Lomborg-errors: "Cool it!"

Historical trends: CO2 and temperature
 
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 Comments to pages 63 - 71 in Cool it!


Since Lomborg wrote `Cool it!´, knowledge about past temperatures has increased, and the pattern presented in the socalled `hockey stick´ curve has been corroborated and extended. A good overview of the most recent evidence may be read here.

LONG HISTORY: CO2 AND TEMPERATURE

Comments to pages 63 - 68 in Cool it!

FLAW
Page 64: " . . it is very likely that in our world additional CO2 from fossil fuels will drive up temperatures. But this was not the case over the past 650,000 years . . "
Flaw:  
The fact that at the end of a glaciation, the rise in temperature precedes the rise in CO2 levels, does not preclude that additional CO2 has driven up temperatures. The relationship between temperature and CO2 is quite complicated, as explained here on Lomborg-errors´ page on the CO2 lag. A main point is that although the first temperature rise in the Southern Hemisphere obviously triggered a rise in CO2, the subsequent temperature rise in the Northern Hemisphere happened several thousand years later, after CO2 had risen. All estimates of what proportion of the temperature rise were due to CO2 , center at around 50 %. As an example, see this quote from the paper by Petit et al. (1999), which is cited by Lomborg as evidence that the CO2 signal comes much later than the temperature signal: "Results from various climate simulations make it reasonable to assume that greenhouse gases have, at a global scale, contributed significantly (possibly about half, that is 2-3°C) to the globally averaged glacial-interglacial temperature change." Lomborg has read this paper, so he should know it.
Although many express the same opinion as Lomborg does, this does not change the fact that he omits an important caveat. The categorical statement "but this was not the case. . " qualifies this text at least as a flaw.

ERROR
Page 65 and figure 17 top right: ". . although he ends up exaggerating a fair amount. In his perhaps most memorable stunt . . "
Error:
Lomborg talks specifically about the movie, because he refers to the "stunt". If you carefully study the graph that Gore presents in the movie, you find out that the point that Gore shows for 2050 is somewhere about 500 ppm, which, as Lomborg recognized in note 302, is correct. So Gore does not exaggerate in the film.

FLAW
Page 65 , figure 17 top right and note 302. In the note: "In his book he clearly shows how CO2 will lie above 600 ppm by 2050. "
Flaw:
Lomborg is not right here. He has overlooked that the legend in Gore´s book is not "CO2", but "CO2  equivalents", which implies that Gore is correct. See details on the Lomborg-error page on Gore-errors, for page 67 in Gore´s book.

(COMMENT)
Page 66 : "Of course, it is entirely misleading to suggest that the expected CO2 increase will mean a three times the warming we saw . . . "
Comment:
Gore does not say that the temperature will rise three times as much. He leaves it to the audience to imagine what the rise will be.

(COMMENT)
Page 66 bottom and figure 18: "Deep sea temperature over the past 67 million years, with today at 0° C."
Comment:
The curve does not give a proper picture of the variations in global temperatures. What is shown, is the deep sea temperature in tropical regions. Much of the deep sea water originates from polar regions, from where it flows to the tropics. But these ocean flows are presumably different in periods with no or little glaciation (before 34 Ma) and periods with much glaciation (e.g. from 34 to 25 Ma). So the curve also reflects differences in ocean currents. In addition, after 34 Ma, the curve does not show temperature (see next paragraph).

