‘A common carbon footprint approach for the dairy sector: The IDF guide to standard life cycle assessment methodology’ published in 2010 has been revised to ensure that it remains practical to use for the dairy sector globally, up-to-date scientifically and aligned with developments in other standards, and with the current draft of the FAO Livestock Environmental Assessment and Performance (LEAP) Partnership guidance, Environmental performance of large ruminant supply chains: Guidelines for assessment . As life cycle assessment often informs policy discussions on the climatic impact of food production, the work of the IDF Standing Committee on Environment’s Action Team on LCA Development Monitoring has continued relevance.
In this first update of the original guide, a minor adjustment has been made in the equation for allocation of emissions between milk and meat at dairy farm level, and the section on carbon sequestration has been expanded. Relevant guidance provided in the FAO LEAP document, ‘Environmental performance of large ruminant supply chains: Guidelines for assessment‘  has also been incorporated into this revision, including a decision tree for production units and co-products, an improved description of the IDF allocation method for milk and meat, guidance on the allocation method for manure, which treats manure as a residual (this is a change from the previous IDF guidance), and more detailed information on attributional and consequential LCA methods.
Greenhouse gases are all gaseous substances for which the IPCC has defined a global warming potential coefficient. They are expressed in mass-based CO2 equivalents (CO2e). The main agricultural greenhouse gases are carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4).
The product carbon footprint is the sum of the greenhouse gases emitted throughout the life cycle of a product within a set of system boundaries, in a specific application and in relation to a defined amount of a specified product. One example of a carbon footprint is obtained by calculating all the GHGs emitted during the production of one litre of semi-skimmed milk, packed in a specific type of paper carton, up to the point when the milk leaves the manufacturing plant gate.
The reference unit that denotes the useful output is known as the functional unit and has a defined quantity and quality, for example a litre of fresh milk of a defined fat and protein content in a defined type of package.
Calculation of the carbon footprint of a product using LCA methodology should be based on the ISO 14000 series, specifically ISO 14040 , ISO 14044  and ISO 14067 ; the recommendations of PAS 2050  should also be taken into account where advised in this document.
Other environmental impacts are commonly included when doing a full LCA (e.g. water use, land use, toxicity, eutrophication, biodiversity), whereas a carbon footprint only includes the climate impact category. The decision to calculate the carbon footprint of a product is a conscious decision to focus on only one environmental indicator.
There are many challenges in calculating a carbon footprint, and calculating one for milk or a dairy product is no exception. To date, there have been several LCA studies investigating and evaluating GHG emissions from milk production [11–22].
However, comparison between these studies is difficult because of differences in system boundaries, allocation methodology and emission factors. It may also be difficult to identify where meaningful reductions in GHG emissions can be made when differences in results can depend more on the methodological differences than real differences in the production system or management [23, 24].
The carbon footprint for milk and dairy products is dominated by the agricultural stage, where three quarters or more of the GHG emissions occur . This is why it is crucial to consider the variables in primary milk production that can affect the carbon footprint outcome, and develop a common approach for allocating the environmental burden from raw milk production between products such as milk, cream, cheese and butter, irrespective of the farm, system, country or even region.
From the outset, the IDF was committed to reviewing existing standardisation work and to collaborate with organisations that were already involved in improving the standardisation of LCA methodology. As emphasised in the Introduction, where a suitable model is already in existence, this has been used.
ISO 14040 ‘Life cycle assessments’  provides an important basis for framework and principles, and ISO 14044 ‘Environmental management – life cycle assessment’  provides requirements and guidelines. ISO took up the task of preparing a standard for ‘Carbon footprints of products’ (ISO/TS 14067) in 2009 and finalised it in May 2013 . The standard consists of two parts: one for assessment and quantification, and one for communication. The IDF is engaged with these processes where practicable.
The British Standards Institute, in collaboration with the UK’s Department for Environment, Food and Rural Affairs (Defra) and the Carbon Trust, has produced a Publicly Available Specification 2050 ‘Specification for the assessment of the life cycle greenhouse gas emissions of goods and services’ .
This British pre-standard sets out an initial comprehensive proposal for the methodology of the product carbon footprint. The original version of the PAS was published in October 2008 and was largely based on the LCA standard ISO 14040. It refers to this standard on a number of points but also deviates significantly from it in some areas. PAS thus represents the first attempt to create a standardised basis for the assessment of greenhouse gas emissions arising throughout the product carbon footprint. An updated version of PAS 2050 was published in 2011 .
The Greenhouse Gas Protocol (GHG Protocol) is the most widely used international accounting tool and allows businesses to understand, quantify and manage GHG emissions. It is a decade-long partnership between the World Resources Institute (WRI) and the World Business Council for Sustainable Development (WBCSD) and brings together stakeholders from business, government, NGOs and academic institutes to develop internationally accepted GHG accounting and reporting standards.
The GHG Protocol provides the methodology for nearly every GHG standard and programme in the world, from the International Standards Organisation to The Climate Registry, as well as hundreds of GHG inventories prepared by individual companies.
Since 2008, the WRI and the WBCSD have convened over 1600 stakeholders from around the world to develop new accounting and reporting standards. The GHG Protocol Product Life Cycle Accounting and Reporting Standard  and the Corporate Value Chain (Scope 3) Accounting and Reporting Standard  were published in late 2011, after undergoing road testing in over 70 companies and through a series of stakeholder consultations.
The IDF guidelines contained in this document are a sector-specific guideline and at a more precise level than the current GHG Protocol developments. Having said that, the IDF has liaised closely with the WBCSD throughout its respective programmes and will continue to do so in the future as developments in this field unfold (Figure 2).