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Interactive: What is the climate impact of eating meat and dairy?

Posted on 25 September 2020 by Guest Author

This is a re-post from Carbon Brief by Daisy Dunne

Food production accounts for one-quarter of the world’s greenhouse gas emissions and takes up half of the planet’s habitable surface.

A taste for meat has had a particular impact on land. The mass of animals raised for slaughter on Earth now outweighs wildlife by a factor of 15-to-1. For example, for every person on the planet, there are approximately three chickens.

Meat and dairy specifically accounts for around 14.5% of global greenhouse gas emissions, according to the UN’s Food and Agricultural Organization (FAO).

If the world is to meet its target of limiting global warming to “well below” 2C, some degree of diet shift will be necessary, scientists say. If it is to strive for the most optimistic target of keeping warming to 1.5C, changes to diet may be even more crucial.

In this interactive Q&A, Carbon Brief explores how greenhouse gas emissions from meat, dairy and other diets compare, as well as whether changes to the production and transportation of meat could help to stem its climate impact.

How do emissions from meat, dairy and other foods compare?

There are several ways to assess the relative climate impact of different food groups. The chart below compares the average greenhouse gas emissions produced per kilogram of different food products.

The analysis, which is based on a study published in Science in 2018, considers all the factors that go into producing food, including the land required for production, the farming process and the transportation and selling stages. (The emissions from each of these stages are discussed in more detail below.)

Greenhouse gas emissions per kilogram for different food groups. Adapted from Dr Hannah Ritchie/Our World in Data (2020) Data source: Poore & Nemecek (2018). Chart by Carbon Brief using Highcharts.

The chart illustrates how the climate impact of beef and lamb dwarfs that of other foods. This is partly down to the biology of how these animals digest food, explains Prof Sir Charles Godfray, a population biologist and head of the Oxford Martin School at the University of Oxford. He tells Carbon Brief:

“In a very broad-brush approach, the products from ruminant animals – sheep, cows and their relatives, animals with four stomachs – they tend to have greater greenhouse gas effects. Part of that is because digestion by ruminants produces a lot of methane.”

Cows and sheep are “ruminants” – meaning that their stomachs contain specialised bacteria capable of digesting tough and fibrous material, such as grass. The digestive process causes the animals to belch out methane, a greenhouse gas that is around 28-34 times (pdf) more powerful than CO2 over a 100-year period.

However, the chart illustrates that producing beef is more than twice as carbon intensive as producing lamb.

One reason for this is that cows take longer to grow and reproduce, meaning the production of beef requires much more feed and land than other types of meat.

The conversion of land for beef production and animal feed is a leading cause of deforestation in many tropical regions, including in the Amazon, where a recent spike in forest fires and clearing has been linked to cattle ranching. Prof Walter Willett, a leading nutritionist at the public health school of Harvard University, tells Carbon Brief:

“Eating beef raised on grain produced in the Amazon is like coal-fuelled power plants – the worst thing you could possibly do.”
The cutting down of tropical forest causes the release of long-held stores of carbon. (Tropical deforestation as a whole accounts for around 8% of global greenhouse gas emissions.)

Grazing cattle need plentiful supplies of grass – meaning farmers often use nitrogen fertiliser on their fields to stimulate plant growth. The production of nitrogen fertiliser causes the release of CO2 and the potent greenhouse gas nitrous oxide (N2O).

(It is worth noting that emissions from beef can vary greatly. See: Do farming and production conditions affect meat and dairy emissions?)

The resource-intensive nature of cattle rearing also explains why, on average, cheese and other dairy products have a higher climate cost than pork and poultry. Also, chickens and pigs are not ruminants and so do not produce as much methane.

The chart also shows that, on average, farmed prawns have a larger climate impact than other types of seafood.

This is partly due to the fact that some parts of southeast Asia have seen a boom in “industrial-scale” aquaculture.

In these systems, prawns are fed with high amounts of fish feed, much of which is wasted and taken up by other marine microorganisms which then release methane into the atmosphere. Aquaculture also often requires carbon-rich mangroves to be cut down, which causes large amounts of CO2 to be released.

Aerial view fish farm in Java, Indonesia, with ponds growing fish and shrimp and other seafood. Credit: Alexey Kornylyev / Alamy Stock Photo.

Aerial view fish farm in Java, Indonesia, with ponds growing fish and shrimp and other seafood. Credit: Alexey Kornylyev / Alamy Stock Photo.