FLAW
Page 66 bottom, figure 18 and note 306: "Deep sea temperature over the past 67 million years, with today at 0° C."
Flaw:
Only when you consult note 206 do you have a chance to note that the curve does not show variations i temperature, but variations in delta 18O, which are due to changes in temperature AND in ice cover. The original paper (Zachos et al. 2001) states that : "The delta 18O temperature scale was computed for an ice-free ocean . . . and thus only applies to the time preceding the onset of large-scale glaciation on Antarctica (~35 Ma). From the early Oligocene to present, much of the variability (~70%) in the delta 18O record reflects changes in Antarctica and Northern Hemisphere ice volume." This means that the temperature range of 12° C in Lomborgs curve after 35 Ma (from +7°C at 25 Ma to -5°C just before recent) includes artifactual fluctuations due to changes in glaciation, which means that it is greatly inflated and that the range should only have been about 3.6° C. According to the original paper, deep sea temperatures changed from 12°C at 50 Ma to 4.5°C at 34 Ma. Thus, over this period, Lomborg´s curve is approximately correct, except that it seems to have been lifted by about 1°C. But after 34 Ma, the curve is too expanded, resulting in water temperatures down to -5° C, which seem unrealistic. It is not true that the graph is presented as by Sorothkin et al. (2007), because in their graph (which suffers from the same flaws) the whole curve is lufted by about 3°C relative to Lomborg´s.

FLAW
Page 67, figure 18 and note 307: "CO2 over the past 60 million years."
Flaw: Lomborg has drawn this curve himself, based on data from several sources which have been fitted together. For the period from 25 Ma to recent, the curve agrees with the original data. But before 25 Ma, none of the original curves or data sets resemble Lomborg´s curve. The raised levels of CO2 are true, but the original curves all have large-scale fluctuations which have disappeared in Lomborg´s version. Lomborg writes that his data are "combined from two different sources, and smoothed". This smoothing has removed nearly all fluctuations. This is important, because the so-called temperature curve has a much finer structure. The reader is left with the false impression that ups and downs in the temperature curve are not paralleled by similar ups and downs in the CO2 curve. This lack of correlation has partially been created by Lomborg´s data treatment. For instance, there were clear fluctuations in CO2 levels at the episodes at 34 Ma and 25 Ma (start and end of the oligocene glaciation), but these fluctuations are barely visible in Lomborg´s graph.

FLAW
Page 67: "Finally, looking at the connection between temperature and CO2, it is clear why Al Gore chose not to show this slide."
Flaw: Lomborg postulates that there is no relationship between variations in temperature and CO2. But he most know that this is not true, because his sources say otherwise. For instance, according to Pagani et al. 2005, temperature and CO2 varied in concert in certain periods, but not in others. They write that global climate and the carbon cycle were linked from the eocene to the late oligocene, and that CO2 levels at the eocene/oligocene boundary could have triggered the rapid expansion of ice on East Antarctica at that time. Pearson & Palmer (2000) write that the cooling 2 - 4 Ma coincided with a CO2 drop from 280 ppm to 210 ppm. The sources also state a lot of other factors that could have changed climate, such as tectonic processes and changing ocean streams around Antarctica. The fact that other factors play a role is absolutely no proof that CO2 does not play a role.

(GROUNDLESS DEROGATION)
Page 67: ". . . it is clear why Al Gore chose not to show this slide."
Flaw: There are many other reasons why Al Gore did not show this slide: 1) It has been drawn by Lomborg, not by any others. 2) The so-called temperature curve does not actually show temperature. 3) The CO2 curve has the flaws stated above.

FLAW OF OMISSION
Page 67: "But the connection seems fairly week. While CO2 declined rapidly around 60-50 milion years ago, temperatures increased."
Flaw: Lomborg wants us to focus on one of those periods when variations of CO2 and temperature are not in concert. He chooses the period 60 - 50 million years ago. The most remarkable event during this period is the large, sudden rise in temperature 55 Ma, when deep sea temperatures rose by 5-6° C, and sea surface temperatures rose by 8°C at high latitudes. This temperature rise lasted for only c. 100,000 years. But this was long enough that many animal species went  extinct. The sudden rise is seen in Lomborg´s figure, although it was larger than shown. Now, interestingly, at exactly the same time (± a time lag that cannot be resolved) there was a large belch of carbon from the oceans into the atmosphere; it is believed that up to 2600 Gt of methane was released from the ocean floor. This would soon have become oxidised to become CO2. This shows extremely clearly that on a time scale that is relevant to us, the two parameters were very closely connected.  Gradual changes of averages over a period of 10 millions of years, probably in connection with movements of the continents and opening up the gateway that allows ocean currents around Antarctica, are on a much larger timescale that is irrelevant to  human society now. The event at 55 Ma is clearly explained and described in Lomborg´s sources. But of course, in his own words, "it is clear why Lomborg chose not to refer to this", even though he focuses on exactly that period when it happened. This must be judged as a deliberate flaw.
    The sudden change in CO2 at 55 Ma is clearly demonstrated in Beerling & Royer (2002), cited by Lomborg. Here, based on leaf stomata, they have a general level of CO2 of about 350 ppm around 55 Ma, which suddenly rises to 800 ppm for at short period (their page 545). Compare this with Lomborg´s figure 18, and you will see how much the estimates of past CO2 levels depend on the methods applied. Also notice that Lomborg cites page 546 in that paper. He can hardly have avoided seing also page 545. But, of course, "it is clear why Lomborg chose not to show this".

