Food production has become a focal point for achieving wider system sustainability as the UK pursues net-zero ambitions to reach a ‘carbon’ neutral/negative economy by 2050 as part of its commitment to the Paris Agreement. This national focus on agri-food systems is vitally important as agriculture covers around 70% of the UK’s terrestrial land mass.

‘Carbon’ is often erroneously used to cover all greenhouse gases (GHGs). However, the non-CO₂ greenhouse gases are significant contributors to the global warming burden and are arguably more challenging to mitigate. Whilst GHG emissions are undoubtedly a global issue in the face of a human-induced climate emergency, other, more local, environmental concerns such as poor surface water quality are also important. This points directly to the need for discussion on whether domestic production is environmentally preferable to importing food from other regions and whether these imports come with environmental costs to the source areas, such as water depletion.

Mindful of this challenge, NRI, Rothamsted Research, University of Surrey and London South Bank University conducted a scoping Life Cycle Assessment (LCA) of a ‘food basket’ containing food items most commonly purchased by consumers in the UK. LCA is a systematic methodology for analysing the environmental impacts of products, processes and services, over their life cycle – from raw material, through manufacture, distribution, use and disposal. It provides information which can guide more efficient resource use and reduce negative impacts.

The study found that beef cattle had the highest impact on climate change while the impact per kilogram of protein for broiler chicken, eggs, raw milk and pigs was not significantly different. Among the crops considered, tomatoes had the highest Global Warming Potential (GWP) score per kg of dry matter. Potatoes, wheat and carrots had the lowest.

The choice of commodities considered was based on consultation and co-design with key agri-food stakeholders. Interim typical examples for the UK were generated based on best available data (2017-present) sourced from the Farm Business Survey of the Department for Environment, Food & Rural Affairs (Defra), the National Greenhouse Gas Inventory Report, and the Agriculture and Horticulture Development Board (AHDB) among other sources. The UK systems were compared against widely used and frequently updated international commercial databases, primarily Agri-footprint and Ecoinvent.

Results were expressed in terms of seven impact categories. The categories were: GWP over a 100-year time frame expressed in CO₂ equivalents, marine eutrophication, freshwater eutrophication, terrestrial acidification, water consumption, land use, and resource use/fossil energy. Eutrophication is a gradual increase in the concentration of phosphorus, nitrogen and other plant nutrients in lakes and rivers, which feeds algal growth in water bodies.

Heated greenhouse crop systems (UK and Netherlands Tomatoes) were found to have a much higher impact on climate change per kg of dry matter than other crops. Horticultural crops generally demonstrate higher impact, partly due to eutrophication. The impact is also due to acidification from high nitrogen use and on-farm emissions, and greenhouse energy requirements (tomato and strawberry) or phosphorus fertiliser use (broccoli and carrot). The burden of water consumption is much higher in Spain and South Africa than in other regions.

Beef cattle’s impact is mainly due to methane from intestinal fermentation, marine eutrophication, and acidification, mainly from ammonia associated with manure storage and management. Lowland sheep had the highest impact on freshwater eutrophication through phosphorus emissions, although this depends on soil quality and run-off risk (which is highly localised), water consumption (also uncertain), and land use.

These findings show that some commodities (e.g. produce from gas-heated greenhouses) have significant impacts across multiple categories, whereas most field crop commodities demonstrate lower impacts. There are trade-offs apparent between heated greenhouses and unheated microtunnels or field systems, with heated greenhouses presenting higher global warming impacts but lower local nutrient losses and eutrophication. Compared to the farm gate, many UK and alternative systems demonstrate similar impact scores. However, there are important distinctions as fruit and vegetable systems in New Zealand and Spain concentrate water demand in water stressed areas, suggesting that exporting to UK consumers embodies localised pressure on the water catchment systems in exporting regions.

The ‘hotspots’ identified by the study show where targeted action could help reduce environmental burdens at the farm level, e.g. reduced gas heating of greenhouses, reusing plastic polytunnel material, more efficient cooling and enhanced installation of renewable capacity. Many of the potential solutions are technically feasible but costly to implement. In some cases, benefits can be achieved without modification of the processes themselves (e.g. sourcing animal feed from value chains that minimize deforestation). Others will require a systems approach and scaled solutions, e.g. availability of waste heat, infrastructure for large manure anaerobic digestion, and grid connectivity to feed in renewable energy etc., which are often beyond the capacity of individual organisations. Achieving reduction across local and global pollutants requires the removal of barriers at different scales, emphasising the importance of both technological, economic and policy-based drivers for change.

Read the original article in our 2023 Annual Review