“The mass consumption of animals is a primary reason why humans are hungry, fat, or sick and is a leading cause of the depletion and pollution of waterways, the degradation and deforestation of the land, the extinction of species, and the warming of the planet.”
Brian Henning, 2011 
Despite decades of international conferences, energy efficiency initiatives, growing investments in the renewable energy sector and a budding global awareness of climate change, anthropogenic emissions and concentrations of carbon dioxide have risen steadily over the past decades. Since 1990, emissions have almost doubled , and current projections indicate this trend is unlikely to slow down in the foreseeable future. In fact, despite the diplomatic success of the 2015 Paris Agreement, rather than being on track for 1.5 degrees temperature rise as stipulated by the multilateral agreement, projections have identified that we are now heading towards a rise in global average temperatures of at least 3 degrees Celsius by 2100.  Beyond 2100, projections indicate we might be heading towards a 4-5° degrees C warming. 
While these small numbers may not appear to indicate anything catastrophic, scientists have estimated that a 3°C increase in average global temperatures could bring ‘outright chaos’ to our societies, sparking a global water crisis, inundating entire regions and provoking a widespread failure in our global food production.  Although we can’t know definitely, they have estimated that a warming of 4°C could result in a reduction of the human population by 80-90%, and past that, the temperature would simply become largely incompatible with human existence.  Clearly, a lot is at stake.
Unfortunately, despite the exciting possibilities emerging with renewable technologies, global investment and uptake in green technologies remains a small fraction of what is required to reduce global emissions. While this is an absolute priority and a necessary step to help mitigate climate change, even if we garnered the necessary political and financial will to invest in these technologies, such solutions will most likely take decades to implement – time which is simply running out.
The good news, however, is that beyond the energy industry, there are other sectors of our economies that could be decarbonised faster which could help us stay under a 3-4 degree scenario. One of these is the agriculture sector. In fact, agriculture is one of the key human activities that impacts our climate and ecosystems.  The cumulative emissions generated by agriculture, forestry and other land use accounts for 24% of global emissions,  and livestock alone is said to be directly responsible for 14.5% of global emissions each year. 
In Australia, agriculture is currently the fourth largest source of greenhouse gas emissions, responsible for 13% of total emissions,  but importantly, of these, two-thirds are the result of just grazing beef and sheep.  The situation is closely mirrored In the United States, where agriculture accounts for 9% of total emissions – which, although gigantic, pale in comparison to its other energy-intensive sectors  – of which livestock is responsible for 42%. 
Given that both per calorie and per gram of protein animal foods are significantly more resource-intensive than plant foods, [12-14] scholars have argued that the cheapest, easiest, fastest and most effective action that can be taken at a global scale to help mitigate climate change is a dietary shift towards consuming more plant-based foods and less meat. [15-18] If livestock’s contribution to environmental problems is a substantial one, the thinking goes, its potential contribution to their solution could be equally large. Furthermore, beyond affording environmental benefits, a reduction in meat consumption to a healthier intake level would also positively reduce the burden of disease associated with its overconsumption. 
Since its inception, Plant Proof has been primarily focused on nutrition – but what good is a healthy diet if we cannot survive on a world threatened by climate change? The point is that focussing entirely on the nutritional aspect of a diet without taking into account its environmental consequences will end up being rather pointless if our planet is uninhabitable. As such, in this article, my aim is to leave ethics, nutrition (for the most part) and my personal choices aside, and focus only on one question: according to the best available scientific data, what is the best diet that the world can adopt if we are going to help mitigate the existential threat posed by climate change?
To answer this, I set out to investigate 6 questions:
- How does plant vs animal agriculture compare in environmental terms?
- Is methane a ‘myth’ as stated by Sarah Wilson?
- Is grass-fed that much better for the environment and can holistic grazing methods as those proposed by Allan Savoury really help mitigate climate change?
- So is the solution to cut back on red meat and replace it with other animals?
- Is Australia really exempt from all the damaging practices used abroad?
- What would happen if we all went vegan?
1. How does plant vs animal agriculture compare in environmental terms?
The first question I set out to investigate is how the environmental burden of a predominantly plant-based diet compares to the average omnivore diet. I will admit, this was not an entirely novel endeavour for me; I have explored the topic before, and have followed extensively many of the studies that have been published over the past few years. Regardless, removing as much of my personal bias as possible, I set out to find the best and most objective data on the topic.
