Abstract
An analysis of the climate impact of various forms of beef production is carried out, with a particular eye to the comparison between systems relying primarily on grasses grown in pasture (‘grass-fed’ or ‘pastured’ beef) and systems involving substantial use of manufactured feed requiring significant external inputs in the form of synthetic fertilizer and mechanized agriculture (‘feedlot’ beef). The climate impact is evaluated without employing metrics such as CO2e or global warming potentials. The analysis evaluates the impact at all time scales out to 1000 years. It is concluded that certain forms of pastured beef production have substantially lower climate impact than feedlot systems. However, pastured systems that require significant synthetic fertilization, inputs from supplemental feed, or deforestation to create pasture, have substantially greater climate impact at all time scales than the feedlot and dairy-associated systems analyzed. Even the best pastured system analyzed has enough climate impact to justify efforts to limit future growth of beef production, which in any event would be necessary if climate and other ecological concerns were met by a transition to primarily pasture-based systems. Alternate mitigation options are discussed, but barring unforseen technological breakthroughs worldwide consumption at current North American per capita rates appears incompatible with a 2 °C warming target.
Generated Summary
This research article analyzes the climate impact of various beef production systems, particularly comparing grass-fed (pastured) beef and feedlot beef. The study evaluates the climate impact across different time scales, up to 1000 years, without employing metrics like CO2e or global warming potentials. The analysis focuses on emissions of CO2, CH4, and N2O, considering factors such as energy inputs, fertilizer use, deforestation, and pasture management. The research aims to assess the long-term effects of different beef production methods and consumption scenarios on climate change, offering insights into potential mitigation strategies. The study uses a climate model to calculate the warming caused by the emissions, providing a detailed comparison of the impacts of various production systems and consumption trajectories. The goal is to understand the environmental consequences of beef production and identify ways to reduce its climate impact, considering the implications of different dietary choices.
Key Findings & Statistics
- The source of 15%-25% of U.S. and global greenhouse gas (GHG) emissions as measured by 100-year global warming potentials [9, 10], and is a key contributor to biodiversity losses [11, 12].
- Beef production strategies vary widely.
- Dedicated beef cattle production, in which calves of both genders subsist nearly exclusively on grazing through weaning (for most around 8-10 months) vary primarily by calves’ post-weaning (i.e., ‘finishing’) life history.
- The key divergence is continued reliance on grazing on the one hand, versus the transition to a fully served diet in large-sale concentrated animal feeding operations (CAFO’s) typically handling many thousands of animals at any given time.
- Importantly, characteristic daily weight gains in CAFO’s are 2–3 times those achieved on grass.
- Table 1: Emissions of the three principal greenhouse gases by various beef production strategies. Emissions of CO2 are given as kg of carbon (C) per kg of bone free beef produced, whereas the emissions of CH4 and N2O are given as kg of gas per kg of bone free beef. The table also gives the kg of CO2-equivalent based on 100 year global warming potentials of 25 for CH4 and 298 for N2O.
- Feedlot midwest: CH4 = 1.4, N2O = 0.6, CO2 = 0.05, CO2e 100 = 35.
- Pastured midwest: CH4 = 1.8, N2O = 0.8, CO2 = 0.06, CO2e 100 = 45.
- Pastured Brazil: CH4 = 0.3, N2O = 1.2, CO2 = 0.03, CO2e 100 = 40.
- Ranch system Sweden: CH4 = 0.3, N2O = 0.8, CO2 = 0.02, CO2e 100 = 27.
- Sweden average beef: CH4 = 1.0, N2O = 0.7, CO2 = 0.02, CO2e 100 = 28.
- Production of beef at a rate of 1 kg of bone-free-beef per year incurs a net carbon release of 3.8-5.7 tonnes C.
- If the peak consumption is maintained indefinitely, the resulting warming at the end of 1000 years is .6 °C-1.6 °C, and in situations where the consumption rate after the peak is phased down to a more sustainable level the transient peak warming is .3 °C-.6 °C.
- For the midwest feedlot system, the equivalent cumulative carbon would be 504 Gt, which all by itself is enough to use up the remaining allocation of cumulative carbon corresponding to a probable warming below 2 °C.
Other Important Findings
- The study concludes that certain forms of pastured beef production have a lower climate impact than feedlot systems.
- Pastured systems that require significant synthetic fertilization, supplemental feed, or deforestation have a greater climate impact than feedlot and dairy-associated systems.
- Even the best pastured system analyzed has enough climate impact to justify efforts to limit the growth of beef production.
- The climate impact is evaluated without employing metrics such as CO2e or global warming potentials.
- The warming due to CH4 essentially stops growing after two decades and that warming due to N2O stops growing after two centuries, whereas the warming due to CO2 emissions continues to grow indefinitely.
