Growing lettuce indoors in Canadian cities can be as climate-friendly as conventional farming, but only in regions where electricity is from renewable sources and thus low-carbon, according to a new McGill-led study.

Researchers found that, when powered by clean energy, controlled-environment urban agriculture (CE-UA) can produce lettuce whose carbon footprint is similar to that of lettuce grown and shipped from California. In Quebec, where electricity is largely generated by hydropower, indoor lettuce production performs on par with conventional supply chains, including in summer, when lettuce is grown locally outdoors.

The picture changes sharply in places that generate electricity using fossil fuels, like Alberta. There, the same indoor systems can generate far higher emissions because of the energy needed for lighting and climate control. The study found climate impacts can exceed those of conventional lettuce production many times over in carbon‑intensive grids.

“The common assumption is that ‘local food = low-carbon food,’ but this study shows that’s not automatically true,” said lead author Estefany Cabanillas, who conducted the research while completing her Master’s in the Department of Bioresource Engineering. “Where your electricity comes from can matter more than food miles.”

The research helps answer a growing question for cities investing in indoor farming: when does it reduce environmental impacts?

Most previous studies have looked at indoor agriculture in a single location. Some, including work in the Netherlands, found it can have a carbon footprint several times higher than conventional farming due to heavy energy use.

This study takes a broader view. The team partnered with a commercial container farm in Montreal and collected a full year of operational data, including energy use, water use and crop yields. They conducted a life-cycle assessment and then modelled how the same system would perform across all 13 provinces and territories, using each area’s electricity mix.

The results highlight a trade-off. Indoor systems use much less land and water than conventional farming, but require more energy.

While the type of energy use remains a concern, the more efficient use of land and water itself could be important in improving food access as climate change increases pressure on farmland and water supplies, the researchers note. As well, indoor systems can provide consistent access to fresh food where supply chains are fragile or costly.

“CE-UA can play a key role in improving food security in remote northern communities in Canada, where fresh produce is limited and often transported long distances,” Cabanillas said.

Comparing controlled-environment-urban agriculture to conventional agriculture across Canada by Estefany Cabanillas, Benjamin Goldstein and Mark Lefsrud was published in Agronomy for Sustainable Development. It was funded by NSERC Alliance, Mitacs and Rvest.