Indeed, the scientific consensus backed by both the Intergovernmental Panel on Climate Change of the United Nations (IPCC), The Lancet – one of the most highly regarded journals in the world – and the largest ever scientists co-signature in history, is that a predominantly or entirely plant-based diet is the single best most environmentally sustainable diet. ,  .
Countless systematic reviews, life-cycle analyses and meta-analyses have concluded that higher consumption of animal-based foods is associated with the highest environmental impacts, whereas increased consumption of plant-based foods is associated with the lowest environmental impact. [14, 20-22] Indeed, even the least sustainable plant food is still significantly more sustainable than the best environmentally performing animal food. 
In the words of a report published by The Lancet, “many studies have assessed environmental effects of various diets, with most finding decreasing effects with increased replacement of animal source foods with plant-based foods. Vegan and vegetarian diets were associated with the greatest reductions in greenhouse-gas emissions and land use, and vegetarian diets with the greatest reductions in water use.” 
This is mostly because raising livestock for human consumption is a grossly inefficient process, and one that requires far more land, water and energy compared to growing plants. Beyond the inputs required by animal farming, ruminant animals such as beef and sheep emit methane, a greenhouse gas that is 28 times more potent than carbon dioxide.  In 2001, the Australian Greenhouse Office reported that the Australian livestock subsector was the nation’s largest source of agricultural greenhouse gas emissions.  Disappointingly, such statistic continues to this day: more than two-thirds of all the emissions attributed to the agricultural sector are the result of grazing beef and sheep. 
Beyond emissions, today livestock is the single largest anthropogenic user of land, occupying alone around 30% of the earth’s ice-free land surface.  The expansion of such production, driven by our ever-growing appetite for meat, is thus a key driver of deforestation, which severely damages the ecosystem and the animal species that live in it.  Importantly, regardless of the copious amounts of land needed to raise cattle on pasture compared to other crops, these animals produce only one gram out of the 81g of protein consumed per person per day. 
In Australia, the agricultural sector alone occupies 51% of the total Australian surface, but of this, 87% is used by grazing cattle (a 9% increase compared to 2015), and 7.8% is used by crops that are both destined for human and animal consumption (a 2% increase compared to 2015).  A report analysed more than 1.6m hectares of land that had been cleared in Queensland between 2013 and 2018 and found that 73% of this clearing occurred to make space for the expansion of grazing beef production alone.  Beef in Australia is thus the number one driver of deforestation and land clearing, which is having devastating effects on soil quality, biodiversity loss and emissions. 
Overall, the bottom line is that raising animals for consumption is a highly inefficient process, one that requires far more land, water and energy while emitting potent greenhouse gases. Although rarely mentioned, our planet is bound by a finite amount of resources and land, and quite, simply raising animals for mass consumption is thus an extremely questionable use of our limited land and resources. 
Conversely, plant foods generally have a significantly lower environmental impact and are implicated in far less water, land and energy use compared to animal agriculture. [14,31,32] Multiple studies have, in fact, concluded that a vegan diet contributes approximately one-half of the GHG emissions of the typical average food consumption. [31,32] In terms of land use, a recent study quantified that 100g of tofu requires 74 times less land use compared to 100g of beef. 
While certain plant foods such as avocados and almonds are often cited as grossly unsustainable foods due to their substantial water usage, their overall impact in terms of greenhouse gases and land use is still significantly lower compared to most animal-based products.  For a thorough comparison of the environmental implications of plant-based and animal-based foods, I invite you to read this recently published paper.
However, there is a concession to make: eliminating meat does not automatically make a diet environmentally sustainable.  Diets rich in heavily processed meat substitutes and in plants grown in monoculture crops that used to be home to a native forest, on which large quantities of pesticides and fertilizers are used, may indeed be just as ecologically destructive. 
The bottom line is that cradle to grave, a predominantly or entirely plant-based diet has consistently been identified as the most environmentally sustainable. Ensuring the plant food is local, not wasted, minimally processed and in season will further reduce its environmental burden.
