Dietary change is essential for forests and climate

Land clearing is a critical climate change issue, relating to the fact that living vegetation (including forest) draws carbon from the atmosphere while the removal of that vegetation releases carbon from the vegetation itself and the soil.

What many of us may assume to be natural landscapes may be very different to what existed before livestock and other environmental pressures were introduced.

In the Australian context, the problem has been exemplified by the following words from authors David Lindenmayer of Australian National University and Mark Burgman from The University of Melbourne [1]:

“It was once possible to walk from Melbourne to Sydney through almost continuous woodland cover, but now much of it is gone and the remaining patches are small and highly disturbed.”

In the global context, a paper in the journal Science from June 2018 by Joseph Poore and Thomas Nemecek indicated that a general transition to an animal-free diet would reduce food production’s land use by 3.1 billion hectares (31 million square kilometres). [2] That is an area similar to (but slightly larger than): (a) Africa; (b) four times the contiguous United States; and (c) four times Australia, as represented in Figure 1.

The figure of 3.1 billion hectares represents 76 per cent of current farm land.

Dr Pep Canadell of Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) has indicated (as reflected in Figure 1) that around one-third of the area (roughly three times the size of India) would need to be reforested. [3] [Footnotes 2 and 3]

Figure 1: Reduction in farm land through transition away from animal-based foods

The findings of Poore and Nemecek reflect the gross and inherent inefficiency of animals as a food source. The inefficiency was highlighted by the authors’ indication that production of meat and dairy products occupies 83 per cent of farm land globally while providing only 37 per cent of protein and 18 per cent of calories. The comparison is depicted in Figure 2.

Figure 2: Land Use vs Nutritional Value of Animal Agriculture

In Australia, using production data from the Department of Agriculture, Fisheries and Forestry and nutritional information for each product from the United States Department of Agriculture (USDA), this author has previously estimated that animal-based foods provide only 19 per cent of protein and 9 per cent of calories, as depicted in Figure 3. [4] [5]

The chart includes products that are exported and/or used as livestock feed.  The inclusion of the latter means there is some double counting of the various nutrients.  However, given animal agriculture’s relatively low output level, the double counting is not significant in most cases.

Figure 3: Nutritional Value of Australian Food Production 2011/12

Poore and Nemecek have stated:

“Today, and probably into the future, dietary change can deliver environmental benefits on a scale not achievable by producers. Moving from current diets to a diet that excludes animal products has transformative potential . . .”

Their findings are consistent with those of other researchers. Here are some examples:

Dr James Hansen, former Director of the Goddard Institute for Space Studies, NASA and co-authors

In a landmark 2008 paper, leading climate scientist Dr James Hansen and co-authors argued that, in addition to dealing with coal-fired power, we would not achieve a critical threshold level of 350 ppm (parts per million) of CO2 in the atmosphere without massive reforestation. [6] The aim would be to reduce CO2 concentrations (at that time around 400 ppm) by drawing them from the atmosphere, while also reducing ongoing emissions.

Hansen had been prompted to establish a target by climate change campaigner and author, Bill McKibben, who adopted the target as the name of the organisation he co-founded,

Hansen et al. stated (with my underline):

“A reward system for improved agricultural and forestry practices that sequester carbon could remove the current CO2 overshoot. With simultaneous policies to reduce non-CO2 greenhouse gases, it appears still feasible to avert catastrophic climate change.”

The authors estimated a maximum sequestration potential of 1.6 gigatonnes of carbon per year through reforestation. With a conversion factor of 3.67, the estimate equates to around 5.9 gigatonnes of CO2 per year.

In a 2013 paper, Hansen and co-authors argued that it was feasible to draw down 100 gigatonnes of carbon through reforestation between 2031 and 2080. [7]

They noted: (a) because of extensive deforestation in earlier decades, there is a large amount of land suitable for reforestation; and (b) although reforestation competes with agricultural land use, land needs could decline by reducing use of animal products, as livestock now consume more than half of all crops.

Johan Rockström, Stockholm University and co-authors

The potential for carbon drawdown indicated by Hansen, et al. equals or exceeds the annual drawdown target of 5 gigatonnes of CO2 established in a “carbon law” articulated by group of leading climate scientists in early 2017, which they indicated would provide a 50 per cent chance of limiting global warming to 1.5°C by 2100 and a 66 per cent chance of limiting it to 2°C. [8]

The authors (Johan Rockström, Owen Gaffney, Joeri Rogelj, Malte Meinshausen, Nebojsa Nakicenovic and Hans Joachim Schellnhuber) stated:

“Agro-industries, farms, and civil society should develop a worldwide strategy for sustainable food systems to drive healthier, low-meat diets and reduce food waste.”