In comparison to meat and dairy, plant-based foods have much smaller carbon footprints. On average, emissions from plant-based foods are 10 to 50 times smaller than those from animal products, according to the Science study.

Notable exceptions on the chart above include coffee and chocolate. Coffee is mostly grown in tropical regions and its production often involves using high amounts of nitrogen fertilisers, which mostly explains why it has a larger climate impact by kilogram than other plant-based foods. Chocolate’s climate impact is mostly caused by the land-use change required to produce cocoa.

However, it is worth noting that both coffee and chocolate do not contribute much to nutrition, says Dr Hannah Ritchie, a senior researcher at the Oxford Martin School and head of research at Our World in Data. Ritchie, who conducted the analysis behind the chart above, tells Carbon Brief:

“One thing to be conscious of when comparing these products is serving size. Many are shocked by coffee's footprint – and that's not to say that coffee doesn't have a reasonably high footprint – but that the serving size is typically smaller.”

The chart below shows the average greenhouse gas emissions for different food products per 100g of protein, rather than for weight alone.

This chart shows that, when protein is considered rather than mass, dark chocolate has the highest footprint. (However, it is worth noting that chocolate typically contains a very small amount of protein in comparison to animal products such as beef and lamb – and therefore a consumer would need to eat much more of it to derive the same amount.)

Greenhouse gas emissions per 100g of protein for different food groups. Adapted from Dr Hannah Ritchie/Our World in Data (2020) Data source: Poore & Nemecek (2018). Chart by Carbon Brief using Highcharts.

Can switching to vegetarian, vegan or other diets help to reduce emissions?

Given that the climate impact of plant-based foods is typically 10 to 50 times smaller than that of animal products, it follows that switching from a largely meat-based diet to a vegetarian or vegan diet could help to reduce emissions.

The chart below shows how much greenhouse gases could be stemmed if the world were to adopt various different diets.

Greenhouse gas savings potential from the global adoption of various diets. Error bars show the spread of results from different studies. Data without error bars are from one study only. Adapted from IPCC (2018). Chart by Carbon Brief using Highcharts.

The analysis comes from a report by the Intergovernmental Panel on Climate Change (IPCC), an independent research group made up of the world’s leading climate scientists. The report defines the different diets referenced in the chart above as follows:

  • Vegan: a completely plant-based diet.
  • Vegetarian: a diet of grains, vegetables, fruits, sugars, oils, eggs and dairy and around one serving of meat or seafood per month.
  • Flexitarian: a diet in which 75% of meat and dairy is replaced by cereals and pulses. (This includes at least 500g of fruit and vegetables and at least 100g of plant-based protein per day – and no more than one portion of red meat a week.)
  • Healthy diet: a diet based on global dietary guidelines, which involves eating less meat and more fruit and vegetables.
  • Fair and frugal: a diet assuming food is shared equally across the world with each person consuming 2800 calories a day. (This involves a relatively low level of animal products.)
  • Pescetarian: a vegetarian diet that includes seafood.
  • Climate carnivore: a diet where 75% of red meat is replaced with other meat.
  • Mediterranean: a diet of vegetables, fruits, grains, sugars, oils, eggs, dairy, seafood and moderate amounts of poultry, pork, lamb and beef.

In the IPCC’s special report on climate change and land, the team of scientists analysed recently published scientific papers that look into how these different diets could help to stem greenhouse emissions.

The chart above displays the total amount of greenhouse gases that could be saved each year by 2050 if the world were to adopt each of these diets, when compared to a “business-as-usual” scenario for 2050. (The “business-as-usual” scenario is based on projections of continued population growth and rising meat intake from the FAO.)

(The chart shows the savings in terms of millions of tonnes of CO2 equivalent [CO2e] – a measure used to compare the emissions from various greenhouse gases.)

Savings come both from ridding the world of the greenhouse emissions associated with livestock production (see: How do emissions from meat, dairy and other foods compare?) and also from sparing land that would otherwise be needed for livestock rearing.

The analysis shows that a global switch to veganism would deliver the largest emissions savings out of any dietary shift.

According to the analysis, a switch to veganism could save almost 8bn tonnes of CO2e a year by 2050, when compared to a “business-as-usual” scenario. (By comparison, all food production currently causes around 13.7bn tonnes of CO2e a year.)

The steep reduction in emissions would partially stem from the freeing up of large amounts of land, which could be used to plant forests capable of removing CO2 from the atmosphere, the IPCC authors say:

“Under the most extreme scenario where no animal products are consumed at all, adequate food production in 2050 could be achieved on less land than is currently used, allowing considerable forest regeneration, and reducing land-based greenhouse gas emissions to one third of the reference ‘business-as-usual’ case for 2050.”