FLAW
Page 67 bottom: " . . flat for the last 20 million years, world temperatures drop 10°C into recurrent ice ages."
Flaw: As stated above, CO2 levels did not remain flat, and world temperatures dropped by 3°C, not by 10° C, because most of the change in the so-called temperature curve is due to glaciation (the water deposited in ice sheets is deficient in 18O, and therefore the content of 18O in ocean water increases).

(COMMENT)
Page 67 bottom: "Looking much further back . . we have .. even less connection between the two".
Comment:
When we look so far back, everything was different: the solar radiation was weaker; atmospheric pressure was higher; the content of oxygen in the atmosphere was different; the continents were placed completely differently; plants were more primitive, and grasses did not exist; at 500 Ma, there were not even land plants yet; animals with high respiration rates did not yet exist.  Conditions then were not comparable to those today.



RECENT HISTORY: CO2 AND TEMPERATURE

Comments to pages 68 - 71 in Cool it!

FLAW
Page 69: "Mann used just tree rings from 22 or more different places . . "
Flaw:
Mann et al. (1999) used  12 proxies, of which 3 were condensed from 28 American tree ring series, 6 were tree rings from other continents, and  3 were ice core data. Mann et al.(1998) used such data plus data from corals and historical records.

(COMMENT)
Page 69 and note 318: " . . . the process tends to churn out a hockey stick."
Comment:
Here, Lomborg refers to the criticism advanced McIntyre & Mc Kitrick (2005). The point is that Mann et al. used a so-called PCA (principal components analysis) to obtain a general temperature pattern for dense clusters of data from NW America. The PCA was performed in such a way that there might arise a so-called artificial hockey stick effect. Huybers (2005), cited in note 318, concluded that whereas the procedure from Mann et al. gives too much hockey stick, the alternative procedure suggested by McIntyre & Mc Kitrick seems to give too little hockey stick. Even so, von Storch & Zorita (2005), likewise cited in the note, test the magnitude of the artificial hockeystick effect and find that it "does not have a significant impact but leads only to very minor deviations." Furthermore, the effect arises only in the process whereby tree ring data from a densely sampled region (NW America) are combined into one single data set. Tree ring data from other regions, which were used by Mann et al. without being combined through a PCA procedure, are not subject to this. So only one of the many proxies used by Mann et al. was subject to the artificial hockey stick effect. So this particular part of the criticism against Mann et al.´s hockey stick has very little substance.

(COMMENT)
Page 69: " . . . combining tree rings over many centuries is fraught with difficulty."
Comment:
Lomborg tries to impart the impression that using tree rings to reconstruct past temperatures is so problematic that we should not trust tree ring reconstructions. This is not true, and it may be added that certain reconstructions based on tree rings yield quite large long-scale variations in temperature (e.g. Esper et al. 2002, here probably because of too restricted geographical coverage).

