Comments to the report
Grazed and confused from the Food Climate Research Network.
I had high
expectations on the report Grazed and
confused, developed under the lead of Tara Garnett from the Food Climate
Research Network. I have been impressed by her previous research on many
aspects of the food system and her capacity to go further than using lifecycle
analyses to provide the Truth. Unfortunately this report doesn’t live up to my
expectations. At all.
By and
large, the conditions differ so much in different parts of the world, that the
kind of generalisation this reports tries to make is rather pointless. It is
like making a global report for “arable farming” and drawing general
conclusions that farming is good or bad.
The introduction
of the report is quite promising and balanced, but that balance is
unfortunately lost in what follows. The authors state in the introduction that
the report will only focus on the effects on the climate and not other aspects,
good or bad, of livestock or grazing. Fair enough, but they mostly forget this
when they report something slightly positive about grazing animals. That is often
dismissed or relativized with other arguments about alternative land use or
something else.
In the
report one can read statements such as “while well-managed systems that are not
implicated in deforestation certainly exist….” giving the impression that
deforestation would be the norm. Such statements must be considered extremely
biased since most grasslands are not the result of deforestation at least for
hundred years.
Admittedly
definitions are difficult, and the report tries to clarify some things
reasonably well in the start. But later on, the report is not helping with a
clear line, but mixes discussions which are relevant for grass grown in
croplands or dramatically altered pastures with native grasslands. They are
very different and what is correct for one is not necessarily correct for the
other. Grasslands in crop rotations (with grains etc.) can only meaningfully be
discussed as part of such a cropping system.
The nature
of grasslands differ enormously. By and large, most grasslands are located in
places where the natural conditions are harsh. And a lot of the grasslands of
the planet are not even grazed by domestic livestock. The alternative use of
this grassland is not obvious. A recent assessment found that 2 billion hectares, i.e. less than
60% of the world’s grasslands, are grazed by domesticated livestock. Meanwhile there are certainly
examples of very productive and very intensively used grasslands.
While this
report has already been used by advocates as a support for that carbon
sequestration in grassland is negligible, it is worth noting that the report
clearly states that carbon sequestration can be significant, that grazing can
increase sequestration and that under certain conditions grazed lands may
sequester more carbon than forests.
*
Now to the more
disturbing “facts” in the report.
The methane
calculations don't consider the research of the Oxford colleague Myles Allen
(2016)[i]
which shows very clearly that the calculations for expressing methane in carbon
dioxide equivalents hides a lot of information. For short-lived greenhouse
gases the comparison with carbon dioxide based on a pulse of emissions gives a
reasonably correct result only in a time span of a few decades. In the longer
term (which this is all about), the more correct comparison is between a pulse of
carbon dioxide and a constant rate in methane emissions. This means that “to achieve a
balance between sources and sinks of greenhouse gases in the very long term,
net emissions of cumulative pollutants such as CO2 need to be reduced to zero,
while emissions of SLCPs [of which methane is one, my comment] simply need to
be stabilised.“ (quote from the research of Myles
Allen and colleagues).
The authors do acknowledge this in the
report, but they don’t seem to consider it in most parts of the report where
they just use the extremely simplified ways of expressing methane in carbon
equivalents.
This should
be combined with
- that
pastures are not expanding on the planet, as a matter of fact they have
decreased last fifteen years (FAOSTAT).
- the
number of grazing cattle have most
likely also not increased.
- the
carbon sequestration In grasslands have most likely taken place over hundreds
of years and even much longer. For example the prairies was converted from
mineral gravel to thick fertile soils over a period of 10 000 years. A lot of the stable carbon in grasslands is
many thousand years old.[ii]
The
analysis in the report of the balance between carbon sequestration and methane
emissions is based on that there is a (ungrazed) grassland and now let us put a
cow that didn't exist before on that grassland. Then we add methane emissions into
the calculation and now we start to measure carbon sequestration. But the
reality is that the cow was there before and its "pulse" of methane emissions
already has happened; the same number of cows over a period of several decades don’t
add methane to the atmosphere as equal amounts are released and broken down
every year. And the carbon sequestration has been ongoing for hundreds of
years. Those things together makes the
calculations in Grazed and confused -- just confused.