(Separate research finds that the emissions savings from a global switch to veganism could actually be as high as 14.7bn tonnes of CO2e a year.)

The second highest emissions savings would be delivered by a global shift to vegetarianism which, in the analysis, still includes around one serving of meat or fish a month. An adoption of this diet could save 6bn tonnes of CO2e a year by 2050, according to the analysis.

Following this is a shift to “flexitarianism” – a diet where three-quarters of meat and dairy is replaced by plant-based alternatives. A global shift to this diet could save just over 5bn tonnes of CO2e a year by 2050, the analysis says.

It is worth noting that, while veganism offers large emissions savings when compared to a “business-as-usual” scenario, the additional benefits become smaller when compared to vegetarianism and flexitarianism, says Willett:

“What if everybody became a vegan? Compared to business as usual, it would reduce emissions a lot. But compared to a more flexitarian diet, the additional reduction is modest. And it might make feeding people harder in some regions because we’re taking off the table meat that was raised on land that can’t seem to be used for other types of food production.”

The analysis also shows that a global shift to “healthy” eating could offset around 4.5bn tonnes of CO2e a year by 2050. 

In addition, the majority of national healthy eating guidelines recommend that their citizens eat less meat and more fruits and vegetables. (For example, Public Health England’s Eatwell Guide suggests the average Briton should eat less red and processed meat and consider choosing low-fat alternatives to dairy.)

study published in 2016 found a global shift towards more plant-based diets that are in line with standard dietary guidelines could reduce global mortality by 6-10% by 2050 in addition to reducing emissions by 29-70%, when compared to a business-as-usual scenario.

How does meat and dairy consumption vary around the world?

A global shift towards a more plant-based diet would help to reduce emissions, but it is worth bearing in mind that every country in the world eats differently.

A country’s diet – and its resulting food emissions – can be based on many factors, including its cultural and religious beliefs, geography and economic status.

In 2019, a group of leading food and climate scientists came together to analyse how different countries around the world eat – and how this might need to change if the world is to reduce the climate impact of food. Willett, who led the project, which is known as the EAT-Lancet Commission, tells Carbon Brief:

“We have this challenge of being able to feed about 10 billion people a diet that’s both healthy and sustainable by 2050. In the end, we found it is possible – but just barely possible.”

For the first part of their analysis, the commission analysed the scientific literature in order to come up with a universal diet that would be healthy and sustainable for all.

The first trees being planted in England's largest forest for more than 30 years at Doddington North Moor

The “planetary health diet”. Credit: The EAT-Lancet Commission (2019).

The “planetary health diet” – illustrated above – is around half fruit and vegetables, with whole grains, unsaturated plant oils and plant-sourced proteins also playing a large role.

The diet allows for around one portion of dairy a day and around one serving of meat a week, says Willett:

“There’s room for some minor meat consumption. We put ranges on all those numbers so there is some room for flexibility, which I think is important because we’re never going to get everybody to eat all one way.”

For the second part of their analysis, they assessed how the dietary habits of different parts of the world would need to change to fit with their proposed planetary diet.

Click here to proceed with the interactive feature

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Comments

Comments 1 to 14:

  1. The printable version is the wrong reference, produces empty page for interactive feature. This comment intended only as signal before being deleted.

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  2. Quite frankly these numbers are useless for a large number of people that aren't sourcing their food that way(which is sort of acknowledged). I just don't see how the numbers can hold up. beef cattle vs dairy really? or sheep or chicken or pork? I've raised them all and can tell you that the energy inputs for beef cattle can consistently be way less than above. Sheep and goats might be slightly more efficient grazers but they make up for it in size comparisons and surface area to volume ratios

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  3. JWRebel @1

    Thanks for the heads-up! The issue should be fixed now and the printable version of the blog post shows up again.

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  4. I'm disappointed to see such misinformation here, I expect better. Imo, anyone using 100-year carbon dioxide equivalent emission factors for methane should probably be ignored, or at least not be published.

    Here are some better atricles on a similar subject:

    - LINK1;

    - LINK2;

    - LINK3.

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    Moderator Response:

    [DB]  Shortened and activated URL's breaking page formatting.

  5. I have said it before here. The idea we can mitigate global warming with a diet shift alone, and not a change in production methods, is absolutely wrong and most likely impossible with current technology.

