Imagine that we are Earth doctors and we are being asked to diagnose the Earth's condition and prescribe a course of action for healing and reversal. Let's take each of the planetary boundaries and examine the root cause for the human induced perturbations in the underlying Earth processes.
Take the number one violated limit in the scientists’ list: the unsustainable extinction of species on the planet. Species are stressed by multiple factors including habitat loss, invasive species, pollution, climate change, and just plain human consumption. But habitat loss through deforestation, desertification and egregious fishing practices such as bottom trawling and drag-net fishing, has been estimated to be responsible for 80% of species extinctions. As for habitat loss on land, in the latest UN Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5), Working Group 3, Chapter 11 breaks down the land use and human biomass consumption figures, sector by sector, from the year 2000, as follows.
72% of the useable landmass of the Earth has been appropriated for human purposes, while 8% is untouched, pristine forest and 20% is abandoned, unused or naturally regenerating land.
11.77 Giga tons of dry matter plant biomass is extracted from all that land for human use. Of that, 60% goes to feed our livestock, 15% is used for bio-fuels, mainly as fuelwood, 13% is used by the processed food industry, 10% goes towards other industrial uses and only 2% is consumed directly by humans in the form of fruits, vegetables, nuts, seeds, grains, etc.
Of the 7.01 Gig tons of plant biomass fed to livestock, we end up with only 0.18 Giga tons of meat, dairy and eggs on our dinner plates, an enormous 39-fold reduction in biomass due to trophic losses and waste.
In contrast, of the 1.78 Giga tons of plant biomass that we extract for human consumption in the form of plant foods, 1.36 Giga tons ends up on our dinner plates, a mere 25% reduction in biomass, mainly due to processing.
We know that the biomass of 7.4 billion humans alone (500 Million metric Tons (MT)) exceeds the biomass of all megafauna (200MT) that existed on Earth between 10K-100K years ago by a factor of 2.5. But as far as the planet is concerned, we are presenting the profile of 44.4 billion humans, not just 7.4 billion humans, once we include the biomass consumed by our domesticated animals!
Since the year 2000, the impact of Animal Agriculture has only become more pronounced since the industry has grown by 30% in that time span. The International Livestock Research Institute (ILRI) scientists estimate that livestock systems occupy 45% of the land area of the planet today. The IPCC has estimated the same figure to be 40%, but as of the year 2000. Where livestock systems occupy land, biodiversity is greatly diminished - for example, wild animals are killed as "intruders" and wild plant species are replaced with fodder - and species extinctions inevitably occur. In the ocean, our fishing practices are so indiscriminately violent and egregious that, for example, we kill 6 times as much marine life as by-catch than the shrimp we harvest. This is why the Center for Biological Diversity, a grassroots environmental organization that is committed to preventing species extinctions, has begun a "Take Extinction off Your Plate" campaign to promote the wide scale adoption of plant-based diets.
The second major safe limit violation, the Nitrogen cycle, is also primarily due to Animal Agriculture since more than half the industrially grown mono-cultured crops of the world that rely on nitrogen fertilizers for production are fed to animals directly.
With respect to the third safe limit violation, the Carbon cycle, human burning of fossil fuels is clearly the number one cause, responsible for an estimated 57% of all anthropogenic greenhouse gas emissions, using a 100-year window for calculating CO2 equivalences of methane and other short-lived greenhouse gases. However, many scientists have questioned the use of a 100-year time window for calculating CO2 equivalences of short-lived greenhouse gases, given the urgent nature of climate change. With a 20-year time window, for instance, methane becomes three times as powerful a greenhouse gas, than over a 100-year time window.
But even here, Animal Agriculture is a substantial contributor to anthropogenic greenhouse gas emissions, with end-to-end lifecycle estimates ranging as high as 51% of the total, if we use 20 year time windows for calculating CO2 equivalents. A good chunk of the fossil fuels are burnt to support this industry for the transportation of feed to animals and the processing, refrigeration and transportation of animal carcasses. In addition, a major portion of the greenhouse gas contributions due to deforestation is because of Animal Agriculture, and a major portion of the soil carbon emissions due to desertification is also because of Animal Agriculture.