In
addition, the discussion on carbon
sequestration is based on two other dubious and unsubstantiated assumptions.
A central
argument in the report, and the basis for a most of the subsequent calculations,
is that over time carbon sequestration will diminish and reach an equilibrium
after “perhaps 30-70 years”. It does seems
like a plausible assumption that sequestration will diminish over time, but the
hard evidence of this is lacking (only one example is cited and this example
has not even measured the actual carbon content), and even more so that the decline
in the rate of sequestration would be so rapid as claimed. The report also
contradicts itself by claiming that observed rates of carbon sequestration
could be legacy effects of the lands much
earlier conversion from arable to grassland. “Much earlier” must be a lot
more than “perhaps 30-70 years”.
The report
makes a big issue of the fact that carbon can be lost from the system if
exposed to draught, fire or flooding. Of course it can, but this can happen
regardless of if there are cows grazing or not. As a matter of fact, grazing animals can very often
reduce the incidence of wildfires in dry landscapes. Many (also this report) suggest
that grasslands can and should be converted to forests, but forests are
certainly exposed to even more such events with fires and storm felling (75
million M3 of trees fell in the storm Gudrun in Sweden 2005).
The fact that grasslands today have such great
pool of carbon, more or less the same as forests[iii], shows that this objection carries
little weight.
The calculations of carbon sequestration in the
report are based on several weaknesses.
-
Measurements of “carbon” are mostly only in the upper layer of soil, often the
top 30 centimetres and sometimes as little as the top 10 cm. Most studies which
have supplied the data for the report have been interested in changes in soil
organic matter as a measure of soil fertility and not the potential for carbon
sequestration. For that purpose the shallow measurements are quite OK. But the
stable carbon fractions which can be stored over a long time are found deeper
down. Admittedly the carbon content deeper down is lower, but it is a lot more
stable. Grassland has a very high proportion of belowground biomass and deep
roots, therefore the carbon stored by grasslands is likely to be distributed
deeper than in arable land. According to Jackson
et al 2017[iv],
native grasslands allocate around 60 % of primary production to roots,
croplands 10 % and forests 20 %.
- Measuring
carbon content in a specific layer of the soil and using that as a measure of
carbon sequestration, omits what happens with the soil in total. Soil can grow
“deeper”, by root activity and “higher” by accumulation of litter and dust on
the top. This is how “soil” is made in the first place. One can very well
sequester a lot of carbon in a soil while the carbon content 0-30 cm remains
constant.
-
Measurements are mostly on “carbon” not differentiating between different forms
of carbon the soil, while it is well known that there are only some fractions of
carbon (humic acids) which are stable.
- The
authors claim that carbon sequestration is most likely to take place in
degraded soils, but the evidence for this is not at all conclusive. Many of the
best soils in the world have been accumulating carbon for a very long term, and
many of the poor soils have been poor for a very long time. From a practical
farming perspective the experience is rather the opposite. A good soil can go
on accumulating carbon for ages, while it is a lot harder, but not impossible,
to increase soil organic matter in poor soils in poor climates.
- Carbon
sequestration is often, and by the authors, seen as having a direct
relationship to nitrogen (N) availability. For instance, the data in figure 7
is calculated from N values and not from actual measurements of carbon. This
assumption of some kind of simple relationship between N and C fluxes is
unsubstantiated. For example, in analysing total N and C fluxes over 75 year
Sochorova et al (2016) found that C content in soil in unfertilized hayfields
was significantly higher than in plots where N fertilizer had been used.[v]
In general, while N stimulate growth, it also stimulate above ground growth at
the expense of below ground growth, and carbon below ground is much more likely
to be stable in the long run. Increased N availability can also stimulate
decomposition of carbon rich materials, something everybody making composts can
easily witness.
*
The report
deals very lightly with the topic of ruminant/grass interactions and gives the
impression that the existence of ruminants in grasslands has little
significance compared to non-grazed grasslands. The role of the manure falling
on the field is mostly seen as a potential source of pollution. But this is a
far too simplistic view of the very complex interactions in nature. For
example, dung beetles and mycorrhiza play an important role, “In pastured
livestock operations, particularly in the tropics, dung beetles help mitigate
greenhouse gas emissions and aid carbon sequestration in part by increasing
grass growth, aerating soil, and delivering manure carbon to mineral surfaces
(Slade et al. 2016)”[vi].
