Example 1
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Limits to rice yields ? (chapter 9) |
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Summary. Lomborg disputes the existence of an
upper limit to rice yields.
As evidence for this he presents a graph purporting to show steady and
continuing increases. Had he then followed this through with a careful
ananlysis of the data it would have shown rice yields levelling off at
about 6.7 tonnes/ha. Instead of doing this he attempts to muddy the
waters by citing an economics working paper (unavailable to anyone else
but Lomborg), whose claims - that rice yields will increase by up to
50% in the longer term - he fails to substantiate.
In his
chapter
9, "Will we have enough food", Lomborg has a paragraph with the
headline: Limits to yields ? He refers here to postulates advanced by
Lester Brown that there is an upper limit to the yield per hectare of
any crop. This limit is set by biological and physiological restraints.
For instance, Brown postulates that the rice yield obtained in Japan in
1983 has not been surpassed since then, and allegedly that this level
indicates
the
maximal possible yield. Lomborg opposes this claim by showing that the
rice yield in Japan has actually grown
slowly, and risen above the 1983 level from 1995 onwards. He argues
that the reason for this slow growth is the lack in Japan of economic
incentive to increase yields. On the other hand, a newly
industrialized country like South Korea, in Lomborg´s words,
"clearly shows a steady increase in yields". This is illustrated by a
graph which, in Lomborg´s view, shows a continuing rise.
Another interpretation of the same graph, however, is that South Korea
has caught up with Japan, and that after it reached the yield level
obtained in Japan in 1983, the growth in yields has nearly stopped
there too.
So, the question is: What is the proper
interpretation of Lomborg´s graph (his Figure 54 on p. 98) ? Does
it show a levelling off, or does it show a steady increase ? Lomborg
does not clarify this question by any objective (e.g. statistical)
method. Instead, he cites two economics working papers - which
according
to Lomborg himself are no longer available - to back up his assertion
that the
pessimistic views are incorrect. As the papers are unavailable,
the
reader has no chance to check the validity of this claim. He proceeds
to cite one of the unavailable documents for the following claim:
"Finally, the outlook for rice is dramatically optimistic -
medium-term increases of 20 percent are within sight, and researchers
expect a long-term increase of 50 percent." It is unclear from where he
or the authors of the of the working paper have got this figure of 50
%, but the 20 % increase apparently refers to a new type of rice
which is being
developed on the Philippines. Lomborg forgets to mention, however, that
this new cultivar is only suitable for tropical and
subtropical regions, not for Japan. He also forgets to mention that
Lester
Brown is aware of this new type of rice, and refers to its
possibilities.
Thus Lomborg tries to support his opinion by
citing
unverifiable sources who tell about expected future rises.
But now let
us look at what the
data actually tell. I have taken the figures from the FAO database
because the source that Lomborg refers to (a USDA web site) is no
longer available
(FAO calcualtes the rice yields in a way different from the method used
by the USDA, but the figures differ from
those of USDA by a constant factor which does not affect the
conclusions). I have divided the time series
into three periods: viz.
1963 -
1975
1975
-
1987
1987
-
1999
For each of these periods, I have calculated the average rice yield in
tons per hectare at the midpoint of the period, and the annual rate of
growth in yield during the period, expressed in percent increase per
year. I have done this for three nations - Japan, South Korea, and
China - and have plotted the growth rate against the yield. The
results are seen in the graph below:
In this graph, C indicates China, J is Japan, and K is (South)
Korea.
One point is clearly aberrant. That is the point for China before 1975,
i.e. during the Mao period. When we disregard this point, where the
yields were low due to political causes, the rest of the points are
grouped nicely along a straight line. In other words there is a clear
correlation between the yield level and the scope for further
growth. We can draw a regression line which meets the horizontal axis
at about 6.7 tons /ha. This would mean that when yields have reached
6.7 tons, the
average growth in yield will be zero, indicating that there is indeed
an upper
limit. Evidently Japan and South Korea have already reached this
limit, and China is approaching it. Higher yields in
certain years are due to favourable weather, and this will be
offset by lower yields in years with unfavourable weather. The long
term average will not rise above 6.7 - provided that no radically new
technological progress is made. This tells us that the average rice
yields in China will soon have reached their maximum. In 1999 yields
were only 6 % short of this maximum, so the scope for increases in food
production in China is therefore not as vast as some would have it.
This analysis therefore solves the problem of
how to make a proper interpretation
of the graphs in Lomborg´s figure 54. If we ask: do
the curves rise steadily, with fluctuations up and down around a
sloping line, or do the curves reach an asymptote, with fluctuations up
and down around a horizontal line, then the answer is clear: there is
an asymptote whose horizontal section has already been reached.
So when Lomborg states on p. 98 (left): "The "wall"
[i.e. limit] Brown has found for Japanese rice yields seems to be
caused by a deliberately misleading example" , the person doing the
misleading is Lomborg. Brown does not, as Lomborg claims, argue
that rises in yield will come to a total halt altogether. The overall impression of
Lester Brown´s text is that of growth
rates that are about to reach zero, but he does not deny the
possibility for some further
increases, although they will be relatively small.
Data from more recent years ( up to 2010) indicate
that rice
yields in South Korea, China and Japan have indeed levelled off more or
less at around 6.7 tons/ha. However, this level is not
necessarily strictly determined by biological and physiological
restraints.
These restraints may be at a higher level. This is illustrated by the
situation in Australia, which has the world´s highest rice yields
per ha (an average of 9 t/ha for 2006-2010). This is partially
due to a new method of more intensive
monitoring of the fields, a procedure called `ricecheck´ , which
was introduced in 1987 (see here). It
seems unknown if this procedure could be adopted also in other
countries.
Thus, with reference to yields in Australia, Lomborg
may be right that the rice yields elsewhere may be increased by 20 % or
more. But his claim that the yields in countries of East Asia are
steadily rising, not levelling off, is definitely wrong. The same type
of data that he uses do infer a levelling off. Considering that he has
taught statistics, he should be the first to decide if the trend is
steady or slowing down. But he fails to do that.
Altogether, Lomborg´s criticism of Brown
is not fully justified, and he is not right that his data "clearly
show
a steady increase in yields" in South Korea.
Therefore, his text is here classified as an error, but there is no
indication that this is a deliberate error.