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Rapid global phaseout of animal agriculture has the potential to stabilize greenhouse gas levels for 30 years and offset 68 percent of CO2 emissions this century

['Michael B. Eisen', 'Department Of Molecular', 'Cell Biology', 'Department Of Integrative Biology', 'Howard Hughes Medical Institute', 'University Of California', 'Berkeley', 'Ca', 'United States Of America', 'Patrick O. Brown']

Date: 2022-02 

Animal agriculture contributes significantly to global warming through ongoing emissions of the potent greenhouse gases methane and nitrous oxide, and displacement of biomass carbon on the land used to support livestock. However, because estimates of the magnitude of the effect of ending animal agriculture often focus on only one factor, the full potential benefit of a more radical change remains underappreciated. Here we quantify the full “climate opportunity cost” of current global livestock production, by modeling the combined, long-term effects of emission reductions and biomass recovery that would be unlocked by a phaseout of animal agriculture. We show that, even in the absence of any other emission reductions, persistent drops in atmospheric methane and nitrous oxide levels, and slower carbon dioxide accumulation, following a phaseout of livestock production would, through the end of the century, have the same cumulative effect on the warming potential of the atmosphere as a 25 gigaton per year reduction in anthropogenic CO 2 emissions, providing half of the net emission reductions necessary to limit warming to 2°C. The magnitude and rapidity of these potential effects should place the reduction or elimination of animal agriculture at the forefront of strategies for averting disastrous climate change.

Competing interests: We have read the journal’s policy and the authors of this manuscript have the following competing interests: Patrick Brown is the founder and CEO of Impossible Foods, a company developing alternatives to animals in food-production. Michael Eisen is an advisor to Impossible Foods. Both are shareholders in the company and thus stand to benefit financially from reduction of animal agriculture. Michael Eisen and Patrick Brown are co-founders and former members of the Board of Directors of the Public Library of Science.

Funding: There was no formal funding of this work. Michael Eisen is an Investigator with the Howard Hughes Medical Institute which funds all work in his lab. Patrick Brown is CEO of Impossible Foods, Inc.

Copyright: © 2022 Eisen, Brown. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Citation: Eisen MB, Brown PO (2022) Rapid global phaseout of animal agriculture has the potential to stabilize greenhouse gas levels for 30 years and offset 68 percent of CO 2 emissions this century. PLOS Clim 1(2): e0000010. https://doi.org/10.1371/journal.pclm.0000010

We calculated the combined impact of reduced emissions and biomass recovery by comparing the cumulative reduction, relative to current emission levels, of the global warming potential of GHGs in the atmosphere for the remainder of the 21st century under different livestock replacement scenarios to those that would be achieved by constant annual reductions in CO 2 emissions.

We used publicly available, systematic data on livestock production in 2019 [ 27 ], livestock-linked emissions [ 3 , 27 ], and biomass recovery potential on land currently used to support livestock [ 1 ] to predict how the phaseout of all or parts of global animal agriculture production would alter net anthropogenic emissions. We then used a simple climate model to project how these changes would impact the evolution of atmospheric GHG levels and warming for the rest of the century.

Our goal here was to accurately quantify the full impact of current animal agriculture on the climate, taking into account the currently unrealized opportunities for emission reduction and biomass recovery together, and explicitly considering the impact of their kinetics on warming. Our approach differs from other recent studies [ 25 , 26 ] in that we did not attempt to predict how global food production and consumption might change with growing populations, economic development, advances in agriculture, climate change and other socioeconomic factors. Nor do we tackle the social, economic, nutrition and agricultural challenges inherent to such a large change in global production.

However, a substantial fraction of the emissions impact of animal agriculture comes from methane (CH 4 ) and nitrous oxide (N 2 O), which decay far more rapidly than CO 2 (the half-lives of CH 4 and N 2 O are around 9 and 115 years, respectively), and recent studies have highlighted the need to consider these atmospheric dynamics when assessing their impact [ 22 – 24 ]. Of critical importance, many of the beneficial effects on greenhouse gas levels of eliminating livestock would accrue rapidly, via biomass recovery and decay of short-lived atmospheric CH 4 , and their cooling influence would be felt for an extended period of time.

The Food and Agriculture Organization (FAO) of the United Nations estimates that emissions from animal agriculture represent around 7.1 Gt CO 2 eq per year [ 5 ], 14.5% of annual anthropogenic greenhouse gas emissions, although this is based on outdated data and likely now represents and underestimate [ 20 ], and recent estimates [ 1 ] suggest that on the order of 800 Gt CO 2 equivalent carbon could be fixed via photosynthesis if native biomass were allowed to recover on the 30% of Earth’s land surface current devoted to livestock production. Thus, crudely, eliminating animal agriculture has the potential to reduce net emissions by the equivalent of around 1,350 Gt CO 2 this century. To put this number in perspective, total anthropogenic CO 2 emissions since industrialization are estimated to be around 1,650 Gt [ 2 ].

Nutritionally balanced plant-dominated diets are common, healthy and diverse [ 13 – 17 ], but are rarely considered in comprehensive strategies to mitigate climate change [ 18 ], and there is controversy about their viability and the magnitude of their climate benefit [ 19 ]. One source of this discordance is that widely cited estimates of livestock contributions to global warming [ 4 , 5 , 20 ] account only for ongoing emissions, and not for the substantial and reversible warming impact of historical land use change [ 1 , 21 ].