2. Is methane a ‘myth’ as proposed by Sarah Wilson?
That’s right – the best-selling author Sarah Wilson has stated that methane is a ‘myth’. Initially, I thought that perhaps Sarah didn’t have access to as much information back in 2012 when she published her blog post. However, given she receives funding from the Australian beef & lamb industry, I’m not sure a thorough review of the science was her prerogative in the first place.
This one the science is pretty solid about, Sarah: methane is very far from a ‘myth’. Methane is a particularly potent greenhouse gas that is released in many processes – some natural, and some provoked by human activity such as rice production, rotting landfills and the belching of ruminant animals such as cows, sheep and goats. While other greenhouse gases such as Carbon Dioxide and Nitrous Oxide have a ‘residence time’ of hundreds of years – meaning that their molecules will persist in our atmosphere for generations to come, methane’s residence time is a mere 12 years. 
However, while it is true that methane does have a significantly shorter lifespan, this does not make it a harmless gas. First, it’s important to understand that methane is a gas that is strikingly effective at trapping heat (which is the process that causes global warming), meaning that even just a little bit of methane can have a large impact on climate change. Indeed, molecule-for-molecule, methane traps 28 times as much heat as carbon dioxide.  This means that methane is 28 times more powerful than carbon dioxide at warming our atmosphere. Therefore, its relatively short lifecycle is offset by the fact that methane is far more potent at trapping heat than carbon dioxide.
Secondly, in theory, methane’s shorter lifespan would mean that if we completely stopped emitting methane today, we could effectively rid our atmosphere of the human-induced portion of it within 12 years. However, methane emissions are constantly being regenerated and topped up, and indeed concentrations have steadily increased. Since the Industrial Revolution, methane concentrations have grown 2.5-fold as a consequence of anthropogenic activity,  although NASA has argued that this number and might have been grossly underestimated.  Scaringly, methane concentrations have shot up since 2007 to levels that are well past those scientists had projected. 
So yes, if we stopped emitting today methane today, a large part of it could be gone within 12 years – but we haven’t and we won’t stop emitting methane any time soon, so this argument is grossly irrelevant.
Where does livestock fit in this scenario? The 1.4 billion cattle that are currently roaming this world together with other grazing animals contribute to a whopping 40% of the annual methane budget. [73, 74] Given that global livestock demand is projected to increase by 70% propelled by population and economic growth,  there is absolutely nothing to suggest that methane concentrations will slow down in the foreseeable future.
The bottom line is that methane is indeed not a myth – it is directly contributing to climate change, and efforts to reduce its emissions are paramount to our successful abatement of global anthropogenic emissions.
3. Is grass-fed that much better for the environment and can holistic grazing methods really help mitigate climate change?
Across the board, it is widely acknowledged that livestock has a staggeringly high carbon footprint and is a major worldwide contributor to greenhouse gas (GHG). [25,37] Emissions from the livestock sector are estimated at 7.1 gigatonnes CO2-eq every year, representing a staggering 14.5% of human-induced GHG emissions at a global level.  However, some have argued that while it is indisputable that conventional factory farming is grossly unsustainable, grass-fed cattle raised on pasture is both more ethical, nutritious and sustainable. [38,39] Indeed, while grass-fed beef may provide both an enhanced quality of life for the animals (although, obviously, they all share the same fate) and a nutritional improvement due to an increased quantity of omega 3s and antioxidants and a reduced amount of fat and antibiotics,  the sustainable aspect of the story is more contended.
The argument, as put forth by its proponents and spearheaded by the rancher (note: not scientist) Allan Savory with his viral Ted Talk, is that ‘holistic’ grazing can suck so much carbon out of the atmosphere that it should be seen as an essential part of the climate solution. It is argued that by feeding pasture via holistic methods of rotational feeding, the nibbling and trampling produced by the cattle can actually stimulate the grass to put down deep roots, actively suck carbon from the atmosphere and store it in the soil. In practice, the theory calls for increasing livestock numbers, rather than reducing them. It is proposed that the amount of carbon removed by this type of grazing can not only exceed the cattle’s total emissions and alleviate desertification, but that it can also absorb enough carbon to effectively return the world’s atmosphere to pre-industrial levels. I’ll be honest with you: when I first saw the Ted Talk, I too believed he might be onto something.
