How much do cattle contribute to greenhouse gases?

To begin with, in regards to accounting for enteric emissions (“cow burps”), most people use global stats. So even if you use 2006 Long Shadow as a reference, and actually read that document, a large portion of that 18% was attributed to land use change specifically in Brazil at peak deforestation rates from 1998 to 2004. If I recall correctly 57% of the GHG’s attributed to cattle was from South America. This report was also just for OECD countries. 2013 Long Shadow scaled the number back some to 14.5% still using 2004-2005 Amazon deforestation rates. Again a global number that still used different Life Cycle Analysis [LCA] methods for different sectors.

More recently the authors of the UN FAO Long Shadow Report, Anne Mottet and Henning Steinfeld, also posted wrote this 2017 article, Cars or livestock: which contribute more to climate change? This article noted that that they used different methodologies for doing Life Cycle Analysis for different sectors (something Dr. Frank Mitloehner pointed this out way back in 2010 about the 2006 report). One way was inclusive of all emissions from the Ag sector, including land use change, and the other was just tail pipe emissions from the transportation sector as shown in the high lit portion of the graphic below.

But guess what, when you look regionally, for example, in North America, deforestation isn’t a large issue. We’ve actually had some afforestation. So when you look at the 2014 UN Climate Change Conference numbers from Lima, Peru, US and North American numbers for Ag are a bit different. Why? Land use change isn’t such a large contributing factor to the LCA’s. US Ag in total is around 8.1%. 26.79% of that 8.1% is from enteric fermentation (cattle burps). What’s 26.79% of 8.1%?…. 2.17% of GHG’s. Add in all of manure management for all livestock, and you’re at approx. 40% of 8.1%  or 3.24% of all GHG’s including land use change. This is noted in the graphic below compiled from UN and IPCC data…not the beef check off program. Note too that less than 0.5% of fresh beef consumed in the US comes from Brazil. Most (85%) US beef is domestically produced. What isn’t  domestically produced largely comes from Canada, Mexico, Australia and New Zealand.

These global or regional numbers also don’t account for soil sinks or tropospheric sinks. These numbers are also based on GWP100 carbon equivalencies. Now that the IPCC’s sixth assessment also recognizes GWP* (chapter 7, p.123) , old GWP20 and GWP100 over account for biogenic cyclical sources of methane (eg. enteric methane) by 3 to 4 times over a 20 year time period. GWP* accounts for the different lifespans of different GHG’s. GWP20 and GWP100 didn’t account for the hydroxyl oxidation of methane in the troposphere. So methane is broken down a lot faster than CO2 and N2O in the atmosphere. I’ve noted this previously in these three blog posts pointing out the problem in so much of the public discourse on GHG’s…that is only looking at the emission side of the ledger. …and not accounting for sinks. 

Personally I follow the range, soil, plant science as well as the atmospheric chemistry science. I try to avoid narratives especially ones from industries, and food religious zealots. (Ironically 2006 LS was primarily intended to create more “intensification” which in this context meant more factory farming). Ruminants and other sources of biogenic methane aren’t the problem. Thermogenic sources (fracked gas, coal bed gas and other fossil fuels) of GHG’s are. Enteric methane is a distraction. Poor land management destroying soil sinks and reducing photosynthesis via desertification, deforestation and ocean acidification are also a huge problem. And yes, cattle and palm oil are part of the problem in tropical regions as I noted in this more recent blog post, The Deforestation Process... Cattle is a very conspicuous driver, though it’s not really the primary driver. Human greed is. 

So what is the real percentage that cattle contribute to climate change?

Any likely percentage of GHG’s from cattle varies a lot based on range management, methods of cropping, accounting for sinks, how emissions are allocated to what sectors, and whether GWP* or GWP100 is used. So a large part of the emission math depends on how the accounting is done. To date, there’s not much comprehensive full life cycle analysis of other sectors including the transportation sector. Plus little to no life cycle analysis has used GWP* not even in papers with AMP grazing showing carbon negative systems where more carbon is sequestered than emitted. Most LCA’s don’t account for soil sinks or soil emissions (due to tillage) . So, in other words, we need better regional and system data, and we can’t really make universal claims. Heck, when LCA’s haven’t been conducted the same way for different sectors, you can’t even give percentage numbers per sector, since you don’t even know how large the pie actually is. 

