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The carbon opportunity cost of animal-sourced food production on land

DOI:10.1038/s41893-020-00603-4
Authors:
Matthew N Hayek at New York University
Matthew N Hayek
Helen Harwatt at Harvard University
Helen Harwatt
William J. Ripple at Oregon State University
William J. Ripple
Nathaniel D. Mueller
Nathaniel D. Mueller
Nathaniel D. Mueller
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Abstract and Figures

Extensive land uses to meet dietary preferences incur a ‘carbon opportunity cost’ given the potential for carbon sequestration through ecosystem restoration. Here we map the magnitude of this opportunity, finding that shifts in global food production to plant-based diets by 2050 could lead to sequestration of 332–547 GtCO2, equivalent to 99–163% of the CO2 emissions budget consistent with a 66% chance of limiting warming to 1.5 °C. Shifting global food production to plant-based diets by 2050 can sequester 99–163% of the CO2 emissions budget towards limiting climate warming to 1.5 °C.
Distribution of carbon in potential vegetation in areas of present-day animal feed croplands and pastures combined for each 5 arcmin grid cell Colour corresponds to the product of land area presently under cultivation multiplied by the potential vegetation carbon density, minus the quantity presently stored in agricultural vegetation.
Distribution of carbon in potential vegetation in areas of present-day animal feed croplands and pastures combined for each 5 arcmin grid cell Colour corresponds to the product of land area presently under cultivation multiplied by the potential vegetation carbon density, minus the quantity presently stored in agricultural vegetation.
… 
Carbon opportunity cost of animal agriculture and atmospheric CO2 emissions grouped by national income tiers CO2 emissions include fossil fuel and cement (grey bars). Carbon opportunity costs are disaggregated by present-day agricultural land type and potential vegetation biomes: croplands in native grassland areas (dark brown), croplands in native forest areas (light brown), pastures in native grassland areas (light green) and pastures in native forest areas (dark green). Error bars are combined 95% confidence intervals for the total carbon opportunity cost across all production categories and biomes in each income category.
Carbon opportunity cost of animal agriculture and atmospheric CO2 emissions grouped by national income tiers CO2 emissions include fossil fuel and cement (grey bars). Carbon opportunity costs are disaggregated by present-day agricultural land type and potential vegetation biomes: croplands in native grassland areas (dark brown), croplands in native forest areas (light brown), pastures in native grassland areas (light green) and pastures in native forest areas (dark green). Error bars are combined 95% confidence intervals for the total carbon opportunity cost across all production categories and biomes in each income category.
… 
Cumulative changes in terrestrial carbon from three dietary scenarios in 2050: BAU, ELC and VGN Scenarios do not include abated emissions associated with agricultural production (for example, ref. ⁷). Positive CO2 indicates a loss of ecosystem vegetation carbon and emissions to the atmosphere; negative indicates CO2 removal via vegetation growth. Error bars are 95% confidence intervals, reflecting various estimates of potential vegetation and distributions of cropland removal from low- and high-carbon biomes.
Cumulative changes in terrestrial carbon from three dietary scenarios in 2050: BAU, ELC and VGN Scenarios do not include abated emissions associated with agricultural production (for example, ref. ⁷). Positive CO2 indicates a loss of ecosystem vegetation carbon and emissions to the atmosphere; negative indicates CO2 removal via vegetation growth. Error bars are 95% confidence intervals, reflecting various estimates of potential vegetation and distributions of cropland removal from low- and high-carbon biomes.
… 
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Brief CommuniCation
https://doi.org/10.1038/s41893-020-00603-4
1Department of Environmental Studies, New York University, New York, NY, USA. 2Animal Law and Policy Program, Harvard Law School, Cambridge, MA,
USA. 3Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR, USA. 4Department of Ecosystem Science and Sustainability,
Colorado State University, Fort Collins, CO, USA. 5Department of Soil and Crop Sciences, Colorado State University, Fort Collins, CO, USA.
✉e-mail: matthew.hayek@nyu.edu
Extensive land uses to meet dietary preferences incur a ‘car-
bon opportunity cost’ given the potential for carbon seques-
tration through ecosystem restoration. Here we map the
magnitude of this opportunity, finding that shifts in global
food production to plant-based diets by 2050 could lead to
sequestration of 332–547 GtCO2, equivalent to 99–163% of
the CO2 emissions budget consistent with a 66% chance of
limiting warming to 1.5 °C.
Restoration of native ecosystems, including forests, is a land-based
option for atmospheric carbon dioxide (CO2) removal1. Ecosystem
restoration is constrained largely by land requirements of food pro-
duction, the largest human use of land globally2. Food production
therefore incurs a ‘carbon opportunity cost’, that is, the potential for
natural CO2 removal via ecosystem restoration on land3,4. This cost
can vary greatly depending on the ‘potential’ or ‘native’ vegetation of
a given region and types of food produced. Animal-sourced foods
such as meat and dairy have large land footprints because animals
typically consume more food macronutrients than they produce5.
