Agriculture, Ecosystems and Environment 141 (2011) 39–48 Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee The effect of methodology on estimates of greenhouse gas emissions from grass-based dairy systems D. O’Brien a,b , L. Shalloo a,∗ , F. Buckley a , B. Horan a , C. Grainger a , M. Wallace b a Livestock Systems Research Department, Animal & Grassland Research and Innovation Centre, Teagasc, Moorepark, Fermoy, Co. Cork, Ireland b School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland article info Article history: Received 17 May 2010 Received in revised form 21 January 2011 Accepted 6 February 2011 Available online 4 March 2011 Keywords: Greenhouse gas Life cycle analysis Intergovernmental Panel on Climate Change method Holstein-Friesian strain Grass-based abstract The objective of this study was to compare two standard methodologies, Intergovernmental Panel on Cli- mate Change (IPCC) method and life cycle analysis (LCA), for quantifying greenhouse gas (GHG) emissions from dairy farms. Both methods were applied to model the GHG emissions from 9 dairy farm systems differing in strain of Holstein-Friesian cow and type of grass-based feed systems using the physical per- formance findings of previously published work. The strains of Holstein-Friesian cow used were; high milk production North American (HP), high fertility and survival (durability) North American (HD), and New Zealand (NZ). The alternate grass-based feed systems were; high grass allowance (HG, control); high stocking rate (HS) and high concentrate supplementation (HC). The milk production systems were modelled using a previously developed integrated economic-GHG farm model. The model calculated GHG emissions using the LCA approach and was extended to quantify GHG emissions using the IPCC method. The study found that the method of reporting GHG emissions (per unit of product or per unit area) affected the ranking of emissions of dairy systems investigated. Greenhouse gas emission were greater when calculated using the LCA method rather than the IPCC method. Both methods found reduc- ing inputs or the intensity of dairy production reduced GHG emissions per hectare. When emissions were expressed per unit of product the methodologies did not rank farming systems in the same order. The effect of feed system on emissions per unit of product was inconsistent between methodologies because the IPCC method excludes indirect GHG emissions from farm pre-chains, i.e. concentrate production. Both methodologies agreed that animals selected solely for milk production (HP) had higher GHG emissions per unit of product relative to strains selected on a combination of traits. The results indicate that if dairy systems targeting a net reduction in global GHG for projected increases in meat and milk production are to be developed, a holistic approach such as LCA, should be used to assess emissions on a per unit product basis. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The production of greenhouse gas (GHG) from livestock activ- ities and their impact on climate change are becoming a major concern worldwide. Globally, livestock activities are estimated to be responsible for 18% of total anthropogenic GHG emissions (Steinfeld et al., 2006). Dairy farming is a major contributor to global livestock emissions (FAO, 2010). Thus, reducing emissions from dairy systems will be essential for some nations attempting to meet Kyoto requirements and the targets of any future inter- national treaty. Consequently, a number of mitigation strategies such as the application of nitrification inhibitors (Dobbie and Smith, 2003), anaerobic digestion of stored manure (Amon et al., 2006) or ∗ Corresponding author. Tel.: +353 25 42306; fax: +353 25 42340. E-mail address: Laurence.Shalloo@teagasc.ie (L. Shalloo). supplementation of livestock diets with protein hormones (Capper et al., 2008) have been suggested to reduce GHG emissions from dairy farms. However, many proposed mitigation strategies have only been assessed by considering on-farm emissions. Greenhouse gas mitigation strategies can effect GHG emissions both on and off- farm (Weiske et al., 2006) and this can alter the overall net benefit of any strategy. Consequently, the evaluation of effective mitiga- tion strategies will only be globally beneficial if carried out using a holistic or full accounting approach. Presently, the standard methodology used for accounting of GHG emissions from all activities (including dairy farming) at the local level is the Intergovernmental Panel on Climate Change (IPCC) method (Bastianoni et al., 2004). However, the IPCC method was developed to prepare transparent and simple inventories on a national scale and not to determine emissions or assess strategies to reduce emissions on a lower scale such as at the farm level (Schils et al., 2006). Recognising this issue, some researchers have used 0167-8809/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2011.02.008