There is an ongoing debate on the magnitude of the role of Animal Agriculture in anthropogenic greenhouse gas emissions. While scientists are supposed to be unbiased observers in the scientific studies they are conducting, such biases are inevitable when personal habits are related to the studies. While estimating the lifecycle impact of Animal Agriculture, almost every scientist is prone to such bias, since the vast majority of scientists in the world consume animal products on a routine basis. For instance, at the largest annual gathering of climate scientists in the world, the American Geophysical Union (AGU) Fall Meetings in San Francisco where 25,000 scientists gathered in 2015, the banquet dinner consisted of steak as the main course. Hardly anyone at the banquet ordered the lactovegetarian meal option, and I was the only one who special-ordered a plant-based, vegan meal. I know this because I was waiting for them to boil some pasta and vegetables for my dinner while the steak knives were clanging all around me.
The traditional framing of climate change is that the human burning of fossil fuels primarily causes it. Deforestation, which is mainly to support animal agriculture, adds a much smaller component. Land and the ocean absorb 55% of those emissions while the other 45% accumulates in the atmosphere causing climate change. With such a framing, we feel disempowered because fossil fuels are such an integral part of our daily lives these days.
But that is the official story. When we study the carbon cycle in detail using the UN IPCC AR5, we discover that the true story is much more nuanced. Fossil fuel burning emits 7.6 Giga tons of Carbon (GtC) annually. Deforestation emits 1.5 GtC annually. But other human activity on land and in the ocean causes 29.3 GtC to be emitted annually through decaying crop biomass, through raising billions of farm animals, through firewood burning, etc. That is nearly 4 times as much carbon emissions as the fossil fuel component! But human activity also causes 34.1 GtC to be sequestered annually through the use of nitrogen fertilizers, CO2 fertilization effects, irrigation and other technologies. The net result is a sequestration of 4.8 GtC, which is about 55% of the emissions due to fossil fuels and deforestation.
This means that, in total, human activity is causing 38.4 GtC to be emitted annually and 34.1 GtC to be sequestered annually. This is where the enormous impact of our food and other consumer choices is hidden – in plain sight.
In 2006, the UN Food and Agricultural Organization (FAO) published the initial estimate of lifecycle impact of Animal Agriculture. The FAO report estimated that the Animal Agriculture industry was responsible for 18% of anthropogenic greenhouse gas emissions, about 50% more than the entire transportation sector, which was estimated to be responsible for 13%. Then, in 2009, two Environmental Assessment specialists from the World Bank Group, Dr. Robert Goodland of the World Bank and Jeff Anhang of the International Finance Corporation (IFC), using the UN IPCC Fourth Assessment Report (AR4) lifecycle impact analysis guidelines, estimated that the Animal Agriculture industry was responsible for at least 51% of all anthropogenic greenhouse gas emissions, in total. Their estimate was a lot higher than the FAO estimate because they included all the Tier 3 contributions that were missing in the FAO estimate, as per IPCC guidelines. They used a 20-year window for calculating CO2 equivalences of short-lived greenhouse gases such as methane, instead of the 100-year window used in the FAO estimate. Clearly, since climate change is an urgent problem that requires immediate action within the next 1-2 decades, using a 20-year window for calculating the impact of methane emissions is actually more appropriate.
