Example 3
|
Air pollution in London in previous
centuries (chapter 15) |
Back to front page
To list of six examples
Summary. When describing how much greater air
pollution in London was in previous centuries, Lomborg presents a graph
pieced together from sections of different datasets. His choice between
different datasets covering the same period bears no relation to their
likely robustness, and seems to have been deliberately made to increase
the impression of a steep decline during the 20th century. Indirectly
calculated figures from before 1900 are without justifiable reason
multiplied by an arbitrary factor of about 5 in order to fit values
around 1900 to the artificially increased steepness of the curve during
the 20th century. This deliberate manipulation makes it look as if air
pollution was much worse in former centuries.
When Lomborg wants to present an optimistic view on air pollution in
cities, he can do that by claiming that the problems were much worse
in the past. To demonstrate this, he uses London as an example (he
could not have used a city like Paris, because Paris was heated by
wood, not by coal). On p.
164
he writes: "Air pollution is not a new phenomenon that has got worse
and worse - it is an old phenomenon, that has been getting better and
better, leaving London cleaner than it has been since medieval times."
His basis for saying so is a paper by the
British environmental scientist Peter Brimlecombe. Brimblecombe used an
existing computer model which calculates air pollutant concentrations
on the basis of the amount of pollutants emitted, the size of the city,
and wind speeds. When appllied to cities of varying sizes at the
present time it gives values which lie within 20 % of the mean values
measured at air pollution monitoring stations in those cities. So it is
fair to assume that it could tell us former pollution levels with
nearly the same precision.
Brimblecombe recorded the size of London in various
years, the amount of coal burned for fuel within the city limits (this
is known), and the sulphur content of the coals used (estimated from
geological knowledge of the coalfields). With this input to the model,
he got the results which are presented in the figure shown below.
We see that the pollution, e.g.
with
sulphur dioxide, peaks near the end of the 19th century, which
agrees with data showing that the number of days in London with
smog
increased much during the latter half of the 19th century. We
also see a steep drop in pollution levels from about the year 1900. The
model produces this drop because the diameter of London grew much at
this point of time, which would have the effect of diluting the
pollution. But this
does probably not fit with what actually happened. Brimblecombe
writes: "The decline shown in the pollutant concentrations
. . seems particularly large, and is probably exaggerated by the
diffuse nature of the outer parts of the city at the turn of the
century. " But unfortunately, to support his point, Lomborg emphasizes
this decline and does not cite the author´s reservations.
Next, Lomborg continues the curves up to modern
times by fitting in data of actual measurements of the air in central
London from about 1930 onwards. Concerning sulphur dioxide, these data
are taken from a paper by D.P.H. Laxen and M. A. Thompson, published in
1987. Below I present a figure from their paper with those curves that
were used by Lomborg.
We need to go into some detail with this figure. First we notice
that in the beginning the measurements are neither systematic nor
continuous. And next we notice that sulphur dioxide has been measured
by two different methods, called A and B. In general, it seems that
method B gives higher values than method A.
Now when we compare this figure from
Laxen and Thompson with the SO2 curve in Lomborg´s
figure 86, we see which parts Lomborg has used. Starting from recent
time and moving backwards, we recognize the course of Laxen´s
curve 9, then curve 6 (the lowest of four parallel curves), then the
two separated pieces of curve 4, and finally, in the oldest part of the
diagram, curve 2, i. e. the upper of three curves. So to the right in
the figure, he picks the lowest curve possible, and to the left in the
figure, he picks the highest curve possible. He does this even though
curve 2 is based on fewer measurements than curve 1; the prominent high
peak at about 1935 is actually based on quite few measurements.
Furthermore, the choice of curves is inconsistent. To the right he uses
curves based on method A, but to the left curves based on method B,
which, as noted above tends to give higher values. By this kind of
selectivity - which is unacceptable in scientific work - he manages to
make the slope from the 1930s till now steeper than it would otherwise
be. Again: it seems that Lomborg has an intention to make the decline
in pollution look as large as possible.
The next trick is the way that
the curves from the two different studies are combined.