(COMMENT)
Page 69 and note 319: " . . . you will tend to get a very flat, uneventful result."
Comment:
Here, Lomborg refers to another point of criticism against Mann et al.´s hockey stick, namley the criticism raised by von Storch et al. (2004). They claim that the regression procedure whereby proxy values are `translated´ to temperature data produces a tendency to underestimate variations over long periods, e.g. over centuries. It seems that they are right, and that their conclusion may be correct: "Past variations may have been at least a factor of 2 larger than indicated by empirical reconstructions."  Lomborg refers also to the paper by D´Arrigo et al. (2006). They treat their tree ring data  with two different statistical procedures (which are called the STD and the RCS methodology, respectively). The STD methodology is similar to the one used by Mann et al. Using  a large set of tree ring proxies, and avoiding the most problematic series in the Mann et al. study, they find the following difference between the highest temperatures during the medieval warm period and the little ice age: In the STD procedure: 0.3°C, in the RCS procedure: 0.5°C. Thus it is true that the procedure applied by Mann et al. does tend to produce relatively low temperature variation over the centuries, but it is not true that this is an inherent property of tree ring data, and the flattening of the stick caused by this procedure is probably not quite as severe as some would have it.
Neither Lomborg nor many other critics of Mann et al. remember to cite another paper by Zorita, von Storch and others (Zorita et al. (2005): Natural and anthropogenic modes of surface temperature variations in the last thousand years. Geophysical research letters 32: L08707). The authors have fed a computer model with three factors influencing climate: solar variation, volcanic eruptions, and greenhouse gases. The model then calculates what the climate would have been during the last thousand years. It may yield a hockey-stick like temperature curve if the climate sensitivity is set at a low level - probably too low. At a more likely level of climate sensitivity, temperature variations are still pretty well correlated with temperature reconstructions from tree rings and other proxies, but the variations up and down in the temperature curve are somewhat higher. Now, the point is that if one accepts this higher climate sensitivity, then the model also predicts that temperatures will increase by about 3.5° C during the twenty first century due to manmade greenhouse gases. So, those who criticize the hockey stick by referring to von Storch et al. and say that temperature variations in the past were rather large, should also consider the other side of the coin which is that IF you accept the alternative temperature curve of von Storch et al., THEN you must also accept the prediction of a 3.5° temperature rise during this century due to greenhouse gas emissions. Lomborg and nearly all other critics forget the latter part.


ERROR
(Page 69), note 320: " NRC (2006) only confirmed with high confidence that present-day temperatures are higher than during any time in the past 400 years, but that less confidence could be placed in the reconstructions for 900 -1600. "
Error:
By subtle means, Lomborg has manipulated the quote such as to change the meaning. He avoids mention of the sentence that follows right after his quote (NRC 2006 p. 18): " ... from A.D. 900 to 1600. Presently available proxy evidence indicates that temperatures at many, but not all individual locations were higher during the past 25 years than during any period of comparable length since A. D. 900." He also neglects another sentence on the same page: ". . . none of the large-scale temperature reconstructions show medieval temperatures as warm as the last few decades of the 20th century." So, temperatures now are higher than any time during the last 400 years, and also higher than the global mean at any time since A.D. 900. By using the word "only" Lomborg tells us that only the first claim is valid, whereas actually both are valid. Due to the little word "only" in Lomborg´s text, this is counted as an error.

ERROR
Page 69 bottom: " This is the only long-term temperature series that is not based just on tree rings"
Error:
The temperature curve of Moberg et al. (2005) is the one that best fits Lomborg´s agenda. Lomborg needs an argument to justify that he presents just this and not others. The argument that he uses is that all the others are based only on tree rings. This is wrong. First, Moberg et al. (2005) include tree ring data. Second, out of the 10 temperature curves that are presented in the IPCC report (4AR, wg1, fig. 6.10b), five are based solely on tree rings, four are based on tree rings plus various other proxies, and one is based solely on glacier data. Thus, Lomborg´s argument is not valid.

ERROR
(Page 69 bottom), note 322: " Moberg [et al.] (2005) are also the only ones to accurately track the only measured temperature, the borehole temperature . . .  "
Error:
This is not true. Borehole temperatures are also "tracked" e.g. by Hegerl et al. (2007) (link) and in the IPCC 4AR report.