When the WorldWatch Institute initially published the Goodland-Anhang estimate, the estimate needed to be debated and corroborated in a scientific journal before gaining legitimacy. The 18% figure from the 2006 UN FAO report was compiled by scientists who were employed by the Animal Agriculture industry (Steinfeld, Herrero et al. consult for the International Livestock Research Institute (ILRI), a think tank for the industry) and therefore, it was prone to be biased. For instance, all of the criticisms of the FAO estimate in the Goodland-Anhang report were clearly valid. Naturally, the ILRI scientists would be inclined to downplay the environmental impact of their industry products, just as the Tobacco Institute scientists were inclined to downplay the health impacts of tobacco. On the Internet, there were a lot of ad hoc criticisms of both estimates with bloggers making arbitrary corrections to either estimate and I described the situation thus in the 2011 book, Carbon Dharma: The Occupation of Butterflies:
"We got an inkling of the impact of animal agriculture when the UN published its Livestock and Climate Change report in 2006, where the livestock sector was calculated to be contributing 50% more greenhouse gas emissions (18%) than the entire transportation sector of the world (12%). Later, in a 2009 Worldwatch Institute report, two UN Environmental Assessment (EA) specialists, Robert Goodland and Jeff Anhang, pointed out that the 2006 UN report failed to take into account the carbon cycle imbalances caused by the conversion of forests to livestock pasture lands. They came up with an estimate that the livestock sector was responsible for 51% of world greenhouse gas emissions but their calculations based on the breathing contribution of livestock were not widely accepted. However, in 2010, Prof. Danny Harvey of the University of Toronto in Canada, building upon the thesis work of Stefan Wirsenius from the Goteborg University in Sweden from 2000, calculated that the average human being is consuming more energy in food than in fuel and shelter combined, when we take into account the embedded plant-based energy input to the animal agriculture systems. And the main reason is that animal agriculture is so inefficient that, on an average, it requires 100 Joules of embedded plant-based energy to produce less than 4 Joules worth of animal foods such as eggs, dairy and meat for human consumption."
However, in late 2011, the scientific community hashed it out in the peer-reviewed Animal Feed Science and Technology (AFST) journal. The principal authors of the 2006 FAO report, Herrero et al., wrote a paper rebutting Goodland and Anhang's criticisms of their work. Goodland and Anhang strongly responded to that rebuttal and basically reiterated their original calculations in the same journal. Herrero et al. then declined to continue the debate.
As per the scientific process, the calculations of Goodland and Anhang stand until there is another peer-reviewed scientific paper that updates their methodology and calculations - perhaps using IPCC AR5 lifecycle analysis guidelines with updated CO2 equivalence factors for methane etc. - and goes through a similar peer-reviewed, scientific scrutiny. Please note that in their Worldwatch report, Goodland and Anhang state that Animal Agriculture is responsible for at least 51% of the global greenhouse gas emissions, i.e., the 51% fraction is a lower bound!
The ILRI scientists later doubled down on their earlier mistakes and reported a smaller 14.5% figure in the UN FAO report of 2013, without any explanation and without addressing the debate points in their AFST journal exchange with Goodland and Anhang! That made their earlier estimate from 2006 even less credible. But then, how can we seriously expect scientists with deep ties to the Animal Agriculture industry to provide credible estimates on the harmful impact of that industry? That’s like expecting scientists from the Tobacco Institute to provide credible reports on the harmful impacts of smoking.
Perhaps the most controversial aspect of the Goodland-Anhang analysis has been their use of estimated CO2 emissions from livestock breathing, as a proxy for soil carbon loss due to Animal Agriculture. The typical argument that critics use is that everyone breathes and therefore, it is all part of the “natural” carbon cycle. But they don’t seem to use the same argument for not counting the methane contribution of livestock. Since all ruminants emit methane, why should livestock methane emissions be treated as anthropogenic? Indeed, the IPCC routinely does count livestock methane emissions as anthropogenic!