Regardless, any food can be grown or raised in ways that have a wide range of outcomes especially in regards to GHG’s and other environmental impacts. For example, palm oil trees grown in monocrops on deforested land (where peat bogs have been drained) have vastly different impacts than palm oil trees grown in dynamic agroforestry systems where abandoned deforested land is being reclaimed and re-forested. Likewise, beef raised on tropical forest cleared of valuable timber or mined for minerals, and needs to wait two years before the land can be planted into soy … a lot different than beef raised on land where grasslands have been restored, soil health has been greatly improved, and soil organic matter has increased from 1/2 a percent to over 8 percent. 

So the HOW and appropriateness of WHERE matter often as much or more than the WHAT. So instead of labeling foods as good or bad, the focus should instead be on improving methods of production, and ideally using best practices in the appropriate places whether that’s to produce, rice, beef, soy, corn, wheat, chicken. pork, alfalfa, almonds, strawberries, potatoes, etc. There’s room for improvement all around even with feedlot finished beef. Why? Feed crops grown with cover crops and integrated livestock, reduce pesticide and syn N use while also reducing the amount of time cattle are in feedlots since with grazing cover crops cattle can achieve similar gains backgrounding those cover crops (and crop residues)  requiring less time in the lots. Less synthetic Nitrogen, for example, means less GHG’s for the production of syn N, less volatized N2O and less leached nitrogen into waterways.

Or, in other words, I’m more interested in optimizing systems than applying global numbers that really don’t relate to certain locations or regions…especially when such global numbers are based on worst, rather than best, practices.. I find relying on ambiguous global numbers creates more paralysis and agendas than it does meaningful solutions. 

Note too, I have zero financial connection to any food industry, beef or otherwise. I have zero financial connections to any ranch or other producer. I don’t receive any discounts or free stuff either from any producer. I have never been paid for anything I’ve written. I’m actually just a huge soil nerd, and I see the role ruminants have in enhancing soil health when those ruminants are managed properly. That management is able to reduce atmospheric CO2 and repair the small water cycle. Here’s one of several things, I’ve written on soil health:  Restoring the plant’s soil microbiome

So, yes, estimates depend on different assumptions, but what’s GWP*?  

If you want to take a deep dive into understanding what GWP* is, here’s a twitter thread by Dr. Michelle Cain discussing the paper on GWP* she co-authored. The lead author was Dr. Myles Allen, a physicist at Oxford, who was part of the 3rd, 4th and 5th IPCC assessment panels This thread has a number of reference articles.  Here below are a couple talks by Cain and Allen as well as an informative podcast

In short, as I noted above, different greenhouse gases have different lifespans. What accumulates in the atmosphere are those gases than exceed the carbon cycle and different carbon sinks. So if more CO2 is emitted than can be cycled by photosynthesis or stored in sinks, more CO2 accumulates. The same with CH4…and excess CH4 breaks down to CO2 and H2O. So excess CH4 can lead to excess CO2. Watch: The Good Carbon Story.

An analogy that can be used to differentiate between different gases with different lifespans is compounding interest on money. The longer the principle remains untouched, the more interest will compound. If you’re constantly removing principle more frequently. then less interest will compound. If you’re not removing any principle very frequently, a lot of interest will compound. So a greenhouse gas that has a short life span, like CH4, is constantly having its principle reduced, so there won’t be as much compounding interest as there is with a greenhouse gas that has a long life span like CO2. Consequently, one can’t make the assertion that CH4 is equivalent to an 28x or 72x amount of CO2 since the gases behave differently in the atmosphere. Prior methods of carbon equivalency GWP20 and GWP100 made this mistake of treating all gases in the atmosphere as if all the gases had the same lifespans and behaved the same way.

Dr Myles Allen on Agricultural emissions and climate change

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