Quantifying the spatial distribution of agriculture’s cumulative car-
bon opportunity cost within this century can inform efforts to limit
global warming to 1.5 °C.
Ongoing agricultural emissions can be abated by shifts to
less-resource-intensive, plant-based diets6,7, but the potential for
cumulative CO2 removal from native vegetation regrowth in areas
occupied by animal agriculture has not previously been calculated
in a spatially explicit manner. Here we quantify the total carbon
opportunity cost of animal agricultural production to be 152.5
(94.2–207.1) gigatons of carbon (GtC) in living plant biomass across
all continents and biomes (Fig. 1 and Supplementary Table 3).
We approximated the potential for CO2 removal in soil and litter
as an additional 63 GtC (Supplementary Table 4). This estimate is
associated with large but unknown uncertainty because of a deficit
of data and the complexity of dynamics of non-living carbon pools
in restored ecosystems.
Pastures for ruminant meat and dairy production represent the
majority of the total carbon opportunity cost—72%—compared
with animal feed croplands, which suppress the remaining 28% of
native vegetation carbon (Supplementary Table 3). Potential pro-
ductivity on remaining cropland is sufficient to supply the current
global population with 78 g capita−1 day−1 of protein (after factoring
losses from both storage and consumer waste), an amount exceed-
ing dietary recommendations, accounting for variation in nutri-
tional requirements among demographic groups and for disparities
in food availability8.
The cumulative potential of CO2 removal on land currently
occupied by animal agriculture is comparable in order of magnitude
to the past decade of global fossil fuel emissions. The largest poten-
tial for negative emissions—74 GtC or 48% of the global total—lies
in upper-middle-income countries (Fig. 2), which will further
increase as meat and dairy production expand. This is approxi-
mately equal to the past 19 years of fossil fuel emissions in these
countries. In high-income countries, in which animal-sourced food
demand is high but plateauing8, the total carbon opportunity cost of
animal-sourced food production is 32 GtC, approximately equal to
the past 9 years of their domestic fossil fuel emissions.
Present-day pasturelands exist in areas of both native forests and
grasslands within all continents (Supplementary Table 3). Pastures
in native forest areas displace 72 GtC—accounting for 68% of pas-
tures’ carbon opportunity cost but only 22% of total pasture area
(Supplementary Table 3 and Supplementary Fig. 2). In native grass-
lands, vegetation may be partially restored by improved grazing
management9, rather than removing animals altogether, although
trade-offs remain with respect to non-CO2 ruminant emissions.
In addition, optimal grazing does not always promote restoration
because ruminants selectively browse native species10 and translo-
cate nutrients11.
To understand the potential future consequences of animal-
sourced food consumption on global CO2 budgets, we modelled
land use of three global dietary scenarios to the year 2050 rela-
tive to the present day (base year 2015). The net CO2 balance was
calculated for a business-as-usual (BAU) diet following economic
trends12, a healthier diet with approximately 70% meat reduction
globally relative to BAU13 (the EAT-Lancet Commission or ELC
diet) and a vegan (VGN) diet with no animal-sourced foods8.
The BAU diet results in land clearing, with land-use-change
emissions of 86 (68–105) GtCO2 (Fig. 3) because optimistic future
improvements in yields are insufficient to meet expected animal
feed demands11.
The ELC and VGN diets result in 332 (210 to 459) and 547 (358
to 743) total GtCO2 removal, respectively, approximately equal to
the past 9 and 16 years of fossil fuel emissions. Ecosystem soil and
litter could remove an additional 135 and 225 GtCO2 for ELC and
VGN, respectively (Supplementary Table 6), but this estimate is
highly uncertain.
Smaller future increases in crop yields would result in less land
sparing and CO2 removal from ELC and VGN diets compared with
present day: 199 and 424 GtCO2, respectively (Supplementary Table
5). However, plant-rich diets would permit even greater mitigation
compared with BAU; lower yields result in greater land-clearing
emissions of 247 GtCO2.