However, while this may indeed be an attractive theory and there is some very limited anecdotal evidence to support it, the theory proposed by Allan Savoury very simply has not been backed up by peer-reviewed research,  but rather stands on the shoulders of Mr Savoury’s self-published articles. Unfortunately, in fact, all of Savoury’s claims have been thoroughly debunked (you can read here for more).
Most notably, a paper in the journal Agricultural Systems, responded to Allan Savoury’s intensive rotational grazing (IRG) theory by stating that:“The vast majority of experimental evidence does not support claims of enhanced ecological benefits in IRG compared to other grazing strategies, including the capacity to increase storage of soil organic carbon…IRG has been rigorously evaluated, primarily in the US, by numerous investigators at multiple locations and in a wide range of precipitation zones over a period of several decades. Collectively, these experimental results clearly indicate that IRG does not increase plant or animal production, or improve plant community composition, or benefit soil surface hydrology compared to other grazing strategies”.
When put to the test here in Australia, trials carried out by the Northern Territory Government over the past 15 concluded that ‘holistic’ cell grazing yielded negligible differences in terms pasture yield, composition or soil carbon compared to continuously grazed paddocks.  Instead, they found that this model simply cost more, while the carrying capacity of soil remained unchanged.  Perhaps this explains why uptake has been so minimal in Australia, with only 0.5% of farmers adopting this practice by the beginning of the century: the model simply does not work. 
More recently, research has concluded that even with the most optimistic figures and the most optimistic assumptions of best practice grazing techniques, net emissions of grazing livestock would still greatly surpass its potential to suck carbon from the atmosphere. A report published by the Environmental Change Institute at Oxford University set out to investigate what the net climate impact of grass-fed ruminants is, taking into account all greenhouse gas emissions and removals.  They concluded that indeed, if properly managed, grazing can result in some of the atmosphere’s carbon to be sequestered in soils. However, the maximum global potential, in the most optimistic conditions and using the most generous of assumptions, would offset only “20%-60% of emissions from grazing cattle, 4%-11% of total livestock emissions, and 0.6%-1.6% of total annual greenhouse gas emissions.” In other words even if gazing cattle can help pull carbon from the atmosphere into the soil, the practice still results in net GHG emissions into the atmosphere (the practice simply emits more than it can help remove). Furthermore, the report also found that soils farmed under ‘holistic’ grazing, reach carbon equilibrium within a few decades.  In other words, this means that any potential benefits associated with the grazing of grass-fed cows are only temporary, while the methane will continue to be emitted so long as cattle are still part of our food system. 
The bottom line is that grazing cattle – even in a best-case scenario with the best-practice ‘holistic management’ methods – are certainly contributing to climate change. Good grazing management simply cannot offset its own emissions, and it certainly isn’t a key solution to our climate change problem.
If anything, contrary to popular belief, they found that grass-fed cows may contribute to anthropogenic emissions more so than cattle grown in intensive farming systems for three reasons. 
1 – By being fed in more intensive, grain-fed systems, cows generally reach slaughter weight faster than grass-fed animals do, thus generating fewer emissions over the animal’s entire lifetime. 
2 – By eating grass, an extremely fibre-rich plant, grass-fed cows belch more often and thus emit more methane than grain-fed cattle. 
3 – While intensive farming methods are certainly less ethical and less nutritious, raising cattle in reduced confines rather than sprawling pasture may reduce the industry’s thirst for land and thus reduce deforestation. 
So although important morally relevant qualitative differences exist between industrial and non-industrial methods of raising cattle, environmentally speaking, there is more to the picture than meets the eye. The bottom line is that while grass-fed beef confers meaningful improvements to the living conditions of cattle and an enhanced nutritional profile compared to grain-fed beef, from a sustainability perspective, grass-fed beef will not only fail to help tackle climate change, but it will directly contribute to it unless its scale is sharply reduced.
I’m sure Allan Savory meant well with his Ted Talk – but unfortunately, his opinion is not backed by science and with over 6.2 million views, he is causing great confusion among the public.
