Quantifying the role of livestock in climate change

Authors: Wolf, Julie

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 8/23/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: Livestock products have both positive and negative impacts on human health, livelihood, and food security. However, the livestock sector also contributes to climate change in multiple and complex ways, which are amplified by how large the sector has grown in recent decades. The most notable impact is emissions of the greenhouse gas methane. Additional impacts include other greenhouse gas emissions; extent of land use and biomass consumption (30% of ice-free global land area is grazed, and ca. 1/3 of crop production is used to feed livestock), ongoing deforestation to create more pasture, pollution by excess nutrients or growth hormones, development and spread of antibiotic-resistant bacteria, and loss of wild biodiversity and habitat. It is difficult to quantify methane emissions from livestock, due to the variability of animals over time and of animal management. Results from multiple methods, including top-down atmospheric measurements of total methane, direct measurements from animal and manure sources, and bottom-up estimates based on animal inventories, must be compared and evaluated. It is also difficult to assess multiple benefits and impacts at once. Newer methods to compare multiple impacts of livestock -- such as emissions intensity (greenhouse gas emissions per unit of product), carbon footprint (CF), and life cycle analysis (LCA) --can summarize multiple impacts across different production systems, regions, and animal species and products. There are still additional considerations, such as decreasing capacity for carbon fixation and storage and vulnerability of livestock production to unexpected disruptions. However, multiple CF and LCA studies conducted to date uniformly show that: i) cattle have the largest impacts via greenhouse gases, land use extent, and land use change, with some regional and production system variation; ii) other livestock products (poultry and swine meat, eggs and dairy) have smaller impacts, iii) plant-based foods have minimal impacts relative to livestock products, and iv) among every crop and livestock food product studied, intensive high-yielding production systems have much lower greenhouse gas emissions and land use impacts per unit production than systems relying on extensive grazing and/or organic production. This is the opposite of how food production systems are commonly perceived in terms of conservationism/environmentalism. Frequent reassessment of the climate change and broader environmental impacts of livestock sector is still needed, because of the ongoing rapid changes in the global extent and practices of livestock agriculture.

Technical Abstract: The livestock sector has grown to massive size, with rapid changes in animal traits and management. Despite gains in productivity, often accompanied by reduced emissions intensity and land use extent, the livestock sector i) is the largest anthropogenic emitter of methane, ii) has significantly reduced global carbon storage and photosynthetic capacities, iii) releases nitrogen and phosphorus to air, water, and/or soil, and iv) has additional impacts, e.g. antibiotic resistance and biodiversity loss. Current assessments underestimate the sector’s contribution to climate warming, by using global warming potentials and neglecting carbon cycle impacts. Nevertheless, methods are evolving to better assess multiple impacts of livestock per unit of food production. These methods uniformly indicate that plant-based foods have miniscule impacts relative to those of livestock foods, and that among livestock products, the impacts of eggs and dairy products < pork and poultry meat < beef and lamb meat.