Solving the climate crisis requires massive cuts to GHG emissions from transportation and energy production. But even in the context of large-scale reduction in emissions from other sources, major cuts in food-linked emissions are likely necessary by 2075 to limit global warming to 1.5°C [ 6 ]. While a reduction of food-linked emissions can likely be achieved by increasing agricultural efficiency, reducing food waste, limiting excess consumption, increasing yields, and reducing the emission intensity of livestock production [ 7 – 12 ], they are not anticipated to have the same impact as a global transition to a plant-rich diet [ 5 , 6 ].

The use of animals as a food-production technology has well-recognized negative impacts on our climate. The historical reduction in terrestrial biomass as native ecosystems were transformed to support grazing livestock and the cultivation of feed and forage crops accounts for as much as a third of all anthropogenic CO 2 emissions to date [ 1 , 2 ]. Livestock, especially large ruminants, and their supply chains, also contribute significantly to anthropogenic emissions of the potent greenhouse gases (GHGs) methane and nitrous oxide [ 3 – 5 ].

Results

Rapid phaseout of animal agriculture would freeze increases in the warming potential of the atmosphere for 30 years The impact of PHASE-POD on CO 2 emissions would be greatest in the period between 2030 and 2060, when biomass recovery on land previously occupied by livestock or feed crops reaches its peak, slowing the rise of atmospheric CO 2 levels during this interval. Atmospheric CH 4 and N 2 O levels continue to increase in both BAU and PHASE-POD during the transition period, but begin to drop in PHASE-POD as the abatement of animal agriculture-linked emissions accelerates. CH 4 , with a half-life in the atmosphere of around 9 years, approaches a new and lower steady-state level towards the end of the century, while N 2 O, with a half-life of around 115 years, does so over a longer time-scale. To capture the combined global warming impact of the changing levels of these GHGs, we calculated radiative forcing (RF), the reduction in radiative cooling by GHG absorption of infrared radiation, using the formulae described in [30, 31] and used in MAGICC6 [29]. Fig 3 shows that with PHASE-POD there would effectively be no net increase in RF between 2030 and 2060. And even after that 30-year pause in the previously monotonically increasing global warming potential of the atmosphere, the difference in RF between the POD and BAU scenarios would continue to increase, due to the absence of direct emissions from animal agriculture and the continuing decay of previously emitted CH 4 and N 2 O towards lower steady-state values. PPT PowerPoint slide

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TIFF original image Download: Fig 3. Phaseout of animal agriculture reduces global warming impact of the atmosphere. Effect of eliminating emissions linked to animal agriculture and of biomass recovery on land currently used in animal agriculture on Radiative Forcing (RF), a measure of the instantaneous warming potential of the atmosphere. RF values computed from atmospheric concentrations in by formula of [30, 32] as modified in MAGICC6 [29] with adjustment for gases other than CO 2 , CH 4 and N 2 O as described in text. https://doi.org/10.1371/journal.pclm.0000010.g003

Rapid phaseout of animal agriculture could achieve half of the emission reductions needed to meet Paris Agreement GHG targets By the end of the century the RF under PHASE-POD would be 3.8 Wm-2 compared to 4.9 Wm-2 for BAU, a reduction in RF equivalent to what would be achieved by eliminating 1,680 Gt of CO 2 emissions (S33 Fig), or 46 years of global anthropogenic CO 2 emissions at the current rate of 36 Gt/year. In 2010, the climate modeling community defined a series of four “Representative Concentration Pathways” that capture a wide range of future warming scenarios, leading to 2100 RF levels of 8.5, 6.0, 4.5 and 2.6 Wm-2 (which is approximately the RF of current atmospheric greenhouse gas levels), respectively [33, 34]. These model pathways were extended after the Paris Agreement to include a target of 1.9 Wm-2. Although the exact relationship between RF and global warming is incompletely understood, 2100 RF values of 1.9 and 2.6 Wm-2 are generally used as targets for limiting warming in this century to 1.5˚C and 2.0˚C, respectively, over the baseline pre-industrial global average temperature [18]. Reducing 2100 RF from 4.9 Wm-2 under BAU to 2.6 Wm-2 would require a reduction of atmospheric CO 2 levels by 204 ppm, equivalent to 3,230 Gt of CO 2 emissions (Fig 4 and S33 Fig), and an additional 47 ppm reduction, equivalent to 750 Gt of CO 2 emissions, would be required to reach 1.9 Wm-2. PPT PowerPoint slide

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TIFF original image Download: Fig 4. Impact of dietary transitions in curtailing global warming. Using projected CH 4 and N 2 O levels in 2100 under business as usual diet as a baseline for RF calculation, we computed the CO 2 reductions necessary to reduce RF from the business as usual diet level of RF = 1.31 to the bovid-free diet level of RF = 4.09 (1300 Gt CO 2 ), the plant-only diet level of RF = 3.83 (1680 Gt CO 2 ), the 2.0° C global warming target of RF = 2.6 (3230 Gt CO 2 ) and the 1.5° C global warming target of RF = 1.9 (3980 Gt CO 2 ). For this analysis we used a corrected RF that accounts for the absence of other gases in our calculation by training a linear regression model on published MAGICC6 output to estimate from CO 2 , CH 4 and N 2 O levels the residual RF impact of other gases. https://doi.org/10.1371/journal.pclm.0000010.g004 Thus the 1,680 Gt of CO 2 equivalent emissions reductions from the phased elimination of animal agriculture, would, without any other intervention to reduce GHG emissions, achieve 52% of the net GHG emissions reductions necessary to reach the 2100 RF target of 2.6 Wm-2 and 42% of the emissions reductions necessary to reach the 1.9 Wm-2 target [18].

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