(COMMENT)
Page 70 top, figure 19: "Northern hemisphere temperature from 900 to 2006 . . "
Comment:
First, it should be noted that over large parts of the southern hemisphere, there was no such medieval warm period (IPCC 4AR, wg1 6.6.2). Second, the curve chosen by Lomborg, that of Moberg et al., is not representative of other reconstructions. The temperature difference between the Medieval warm period and the LIttle Ice Age is here 0.7°, which may be compared for instance to the two values of 0.3° and 0.5° referred to above in relation to note 319. To cite section 6.6.1 in the latest IPCC report p. 471: "This reconstruction displays the warmest temperatures of any reconstruction during the 10th and early 11th centuries. . " and p. 473 "only one (Moberg et al., 2005) indicates persistent hemispheric-scale conditions . . that were as warm as those in the 1940s and 50s. However, the long time scale variability in this reconstruction is determined by low resolution proxy records that cannot be rigorously calibrated against recent instrumental temperature data. . ". Third, the curve of Moberg et al. has been smoothed so strongly that the marked fluctuations on a decade-scale have disappeared. The medieval warm period was not uniformly warm, and the little ice age was not uniformly cold. There is nothing wrong in itself in presenting this curve, but it is a bias not to state clearly that it is not representative.

FLAW OF OMISSION
Page 70  and note 324: Lomborg refers to a number of local episodes where the climate was relatively warm, but fails to mention that these are not representative of the trends on a global or hemispherical scale.
Flaw:
It is generally recognized that the warm periods in the northern hemisphere during approximately the period 900 - 1400 were not simultaneous. The relative warmth was not a simultaneous global trend, like the trend we see today. Lomborg cites the reference Hughes & Diaz (1994), but Lomborg´s text does not agree very well with the conclusion of that paper, which is that "These warmer regional periods were not strongly synchronous. Evidence from other regions . . indicates that the climate during that time was little different to that of later times . . . the avialable evidence does not support a global Medieval Warm Period." For instance, their figure 3 shows that a warm period occurred at 1400 in N Fennoscandia, which was a cold period in NW Europe. D´Arrigo et al (2006), which has also been read by Lomborg, shows that the warm periods were not synchronous in America and in Eurasia. And Burroughs (1997), likewise cited by Lomborg, also stresses that the Medieval warm period was not a synchronous trend all over the northern hemisphere. On the page cited by Lomborg, it says: "Again we see a patchy combination which provides little indication as to whether any pronounced global changes were in train."
This has an important consequence in relation to the "hockey stick" curve. If the medieval warm episodes are in different regions in different periods, then the global average will show a relatively flat curve, with no marked warmth at any time.

(COMMENT)
Page 70: "This was the period when the warmer climate and reduced sea-ice made possible the colonization of the otherwise inhospitable Greenland and Vinland  . . by the Vikings."
Comment:
According to norse records kept on Iceland, the sea-ice situation around south Greenland at the time when it was colonized by the vikings was not different from the situation as it was during the first decades of the 20th century (Ogilvie & Jonsson (2001): Climatic Change 48: 9-52). This gives a slightly different impression than fig. 19 in Cool it, where the years around 1000 are slightly warmer than the years just after 1900. Other sources (here) indicate a situation around 1000 more like the latter half of the 20th century, which is more in accordance with Lomborg´s presentation.

(COMMENT)
Page 70: "In Alaska, the mean temperature was 2-3° warmer in the eleventh century . . "
Comment:
This is correctly cited from Lomborg´s source, but it seems improbable. According to the source, this is based on tree ring data, but according to data which Lomborg has seen (D´Arrigo et al. 2006), there seems to be only one long series of tree ring data from Alaska, and this shows a relatively warm period (approximately like in the mid 20th century) in the tenth century, whereas the eleventh century was considerably colder there.