The figure
10 shows the theoretical relationships between stocking rates, methane emission
and carbon sequestration. It shows that with a stocking rate of 0,5 cows long
term net sequestration is possible (also with all the limitations discussed
above), while it is impossible for higher stocking rates of 1 and 2 animals per
hectare. If we divide the global grazing livestock (say of half a billion
livestock units, which is probably a big exaggeration) with global grasslands
of say 2.6 billion hectares, we get a stocking rate in the range of 0.2. Such
low stocking rate would, with the authors own calculation, have the potential
to sequester more carbon than the methane emissions. The authors include no
such graph but instead shows the result for 0.5, 1 and 2 livestock units per
hectare. But 2 livestock units per
hectare is a density ten times higher than even a high estimate of average
global grazing intensity.
The report
claims that most extensive grazing systems are important sources of fossil fuel
derived CO2 emissions. There are pastoralist systems that use no fossil fuel
derived inputs whatsoever, apart from the odd veterinary medicine. Of course
there are others which use fences and motorcycles. But it is hard to imagine
that this could have any significance compared the massive amounts of fossil
fuel used in agriculture for machinery, pumps, fertilizers, dryers etc.
*
We live in
a world where the whole agriculture system is unsustainable, including the
production of staple foods such as wheat and potatoes. By and large the whole
system is driven by global markets and competition, massive use of chemical
fertilizers, fossil fuels and pesticides, which in turn has created an enormous
overproduction of agriculture crops. This unsustainable system is driving
deforestation for palm oil, cattle grazing, cocoa, coffee or soybean
cultivation. This unsustainable system is driving enormous waste, a rapid
increase in chicken and pork consumption and obesity. This unsustainable system
leads to massive emissions of greenhouse gases, massive pollution and loss of
bio-diversity.
Grazing
animals are not the big problem in the food system. As a matter of fact,
grazing and other forms of traditional livestock management are endangered
forms of agriculture in many parts of the world, simply
because they can’t compete with industrial farming practices.
A
sustainable agriculture and food system will look different in different
locations; after all, local adaptation is a key characteristic of any
sustainable system. Therefore, the number of livestock and the ways they are
integrated in the food system (and how much animals products that can be
consumed) will differ enormously in the same way as it has done historically. Trying
to conclude that pasturing is “bad” or that eating meat is “not sustainable” is
pointless on a ´global level.
Both
grasslands and forests can play an important role for carbon sequestration.
Even arable land can sequester carbon, but currently they are mostly doing the
opposite. There are big knowledge gaps about which methods work under which
conditions, even if there are many pointers as to which processes are most
efficient. There are also most likely trade-offs where carbon sequestration in
the soil will be in conflict with carbon for use as food, paper, timber, feed. I
wish the Food Climate Research Network would direct its energy into looking
into how to improve carbon sequestration while enhancing bio-diversity without
reducing the carbon available for use by human kind.
[i] Allen
MR, Fuglestvedt JS, Shine KP, Reisinger A, Pierrehumbert RT, Forster PM 2016:
New use of global warming potentials to compare
cumulative and short-lived climate pollutants. Nature Climate Change doi: 10.1038/nclimate2998
[iii]
Harden, Jennifer W. et al. Networking our science to characterize the state,
vulnerabilities, and management opportunities of soil organic matter, Glob
Change Biol. 2017;1–14.
[iv] Jackson
B. Jackson et al, The Ecology of Soil Carbon: Pools, Vulnerabilities, and
Biotic and Abiotic Controls Annu. Rev. Ecol. Evol. Syst. 2017. 48:419–45
[v] Sochorova et al, Long-term agricultural management maximizing
hay production can significantly reduce belowground C storage, Agriculture,
Ecosystems and Environment 220 (2016) 104–114
[vi] Jackson
B. Jackson et al, The Ecology of Soil Carbon: Pools, Vulnerabilities, and
Biotic and Abiotic ControlsAnnu. Rev. Ecol. Evol. Syst. 2017. 48:419–45