PBL Netherlands Environmental Assessment Agency

The PBL Netherlands Environmental Assessment Agency has stated: [9]

“. . . a global food transition to less meat, or even a complete switch to plant-based protein food [was found] to have a dramatic effect on land use. Up to 2,700 Mha of pasture and 100 Mha of cropland could be abandoned, resulting in a large carbon uptake from regrowing vegetation. Additionally, methane and nitrous oxide emissions would be reduced substantially.”

They said that a plant-based diet would reduce climate change mitigation costs by 80 per cent. A meat-free diet would reduce them by 70 per cent. Their assessment was based on a target of 450 ppm. The issue is even more critical when aiming for 350 ppm.

The University of Minnesota

The position is further highlighted by the fact that a 2013 paper from the Institute on the Environment at the University of Minnesota stated: [10]

“The world’s croplands could feed 4 billion more people than they do now just by shifting from producing animal feed and biofuels to producing exclusively food for human consumption.”

Animal feed crops represent 90% of the estimated figure (in turn representing 3.6 billion people), and biofuels only 10%.

The paper’s lead author, Emily Cassidy, has said:

“We essentially have uncovered an astoundingly abundant supply of food for a hungry world, hidden in plain sight in the farmlands we already cultivate. Depending on the extent to which farmers and consumers are willing to change current practices, existing croplands could feed millions or even billions more people.”

Institute for Social Ecology, Vienna

A paper from researchers at the Institute for Social Ecology, Vienna, published in April 2016, reported on the potential to avoid further deforestation while feeding a growing global population. [11] They considered 500 food supply scenarios using forecasts for crop yields, agricultural area, livestock feed and human diet supplied by the FAO. The lead author, Karl-Heinz Erb, has stated: [12]

“The only diet found to work with all future possible scenarios of yield and cropland area, including 100% organic agriculture, was a plant-based one.”

Marco Springmann, University of Oxford and co-authors

In a paper published in October 2018, Marco Springmann and co-authors reported that the food system is a major driver of climate change, changes in land use, depletion of freshwater resources and pollution of aquatic and terrestrial ecosystems. [13]

The report suggested that globally, consumption of beef must reduce by 75 per cent, pig meat by 90 per cent and eggs by 50 per cent. In wealthy nations such as the USA and UK, beef consumption must reduce by 90 per cent and cows’ milk by 60 per cent. [14]

The lead author, Marco Springmann, has said [15]:

“We can eat a range of healthy diets but what they all have in common, according to the latest scientific evidence, is that they are all relatively plant based”

Climate and Land Use Alliance

In relation to forests generally, prominent climate scientists issued a statement in October 2018 prior to the Intergovernmental Panel on Climate Change (IPCC) issuing a major report on the impacts of 1.5°C of warming. [16] They said:

“In advance of the IPCC report, we highlight five often overlooked reasons why limiting global warming requires protecting and sustainably managing the forests we have, and restoring the forests we’ve lost.”

“Our planet’s future climate is inextricably tied to the future of its forests.”


Objective evidence overwhelmingly indicates that we must move away from animal-based food consumption if we are to have any chance of saving and regenerating our forests and retaining a habitable planet.

Any measures to improve the environmental performance of the livestock sector are likely to represent little more than tweaking around the edges, as the adverse impacts are on a different paradigm to those of the non-animal alternatives.


Paul Mahony


  1. The author has used some of the information contained in this article elsewhere. It is included here for completeness.
  2. Afforestation (the planting of new forests on land that has not historically contained forests) or the regeneration of prior vegetation (including forests) would seem to be complementary approaches where conditions are suitable. Outside cleared areas, original vegetation that had disappeared due to grazing pressures could also regenerate with the removal of livestock. Careful management may be required under all approaches in order to deal with exotic grasses and other issues that may have been introduced by graziers.
  3. Dr Canadell’s estimate of land area is based on a requirement to remove 10 gigatonnes of CO2 from the atmosphere each year. That figure exceeds the maximum sequestration potential estimated by Dr James Hansen and co-authors and the “carbon law” figure from Johan Rockström and co-authors, both of which are referred to within this article.