(COMMENT)
Page 70: "The Japanese cherry blossom . . . "
Comment:
Lomborg´s source has the following sentence: "After a brief interval of cold winters in Japan, the cherry blossoms returned to early blooming in the twelfth century." By inference, the eleventh century must then have been cold in Japan - just that period that allegedly had very warm temperatures in Alaska. If Lomborg had given the full quote, it would have been apparent that the waves of warm weather were not synchronous.

(COMMENT)
Page 70 and note 328: ". . . glaciers advanced rapidly in Greenland, Iceland, Scandinavia and the Alps . "
Comment:
Lomborg dramatizes what happened. The main theme of the source mentioned in note 328 (Matthews & Briffa 2005) is that the little ice age was not particularly synchronous in different parts of the northern hemisphere. The article says: ". . beyond the European Alps, and to a lesser extent in Scandinavia and North America, data on the precise timing of  variations in glacier size during this broad time interval are still patchy. Consequently, several controversial issues remain, including . . . the degree of synchroneity between glaciers from the different regions." For instance, while the best studied glacier in the Alps advanced around 1300 and receded around 1400, the glacier in Norway that Lomborg writes about, Bjørnbreen, receded around 1200 and then stayed short until around 1500, when it advanced continuously during the following centuries. The lack of synchroneity is also the theme of this paper.

FLAW
Page 70 bottom and note 330: ". . crop practices changed throughout Europe to adapt to a shortened and less reliable growing season, causing recurrent famines."
Flaw:
The picture painted by Lomborg here is a rather stereotypic picture of a sustained cold period. But what his source (Burroughs) tries to do, is exactly to decompose that stereotype. It says, on the page cited by Lomborg: "This growing body of work shows that . . the real situation is not quite as stark as the simple stereotype suggests." There is no mention of a change in crop practices, and although the recurrent famines are precisely described, it is also stated that the worst famine occurred when there was a series of bad years in an otherwise benign period. It is explained that Malthusian population growth contributed to the famines. Lomborg´s formulation is taken from Reiter (2000), not from Burroughs as indicated.

FLAW OF OMISSION
Page 70-71: When reading Lomborg´s text, you get the impression of a sustained cold period during the Little Ice Age.
Flaw:
The period was characterized by short  periods (decades) of very cold weather, alternating with other periods of benign weather. For instance, the book by Burroughs, cited by Lomborg, says: ". . the interpretation of the Little Ice Age as a period of sustained cold breaks down . . in the subsequent decades. . . the cold of the 1590s is not maintained. . The annual figures for the Central England Temperature series confirms the exceptionally low temperatures of the 1690s  . . The first striking feature of these records is the sudden warming from the 1690s to the 1730s. In less than 40 years the conditions went from the depths of the Little Ice Age to something comparable to the warmest decades of the twentieth century." The same variability is clearly presented in the book by Le Roy Ladurie, which Lomborg also uses as a source.

FLAW
Page 71 top:  "Possibly the worst winter in France in 1693 is estimated to have killed several million  people  - about 10 % of the population."
Flaw:
In Lomborg´s source, on the cited page, the author says: "During the 1680s the growing season had been warm and dry and produced, in northern France and England, a series of such superb harvests that the price of wheat had begun to decline. But not for long. In 1687 began the dreadful cold seasons . . " but also, speaking of the 1690s:  ". . several major food crises. One of these was among the worst famines in the whole seventeenth century: the failed harvest of 1693 caused an apocalyptic, medieval-type dearth which killed millions of people in France and the neighbouring countries." Lomborg´s flaws are: 1) he omits mentioning the decades just before (and just after), when the weather was quite benign. Second, the millions of people that died were not just in France, but in several countries; therefore, the estimation based on the population size of France is not valid. The figure of 10 % does not occur in the source.

FLAW
Page 71 top:  ". . with Lake Superior iced over till June in 1608" .
Flaw:
The source says: "In 1607-8 ice persisted on Lake Superior until June." So whereas Lomborg postulates that the whole lake was covered by ice, the source says only that remnants of ice persisted.