4. So is the solution to cut back on red meat and replace it with other meat?
As stated in the latest IPCC report, beef has consistently been identified as the single food with the greatest impact on the environment, in terms of GHG emissions and land use per unit of commodity.  Indicative of the environmental burden posed by this food is the finding that in the United States, 4% of food sold by weight is beef, and yet this food accounts for 36% of food-related emissions.  So this begs the question – is other meat more sustainable? If so, by how much?
This question, thankfully, has been extensively explored. Scientist from the Eat Lancet Commission have concluded that a diet which replaces ruminants (such as beef, sheep and goat) with other alternatives such as fish, poultry, and pork, – dubbed a ‘Climate Carnivore’ diet by the IPCC – yield considerable reductions in both environmental inputs and outputs – although still to a much smaller extent compared to plant-based alternatives. [16,68] At the end of the day, while poultry and pork are less resource-intensive foods compared to beef, they still significantly outweigh the environmental impact of plant foods. [14,48]
Indeed, the sustainability potential of diets is a spectrum: the fewer animal-based foods and red meat, the more the environmental benefit.  Below is a table produced by the latest IPCC report which compares different diets and their climate change mitigation potential which evidences this spectrum.  At the top of the list is a vegan diet – with no animal-based foods, and below that are each dietary patterns with their corresponding potentials. It’s important to note that although the Mediterranean diet features last amongst mitigation-potential diets, their definition of this diet is a rather modern one that features “vegetables, fruits, grains, sugars, oils, eggs, dairy, seafood, moderate amounts of poultry, pork, lamb and beef”.  Therefore, those following the original interpretation of the Mediterranean Diet – that is, a mostly plant-focused diet – would probably align more with the ‘Flexitarian’ diet, ranked third by the IPCC.
This is of particular importance in Australia, where per capita meat consumption is one of the highest in the world. Worldwide, in fact, each person consumes an average 43 kilograms of meat a year, but in Australia, each person consumes around a whopping 116 kilograms per year,  having recently surpassed the United States. Worryingly, all projections seem to indicate that such elevated consumption patterns are destined to increase, rather than decrease. According to projections by the Australian Government itself, demand will drive a sharp increase in cattle from 26 million (yes, there is currently more cattle than people in Australia) to 39.7 million in 2050. 
The bottom line is that it isn’t all or nothing: any reduction in meat consumption will yield a corresponding benefit.
5. Is Australia exempt from all the damaging practices in industrial farming used abroad?
There is a common perception, which I am also often guilty of, that all the facts, data and statistics regarding factory farming and its damage to the environment somehow do not apply to Australia. Both domestically and internationally, Australian meat is perceived as a premium product that is pure and free from damaging conventional and intensive practices. Curious to investigate the accuracy of these claims, I set out to find out what the real situation is in Australia.
First off, it is true that compared to the global average of only 8.4% of cattle being fed on pasture,  Australia has historically fared quite well, with around 98% of Australia’s national herd being raised on grass pasture.  However, while most cattle are indeed raised on pasture, the majority of them are sent to a feedlot for around 100 days to be fattened up with grain before slaughter.  This means that even grass-fed beef, unless certified, could have been subjected to both a nutritionally-poor diet and inhumane living conditions. That was certainly news to me as I am sure it is to you!
In recent years, due to the extensive drought conditions, the number of cattle fed entirely on grain in feedlots has reached record highs.  These days, according to the Australian Lot Feeders Association themselves, approximately 40% of Australia’s total beef supply and 80% of beef sold in major domestic supermarkets is sourced from the cattle feedlot sector. 
In terms of hormonal use, in Australia, hormonal growth promotants are used on about 40% of Australian cattle to promote weight gain.  The hormones are generally administered as small implants placed under the skin on the back of the ear which over the course of 100-200 days, slowly release a low dosage of hormones which stimulate growth.  While these are completely legal and are considered safe in Australia, Hormonal Growth Promotants have been banned in the European Union, which states that any increase in dietary hormone levels associated with consumption of meat poses an unacceptable increase in the risk of adverse health consequences such as cancer. 