Both livestock CO2 and methane emissions need to be counted since the biomass of livestock today is an entirely man-made, extraordinary and unprecedented burden on the ecosystems of the Earth. According to paleobiologist, Prof. Anthony Barnosky of UC Berkeley, the biomass of all megafauna stayed fairly constant at around 200MT from 100,000 years ago until about 10,000 years ago, when humans overspread the Earth and caused the Quaternary extinction of large megafauna. From 10,000 years ago until about 400 years ago, there weren’t too many species extinctions and the global biomass of megafauna slowly recovered to 200MT, mainly as a result of increased livestock and human population.
However, since the industrial era, the biomass of megafauna exploded from 200MT to about 1500MT today, with humans accounting for 500MT and our domesticated animals accounting for most of the rest, with the biomass of all wild megafauna reduced to a mere 2-3% of the total. The breathing contribution of all that excess biomass is clearly out of balance with the natural carbon cycle and it shows in the rapidly spreading deserts of the world. The breathing contribution of livestock stands out since our livestock population is an unnatural mix of mostly young animals that eat and metabolize at 2.5 times the rate as one would expect from their biomass alone. In fact, the IPCC AR5 figures show that our livestock population metabolizes 5 times as much dry matter biomass (4.69 Gt) as all human beings put together (0.93 Gt). Though our livestock weigh about 1000MT, they present the profile of a biomass that weighs 2500MT! All that excess metabolization results in CO2 emissions and should be counted, even as per IPCC AR5 guidelines. Therefore, Goodand and Anhang’s use of the breathing contribution of livestock as a proxy for soil carbon loss is appropriate and even has precedence in the scientific literature.
Fossil fuel burning produces significant CO2 emissions, the prime culprit for ocean acidification. However, if the scope of Animal Agriculture diminishes considerably and regenerating forests sequester some of the excess CO2 in the atmosphere, the acidity of the ocean will diminish as the dissolved CO2 in the ocean outgases into the atmosphere again.
As for fresh water, 55% of human fresh water use is for Animal Agriculture in the US, while the fossil fuel industry accounts for about 25% of fresh water use.
With respect to ozone depletion, one of the primary mechanisms for it is during the conversion of methane to CO2 in the upper atmosphere. In turn, Animal Agriculture is one of the primary sources of anthropogenic methane emissions. However, among fossil fuels, natural gas systems leak methane as well, though the true magnitude of these leaks is in dispute.
With respect to aerosol loading, the major source of human emissions of aerosols is during the burning of fossil fuels.
Finally, with respect to chemical pollution, most of the herbicides, pesticides and insecticides are used in the agricultural production of animal feed. Most of the pharmaceuticals are ingested to treat human diseases that occur due to the consumption of animal foods. Therefore, if Animal Agriculture ceases, a significant portion of the chemical pollution on the planet will cease as well, though it will take a while for the existing pollution to be sequestered by regenerating forests.
As Earth physicians, let us imagine that we are asked to write a prescription for each and every human being to fill so that humanity's overall relationship with the Earth changes to a more benign, safer, steady state version. What should we tell people to do? Should we tell them to focus on weaning themselves from fossil fuel use, i.e., go solar, or should we encourage the ongoing transition away from animal products, i.e., go vegan?
The best way to answer this question is to do a sensitivity analysis through a simple thought experiment. Imagine that we wave a magic wand and get everybody to go vegan instantly. This immediately impacts 8 of the 9 planetary boundaries and instantly begins to reduce the violated safe limits as well. If everybody went vegan, it would immediately release 35-40% of the land area of the planet back to Nature, to regenerate forests and re-wild the planet.
1) Since habitat gets returned to wildlife, the safe limit violation on species extinction rates would be reduced immediately.
2) The safe limit violation on the nitrogen cycle gets reduced immediately as we replace the 0.18 Gt of dry biomass of animal-based foods, (and 0.09Gt of seafood biomass), with equivalent plant-based foods, derived from crops. This is because, as of 2000, according to the UN IPCC figures, 3.14 Gt of crop-based dry-matter biomass was going directly to feed livestock and almost all of that required nitrogen fertilizers. Let's say we need to use twice as much plant crop biomass to produce the plant-based food equivalents for the 0.27Gt of animal-based foods. Then, we need to raise 0.54 Gt of plant crop foods for the plant-based substitutes instead of 3.14Gt, meaning that around 80% of those plant crops can be eliminated, thereby reducing nitrogen fertilizer use by 40% overall.