Ceasing fossil fuel use is necessary to limit global warming, but
CO2 removal following plant-rich dietary shifts could substantially
The carbon opportunity cost of animal-sourced
food production on land
Matthew N. Hayek 1 ✉ , Helen Harwatt2, William J. Ripple3 and Nathaniel D. Mueller 4,5
NATURE SUSTAINABILITY | VOL 4 | JANUARY 2021 | 21–24 | www.nature.com/natsustain 21
Content courtesy of Springer Nature, terms of use apply. Rights reserved
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  • Oct 2018
Background Sustainable diets are intended to address the increasing health and environmental concerns related to food production and consumption. Although many candidates for sustainable diets have emerged, a consistent and joint environmental and health analysis of these diets has not been done at a regional level. Using an integrated health and environmental modelling framework for more than 150 countries, we examined three different approaches to sustainable diets motivated by environmental, food security, and public health objectives. Methods In this global modelling analysis, we combined analyses of nutrient levels, diet-related and weight-related chronic disease mortality, and environmental impacts for more than 150 countries in three sets of diet scenarios. The first set, based on environmental objectives, replaced 25–100% of animal-source foods with plant-based foods. The second set, based on food security objectives, reduced levels of underweight, overweight, and obesity by 25–100%. The third set, based on public health objectives, consisted of four energy-balanced dietary patterns: flexitarian, pescatarian, vegetarian, and vegan. In the nutrient analysis, we calculated nutrient intake and changes in adequacy based on international recommendations and a global dataset of nutrient content and supply. In the health analysis, we estimated changes in mortality using a comparative risk assessment with nine diet and weight-related risk factors. In the environmental analysis, we combined country-specific and food group-specific footprints for greenhouse gas emissions, cropland use, freshwater use, nitrogen application, and phosphorus application to analyse the relationship between the health and environmental impacts of dietary change. Findings Following environmental objectives by replacing animal-source foods with plant-based ones was particularly effective in high-income countries for improving nutrient levels, lowering premature mortality (reduction of up to 12% [95% CI 10–13] with complete replacement), and reducing some environmental impacts, in particular greenhouse gas emissions (reductions of up to 84%). However, it also increased freshwater use (increases of up to 16%) and had little effectiveness in countries with low or moderate consumption of animal-source foods. Following food-security objectives by reducing underweight and overweight led to similar reductions in premature mortality (reduction of up to 10% [95% CI 9–11]), and moderately improved nutrient levels. However, it led to only small reductions in environmental impacts at the global level (all impacts changed by <15%), with reduced impacts in high-income and middle-income countries, and increased resource use in low-income countries. Following public health objectives by adopting energy-balanced, low-meat dietary patterns that are in line with available evidence on healthy eating led to an adequate nutrient supply for most nutrients, and large reductions in premature mortality (reduction of 19% [95% CI 18–20] for the flexitarian diet to 22% [18–24] for the vegan diet). It also markedly reduced environmental impacts globally (reducing greenhouse gas emissions by 54–87%, nitrogen application by 23–25%, phosphorus application by 18–21%, cropland use by 8–11%, and freshwater use by 2–11%) and in most regions, except for some environmental domains (cropland use, freshwater use, and phosphorus application) in low-income countries. Interpretation Approaches for sustainable diets are context specific and can result in concurrent reductions in environmental and health impacts globally and in most regions, particularly in high-income and middle-income countries, but they can also increase resource use in low-income countries when diets diversify. A public health strategy focused on improving energy balance and dietary changes towards predominantly plant-based diets that are in line with evidence on healthy eating is a suitable approach for sustainable diets. Updating national dietary guidelines to reflect the latest evidence on healthy eating can by itself be important for improving health and reducing environmental impacts and can complement broader and more explicit criteria of sustainability. Funding Wellcome Trust, EAT, CGIAR, and British Heart Foundation.
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Reducing food's environmental impacts through producers and consumers
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The global impacts of food production Food is produced and processed by millions of farmers and intermediaries globally, with substantial associated environmental costs. Given the heterogeneity of producers, what is the best way to reduce food's environmental impacts? Poore and Nemecek consolidated data on the multiple environmental impacts of ∼38,000 farms producing 40 different agricultural goods around the world in a meta-analysis comparing various types of food production systems. The environmental cost of producing the same goods can be highly variable. However, this heterogeneity creates opportunities to target the small numbers of producers that have the most impact. Science , this issue p. 987
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Defining a land boundary for sustainable livestock consumption
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  • May 2018
The need for more sustainable production and consumption of animal‐source food is central to the achievement of the sustainable development goals: within this context, wise use of land is a core challenge and concern. A key question in feeding the future world is: how much animal‐source food should we eat? We demonstrate that livestock raised under the circular economy concept could provide a significant, non‐negligible part (9‐23g/per capita) of our daily protein needs (~50‐60 g/per capita). This livestock then would not consume human‐edible biomass, such as grains, but mainly convert leftovers from arable land and grass resources into valuable food, implying that production of livestock feed is largely decoupled from arable land. The availability of these biomass streams for livestock then determines the boundaries for livestock production and consumption. Under this concept, the competition for land for feed or food would be minimized and compared to no animal‐source food, including some animal‐source food in the human diet could free up about one quarter of global arable land. Our results also demonstrate that restricted growth in consumption of animal‐source food in Africa and Asia would be feasible under these boundary conditions, while reductions in the rest of the world would be necessary to meet land use sustainability criteria. Managing this expansion and contraction of future consumption of animal‐source food is essential for achieving sustainable nutrition security. This article is protected by copyright. All rights reserved.