- The two phase-out cases illustrate that the warming due to CH4 and N2O is reversible, whereas the warming due to CO2 is not (at least not on any time scale of relevance to human societies).
- The higher CO2 emissions in the midwest feedlot case lead to a persistent warming of .1 °C if beef consumption is phased out starting at 100 years, and .2 °C if the phase-out begins at 200 years.
- For the Brazil pastured case there is very little persistent warming.
- With a phase-out at 100 years the peak warming in the Brazil pastured case is worse than the peak warming in the midwest feedlot case, because CH4 exerts a dominant role on these time scales; in the midwest feedlot case the peak warming is due in equal measure to CH4 and N2O, whereas in the Brazil pastured case, most of the warming comes from CH4 If phase-out is delayed to 200 years, however, the effect of N2O and CO2 become more important, and the peak warming in the two cases becomes nearly equal.
- The Sweden ranch system has low emissions of CO2 and CH4.
- In the perpetual consumption cases that the differences between the methods become most pronounced.
- Production systems such as CAFO’s (exemplified by the midwest feedlot case) require high external inputs from fossil fuels for energy and fertilizer feed-stocks, and the resulting high CO2 emissions lead to a comparitively high degree of irreversible warming.
- The midwest pastured example shows that ‘grass-fed’ systems do not necessarily produce low CO2 emissions, but suitably designed pastured systems, as in the Sweden ranch or Brazil pastured systems can have very low CO2 emissions if no deforestation is involved in producing the pasture land.
- Dairy associated systems (e.g. Sweden average beef) can, however, have climate impact similar to or lower than the purely pastured Brazil system at all time scales, highlighting the potential benefits of hybrid systems.
- The highly optimized Sweden ranch system shows that careful management practices can significantly reduce the high CH4 emissions.
Limitations Noted in the Document
- The study focuses on the climate effects of various beef production systems, without addressing the nutritional aspects of beef in the human diet.
- The study’s analysis of the climate impact of beef production is mediated chiefly by production of the greenhouse gases CO2, CH4 and N2O.
- The study does not factor in carbon sequestration as a climate benefit of pastured beef production.
- The study recognizes the need to go beyond CO2e 100 and to consider impacts at multiple time scales, but the problem cannot adequately be addressed simply through choice of metric, since all metrics that aggregate effects of gases with disparate lifetimes have serious shortcomings of one sort or another.
- The peak consumption rates assumed in the BAU family are not necessarily realizable, as it is far from certain that so much beef could be produced annually by any means, and it is virtually certain that such production rates could not be attained by pastured methods.
- The projected rate of growth of bovine meat consumption out to 2050 is 1.2% per year [42], which would yield Cm/Co = 3.3 if extended out to 100 years.
- The equations for the BAU family are given in the supplementary data.
- In cases where the required pasture was produced by tropical deforestation) and the cumulative carbon in the form of direct CO2 emissions over 1000 years. The final column gives the net of all cumulative carbon and CCeq associated with beef production at a rate of 1 kg yr¯¹. Deforestation effects associated with extratropical pastured production have not been evaluated.
Conclusion
The analysis emphasizes the importance of examining greenhouse gas emissions individually rather than aggregating them into metrics like CO2e, which can distort the comparison of climate impacts. The study underscores the need for life-cycle assessments to report individual greenhouse gas emissions for a proper assessment of climate damage. The results indicate that beef production has significant climate impacts, with the choice of production method and consumption levels playing a crucial role. The study highlights that beef production contributes significantly to greenhouse gas emissions, especially if current consumption trends continue. The study highlights that the warming due to CH4 emissions essentially stops growing after two decades, whereas the warming due to CO2 emissions continues to grow indefinitely. The research suggests that while pastured systems can have lower climate impacts than feedlot systems, factors such as deforestation and fertilizer use can negate these benefits. The Swedish ranch system emerges as a promising model, with low CO2 emissions and effective management practices. The study’s findings point towards policies that could promote alternatives to beef and emphasize the need for sustainable production practices to mitigate climate change. The analysis concludes that substantial growth in worldwide beef consumption is incompatible with limiting warming to a 2°C target, suggesting the need for changes in dietary preferences and production methods. Ultimately, the study underscores that understanding beef production’s environmental impact requires a nuanced approach that considers the varying timescales and the individual contributions of each greenhouse gas.
IFFS Team Summary
- This paper follows that impact of cattle farming in feedlots vs pasture to 1000 year timeline
- It shows how CH4 and NO2 have potent effects, and reach steady states after many decades
- If meat consumption is reduced it still takes many decades to reabsorb the NO2 and CH4
- In the absence of deforestation, factory farms have greater long term CO2 emissions due to fossil fuel use
- Deforestation related emissions are not covered in this paper
- The next three references should be viewed together: