Getting to the bottom of Greenhouse Gasses: Part 2

7 Apr

If you didn’t catch Part I, you might want to go get caught up. Don’t worry, I’ll just wait here.

So, About that UN report. You remember, that scary one called Livestocks Long Shadow, the one that said meat is ruining the environment? Well it has some unpleasant things to say about today’s meat industry, namely, that it is a big emitter of greenhouse gasses, and a big contributor to environmental degradation.

The environmental degradation caused by large confinement operations is pretty well known.  You’ve got some pretty unpleasant problems with runoff and water quality, as well as problems with odor and air pollution.

But the UN report has some criticisms for pasture-based livestock as well.  In fact, the single biggest source of greenhouse gasses in animal production is from “Land Use and Land Use Change.”

To make matters worse, there is even an Australian study that claims that grassfed beef emits more greenhouse gas than lot-fed (confinement) beef does.

lot-fed beef in Australia is favorable, since this production system generates lower total GHG emissions than grass-fed production.”

Oh No!

To get to the bottom of the issue, I tracked down a copy of the article from the journal Environmental Science & Technology.   I wanted to see exactly what their methodology was; how they were coming up with their numbers.

I’ll save you all of the boring academic writing and summarize what they did.

The study’s authors found that cattle in feedlots eat a higher-energy diet than cattle eating grass.  Higher-energy equals higher weight-gain.  So the cattle gain weight faster which means that the feedlot cows are slaughtered at a younger age, and have less time to burp up methane.  Their grain diet also contributes to slightly fewer burps per day than a cow that’s eating grass.

So even though the feedlot cattle require more energy to grow the grain and transport it to the cows, their reduced methane emissions (burps) and shortened lifespan are enough to put them ahead of grassfed cattle.

Sadly the Australians are not alone.  There are other studies that back them up.

“Total CH4 emission (enteric + manure) was least for the [Grain] diet, whereas N2O and CO2 emissions were greatest for the [Grain] diet. Total greenhouse gas emissions were least for the [Grain] diet when [Carbon] sequestration by grasslands was not taken into account.”

Wow, this looks bad for grassfed beef doesn’t it?  I mean, who would have thought that cows eating grass are worse for climate change than feedlot cattle?  It kinda sets you back on your heels a bit when the more natural option is calculated out to be worse for the environment.

But don’t run screaming for the exits just yet.

Did you catch the last line from that quote?

“Total greenhouse gas emissions were least for the [Grain] diet when [Carbon] sequestration by grasslands was not taken into account.”

Hmm, that sure sounds odd.  So the scientists in this study know that the grass pastures that cattle graze on take carbon out of the air and sequester it underground, cancelling out some of the greenhouse gasses that the cattle emit, but they don’t count them in their study.  The Australian study is the same way. It does not subtract the carbon sequestration of the pasture from the emissions of the grassfed cattle.  So is this some big conspiracy to make grassfed beef look bad?  Well, I’m no big believer in conspiracy theories, so there is probably a better explanation.

If we dig into the UN report, we get a hint about why that may be.

The full potential for terrestrial soil carbon sequestration is uncertain, because of insufficient data and understanding of SOC dynamics at all levels, including molecular, landscape, regional and global scales (Metting et al., 1999). According to the IPCC (2000) improved practices typically allow soil carbon to increase at a rate of about 0.3 tonnes of carbon per hectare per year.

So the science about grassland carbon sequestration is far from thorough, but they can safely agree that “improved practices” can sequester 1/8 ton of carbon per acre per year.

The USDA has a different estimate of carbon sequestration by grasslands:

[USDA scientists] estimate that these 36 million acres of CRP lands can store 7 to 13 million metric tons of carbon a year for the next 25 years.

So that leave us an estimated 0.19 – 0.36 tons/acre/year!  That’s quite a big number.  That means a 50 acre farm could put away up to 18 tons of carbon per year.  And keep in mind that that estimate is for CRP fields, which are essentially unmanaged, with no animals on them.  With actively managed mob-grazed pastures there is no telling how much carbon they could sequester.

One of the goals of mob-grazing is to make the cattle trample carbon into the soil in the form of dead leaves, grass stems, and hay.  When a herd of cattle is actively made to bring carbon-containing dry matter into contact with the soil carbon sequestration is bound to happen at a higher rate.

It looks like there is currently a gap in the scientific data.  A gap between current cutting-edge grazing practices (mob-grazing) and the data on pasture carbon sequestration.  But while the knowledge gap exists, the scientists are still excited about the potential, proclaiming that better grazing could lead to: “substantial increases in carbon pools.”

And from the UN report:

Improved grassland management is another major area where soil carbon losses can be reversed leading to net sequestration, by the use of trees, improved species, fertilization and other measures. Since pasture is the largest anthropogenic land use, improved pasture management could potentially sequester more carbon than any other practice.

So this is the state of our science today.  We know that our grasslands and pastures sequester carbon, but we don’t really can’t say how much.  If we knew how much, we could factor that into the equation and I have a feeling that grassfed beef would look a lot better in the comparison.

My back-of-the-napkin calculations put grassfed beef’s carbon footprint equal to that of US feedlot beef when using numbers from the USDA’s CRP study and the Australian study.  I can find no studies that examine the carbon sequestration of mob-grazed pastures, but I suspect that when those studies are done, the results are going to blow people away (in the good way).

 

Stick around for Part 3, in which we discuss ways to reduce the carbon footprint of our cattle.

3 Responses to “Getting to the bottom of Greenhouse Gasses: Part 2”

  1. emily May 9, 2012 at 6:23 pm #

    I wrote a long reply but entered the wrong “captcha” and it was deleted, very annoying!

    So I will give the short version.

    for studies on carbon sequestration and cows check out Whendee L. Silver
    Silver Lab, University of California, Berkeley.
    She is working with Marin Carbon Project
    http://www.marincarbonproject.org/programs.php

    Also look at the Work of Christine Jones, a phD in Australia
    http://cesanluisobispo.ucdavis.edu/files/136179.pdf

  2. emily Townsend May 9, 2012 at 6:34 pm #

    oops that last link is from UC Davis it has many other resources at the end.

    keep up the great work!
    We need a certification program pronto that will create a market for carbon sequestering beef!

    Em

    • Andrew May 9, 2012 at 8:18 pm #

      Thanks for the info Emily!

      There is definitely more to learn about this carbon sequestration business.

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