If I enjoy a steak, am I killing the planet?

Almost every day, we can see headlines warning us about how dangerous Green House Gases (GHG) produced by cows are for the Earth. You can see an example here. According to those headlines, eating beef is one of the main causes of global warming, then, in order to stop or even reverse it, we should all stop –or at least reduce- our beef (and milk) consumption.

One more reason we find on the media to quit on beef is the amount of water needed to produce it which is normally said to be close to 2,000 gallons per pound or almost 700 gallons per burger

But are the figures above true? Let’s check the facts, let’s take some perspective from the media hype which quite often simplify on a short, and often times alarmist, headlines subjects that can be pretty complex.

Ruminants (cows, sheep, goats) have a unique digestive system. They have a stomach with 4 different compartments of which the biggest one, the rumen, is a laboratory, full of bacteria, fungi and protozoa that digest cellulose (the polisacarid that builds up the wall of vegetal cells, what we commonly call fiber) and get from it the key sugars and volatile fatty acids that ruminants need to live.

Figure 1: The rumen is a lab full of micro-organisms that break down cellulose and deliver key nutritional elements that allow the animal to grow and produce milk.

Cellulose is the most frequently found organic molecule on the planet. 50% of wood’s composition is based on it. 90% of cotton composition is cellulose too.

Some other herbivores such as horses and rabbits have bacteria in their cecum who can also break cellulose down, but no animal is so specialized as ruminants are. When cellulose is digested in the rumen, one of the by-products released is methane gas (CH4) which cows eliminate by burping.

And here is where things start to become tough for cows, because this gas has a potent greenhouse effect and is one of the key factors that drives global warming. First of all, we have to clarify that ruminants are not by any means the sole or even the most important source of methane, there are some others such as forests, wetlands, wild ruminants, fossil fuels, natural gas, fracking, rice fields and even termites (who are also able to break wood down and digest it).

To put things into perspective, we must also say that of total GHG emmissions, methane accounts for 16% and of this total, ruminants contribute to a fraction of 17%, as we can see in the pie below:

Figure 2: Source % of total methane emmissions de metano a causa de distintas fuentes. Livestock digestión accounts for 17% of the total.

But, what is methane contribution to global warming? There is a ranking, accepted by the scientific community called Global Warming Potential (GWP) that compares the amount of energy absorbed by a given gas for a given period of time and benchmarks it against the same amount of energy absorbed by CO2. Generally, GWP is measured in a 100 years period. GWP of CO2 is 1 and from it, we can calculate GWP of the rest of the gasses.

Based on the above, methane GWP in 100 years is 28. That means that the capacity of methane to absorb heat from the atmosphere 28 times higher than CO2. This is why, it would be really interesting to reduce methane in order to mitigate global warming and hence, reduce beef consumption could be considered as a good strategy to this end.

Figure 3: Methane molecule: One central carbon with four hydrogens.

However, things are a little more complicated. Methane is a very particular gas and benchmarking it against CO2 over a 100 years period may take us, as a recent study from Oxford University proves, to wrong conclusions

Released CO2 stays in the atmosphere for more than a thousand years while methane stays around 10. This is why to measure methane in a 100 years period is not appropriate. Once methane burped by cows is released it suffers some chemical reactions with OH radicals and becomes CO2 but that CO2, will be used by the plants to complete photosynthesis, that is to say, this CO2 is quickly sequestered, taken out from the atmosphere to be transformed again into cellulose, as an integral part of the tissue of plants. So, if a herd of cattle does not increases its size, the impact of this population on global warming amounts to zero. Conversely, if atmospheric methane is produced by fossil fuels such as natural gas or fracking, that methane is not part of the carbon cycle, it brings a net increase of the total amount of methane and it does contribute to the atmosphere warming.

Figure 4: Carbon cycle:  Methane, contrary to other GHG is degraded in the atmosphere to CO2. The  CO2 originated from methane is part of a natural cycle and is not additive because plants will use it for their own growth. Conversely, methane originated from fossil fuels is not part of this natural cycle and plants and seas have not capacity to absorb it.


But there is more: Ruminants graze and by doing so they contribute to sequester carbon in the soil. Pastures and ruminants have evolved together and they influence each other. Everything is inter-connected: the amount of carbon in the soil determines the water retention capacity it has. This determines the growth of the plants there. Those plants will determine the rythm of transpiration and water vapor elimination. This will impact on the formation of OH radicals in the atmosphere and then will dictate methane oxidation and its conversión into CO2. Plants take this gas and convert it into plant matter through the photosynthesis process.

Many studies prove that the right management of cattle and pastures increase carbon sequestration, reducing then GHG from the atmosphere.

Besides, ruminants produce manure, which reduces the need of chemical fertilizers, with the consequent reduction of GHG emmissions.