    The whole idea hatched from the supposed benefit of using grain for ethanol production instead of meat production, then using the ethanol along with as yet undeveloped CCS technology and putting those CO2 emissions far underground in old wells etc. This would give a supposed negative carbon footprint.

    There are even a few pilot CCS power plants that managed to put some carbon emissions in the ground this way. But at a huge cost and loss of efficiency as great or greater than any benefit derived.

    Solar and wind are far more cost effective and efficient ways to generate energy. And soil sequestration is a far more cost effective and efficient way to sequester carbon.

    Once you realise this, then you can easily see that it is not the tomato nor the beef on your plate that determines the carbon footprint of your diet, but rather how that food was produced. Methods that improve soil carbon whether producing vegetable or animal foods will lower your carbon footprint. For this reason it is entirely possible to have a tomato with a significantly larger carbon footprint than a 8 oz steak.... if the tomato was produced on land with degrading soil  then shipped 100's of miles and the beef was produced on local land with regenerating soil.

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  6. Soil can't save us, nor can sequestration of the coal power plants themselves.

    I hate nuclear but it is the only solution for big cities.

    Solar and wind are here but the profit motive still needs to be engineered... Electric cars depend on all of this!

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    Moderator Response:

    [PS] Assertions with no supporting evidence are simply sloganeering. Put up evidence to back you what claim.

  7. About 10 years ago SkepticalScience posted an article entitled “Does breathing [by humans] contribute to CO2 buildup in the atmosphere?”
    (see here ) Their answer to the question was "no". Their reasoning was based on the carbon cycle: what goes in must come out. So nothing can change, except that it does.

    Now we have another article on the same site that effectively argues the opposite: that breathing from farm animals contributes to global warming. The problem is that both these articles are wrong, at least in part, because they both fail to distinguish between the steady state and systems that are evolving over time.

    As I pointed out in comment @152 in response to the first article, and also on my own blog (see Post 36), the carbon cycle only applies to the steady state. By definition climate change implies evolution over time. If the number of cows increases then they will change the distribution of carbon between the different reservoirs (air, plants, soil) until a new equilibrium distribution of carbon is achieved. In effect they divert carbon directly into the atmosphere that would otherwise have first entered the soil and then decomposed. I have estimated that the increase in atmospheric CO2 since 1900 due to the increase in human and livestock populations over the same time period to be (much) less than 30 ppm. That increase in CO2 is not going to end life on Earth. In fact it is less than the current increases we are seeing from fossil fuels every 15 years. Vegan lifestyles are not going to save the planet.

    So when examining climate change it is the change in the number of animals and humans that is is crucial, not their actual number. And, since 1900, livestock numbers have increased dramatically, while over the same time period the human population has nearly quadrupled. That is the elephant in the room that no-one will discuss, and no amount of vegan virtue signalling will compensate for that.

    The problem with this article, and others like it, is that it seeks to equate emissions from cows with emissions from fossil fuels. That is bad science. Even if animals and cars produce the same amount of CO2 and/or methane, they will not cause the same increase in atmospheric CO2 levels because they are acquiring their carbon input from entirely different sources. One is largely self-sustaining, returning the CO2 from whence it came (the atmosphere), with only slight changes to the balance of carbon in the different reservoirs of the carbon cycle due to its own rate of change; the other continuously adds more new carbon to the carbon cycle, starting with the atmosphere, and so dramatically changes the balance of carbon in the different reservoirs. Eating less meat is no substitute for consuming less fossil fuels.

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  8. Slarty Bartfast @7,

    The main error you make is that 'breathing' concerns "the act or process of taking air into your lungs and releasing it." And it results in carbon being added to the 'release' in the form of CO2. (Of course, pedantically plants and 'lower' animals also breathe but without lungs.) The carbon in this cycle was originally sourced from the atmosphere as CO2. So any concern would be if the pools of carbon stored outside the atmosphere in this carbon cycle CO2[atmosphere]  > C[biosphere]  > CO2[atmosphere] were to alter, as happens for instance when large forests are chopped down.

    Unlike the breathing of us billions of humans, the "breathing" you are considering has a different composition and isn't considered to be 'breathing' as it does not concern the lungs (or the equivalent in plants & 'lower' animals) and often comes out of a different orifice. The situation is certainly not the same, as you may or may not argue (it is difficult to tell what you argue), as the carbon cycle being considered is fundamentally different. CO2[atmosphere] >  C[biosphere] > CH4[atmosphere] > CO2[atmosphere].

