|Historical trends: CO2 and
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.
HISTORY: CO2 AND TEMPERATURE
- 68 in Cool it!
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
. . "
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.
Page 65 and figure 17 top right: ". . although he ends up exaggerating
a fair amount. In his perhaps most memorable stunt . . "
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.
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. "
Lomborg is not right here. He has overlooked that the legend in
Gore´s book is not "CO2", but "CO2
that Gore is correct. See details on the
Lomborg-error page on Gore-errors,
in Gore´s book.
Page 66 : "Of course, it is entirely misleading to suggest that
the expected CO2 increase will mean a three times the warming we saw .
. . "
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.
Page 66 bottom and figure 18: "Deep sea temperature over the
past 67 million years, with today at 0° C."
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).
Page 66 bottom, figure 18 and note 306: "Deep sea temperature over the
past 67 million years, with today at 0° C."
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 18O,
changes in temperature AND in ice cover. The original paper (Zachos
2001) states that : "The 18O
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 18O
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.
Page 67, figure 18 and note 307: "CO2 over the past 60
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.
Page 67: "Finally, looking at the connection between temperature and CO2,
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.
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
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
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
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".
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
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
Page 67 bottom: "Looking much further back . . we have .. even
less connection between the two".
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.
HISTORY: CO2 AND TEMPERATURE
Comments to pages 68 - 71 in Cool it!
Page 69: "Mann used just tree rings from 22 or more different places .
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.
Page 69 and note 318: " . . . the process tends to churn out a
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
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.
Page 69: " . . . combining tree rings over many centuries is
fraught with difficulty."
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).
Page 69 and note 319: " . . . you will tend to get a very flat,
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
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.
(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. "
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
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.
Page 69 bottom: " This is the only long-term temperature series that is
not based just on tree rings"
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.
(Page 69 bottom), note 322: " Moberg [et al.] (2005) are also the only
ones to accurately track the only measured temperature, the borehole
temperature . . . "
This is not true. Borehole temperatures are also "tracked" e.g. by
Hegerl et al. (2007) (link)
IPCC 4AR report.
Page 70 top, figure 19: "Northern hemisphere temperature from
900 to 2006 . . "
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
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
of that paper, which is that "These warmer regional periods were not
strongly synchronous. Evidence from other regions . . indicates that
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
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."
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
Page 70: "In Alaska, the mean temperature was 2-3° warmer in the
eleventh century . . "
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.
Page 70: "The Japanese cherry blossom . . . "
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.
Page 70 and note 328: ". . . glaciers advanced rapidly in Greenland,
Iceland, Scandinavia and the Alps . "
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.
Page 70 bottom and note 330: ". . crop practices changed throughout
Europe to adapt to a shortened and less reliable growing season,
causing recurrent famines."
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.
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.
Page 71 top: "Possibly the worst winter in France in 1693 is
estimated to have killed several million people - about 10
% of the population."
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.
Page 71 top: ". . with Lake Superior iced over till June in 1608"
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.