When it comes to antibiotic use in Australian Livestock, its use has historically been hidden behind a veil of secrecy.  However, after the World Health Organization identified ‘antibiotic resistance’ caused in large part by the oblivious consumption of antibiotic-ridden meat as a major public health threat, this prompted the industry to look into how much antibiotic was being administered to their livestock.  Information regarding antibiotic use was thus voluntarily collected and summarized in a report published by the Meat and Livestock Association of Australia.  The report concluded that “a number of common antibiotics (penicillins, tetracyclines, sulfonamides) are widely used in the industry for treatment of infectious conditions. […] In grazing cattle, procaine penicillin is used to prevent or treat pasture bloat, and in dairy cattle, virginiamycin is used to reduce the risk of ruminal acidosis. Ionophores are used widely for bloat prevention, as rumen modifiers where grain is fed and anticoccidials in feedlots and dairies. The dairy industry uses the macrolide tylosin in feed to control liver abscess.” So, according to their statement, although no specific figures are offered, antibiotic use in the livestock sector is widespread, even amongst grass-fed beef. Per numerous of my podcast episodes, particularly the episodes with Gastroenterologist Dr Will Bulsiewicz, avoiding unnecessary exposure to antibiotics is crucial in developing and maintaining a healthy gut microbiome.
Grass-fed beef that has been certified under third party certifications such as the Pasturefed Cattle Assurance System or Grasslands Pasturefed Standard is generally guaranteed to have been sourced by cattle fed 100% on pasture which is free of antibiotics and hormones. So if you were to keep small amounts of red meat in your diet this is the type you would want to be consuming. However I want to make it clear, both your health and the planet’s would be greatly improved by completely eliminating all forms of red meat regardless of whether they are free-range, grass-fed or grain-fed.
6. What would happen if we all went vegan?
A common argument that is put forth by those in the pro-carnivore camp is that at the end of the day, livestock plays an essential role in our ecosystem by promoting both soil health and providing the manure that naturally fertilizes plants.
Indeed, it has been recognized that limited animal grazing can be good for soils. By curbing the growth of shrubs, by spreading seeds with their hoofs and by stimulating grass growth with their trampling, grazing animals can improve the composition of soils, plants and nutrients while promoting biodiversity. 
However, on the other hand, the truth remains that overgrazing, which affects the majority of pasture land,  undoubtedly contributes to the disappearance of plant species that benefit soils and subsequently leads to a grave loss in biodiversity.  Importantly, excessive grazing also leads to soil erosion, reduced soil fertility, water infiltration, and a loss in its capacity to store water. 
Furthermore, in arid terrain (such as the one that spans a large quantity of the Australian territory), livestock is more likely to destroy grass and other vegetation than to protect it.  As pointed out by the International Journal of Biodiversity, “published comparisons of grazed and ungrazed lands in the western US have found that rested sites have larger and more dense grasses, fewer weedy forbs and shrubs, higher biodiversity, higher productivity, less bare ground, and better water infiltration than nearby grazed sites.” 
When it comes to animal manure, I’ve often heard that it plays an essential role in promoting plant and soil health while also reducing the need for synthetic fertilizers. It is stated that if we reduced or got rid of all grazing animals, we would have to produce more synthetic fertilizers to replace animal manure, and the net benefits for the environment would be dubious. However, upon further investigation, it appears that currently, manure supplies are both local, unreliable and underutilized, accounting for a very small portion of all the nutrient masses used in agriculture. The main source of fertilizers for crops are synthetic, and thus, in other words, not much would change in a “100% plant-based scenario”. If anything, the need for synthetic fertilizer would dramatically be reduced if we got rid of all grazing animals – as we would be freeing up large amounts of feed crops. 
Ultimately, the question is: at a global level, what would happen to our soils if we theoretically got rid of all grazing livestock? The evidence on this matter, according to my research, does not appear to be clearcut.
It seems that although mass consumption of meat is driving the sector towards unprecedented rates of deforestation and its subsequent effects on soil health, erosion and biodiversity, a complete removal of grazing animals also has the potential to reduce biodiversity because, without the grazing to cull plant growth, “a thick canopy of shrubs and trees develops which intercepts light and moisture and results in overprotected plant communities which are susceptible to natural disasters”, according to the Food and Agriculture Organization of the United Nations. 