[1] Lindenmayer, D. and Burgman, M., “Practical Conservation Biology” (2005, CSIRO Publishing), p. 235, and

[2] Poore, J., and Nemecek, ,T., “Reducing food’s environmental impacts through producers and consumers”, Science, 01 Jun 2018, Vol. 360, Issue 6392, pp. 987-992
DOI: 10.1126/science.aaq0216,

[3] Nogrady, B., “Negative emissions tech: can more trees, carbon capture or biochar solve our CO2 problem?”, The Guardian, 5 May 2017,

[4] Dept of Agriculture, Fisheries and Forestry, “Australian Food Statistics 2011-12”,

[5] USDA National Nutrient Database for Standard Reference at via Nutrition Data at

[6] Hansen, J; Sato, M; Kharecha, P; Beerling, D; Berner, R; Masson-Delmotte, V; Pagani, M; Raymo, M; Royer, D.L.; and Zachos, J.C. “Target Atmospheric CO2: Where Should Humanity Aim?”, 2008, Open Atmos. Sci. J., 2, 217-231, doi:10.2174/1874282300802010217, including Figure 6(b),

[7] Hansen J, Kharecha P, Sato M, Masson-Delmotte V, Ackerman F, Beerling DJ, et al. (2013) Assessing “Dangerous Climate Change”: Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature. PLoS ONE 8(12): e81648.

[8] Rockström, J., O. Gaffney. J. Rogelj, M. Meinshausen, N. Nakicenovic, and H.J. Schellnhuber (2017) “A roadmap for rapid decarbonization”, Science 355: 1269-127,, cited in Dunlop, I. and Spratt, D., “Disaster Alley: Climate Change Conflict and Risk, June 2017,

[9] Stehfest, E, Bouwman, L, van Vuuren, DP, den Elzen, MGJ, Eickhout, B and Kabat, P, “Climate benefits of changing diet” Climatic Change, Volume 95, Numbers 1-2 (2009), 83-102, DOI: 10.1007/s10584-008-9534-6 (Also

[10] Emily S Cassidy et al., 2013 Environ. Res. Lett. 8 034015 doi:10.1088/1748-9326/8/3/034015, cited in University of Minnesota News Release, 1 Aug 2013, “Existing Cropland Could Feed 4 Billion More”,

[11] Erb, K-H, Lauk, C., Kastner, T., Mayer, A., Theurl, M.C., Haberl, H., “Exploring the biophysical option space for feeding the world without deforestation”, Nat. Commun. 7:11382 doi: 10.1038/ncomms11382 (2016), and

[12] Kehoe, L., “Can we feed the world and stop deforestation? Depends what’s for dinner”, The Conversation, 20 Apr 2016 (Updated 26 Apr 2016),

[13] Springmann, M., Clark, M., Mason-D’Croz, D., Wiebe, K., Bodirsky, B. L., Lassaletta, de Vries, W., Vermeulen, S.J., Herrero, M., Carlson, K., Jonell, M., Troell, M. DeClerck, F., Gordon, L.J., Zurayk, R., Scarborough, P., Rayner, M., Loken, B., Fanzo, J., Godray, H.C.J., Tilman, D., Rockström, J. & Willett, ,W., “Options for keeping the food system within environmental limits”, Nature, volume 562, pp. 519–525 (2018),

[14] Carrington, D., “Huge reduction in meat-eating ‘essential’ to avoid climate breakdown”, The Guardian, 11 October 2018,

[15] McGrath, M., “‘Flexitarian’ diets key to feeding people in a warming world”, BBC News, 11 October 2018,

[16] Climate and Land Use and Alliance, “Five Reasons the Earth’s Climate Depends on Forests”,


Clive, “Wyre”, Flickr, CC BY-NC-ND 2.0,

Monphoto, “Blue map of Africa”, Shutterstock

skvoor, “United States map light blue map with shadow”, Shutterstock

skvoor, “Australia map light blue map with shadow”, Shutterstock

2 thoughts on “Dietary change is essential for forests and climate

  1. Thank you for this post! I really enjoyed it and appreciate all the scientific research cited. I hope we can spread this message so more and more of the population knows what’s at stake and get inspired to change their daily habits and lifestyle


    1. Thank you Bailey, I appreciate your feedback. Momentum certainly seems to be building.


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