during the 1950s, but reduced after that, especially strongly after 1980.

P. 180 left: (COMMENT)

" . . since the 1950s trees have begun to grow faster and faster , and this is due . . " Comment: It is true that this is partially due to the excessive pollution of the air with nitrogen compounds. It is also, however, due to the effect of acids on the soil system: In the first instance, acids increase the liberation of Mg, Ca and ammonium ions from the soil particles, thereby putting more nutrients at the treesīdisposition. But as this process continues, the liberated ions leach out of the top soil, and the supply diminishes in the long term. Recent investigations in Norway, referred to by Gundersen (ref. on top of this web page) demonstrate that from the late 1950s to the late 1970s, trees in areas of high acid load had their growth stimulated more than trees in less affected areas. But after the late 1970s, it has been opposite, and by now the trees in the most affected areas grow less than normally - although the N supply from the air is still very large. So, evidently, the growth increase was a temporary phenomenon due to the liberation of cations from the soil particles, and is now followed by a growth decrease.

P. 180 top right: ERROR

"Today we know, however, that this was purely due to a change in the method of calculation." Error: The fact is that we know today that this was not purely due to a change in the method of calculation. The reference in note 1311 is mainly to Gundersen et al., 1998. This reference is repeatedly misused deliberately by Lomborg, as explained for note 1306.

P. 180 right: ERROR

"One theory frequently advanced is that pollution does not directly cause damage to the trees (as was assumed by the acid rain theory) . ." Error: Firstly, the acid rain theory is being corroborated more and more strongly and should not be referred to in the past tense. Secondly, it is not true that the theory assumes that the effect is mainly a direct effect of acids that drop unto the leaves. Thirdly, we should mention a conference summary statement that tells us what is the consensus among experts (Rohde et al. (1995): Water, air and soil pollution 85 (1): 1-14.). Lomborg has read this paper (as is evident from a Danish text, "Godhedens Pris"), but he has omitted it from his treatment of the subject in TSE. In this text we read that: "We know with confidence that in parts of northern Europe, forest soil pH has decreased by 0.5-1.0 units during the past 30-60 years, at least partly as a result of acid deposition. This has led to reduced root distribution of forest trees." Thus, Lomborg knows that the connection between sulfur emission and damage to the root systems of forest trees has been established with "confidence", and when he gives an impression different from this, his text is deliberately misleading.

P. 180 right: (COMMENT)

"This theory is not easy to put to the test . . " Comment: This is true, but as is evident from e.g. Puhe & Ulrich (loc. cit.), the difficulties have to a great extent been overcome, and the theory has been more or less verified. So, here again, Lomborgīs text is somewhat misleading.

P. 180 right: FLAW

". . in comparing the various areasī pollution with forest death, there is very little or no correlation." Flaw: Lomborgīs reference to this statement is Abrahamsen et al., 1994. They present data that 20 % of the variation in forest damages in the different regions of Germany can be explained by variations in wet deposition of N and S; this translates into a correlation coefficient of 0.45. Considering that conditions of soil types, climate etc. differ between regions, this is hardly "very little correlation". It should be noted that elsewhere (p. 117) Lomborg is content with a non-significant correlation of only r = 0.2. It seems that to Lomborg, a correlation is good enough if it goes in the direction that he wants, and not good enough if goes contrary to what he wants, and that questions of the size of r, or of significance, are irrelevant to him. Thus, his text is deliberately biased. Concerning the correlation between forest death and pollution between countries in Europe, it is evident from a text that Lomborg could have read, that such a correlation does exist (Lorenz (1995): Water, air and soil pollution 85: 1221-1226). Altogether, Lomborgīs sentence, seen in combination with the preceding sentences, gives the reader a clear impression that the theory that acid rain causes damage to forest trees, is not substantiated. The opposite is true, and Lomborg knows that. So, the whole paragraph is deliberately misleading.

P. 180 right: (COMMENT)

" . . the European Environment Agency concludes that `a causal connection cannot . . be established between an input of acid deposition . . and observed foliage reduction." Comment: The quote is correct, but somewhat misleading. The EEA report states that "Extensive damage to trees, in the form of defoliation and discoloration, has been reported . . ". But then, when they come to the causes of this phenomenon, they state that other causes may be in play besides acid rain, and it is therefore that a causal connection with acid deposition cannot be established.

P. 180 right: FLAW

"Actually, the EEA finds that monitoring results show an ever increasing defolitation, despite reductions . . " Flaw: When the effects of S deposition go via the soil system, it is natural that the state of the soil reflects not just present deposition, but also deposition during the preceding years. Furthermore, when the critical load of the soil system is exceeded - which is still the case in central Europe - then this means, by definition, that the chemical conditions in the soil continue to deteriorate (but at a slower pace than before). Thus, it is no contradiction that defoliation increases at the same time as SO2 emission has become slower. We can compare this with a person who is forced to drink dilute sulfuric acid. He gets sick from that. If then we force him to drink even more sulfuric acid, albeit only half as concentrated, he will continue to get even more sick, in spite of that we have reduced the acid concentration. Has Lomborgīs source (EEA) recognized this ? Yes ! They write: "Soil acidification is a slow process, however, and will still continue in areas where critical loads are exceeded, with possible long-term effects." If Lomborg had included this sentence, which stands right next to the sentence that he did quote, then he would lose his point that there is no connection between SO2 emission and defoliation. It seems evident, therefore, that his text is deliberately misleading.