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  9. Slarty Bartfast @ 7: "As I pointed out in comment @152 in response to the first article, and also on my own blog (see Post 36), the carbon cycle only applies to the steady state. "

    And as was pointed out to you on that thread, you are horribly, completely, absolutely wrong is saying that it only applies to the steady state.

    Since you begin with a false assertion, nothing else you say about carbon cycles bears much resemblance to reality.

    [Note that Slarty's reference to comment numbers above are on a different thread; Slarty has included links in his comment.]

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  10. I think slarty is saying that normally breathing and cattle releasing methane are carbon neutral, but the big explosion in numbers of cattle and humans since 1900 has thrown things out of equilibrium, with the ultimate result of high plant and meat consumption leading to degraded carbon sinks leading to more CO2 released from those sinks into the atmosphere. This looks correct to me. Where is the flaw in his reasoning?

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  11. @10 nigelj

    You are correct. That is exactly what I am arguing. But I am also arguing that the actual percentage change in the carbon sinks due to "the big explosion in numbers of cattle and humans since 1900" is still relatively small when compared to the impact of fossil fuels. 

    I am also arguing that the two contributions are fundamentally different. If future carbon emissions from cattle and humans were to remain constant over time, then there will be no change in the carbon sinks. That means no future increase in atmospheric CO2 or methane levels. However, if fossil fuel emissions remain constant at current levels, then there will still be a continual increase in atmospheric CO2 levels over time.

    That is why I say you cannot equate the two.

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  12. nigelj:

    Where Slarty gets things wrong is in assuming that there is some "steady state" or "equilibrium" that has been remaining constant prior to recent human activity.

    For example, in comment #7, he states "In effect they divert carbon directly into the atmosphere that would otherwise have first entered the soil and then decomposed." Decomposition also releases carbon to the atmosphere. In some ecosystems this decomposition is extremely rapid; in others somewhat slower. Many different parts of the carbon cycle act at different rates, and those rates all vary over time - so carbon stores vary over time.

    I am most faimliar with the carbon budget of the boreal forest. Boreal forests have cycles of growth, cycles of fire, cycles of decomposition, cycles of changes in fluxes and stores. This happens naturally. Dynamics are affected by human activities such as harvesting and forest management - but this is not some alteration from a mythical "steady state" where "nothing changes".

    All carbon stores and fluxes are dynamic. Slarty's post #7 also contains the phrase "Their reasoning was based on the carbon cycle: what goes in must come out. So nothing can change, except that it does."

    His position that our understanding of the carbon cycle implies "nothing can change" is a strawman. He clearly does not understand the carbon cycle - how it works in reality, how it is modelled.

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  13. nigelj @10,

    While Slarty Bartfast has not fully set out what he is saying, he is apparently still signed up to the description he set out on the 'breathing contribution' thread @152 & 155. On the strength of your comment @10, Slarty Bartfast @11 tries to also sign you up to it, saying your comment @10 is "exactly what I am arguing."

    If you examine what is set out on that other thread, Slarty Bartfash appears to be saying that the CO2 emissions from a reservoir of carbon within the carbon cycle will be fixed by the nature of that reservoir. The reservoirs are listed as Soils, Plants, Animals, Atmosphere, Ocean and from the Soils a reservoir of 1,500Gt(C) is emitted 60Gt(C) of CO2 annually, 4% of its volume. From Animals the ratio of emissions-to-reservoir had been calculated as 800% (calculated @152 in that thread). As the reservoir of Animal carbon has increased with burgeoning human population and livestock herds, the Animal reservoir is considered increased, with its increased emissions balanced by an identical reduction in the Soils emissions. To achieve this Soils emissions reduction, which is fixed at 4% of reservoir, the Soils reservoir must shrink by 63Gt(C) while the increase in the Animal reservoir with its emissions 800%  of reservoir will only increase by 0.3Gt(C).

    "There is only one other place that most of the remaining 62.7 GtC can go: the atmosphere." This then is the origin of Slarty Bartfast's 30ppm atmospheric CO2 increase. I would hazard a guess that is not something you would feel entirely happy signing up to.

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  14. MAR @13, I've now read 152 onwards, and yes I'm not entirely happy signing up to Slartys maths, because the loss of carbon from deforestation and degraded soil sinks could go to several places, its not proven which, although I think its likely some would end up in the atmosphere.

    Fwiw, I do think a  low meat diet makes sense. RB is probably right that you can get grazing land soils to sequester more carbon, but that will take time to scale up globally, so eating less meat is a practical thing that is immediately possible.

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