3) The safe limit violation on the carbon cycle gets reduced as regenerating forests sequester CO2 from the atmosphere in trees, plants, insects, animals, birds, and in the soil. Along with Prof. Atul Jain of the University of Illinois at Urbana-Champaign and his graduate student, Shijie Shu, I presented a paper on this so-called “Lifestyle Carbon Dividend” at the AGU Fall meeting in December 2015. Using the Integrated Science Assessment Model (ISAM) that Prof. Jain’s team developed at the University of Illinois, we estimated that recovering forests can sequester 265 Giga tons of Carbon (GtC) on just the 41% of current grasslands that used to be forests in 1800. That is more carbon than has accumulated in the atmosphere since 1750 (240 GtC)!
4) As the CO2 in the atmosphere gets sequestered in regenerating forests, the acidification of the ocean reduces as well, as the ocean outgases CO2 to reach a new equilibrium.
5) Around 40% of the cropland can be returned to Nature thereby mitigating the land use planetary boundary.
6) Around 50% of the fresh water use is avoided as Animal Agriculture ceases. Besides regenerating forests create more fresh water as well.
7) As methane emissions are reduced, ozone depletion is ameliorated as well.
8) The regenerating forests begin to sequester chemical pollutants, and as humans stop ingesting chemical pollutants through animal-based foods and become healthier, their production of excreted pharmaceuticals also reduces.
Next, let us consider a second thought experiment. Imagine that we can wave the same magic wand and turn our entire energy infrastructure over to solar, wind and other clean sources instantly so that fossil fuels no longer have to be burnt to run the human enterprise. Let us assume that we leave everything else unchanged as at present so that we continue to eat animal foods and indeed, double our consumption by 2030 as envisioned by the UN FAO. As a result of this instant change to our energy infrastructure, we stop pumping a majority of the greenhouse gases, especially carbon dioxide (CO2), into the atmosphere and we immediately stop exacerbating human impact on 4 of the 9 planetary boundaries. That is the good news. But the bad news is that,
1) The surface temperature of the planet will start increasing at a faster rate and it will increase approximately by an additional 0.5 deg C (1 deg F) within a decade as aerosols disappear from the atmosphere. This temperature increase occurs because when we burn fossil fuels, we not only pump greenhouse gases into the atmosphere, but we also simultaneously pump aerosols such as sulphur dioxide (SO2) that are partially shielding us from the true impacts of our greenhouse gas emissions. While CO2 persists for hundreds of years in the atmosphere, aerosols precipitate and disappear from the atmosphere within a couple of weeks thereby exposing us to the true effects of our greenhouse gas emissions to date. Think of aerosols as the haze that prevents the sun from shining brightly on our Earth. When the haze disappears, the Earth heats up.
Using the fever analogy, the Earth's temperature will rise from a 38 deg C (100 deg F) fever to a 38.5 deg C (101 deg F) fever within a decade even though we have stopped burning fossil fuels completely. Personally, with a 100 deg F fever, I can still function in my day-to-day life, but with a 101 deg F fever, I'm resting in bed waiting for the fever to subside. That extra 1 deg F temperature increase can have serious repercussions for us on the planet as well. This is why the eminent climate scientist, Dr. Jim Hansen, has concluded that we need to keep pumping aerosols into the atmosphere even after we phase out fossil fuel burning in a Faustian bargain to avoid excessive temperature increases. It is very likely we will have to do that by extracting the sulphur from coal in a chemical process and then burning the sulphur alone with little to no benefit whatsoever. And suffer the resulting consequences of acid rain falling on our heads.