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The opportunity cost of animal based diets exceeds all food losses
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  • Mar 2018
Significance With a third of all food production lost via leaky supply chains or spoilage, food loss is a key contributor to global food insecurity. Demand for resource-intensive animal-based food further limits food availability. In this paper, we show that plant-based replacements for each of the major animal categories in the United States (beef, pork, dairy, poultry, and eggs) can produce twofold to 20-fold more nutritionally similar food per unit cropland. Replacing all animal-based items with plant-based replacement diets can add enough food to feed 350 million additional people, more than the expected benefits of eliminating all supply chain food loss.
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Feed conversion efficiency in aquaculture: Do we measure it correctly?
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Globally, demand for food animal products is rising. At the same time, we face mounting, related pressures including limited natural resources, negative environmental externalities, climate disruption, and population growth. Governments and other stakeholders are seeking strategies to boost food production efficiency and food system resiliency, and aquaculture (farmed seafood) is commonly viewed as having a major role in improving global food security based on longstanding measures of animal production efficiency. The most widely used measurement is called the 'feed conversion ratio' (FCR), which is the weight of feed administered over the lifetime of an animal divided by weight gained. By this measure, fed aquaculture and chickens are similarly efficient at converting feed into animal biomass, and both are more efficient compared to pigs and cattle. FCR does not account for differences in feed content, edible portion of an animal, or nutritional quality of the final product. Given these limitations, we searched the literature for alternative efficiency measures and identified 'nutrient retention', which can be used to compare protein and calories in feed (inputs) and edible portions of animals (outputs). Protein and calorie retention have not been calculated for most aquaculture species. Focusing on commercial production, we collected data on feed composition, feed conversion ratios, edible portions (i.e. yield), and nutritional content of edible flesh for nine aquatic and three terrestrial farmed animal species. We estimate that 19% of protein and 10% of calories in feed for aquatic species are ultimately made available in the human food supply, with significant variation between species. Comparing all terrestrial and aquatic animals in the study, chickens are most efficient using these measures, followed by Atlantic salmon. Despite lower FCRs in aquaculture, protein and calorie retention for aquaculture production is comparable to livestock production. This is, in part, due to farmed fish and shrimp requiring higher levels of protein and calories in feed compared to chickens, pigs, and cattle. Strategies to address global food security should consider these alternative efficiency measures.
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Unexpectedly large impact of forest management and grazing on global vegetation biomass
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Carbon stocks in vegetation have a key role in the climate system. However, the magnitude, patterns and uncertainties of carbon stocks and the effect of land use on the stocks remain poorly quantified. Here we show, using state-of-the-art datasets, that vegetation currently stores around 450 petagrams of carbon. In the hypothetical absence of land use, potential vegetation would store around 916 petagrams of carbon, under current climate conditions. This difference highlights the massive effect of land use on biomass stocks. Deforestation and other land-cover changes are responsible for 53-58% of the difference between current and potential biomass stocks. Land management effects (the biomass stock changes induced by land use within the same land cover) contribute 42-47%, but have been underestimated in the literature. Therefore, avoiding deforestation is necessary but not sufficient for mitigation of climate change. Our results imply that trade-offs exist between conserving carbon stocks on managed land and raising the contribution of biomass to raw material and energy supply for the mitigation of climate change. Efforts to raise biomass stocks are currently verifiable only in temperate forests, where their potential is limited. By contrast, large uncertainties hinder verification in the tropical forest, where the largest potential is located, pointing to challenges for the upcoming stocktaking exercises under the Paris agreement.
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Natural climate solutions
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  • Oct 2017
Significance Most nations recently agreed to hold global average temperature rise to well below 2 °C. We examine how much climate mitigation nature can contribute to this goal with a comprehensive analysis of “natural climate solutions” (NCS): 20 conservation, restoration, and/or improved land management actions that increase carbon storage and/or avoid greenhouse gas emissions across global forests, wetlands, grasslands, and agricultural lands. We show that NCS can provide over one-third of the cost-effective climate mitigation needed between now and 2030 to stabilize warming to below 2 °C. Alongside aggressive fossil fuel emissions reductions, NCS offer a powerful set of options for nations to deliver on the Paris Climate Agreement while improving soil productivity, cleaning our air and water, and maintaining biodiversity.
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