## 4 Discussion
### Proposed Framework for Measuring Energy Use in Greenhouse Agriculture  
Based on these limitations we propose a framework that would, in our view, allow for considerably more accurate measurement and understanding of energy use in greenhouse production systems and indeed in all agricultural systems. We propose that this framework is centred around conducting several LCAs at regular intervals for all crops in different production systems in all countries. In practice this would first require the categorization of production systems and the identification of'standard' systems in each country. At a later stage non-standard and non-conventional production systems can also be considered. We also recommend that a wide, accurate and measurable definition of direct and indirect energy is included in these studies. Though indirect energy is consumed prior to the farm it can clearly be attributed to the agricultural sector and is important to be included.  
In such a system, an effective approach to conducting individual LCA for crops in each production system needs to be developed. For energy use we propose that the LCA methodology uses a wide, standardized, and detailed categorisation of energy inputs. The categories that we propose include energy use for: seeds; soil; growing media; pesticides; fertilizers; diesel use for machinery, heating and ventilation; electricity use for machinery, heating, ventilation, irrigation, storage, machinery. Such a process that also differentiates between the likely main energy sources, diesel and electricity, would support a detailed understanding of energy inputs in greenhouses. We consider this overall categorisation particularly important as, currently, a small number of non-standardized energy use categories are generally used between LCAs. For instance, one LCA might have the categories fertilizers, pesticides, diesel use, and lighting, while another one might have fertilizers pesticides, machinery use, and electricity. In practice, this makes effective comparisons extremely difficult and prone to errors as these categories often overlap, are not exclusive and often there is little transparency on what was included in each of these inputs.  
In addition, it would be useful if results are presented as energy use per hectare, as well as energy use per kilogram/tonne and also include uncertainty and confidence intervals.  
A major drawback of existing LCAs in agriculture is that they generally do not include any degrees of uncertainty. This entire methodology would need to rely on detailed data that rely on accurate real-world parameters and/or accurate database reference values. For this to occur considerable effort is required for the finding of accurate and updatable parameters and reference values. Once a large number of LCAs have been conducted, using appropriate statistic tools, an effective meta-analysis can be conducted that provides accurate greenhouse energy use profiles in different countries and production systems.  
In our view such a framework can also be applied to the open-field agriculture and livestock sectors. This is a large piece of work that requires significant funding to be carried out but would support a more detailed understanding of energy use in agriculture and support effective policy and interventions for the transition away from fossil-based agriculture.