P. 180 right: ERROR

". . and that the cause may instead be due to the aging of the monitored tree stands." Error: In the EEA report, the sentence says: "This may partly be due to the ageing of forest stands." Thus, Lomborg has replaced the word "partly" by the word "instead". That may seem to be a minor change, but actually it changes the meaning. If EEA thought , for instance, that 30 % of the effect maight be explained by the ageing of the forest stands, this will now in Lomborgīs version have become 100 %. Actually, there is documentation that in some cases, ageing does not at all contribute to the deteriorating state of the trees (e.g. Puhe & Ulrich, loc. cit. p. 171). But Lomborg exchanges one cause - pollution - with anothere cause - ageing of the stands - simply by manipulations of the language. Thus, his text is deliberately misleading.

P. 180 right: ERROR

" . . a German scientist . . found that the proportion of damaged trees was just as great then as it is today." Error: The scientist referred to is O. Kandler, a specialist in fungal diseases. Kandler did analyze old potographs of sick trees, which looked precisely like the "new type of forest damage" discussed now. But his photographs dealt only with single trees - not the proportion of trees - and thus did not tell anything about whether such fungus disaeases had become more common. In a discussion with Ulrich in 1988-9, Kandler postulated that the proportion of damaged trees today is the same as always. But only two years later he published a new paper (Kandler, 1990: Plant disease 74: 4-12), in which he presents photos of spruces with yellow needles, taken in 1984-86 in Schwarzwald, and he writes that the increased proportion of such trees in 1984-86 was not due to fungal infections, but to Mg deficiency, which might have been triggered by drought. This is precisely what would be expected according to the theories on the effects of acid rain.

P. 180 right: FLAW

"Foliage loss is in reality simply a non-specific expression that applies to numerous specific, familiar diseases . . " Flaw: This is misleading. That kind of defoliation which has been monitored since 1983, is not just due to diseases. One of the main symptoms recorded is the yellowing of needles. Yellowing means lack of chloropyll, which again goes back to a defiency of Mg, as Mg is a necessary part of chlorophyll. The theories on the effect of acid rain are specifically that the availability of divalent cations (Ca and Mg) is reduced. As to Ca, this is important for the development of the roots. Therefore, calcium deficiency may lead to smaller root systems with fewer fine root hairs, and this will make the trees more susceptible to drought, and in that way lead to foliage loss. Thus, many of the damages seen are not, as Lomborg postulates, due to diseases (in the sense of infections with microorganisms).

P. 180 right: FLAW

" . . and the reason why we have started worrying about it is that we have started monitoring this loss". Flaw: This is not true. The worrying started around 1980, and the monitoring was started as a consequence of this. There is ample explanation why the "new type of forest damages" were suddenly seen around 1980. This was precisely the point of time when the annual growth of spruces of all ages in the Harz and Schwarzwald suddenly declined, and when the Mg/Al ratio in forest soil in central Germany had just dropped considerably (Puhe & Ulrich, loc. cit.). This was also just a few years after considerable drops in soil pH in Germany as well as in Sweden (Schulze (1989): Science 244: 776-783). So, the evidence is that the forest damages were really "a new type", and that they appeared around 1980.

P. 180 right: FLAW

". . it was probably reasonable to reduce SO2 emissions from the point of view of health . . But . . " Flaw: As explained in the comment for p. 179 bottom right, the spared damages to buildings represent an amount of money roughly half of the cost of reductions in sulfur emissions. Thus, the regards to damages on buildings are another good reason to reduce emissions. Add to this expenditures for liming of acidified forests and lakes, loss of trout fishing, reduced tree growth in certain areas etc. etc. But all these effects that are not directly related to human lives, are completely ignored by Lomborg, or belittled without justification

P. 180 bottom right: FLAW

"But acid rain was simply not the terrible threat . . ". Flaw. This is not quite correct. The threat is still there. As Lomborg knows, the critical load is exceeded over great parts of Europe, which means that the conditions are still deteriorating. But probably, Lomborg has not understood the concept of critical load, although it is explained e.g. in the EEA report that he has read.

P. 180 bottom right: FLAW

"The anticipated, large-scale forest death never took place." Flaw: This is more or less correct, but the cause is that sulfur emissions were actually reduced. However, over large parts of Europe, the critical load is still exceeded, which means that the story has not ended yet. The state of the forest soils and some lakes is still deteriorating. And, in accordance with this, the condition of some forests is also still deteriorating. Figure 8.7 in Puhe & Ulrich (loc. cit.) demonstrates that the proportion of defoliated trees has been rather steadily increasing in south Germany and north.west Germany from 1984 to 1996. Thus, we have not yet seen the end result.

P. 180 bottom right: WRONG STATEMENT

"Unfortunately, the myth lives on in many places. " Error: Already in 1998, an article by 4 leading Danish experts stated clearly that acid rain is not a myth. Lomborg has the right to disagree with the experts only if he can demonstrate that he has a fuller understanding of the subject than they have. He has not. On the contrary, his chapter 16 demonstrates that he does simply not understand the subject that he is writing about. Instead of basic knowledge of the subject, Lomborg puts linguistic manipulations to make a text that is deliberately misleading from the start to the end.


"Simple. But not borne out by the evidence." Error: Lomborg is wrong, and the newspaper article is right. It is absolutely correct that sulfur in the atmosphere is one of the main sources of acid rain. And there is a large and growing amount of evidence that acid rain kills forests.