2) The CO2 in the atmosphere will not diminish for hundreds of years and therefore, the violated limit on the carbon cycle will stay violated for hundreds of years as well, even though we no longer burn any more fossil fuels. Furthermore, since our land use changes will continue unchecked, CO2 emissions from deforestation, desertification and methane emissions will continue to add to the atmospheric CO2 levels.
3) As the CO2 concentration in the atmosphere increases due to deforestation, the ocean will continue to become more acidic, but not as much as it would with the additional burning of fossil fuels.
Therefore, in this second experiment, the conversion of the energy infrastructure does nothing to heal the climate and would actually make the situation worse.
As Earth doctors, our diagnosis task is a no-brainer, really. Considering all the symptoms that the Earth is exhibiting and considering the results of our thought experiment, we can now see that it is primarily Animal Agriculture, which has deliberate, institutionalized violence on other beings implemented on a gargantuan scale, that is the main source of the cancer underlying the Earth's fever. Just among land animals alone, 200 million of them are being directly slaughtered each and every day for food all over the world. If we count sea animals and the by-catch of sea animals during industrial fishing, the total is on the order of a few billion animals each and every day to sustain the appetites of 7.4 billion human beings. Billions of animals are being routinely enslaved, forcibly impregnated, with their menstrual secretions harvested, their maternal secretions harvested, and then they are slaughtered, most when they are still just babies. Every one of these acts is an act of institutionalized violence and every form of animal husbandry on this planet performs almost every one of these acts of violence. Even the certified, highest rated, "humane" meat, dairy or egg producing small farm performs almost all these acts of violence on a routine basis. This is the primary reason for all the violated limits in the scientists' list. This is the "cancer" underlying the "fever," the cancer that is eating away at the Earth.
But this is like a rare form of cancer that is eminently curable. We are already waking up to reverse that cancer by voluntarily changing our consumption patterns. Despite the deafening silence on this issue from climate scientists and mainstream environmentalists, who are naturally frightened of the system implications as an industry directly and indirectly employing a billion people bites the dust, the Miglets are already leading a global transition towards veganism. Surely, as a species, we can figure out better ways to guarantee economic security for people without requiring them to destroy the planet?
However, that doesn’t mean we should stop converting our energy infrastructure over to clean sources. In fact, the two steps, go vegan and go solar, will be accomplished simultaneously. Those of us in the global North who have access to food abundance will go vegan right away and then convert the energy infrastructure over to clean sources over the next 1-2 decades as solar technologies get produced in volume. This is the optimal order for the change to occur since the carbon sequestration due to the vegan transition will then compensate for the temperature increase due to the atmospheric aerosol reduction from the clean energy transition.
 Habitat loss is the primary cause of species extinctions: http://wwf.panda.org/about_our_earth/species/problems/habitat_loss_degradation/
 Please use the flow diagram on Page 836 of the document: https://www.ipcc.ch/pdf/assessment-report/ar5/wg3/ipcc_wg3_ar5_chapter11.pdf
 Barnosky, A., “Megafauna Biomass Tradeoff as a Driver of Quaternary and Future Extinctions,” Proceedings of the National Academy of Sciences, vol. 105, suppl. 1, pp. 11543-11548, 2008, doi: 10.1073/pnas.0801918105. http://bit.ly/2bDbfZ0
