Invited review: A position on the Global Livestock Environmental Assessment Model (GLEAM).

The livestock sector is one of the fastest growing subsectors of the agricultural economy and, while it makes a major contribution to global food supply and economic development, it also consumes significant amounts of natural resources and alters the environment. In order to improve our understanding of the global environmental impact of livestock supply chains, the Food and Agriculture Organization of the United Nations has developed the Global Livestock Environmental Assessment Model (GLEAM). The purpose of this paper is to provide a review of GLEAM. Specifically, it explains the model architecture, methods and functionality, that is the types of analysis that the model can perform. The model focuses primarily on the quantification of greenhouse gases emissions arising from the production of the 11 main livestock commodities. The model inputs and outputs are managed and produced as raster data sets, with spatial resolution of 0.05 decimal degrees. The Global Livestock Environmental Assessment Model v1.0 consists of five distinct modules: (a) the Herd Module; (b) the Manure Module; (c) the Feed Module; (d) the System Module; (e) the Allocation Module. In terms of the modelling approach, GLEAM has several advantages. For example spatial information on livestock distributions and crops yields enables rations to be derived that reflect the local availability of feed resources in developing countries. The Global Livestock Environmental Assessment Model also contains a herd model that enables livestock statistics to be disaggregated and variation in livestock performance and management to be captured. Priorities for future development of GLEAM include: improving data quality and the methods used to perform emissions calculations; extending the scope of the model to include selected additional environmental impacts and to enable predictive modelling; and improving the utility of GLEAM output.

Issues and options in addressing the environmental consequences of livestock sector's growth.

The growth of the livestock sector is being achieved at substantial environmental costs. Today, livestock are a major stressor of the global environmental, occupying a quarter of emerged land (including a third of arable land), contributing close to a fifth of the anthropogenic greenhouse gas emissions, using eight percent of all water resources and threatening a wide range of endangered species. At the same time, livestock are also a crucial engine of rural growth and a tool for improving food security. Policies are required to guide the sector in achieving sometimes conflicting development objectives. Potential pathways include encouraging resource use efficiency, correcting for environmental externalities and accelerating technological change.

Policy options in addressing livestock's contribution to climate change.

There is a great potential to reduce greenhouse gas (GHG) emissions related to livestock production. For achieving this potential will require new initiatives at national and international levels that include promoting research and development on new mitigation technologies; deploying, diffusing and transferring technologies to mitigate emissions; and enhancing capacities to monitor, report and verify emissions from livestock production. This study describes the sources of livestock-related GHG emissions and reviews available mitigation technologies and practices. We assess the main policy instruments available to curb emissions and promote carbon sinks, and discuss the relative merits of alternative approaches. We discuss recent experiences in countries that have enacted mitigation strategies for the livestock sector to illustrate some of the key issues and constraints in policy implementation. Finally, we explore the main issues and challenges surrounding international efforts to mitigate GHG emissions and discuss some possible ways to address these challenges in future climate agreements.

Livestock production systems in developing countries: status, drivers, trends.

This paper describes and assesses the current status of livestock production systems, the drivers of global livestock production, and the major trends in such production. The analysis covers the six major livestock species: cattle and buffaloes, goats and sheep, pigs and chickens. Global drivers of the livestock sector include economic growth and income, demographic and land use changes, dietary adjustments and technological change. The rate of change and direction of livestock development vary greatly among world regions, with Asia showing the most rapid growth and structural change. The paper also examines system dynamics, by analysing the ways livestock production has adjusted to external forces. A brief discussion of how these trends link to food safety concludes the paper.