Cattle methane emmissions vary dramatically across geographies. In the US there are today less dairy cows than in the ‘40s – 9M today vs 25M then- although milk production is 6 times higher today than then: around 50 lb/day per cow

Conversely, cows in a country like India, where they are not part of the local diet due to religious reasons, produce on average 6 lb/day. There are some 300 M cows there.

It would be then possible to significantly reduce the number of animals and produce the same or even higher amounts of milk and beef by implementing better, more modern genetics, nutrition and health programs as developed economies do.

Figure 5: On the left, the graph shows the level and evolution of GHG (CH4 y N2O) in developing countries. On the right, the same data in developed countries

Figure 6: As productivity increases thanks to better health, genetics and nutrition, the total number of animals needed decreases.


Moreover, about 90% of what a cow eats is not edible by humans. So, without ruminants, a huge amount of vegetal by-products such as corn stalks, cotton seeds, fruit peels or beet pulp should have to be destroyed. That would also result in GHG emissions that we avoid thanks to cows.

Figure 7: Cows eat mostly vegetable by-products which are non edible by humans

In fact, if all livestock production was to be eliminated in the US the net GHG reduction will only amount to a 2.6% according to a study conducted in Arizona University (see bibliography).

At the beginning of this article, I alluded to another controversy related to beef production: the use of water. Media point this out frequently, with alarming headlines in which it is often stated that a almost 2,000 water gallons are needed to produce 1 lb of beef. See here an example.

Let’s see a detailed account of water use in cattle production. This will give us an idea of the real situation which is not easy to summarize in a press headline.

According to the UNESCO for water institute education, of the total amount of water used in all agriculture processes, 29% is used by livestock. And according to this same institution, 87% of the water used by animals comes from rain (what experts call green water), this means this water will not be lost, it is a part of the water cycle, it will always be recovered whether there is or not cattle that uses it.

Figura 8: Rain water is part of the water cycle. It is not lost, it always comes back.


The missing 13% comes from blue water, water from rivers and gray water, which is water contaminated after industrial and urban use. It is part of water recycling.

Figure 9: Use of different types of waters in one European country and at global level.

Based on the above, it is sound evidence that the real water use to produce 1 Lb of beef is somewhere between 1-150 gallons of water, depending on geographies and production systems.

Obviously the livestock industry must continue to improve to reduce GHG emmissions and water use. There are technical measures to be implemented, and we have already seen the differences between more and less developed countries.

Any activity has an environmental impact, and agriculture and animal production are not exceptions.

Now, data shows that the press hype against beef is not based on sound science. Cows were here much before than us and their impact on the environment is relatively low and it can be improved. Not all industries can state the same.

So, if you decide to eat a stake, I can only say: Enjoy!



Michelle Cain, Myles Allen, John Lynch. Net zero for agriculture. (University of Oxford) Published by the Oxford Martin Programme on Climate Pollutants

Robert W. Howarth. Ideas and perspectives: is shale gas a major driver of recent increase in global atmospheric methane? Biogeosciences, 2019

Stanley et al. Impacts of soil carbon sequestration on life cycle greenhouse gas emissions in Midwestern USA beef finishing systems. Agricultural Systems. Volume 162, May 2018, Pages 249-258

J.R.Knapp Invited review: Enteric methane in dairy cattle production: Quantifying the opportunities and impact of reducing emissions. Journal of Dairy Science. Volume 97, Issue 6, June 2014, Pages 3231-3261

Paul J. Crutzen, Ingo Aselmann & Wolfgang Seiler (1986) Methane production by domestic animals, wild ruminants, other herbivorous fauna, and humans, Tellus B: Chemical and Physical Meteorology, 38:3-4, 271-284

Gregory J. Retallack. Global Cooling by Grassland Soils of the Geological Past and Near Future Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403; email: [email protected] Annu. Rev. Earth Planet. Sci. 2013. 41:69–86

  1. Ledyard Stebbins Source: Annals of the Missouri Botanical Garden, Vol. 68, No. 1 (1981), pp. 75-86 Published by: Missouri Botanical Garden Press Stable URL: http://www.jstor.org/stable/2398811 Accessed: 14/04/2010 12:46

Robin R. Whitea. Nutritional and greenhouse gas impacts of removing animals from US agriculture. PNAS November 28, 2017 114 (48) E10301-E10308

Bradley G. Ridoutt et al. Water footprint of livestock: comparison of six geographically defined beef production systems. The International Journal of Life Cycle Assessment. February 2012, Volume 17, Issue 2, pp 165–175

Greg M. Peters et al. Accounting for water use in Australian red meat production. The International Journal of Life Cycle Assessment. March 2010, Volume 15, Issue 3, pp 311–320| Cite as

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