BY ANTHONY KING | 16 FEBRUARY 2024
A new study reports a large carbon footprint for urban community farms, but comparing embodied carbon could be misleading.
A large-scale study of urban agriculture has disappointed many of its proponents. The analysis found that the carbon footprint from its food was six times greater than for conventional agriculture (Nature Cities, doi: 10.1038/s44284-023-00023-3).
‘Urban agriculture is generally regarded as a sustainability intervention, but there is not a lot of quantitative evidence to back that up as far as climate change goes,’ says Jason Hawes at the University of Michigan, who led the study. Data was collected through citizen science from 73 sites of low-tech urban agriculture in France, Germany, Poland, the UK, and the US. The embodied greenhouse gases and synthetic nutrient footprints were compared to conventional farm produce sold in each of the five countries.
The on-farm impacts, processing, and transportation of the food produce were considered. For fruits and vegetables, urban agriculture emitted 0.42kg of CO2 equivalent per serving, while conventional produce emitted 0.07kg. The study does not suggest that urban agriculture is bad. ‘Urban agriculture has some really good benefits for cities and for people,’ Hawes says. ‘But we need to think critically about how we might improve its carbon footprint.’ Commercial market gardens and individual gardens were similar on average in terms of emissions.
While offering health and social benefits for the people they bring together, community gardens were found to be the most carbon-intensive, largely owing to infrastructure such as raised beds, paths, and garden sheds. One way to substantially cut emissions would be to reuse building materials, rather than use virgin materials. Another is to avoid short-term community gardens, where infrastructure is built and then soon dismantled.
Some urban crops, such as tomatoes, outperformed conventional agriculture. Urban food growers could maximise carbon benefits by selecting crops conventionally grown – not in heated greenhouses – to replace air-freighted produce. There was huge variation between sites. Seventeen of the 73 study sites performed better than conventional agriculture, with 43% of market gardens and 25% of individual gardens being more climate-friendly. ‘We try to highlight the nuances and explain our headline results,’ says Hawes.
Andre Viljoen, urban sustainability expert at the University of Brighton, UK, notes that lots of the embodied emissions were related to community facilities, such as a meeting space on a small site for growing food.
It is important to look beyond the headline figure on emissions, says Viljoen: ‘Once you look at the details of the paper, you realise that the actual environmental impact of urban agriculture – if you take just the growing of the crops – is not significantly different to conventional growing, and in some cases better.’
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