Brimblecombe´s curve ends in 1929 with values slightly below 100
µg, whereas Laxen´s curve, in Lomborg´s version,
starts around 1934 with a value about 400 µg, i.e. 5 times as
much. So Lomborg assumes, without any actual knowledge about this, that
levels in the city center are 5 times as high as the average values
over the whole city, because with this assumption he can make a smooth
junction of the two curves. In note 1163 Lomborg writes
how he has done this: "This necessitates an upwards adjustment of
Brimblecombe´s data by approximately a factor 4." (well, 5 is
approximately 4, isn´t it?). So whereas the
maximum concentration per m³ of SO2 in the late
19th century is given by Brimblecombe as around 180 µg, this is
increased by Lomborg to 900 µg, as we see in
his figure. So actually he has multiplied the whole curve by a factor
5. He defends this manipulation as follows in note 1163: "However,
since Brimblecombe´s model data are averages for London as a
whole, it must be assumed that central London was much more polluted,
in line with actual measurements." But this reasoning is flawed. London
in earlier times had a smaller diameter, with shorter distance to
unpolluted surroundings, so the difference between the air quality of
the center and the average for the whole city has not been constant.
Brimblecombe also gives data for Epping Forest, about 20 km from the
centre of London. Here we had 70-125 µg of SO2 per m³ around
1970, at a time when the values in the center of London were 200-250
µg per m³. So it is not true that the values in the center
are up to 5 times higher than the average for greater London. The
maximum centre/average ratio that one could justify is a factor of
somewhat less than 2.
Remember
that the right part of Brimblecombe´s curve probably declines too
steeply, and that the values after the year 1900 should probably have
been higher. Taking this into consideration, it would not be necessary
to multiply the curve by as much as 5 in order to make it fit with the
actual measurements. And remember also that the left part of the curve
from Laxen has been made
steeper by Lomborg. Only by multiplying the Brimblecombe curve could he
make its slope fit
in with the artificially increased
steepness of the curve from 1931 onwards.
In any case, Lomborg purports to use only "the
facts" - the actual
figures - so by his own standard he is not allowed to multiply the
figures by 5 when it happens to suit him.
If the curve had not been multiplied by 5,
what would Lomborg´s figure have looked like ? In that case we
would have had a concentration of about 180 µg around 1850, and a
concentration of 300-400 µg around 1935. So the curve would
then have shown that pollution was less in former times, and had
increased until shortly before the big smog catastrophe in
1952. In that case, Lomborg would not have been able to back up his
assertion.
Lomborg´s statement that ". . the
levels of the 1980s-1990s are below
the levels of the late sixteeenth century" are definitely false,
because even if we assume that a multiplication of Brimblecombe´s
curve might be justified for those time periods when London had a
large diameter, this would certainly not be justified for the early
years, when London had a small diameter. That is, the values given in
Lomborg´s figure for the time before and around 1600 are
certainly very wrong.
In short, Lomborg´s postulate -
that air pollution
was much worse from 1700 to 1900 than after 1900 - is most likely not
true, and his postulate that London in the 1980s-1990s was cleaner than
in medieval times is definitely unjustified. To
multiply figures from one period by any factor that one likes, in order
to make them larger than those of another period, is gross
manipulation.
Some people think that even though Lomborg´s
curves are not correct, this does not change the big picture which is
that the air quality of London today has improved greatly relative to
what it was. In their view, this is heartening to know, and Lomborg is
right in telling this good story. However, they fail to see that
Lomborg has an agenda: He wants to give us the impression that the air
quality has improved gradually from about 1850 "by itself", and that
this improvement bears no relation to the passing of the Clean Air Act
in 1956 (p. 170). However, had his curves not been manipulated, we
would have seen that air pollution culminated in 1935 and 1952, and
that the situation improved only when the Clean Air Act was passed. So
the agenda is: does it, or does it not, help to combat pollution by
inforcing restrictions? If we accept Lomborg´s view - that it
does not help - then citizens of many large cities around the world
will not be able to experience the same heartening facts that the
citizens of London experience today.