The answer, therefore, appears to be somewhere in the middle: some grazing livestock can offer benefits to our soils and vegetation, but we definitely don’t need anywhere near as much as we have today. In other words, it is not grazing animals per se that are problematic – but rather it is the sheer scale of the industry that is posing a threat to our sustainability.
Another added factor to consider is that some terrain currently being used by grazing livestock simply is not suitable for growing other crops, particularly in Australia. In semi-arid areas such as those in Australia, there are few, if any realistic and financially viable alternatives of land use other than continued grazing of cattle.
Beyond soil health, many important benefits could be reaped if we removed all livestock animals from our terrain. For starters, we could substantially reduce the copious methane and the overall emissions related to animal agriculture. In addition, the crops that are currently grown to feed animals could be diverted for human consumption, thus boosting food security. In Australia, in fact, the majority of grains grown are used in animal feed, as visible in the table below.
Recently, a study published in the prestigious journal Nature quantified that if all U.S Americans switched to plant-based foods and gave up animal products entirely while still maintaining current levels of protein consumption, the need for cropland, nitrogen fertilizer and the emissions generated would be reduced by 30-50%, while the need for irrigated water would increase by 5-15%. Another study quantified that by replacing all animal foods with plant-based foods in the United States, they would be able to grow enough extra crops to feed 350 million additional people. 
Nutritionally speaking, the overconsumption of meat is now a leading cause of obesity (with its attendant health effects) as well as a leading cause of many chronic or noncommunicable diseases, both in developed and developing nations.  Indeed, the majority of those living in the developed world and a growing number of individuals in developing nations eat far more animal foods than is healthy.  Thus, reducing or altogether eliminating animal foods from our plates could substantially reduce the burden of disease and its financial and environmental consequences. 
Ultimately, while this may be an interesting hypothetical question to explore, it is grossly unrealistic that such a scenario will ever become a reality. Meat and dairy are more than just food – in ways, they have transcended the culinary realm to which they belong and arguably become inextricably woven into the social fabric of our cultural identity. It’s hard to imagine a future in which scenario in which they will play a marginal role in our diets. In addition, many rural societies will continue to depend on animal protein to meet their nutritional needs and to sustain their livelihoods for decades to come.
In short, we don’t have to worry about what will happen if we all went vegan because it will likely never happen. There is, however, a very strong argument for the majority of people who are lucky enough to have access to an abundance of foods to adopt a well-balanced entirely or mostly plant-based diet. Not only will this in part offset the emissions caused by those who will continue to consume animal foods – but it will have undeniable health benefits. With this context in mind, if you can successfully adopt a 100% plant-based diet it is, without a doubt, the single best thing you can do for planetary health.
The bottom line is that, beyond ethical considerations, current meat consumption is grossly unsustainable from both a health and environmental perspective. This is not about being a vegan or pushing a plant-based message – the simple, environmental truth is that we need to eat less meat and dairy – much less. Our challenge is clear: ahead of the population growth our planet is expected to be subjected to, we need to produce more food than ever before, but do so in a way that emits drastically fewer emissions than at present. Quite simply, in a world of almost 8 billion people with a finite amount of land and resources, current rates of meat consumption simply cannot be sustainably maintained. While meat may play a pivotal role in enabling those who live in impoverished societies to meet their nutritional requirements and sustain their livelihoods, its role is indeed limited in affluent nations which boast an abundance of dietary options. 
Yes – grazing livestock does have a place in a sustainable food system – but that place is extremely limited. Does this mean you should take up the occasional meat dish? Not if you have a choice – by sticking to plant foods you will effectively offset the environmental burden posed either by those who either refuse to reduce their consumption or those who require meat to meet their nutritional requirements in rural societies. But this also means that if family and friends aren’t quite ready to give up their favourite animal-based foods, you can let them know that even a modest reduction in the frequency of these foods can yield meaningful results. Remember, to create a better world we need ‘buy in’ from billions of people. Rather than millions adopting a plant-based diet perfectly, we need billions doing it imperfectly.
Indeed, the bottom line, and take home message is that the diet that is good for you is good for the planet and each of us should be doing our best to lower the environmental footprint of our plate where we can. 
This blog was co-written with Katherine Annesi from the Department of Sustainability at the University of Sydney. Thank you, Katherine, for your diligent approach to this topic.
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