This information below comes from a research letter
published in a journal recently entitled Climate metrics and the carbon footprint of livestock products: where's the beef?, and deals with the subject of metrics and
greenhouse gas emissions. I must confess
that I glanced at this paper last Friday afternoon, and quickly moved it to my
Monday pile, and have now re-read it refreshed after the weekend, when it now
makes more sense.
Metrics are inherently fairly complicated things, and
measuring the Carbon footprint of products has never been an easy task. Add to this the intricacies which come with
measuring the footprint of agricultural products and it tends to make the brain
As an industry however we need to reduce the carbon
footprint of our products in order to minimise the warming potential, the
effects of climate change, and improve business efficiency.
Because of this, there are a group of clever scientists that
have devoted their careers (and still are) to developing robust methodologies
to measure climate impacts. The “Global
Warming Potential (GWP)” is a commonly used method which assigns different values
to different greenhouse gases and provides a common figure that can be
However when looking at agriculture, unlike many other industries,
carbon dioxide isn’t really the big problem.
Emissions of nitrous oxide (from soils and fertilisers) and methane
(from ruminant livestock and manure storage and handling) pose much more of a
problem than the carbon dioxide that is used on-farm. Add to this that the “intensity” of these
gases in terms of their effect on climate change is higher and we start to see
the difficulties that arise.
Due to this large share of non-carbon dioxide greenhouse gas
emissions that arise from agriculture, the way that the calculation is done and
the method used is crucial when policy makers and scientists are looking at the
contribution of agriculture to global greenhouse gas emissions.
This paper (which if you are in the mood for, you can read
in full here), examines this issue in lots of detail and looks at whether in agriculture,
instead of using the 100 year global warming potential (GWP100)
there is a better way of describing it.
The method that it looks at is the global temperature change potential.
A couple of definitions
Global Warming potential (100
years)The Global Warming Potential (GWP) is a
useful metric for comparing the potential climate impact of the emissions of
different Long Lived Greenhouse Gases. Global
Warming Potentials compare the integrated radiative forcing (the change in
energy in the atmosphere due to a greenhouse gas) over a specified period
(e.g., 100 years) from a unit mass pulse emission and are a way of comparing
the potential climate change associated with emissions of different greenhouse
Global Temperature change potential (GTP) – the global
temperature change potential can be defined as the temperature impact at a
future point in time due to an emission pulse of the gas, divided by the temperature
change of an emission pulse of carbon dioxide.
The study recommends that metrics used to assess greenhouse gas
emissions should be re-examined. We all
recognise that agriculture is a dynamic changing system and assigning values to
products will always be challenging. The study argues that basing current GHG metrics solely on temperature
impact in 100 years is inconsistent with the current global climate goal of
limiting warming to 2degrees C, a limit that is likely to be reached well
within 100 years.
A reasonable GTP (global temperature change potential) value for
methane, (accounting for current projections for when 2 degrees centigrade
warming will be reached) is about 18,
which calculates the carbon footprint as being 20% lower than if it was measured
However by using this GTP method and using a 2 degrees C limit, this
results in the methane valuation increasing rapidly over time as the
temperature ceiling is reached. This means
that the carbon footprint would rise by around 2.5% per year, and as such would
then overtake the original result using GWP in 10 years.
This shows that using the GTP method would show positive results in the
short term, however over a longer term the impact on the livestock sector would
be much larger.
So what does this mean?
having read it through twice, it means that although this other method seems to
show the emissions in a more positive light in the short term, it catches up in
the long term. It just goes to show that
statistics can be made to show different things depending on how they are
reported. However it’s good that the
statisticians and other clever people are at least recognising that agriculture
is complicated in terms of measuring and that it needs more thought.
In the meantime, what does this mean on the farm? Well to me, it shows that while they argue
over the best method, we all have a chance at home to make our systems as
productive as possible (which will be a good thing for the carbon footprint of
the farm, and our pocket).
To read it in full please click here.