Abstract
This paper presents the results of a systematic literature review of greenhouse gas emissions for different food categories from life cycle assessment (LCA) studies, to enable streamline calculations that could inform dietary choice. The motivation for completing the paper was the inadequate synthesis of food greenhouse gas emissions available in the public domain. The paper reviewed 369 published studies that provided 1,718 global warming potential (GWP) values for 168 varieties of fresh produce. A meta-analysis of the LCA studies was completed for the following categories: fresh vegetables (root vegetables, brassica, leaves and stems); fresh fruits, (pepo, hesperidium, true berries, pomes, aggregates fruits and drupes); staples (grains, legumes, nuts, seeds and rice); dairy (almond/coconut milk, soy milk, dairy milk, butter and cheese); non-ruminant livestock (chicken, fish, pork); and ruminant livestock (lamb and beef). The meta-analysis indicates a clear greenhouse gas hierarchy emerging across the food categories, with grains, fruit and vegetables having the lowest impact and meat from ruminants having the highest impact. The meta-analysis presents the median, mean, standard deviation, upper and lower quartile, minimum and maximum results for each food category. The resultant data enables streamline calculations of the global warming potential of human diets, and is illustrated by a short case study of an Australian family’s weekly shop. The database is provided in the Appendix as a resource for practitioners. The paper concludes with recommendations for future LCA studies to focus upon with respect to content and approach.
Generated Summary
This meta-analysis, conducted following the PRISMA Statement protocol, examines greenhouse gas (GHG) emissions across different food categories. The study reviewed 369 published Life Cycle Assessment (LCA) studies from the last 15 years, encompassing journal papers, conference proceedings, and Environmental Product Declarations (EPDs), to generate a database of Global Warming Potential (GWP) values. The primary objective was to enable streamline calculations for dietary choices by synthesizing available data on food-related GHG emissions. The meta-analysis included data on fresh fruits, vegetables, staples, dairy, non-ruminant livestock, and ruminant livestock. The aim was to identify GWP values for individual foods and identify areas where there is strong agreement in the GWP values, using box-whisker plots and statistical analysis to understand the spread of the data points. The study also incorporates a short case study of an Australian family’s weekly shop to illustrate the potential application of the GWP data and provide recommendations for future LCA studies.
Key Findings & Statistics
- The meta-analysis reviewed 369 published LCA studies, generating 1,718 GWP values for fresh produce.
- The majority of GWP values (58%) were from the last five years.
- The study covered a variety of food categories including: fresh vegetables, fruits, staples, dairy, non-ruminant livestock and ruminant livestock.
- Vegetables: field-grown vegetables showed a median GWP value of 0.37 kg CO2-eq/kg.
- Fruits: Field-grown fruit exhibited a median GWP value of 0.42 kg CO2-eq/kg.
- Cereals: Cereals (except rice) and pulses had median GWP values of 0.50-0.51 kg CO2-eq/kg.
- Tree Nuts: Tree nuts (1.20 kg CO2-eq/kg) had slightly higher values.
- Rice: Rice had the highest impact among plant-based crops, with a median of 2.55 kg CO2-eq/kg.
- Non-Ruminant livestock: Fish had a median GWP value of 3.49 kg CO2-eq/kg (BFM), chicken 3.65 kg CO2-eq/kg (BFM) and pork 5.77 kg CO2-eq/kg (BFM).
- Dairy: Dairy products such as cheese and butter also showed medium GWP values.
- Ruminant Livestock: Lamb and beef exhibited the highest median GWP values (25.58 and 26.61 kg CO2-eq/kg BFM respectively).
- Detailed GWP values for individual foods: The lowest median GWP was found in onions (0.17 kg CO2-eq/kg), and the highest values were observed in beef (26.61 kg CO2-eq/kg BFM) and buffalo (60.43 kg CO2-eq/kg BFM).
- European Focus: The majority of the GWP values were European-centric, with the British Isles and Europe accounting for a large portion of the data.
- GWP Value Variation: There was a notable variation in GWP values based on geographic location, especially for pork, with European pork having a lower median GWP.
Other Important Findings
- The meta-analysis identified a clear hierarchy of GWP values, with plant-based foods generally having lower impacts than animal-based products.
- Within the fish category, specific species showed varying GWP values.
- The study highlights the impact of heating methods on greenhouse gas emissions in greenhouse-grown produce.
- The analysis emphasizes the importance of considering the geographic location of food production when assessing GWP values.
- The paper provided an example of how the GWP data can be used to compare the GWP of different diets in a streamlined manner, identifying areas for improvement.
Limitations Noted in the Document
- The study acknowledges that its streamlined results may be less accurate than detailed process-based LCAs.
- The meta-analysis primarily used GWP as an environmental indicator, with other metrics such as land and water use not included.
- The representation of food categories in LCA studies was found to be unequal, particularly for certain foods like tree nuts and quinoa.
- The system boundaries used in the LCA studies varied, making direct comparisons challenging.
- The study does not fully account for all aspects of the food lifecycle, such as consumer behavior, disposal of food and packaging, and human excretion.
Conclusion
In conclusion, this meta-analysis successfully synthesizes a substantial body of LCA data to create a comprehensive overview of greenhouse gas emissions across various food categories. The findings highlight a clear hierarchy of environmental impacts, with significant differences between plant-based and animal-based products, as well as variations within specific food groups. This study emphasizes the importance of considering geographic location and production methods. The study highlights key trends, for instance, the broad variation in GWP values between species for the fish category, and the dominance of Europe in LCA publications. A key recommendation is to study the underrepresented food types and study the underrepresented food types, ideally following protocols that assist future comparison. This highlights how choices about food can have a real impact on our carbon footprint. The authors’ position when reading the meta-analysis is that the variation in farming methods and conditions has a more significant impact on the presented GWP values than methodological choices or publication type. Furthermore, the study also underscores the potential of using the compiled database to streamline accounting, informing more sustainable dietary choices. By making this information readily available, consumers and other stakeholders can be better informed when making choices, particularly by selecting food from differing categories. This type of analysis not only informs individual choices but also lays the groundwork for broader strategies to lower the environmental impact of our food systems.