Abstract
Climate change mitigation policies tend to focus on the energy sector, while the livestock sector receives surprisingly little attention, despite the fact that it accounts for 18% of the greenhouse gas emissions and for 80% of total anthropogenic land use. From a dietary perspective, new insights in the adverse health effects of beef and pork have lead to a revision of meat consumption recommendations. Here, we explored the potential impact of dietary changes on achieving ambitious climate stabilization levels. By using an integrated assessment model, we found a global food transition to less meat, or even a complete switch to plant-based protein food 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 emission would be reduced substantially. A global transition to a low meat-diet as recommended for health reasons would reduce the mitigation costs to achieve a 450 ppm CO2-eq. stabilisation target by about 50% in 2050 compared to the reference case. Dietary changes could therefore not only create substantial benefits for human health and global land use, but can also play an important role in future climate change mitigation policies.
Generated Summary
This study, published in Climatic Change in 2009, investigates the potential of dietary changes to mitigate climate change. The research employs the Integrated Model to Assess the Global Environment (IMAGE) to simulate various dietary scenarios and assess their impact on greenhouse gas emissions, land use, and mitigation costs. The study focuses on four dietary variants: complete substitution of ruminant meat (NORM), complete substitution of all meat (NoM), complete substitution of all animal products (NoAP), and a healthy diet variant (HDiet) based on dietary recommendations. The study also explores the effects of these dietary changes in the context of ambitious climate stabilization targets, aiming to achieve a 450 ppm CO2-eq. stabilization level. The primary methodology involves comparing the effects of these dietary changes to a reference scenario without dietary changes. The study also incorporates sensitivity analyses to address uncertainties in the carbon cycle and agricultural systems, providing a comprehensive assessment of the implications of dietary transitions on climate change mitigation.
Key Findings & Statistics
- Greenhouse Gas Emissions: Livestock production accounts for approximately 18% of global greenhouse gas emissions.
- Land Use: The livestock sector is responsible for 80% of total anthropogenic land use. Ruminants require more than 25% of the global land surface, and about 70% of global agricultural land.
- Temperature Increase: Without climate policy, greenhouse gas concentrations may cause global mean temperature to rise by up to 7°C compared to pre-industrial levels by the end of the century.
- Emission Reduction Target: To limit temperature increase to less than 2°C, greenhouse gas concentrations need to be stabilized below 450 ppm CO2-eq.
- Dietary Variants: The study examines four dietary variants: NORM (complete substitution of ruminant meat), NoM (complete substitution of all meat), NoAP (complete substitution of all animal products), and HDiet (healthy diet).
- Land Use Changes: A global transition to a diet with less meat could lead to the abandonment of up to 2,700 Mha of pasture and 100 Mha of cropland.
- Mitigation Costs: A global transition to a low-meat diet, as recommended for health reasons, would reduce the mitigation costs to achieve a 450 ppm CO2-eq. stabilization target by about 50% in 2050 compared to the reference case.
- Global Population, GDP, and Emissions (Reference Scenario):
- 2000: Population 6,093 million inhabitants, GDP per capita US$ 5,584, Energy 7.6 GtC-eq per year, Industry 0.5 GtC-eq per year, Land use 3.0.
- 2030: Population 8,236 million inhabitants, GDP per capita US$ 10,282, Energy 12.9 GtC-eq per year, Industry 0.8 GtC-eq per year, Land use 3.3.
- 2050: Population 9,122 million inhabitants, GDP per capita US$ 16,012, Energy 15.1 GtC-eq per year, Industry 1.0 GtC-eq per year, Land use 3.3.
- Land-Use Emissions (2000 and 2050, GtC eq.):
- 2000: Reference 3.0,
- 2050: Reference 3.3, NORM 1.7, NoM 1.5, NoAP 1.1, HDiet 2.1.
- Consumption of Animal Products (OECD, 2000):
- Beef, sheep and goat meat: 24 kg/capita/year.
- Milk: 126 kg/capita/year.
- Pork: 31 kg/capita/year.
- Poultry and eggs: 38 kg/capita/year.
- Consumption of Animal Products (OECD, 2050):
- Beef, sheep and goat meat: 30 kg/capita/year.
- Milk: 141 kg/capita/year.
- Pork: 37 kg/capita/year.
- Poultry and eggs: 47 kg/capita/year.
- Consumption of Animal Products (BRIC, 2000):
- Beef, sheep and goat meat: 8 kg/capita/year.
- Milk: 48 kg/capita/year.
- Pork: 16 kg/capita/year.
- Poultry and eggs: 16 kg/capita/year.
- Consumption of Animal Products (BRIC, 2050):
- Beef, sheep and goat meat: 15 kg/capita/year.
- Milk: 90 kg/capita/year.
- Pork: 25 kg/capita/year.
- Poultry and eggs: 27 kg/capita/year.
- Consumption of Animal Products (Other, 2000):
- Beef, sheep and goat meat: 9 kg/capita/year.
- Milk: 43 kg/capita/year.
- Pork: 4 kg/capita/year.
- Poultry and eggs: 13 kg/capita/year.
