Elsevier

The Lancet

Volume 374, Issue 9706, 12–18 December 2009, Pages 2016-2025
The Lancet

Series
Public health benefits of strategies to reduce greenhouse-gas emissions: food and agriculture

https://doi.org/10.1016/S0140-6736(09)61753-0Get rights and content

Summary

Agricultural food production and agriculturally-related change in land use substantially contribute to greenhouse-gas emissions worldwide. Four-fifths of agricultural emissions arise from the livestock sector. Although livestock products are a source of some essential nutrients, they provide large amounts of saturated fat, which is a known risk factor for cardiovascular disease. We considered potential strategies for the agricultural sector to meet the target recommended by the UK Committee on Climate Change to reduce UK emissions from the concentrations recorded in 1990 by 80% by 2050, which would require a 50% reduction by 2030. With use of the UK as a case study, we identified that a combination of agricultural technological improvements and a 30% reduction in livestock production would be needed to meet this target; in the absence of good emissions data from Brazil, we assumed for illustrative purposes that the required reductions would be the same for our second case study in São Paulo city. We then used these data to model the potential benefits of reduced consumption of livestock products on the burden of ischaemic heart disease: disease burden would decrease by about 15% in the UK (equivalent to 2850 disability-adjusted life-years [DALYs] per million population in 1 year) and 16% in São Paulo city (equivalent to 2180 DALYs per million population in 1 year). Although likely to yield benefits to health, such a strategy will probably encounter cultural, political, and commercial resistance, and face technical challenges. Coordinated intersectoral action is needed across agricultural, nutritional, public health, and climate change communities worldwide to provide affordable, healthy, low-emission diets for all societies.

Introduction

The food system is a major contributor to global greenhouse-gas emissions. Greenhouse gases are produced at all stages in the system, from farming and its inputs through to food distribution, consumption, and the disposal of waste.1 The latest Intergovernmental Panel on Climate Change report estimated that agriculture alone accounts for about 10–12% of global greenhouse-gas emissions, and emissions from this sector are expected to rise by up to half again by 2030.2 Agriculturally-induced change in land use—such as deforestation, overgrazing, and conversion of pasture to arable land—presently accounts for a further 6–17% of global greenhouse-gas emissions.3

About half of all food-related greenhouse-gas emissions are generated during farming. Farm-stage emissions include nitrous oxide and methane from livestock, and carbon dioxide from agriculturally-induced change in land use, especially deforestation.4, 5 Nitrous oxide (from pasture land and arable land used to grow feed crops) and methane (from the digestive processes of ruminant animals such as cows and sheep) account for 80% of all agricultural greenhouse-gas emissions.4 The emissions per unit of livestock product vary by animal type and seem to be higher in beef, sheep, and dairy farming than in pig and poultry farming (figure 1).6 However, the ability of cattle and sheep to graze on land unsuited to other forms of farming, and the emissions associated with the production of feeds for pigs and poultry complicate the interpretation of this difference (panel 1). By 2030, rising demand for meat, especially in countries with transition economies,8, 9, 10 is expected to drive up livestock production by 85% from that in 2000, which will substantially affect emissions.11 Once foodstuffs leave the farm, the bulk of food-related emissions arise from use of fossil fuels.

The food system contributes to health benefits and harms through the availability, quality, and affordability of food. Animal foods are important sources of protein, energy, and nutrients—such as iron, calcium, vitamin B12, and zinc12—especially for children and for undernourished populations in low-income countries,13 but are also major sources of saturated fats in the human diet.14 In all but the poorest countries, diets are becoming high in saturated fat and sugar, and low in fruit and vegetables.15 In addition to other behaviours such as physical inactivity and tobacco use, such diets are a leading cause of non-communicable diseases, including cardiovascular disease, some cancers, and type 2 diabetes.16

Key messages

  • The agriculture sector contributes 10–12% of total greenhouse-gas emissions worldwide. Deforestation and other changes in land use contribute an additional 6–17% of global emissions. Production of foods from animal sources is the major contributor to emissions from the agricultural sector.

  • Global demand for animal-source foods is projected to increase substantially over the next 30 years, especially in transition economies.

  • Technological strategies within the food and agriculture sector, such as improved efficiency of livestock farming, increased carbon capture through management of land use, improved manure management, and decreased dependence on fossil-fuel inputs, are necessary but not sufficient to meet targets to reduce emissions.

  • A combination of agricultural technological improvements and reduction in production of foods from animal sources could provide an effective contribution to meet national and global targets to reduce emissions.

  • Concomitant reductions in consumption of livestock products in high-consumption populations could substantially benefit public health, for example via reductions in ischaemic heart disease.

  • Policies to reduce emissions in the agricultural sector must ensure that the nutritional requirements of populations that might benefit from consumption of some foods from animal sources are not compromised.

We aim to describe strategies that could substantially reduce farm-stage greenhouse-gas emissions in the food and agriculture sector by 2030, to meet targets recommended by the UK Committee on Climate Change, and to show and quantify the major effects on public health.

Section snippets

Potential strategies to reduce emissions

From expert reports we identified four strategies to reduce greenhouse-gas emissions in the food and agriculture sector, with a focus on the livestock sector in view of the dominant contribution of processes in livestock production to agricultural emissions:4 improved efficiency of livestock farming; increased carbon capture through management of land use; improved manure management; and decreased dependence on fossil-fuel inputs.3, 17, 18 Reduced production and consumption of foods from animal

Pathways to health

We mapped the pathways from our selected strategies to reduce emissions to the most plausible nutrition-related health outcomes (figure 2). Technological strategies are necessary components of efforts to reduce emissions, but they will have little effect on health. By contrast, change in dietary intake of saturated fat from animal sources is a major pathway to population health. Consistent experimental and epidemiological evidence has linked intake of saturated fat with cardiovascular disease,

Estimation of the effect on population health

To analyse the effect of reduced consumption of foods from animal sources on population health, we focused on changes in livestock production, the estimated shifts in intake of saturated fat and cholesterol at a population level, and the burden of cardiovascular disease, specifically ischaemic heart disease and stroke. We used Comparative Risk Assessment for modelling, as described in the first paper in this Series,28 and briefly outlined in webappendix pp 1–2. We used case studies from the UK

Discussion

Urgent and substantial actions are needed to reduce greenhouse-gas emissions and thus stabilise the world's climate before the extent of climate change becomes obviously dangerous. Our combined strategy of agricultural technological change and decreased livestock production would reduce emissions in the agriculture sector. Moreover, our model indicated that the commensurate reductions in consumption of saturated fat and cholesterol from animal sources would substantially decrease deaths and

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