 Goodland, R and Anhang, J, “Livestock and Climate Change,” Worldwatch Institute report, 2009. http://bit.ly/TYv58d
 Herrero et al, “Livestock’s Long Shadow,” FAO report, 2006. http://bit.ly/1uTv8Tl
 A good explanation of the IPCC Tier 1, 2 and 3 reporting mechanisms can be found in http://bit.ly/1YJJIbg
 A good discussion of the 20 year vs 100 year time window can be found in http://bit.ly/1J8CUO2
 Rao, Sailesh, Carbon Dharma: The Occupation of Butterflies, Climate Healers, ISBN-13: 9781467928458, Oct. 2011. http://www.carbondharma.org
 Herrero, et al. “Livestock and Greenhouse Gas Emissions: The Importance of Getting the Numbers Right,” Volumes 166-167, Pages 779–782, June 2011, DOI: http://dx.doi.org/10.1016/j.anifeedsci.2011.04.083
 Goodland, R and Anhang, J, “Livestock and greenhouse gas emissions: The importance of getting the numbers right, by Herrero et al. [Anim. Feed Sci. Technol. 166–167, 779–782],” Volume 172, Issues 3-4, Pages 252–256, March 2012, DOI: http://dx.doi.org/10.1016/j.anifeedsci.2011.12.028
 There is a notation on the Animal Feed Science and Technology journal page that Herrero et al declined to continue the debate. http://dx.doi.org/10.1016/j.anifeedsci.2011.12.028 . Please see explanation at http://bit.ly/240nYcD
 Gerber, P.J., et al, Tackling climate change through livestock – A global assessment of emissions and mitigation opportunities, FAO, 2013, http://www.fao.org/3/i3437e.pdf
 Barnosky, A., “Megafauna Biomass Tradeoff as a Driver of Quaternary and Future Extinctions,” Proceedings of the National Academy of Sciences, vol. 105, suppl. 1, pp. 11543-11548, 2008, doi: 10.1073/pnas.0801918105, http://bit.ly/2bDbfZ0
 Chianese, et al, “Simulation of Carbon DiOxide Emissions from Dairy Farms to Assess Greenhouse Gas Reduction Strategies,” Transactions of ASABE, vol 52, no 4, pp. 1301-1312, 2009. http://1.usa.gov/256NvDf
 Jacobson, M. F. “More and Cleaner Water.” In Six Arguments for a Greener Diet: How a More Plant-based Diet Could save Your Health and the Environment. Washington, DC: Center for Science in the Public Interest, 2006. http://www.cspinet.org/EatingGreen/pdf/arguments4.pdf
 Allen, et al. “Fossil Fuels and Water Quality,” Chapter 4, The World’s Water, Vol 7, 2012, http://bit.ly/1FouO2h
 A 2014 satellite study confirmed that livestock produced more methane than fossil fuel sources in the US: http://bit.ly/1uMxHDj
 Szidat et al, “Contributions of fossil fuel, biomass-burning, and biogenic emissions to carbonaceous aerosols in Zurich as traced by 14C”, J. Geophysical Res., Volume 111, Issue D7, April 2006, http://onlinelibrary.wiley.com/doi/10.1029/2005JD006590/full
 Prof. T. Colin Campbell estimates that 70% of the pharmaceutical intake can be avoided if humans stop consuming animal foods, http://www.forksoverknives.com/the-film/
 This estimate is based on the observation that 35% of the land area of the planet is currently used to grow fodder to feed livestock. In addition, half the biomass from cropland is consumed by livestock as well. The argument being made is that if the biomass from cropland is fed directly to humans, then the grazing land for cattle will be freed up for ecosystem restoration. See IPCC AR5 WG3 Chapter 11, page 836: https://www.ipcc.ch/pdf/assessment-report/ar5/wg3/ipcc_wg3_ar5_chapter11.pdf
 This assessment is based on the observation that grain-feeding of livestock is prevalent mainly in the affluent nations of the world.
 This is a lower bound since crops that don’t use chemical fertilizers, as grown in the developing world, are used for human consumption directly.
 Rao, S., Jain, A. K., Shu, S., “The Lifestyle Carbon Dividend: Assessment of the Carbon Sequestration Potential of Grasslands and Pasturelands Reverted to Native Forests,” AGU Fall Meeting, Dec 2015, https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/67429
 Hansen et al, “Doubling Down on Our Faustian Bargain,” Huffingtonpost, Mar 2013, http://huff.to/1OED5l0