- Consumption of Animal Products (Other, 2050):
- Beef, sheep and goat meat: 16 kg/capita/year.
- Milk: 54 kg/capita/year.
- Pork: 6 kg/capita/year.
- Poultry and eggs: 21 kg/capita/year.
- Crop Yield Increase (2000-2050): 40-71%.
- Grass Yield Increase (2000-2050): 31-54%.
- Reduced Emissions (2050, compared to reference):
- NoRM: 1.7 GtC eq.
- NoM: 1.5 GtC eq.
- NoAP: 1.1 GtC eq.
- HDiet: 2.1 GtC eq.
- Abatement Costs (as fraction of GDP, 2005-2050, default discounting): Reference 1.04%, NORM 0.31%, NoM 0.27%, NoAP 0.20%, HDiet 0.48%.
- Abatement Cost Range Relative to the Reference: 29-31% (NORM), 25-38% (NoM), 17-22% (NoAP), and 45-48% (HDiet).
- Reduction in Cumulative Emissions (NoAP): The cumulative emission reduction in the 2010-2050 period amounts to 17% for CO2, 24% for CH4 and 21% for N2O.
Other Important Findings
- The study utilizes the IMAGE 2.4 model, a framework for assessing global environmental change and exploring the long-term dynamics of demographic, economic, and agricultural developments.
- The research considers a reference scenario (business-as-usual) and four dietary change scenarios involving partial or complete substitution of meat with plant proteins.
- The study uses the FAIR (Climate Policy Model) to calculate global emission pathways that lead to a stabilization of the atmospheric greenhouse gas concentration.
- The energy system is modeled using TIMER to describe the long-term dynamics of the production and consumption of primary energy carriers.
- The agricultural model distinguishes seven crop groups and five animal categories and calculates crop and pasture productivity using the Agro-Ecological Zone (AEZ) approach.
- The study acknowledges the importance of non-CO2 emissions from agriculture and livestock, including methane and nitrous oxide.
- The carbon cycle is modeled in IMAGE, focusing on the exchange between terrestrial ecosystems and the atmosphere.
- The impact of dietary changes on the energy sector is accounted for, recognizing the decreased energy use due to the substitution of animal products.
- The HealthyDiet variant aligns with recommendations from the Harvard Medical School for reduced meat consumption.
- The dietary transitions, such as those in the NoRM and NoM scenarios, have substantial effects on global land use, particularly pasture area.
- The study examines the potential for bioenergy crops on abandoned agricultural land and grasslands.
- The study investigates the impact of dietary changes on mitigation costs, with significant reductions observed in the dietary variants.
- The sensitivity analysis explores the impact of CO2 fertilization, recovery of natural vegetation, and agricultural system feedbacks on the results.
- The study notes the importance of the choice of the discount rate on the results of climate policy scenarios and mitigation costs.
- The study acknowledges the uncertainty in the potential contribution and cost of abatement options.
Limitations Noted in the Document
- The study acknowledges the potential limitations in the assumptions made regarding meat consumption, particularly the income-driven increase in per capita meat consumption.
- The study’s global implementation of dietary changes may lead to higher meat intake than in the reference case in some areas of the world, potentially underestimating the impact.
- The study notes the absence of implementation or other costs associated with the transition to alternative diets.
- The study acknowledges uncertainties related to the carbon cycle, including CO2 fertilization and the recovery time of natural vegetation on abandoned land.
- The analysis of dietary changes is implemented globally without regional differentiation.
- The study acknowledges that the costs associated with the transition may be underestimated.
- The study does not account for potential socio-economic implications, such as the effects of health changes on GDP and population numbers.
Conclusion
The study’s findings emphasize that shifts in dietary patterns can play a pivotal role in decreasing greenhouse gas emissions alongside conventional mitigation strategies. The research highlights that the transition to diets with reduced meat consumption can lead to considerable reductions in agricultural land use, with significant consequences for climate change mitigation and costs. A key finding is the substantial potential for reducing greenhouse gas emissions and mitigation costs through dietary changes, especially in the NoRM, NoM, and NoAP scenarios. The study underscores the importance of the carbon cycle, particularly the carbon uptake by regrowing vegetation on abandoned agricultural land, and how this impacts mitigation efforts. The study also illustrates how dietary changes can substantially reduce mitigation costs compared to the reference scenario, and the HealthyDiet variant shows significant effects. The research acknowledges uncertainties related to the carbon cycle, the recovery period of natural vegetation, and the potential feedbacks on the agricultural system. The study suggests that a transition to a low-meat diet could lead to land availability for other purposes like energy crops or nature reserves. The study also suggests that changes in dietary patterns could lead to land availability for other purposes such as energy crops or nature reserves, and the regrowth of vegetation on these abandoned areas leads to a substantial, though transient, uptake of CO2. The study’s conclusion underscores the potential of dietary changes as an effective mitigation strategy, suggesting that the integration of such changes into policy could offer substantial benefits for both climate and health. It is important to note that the benefits of dietary change extend beyond climate mitigation, impacting human health and land use. The study concludes with a call to action to consider dietary changes as an essential component of future climate change mitigation strategies.