Study shows how biochar helps green roofs remove methane from the atmosphere
Researchers from the Institute of Forestry and Conservation at the University of Toronto’s John H. Daniels Faculty of Architecture, Landscape, and Design have shown that adding biochar — a charcoal-like material made from wood waste — to green roof growth media substantially increases the roof’s ability to remove methane, a potent greenhouse gas, from the atmosphere.
The five-year field study, conducted on the Green Roof Innovation Testing Laboratory (GRIT Lab) located on the U of T’s Daniels Building rooftop, finds that green roofs amended with biochar consistently absorbed more atmospheric methane than conventional green roofs, with uptake rates five times higher during peak periods. Importantly, the increased methane removal was not accompanied by higher carbon dioxide emissions.
“Green roofs are already recognized for reducing urban heat and managing stormwater, but our findings show they can also play a direct role in removing methane from the atmosphere,” says Imrul Kayes, lead author of the study and a PhD candidate. “What is particularly exciting is that a single biochar application continued to enhance methane uptake over five years, demonstrating that relatively simple modifications to green roof design can provide durable climate benefits. As cities continue to expand green infrastructure, integrating biochar into green roof substrates offers a practical and scalable way to enhance their contribution to climate change mitigation.”
The researchers found that biochar improves the physical properties of engineered green roof substrates, creating conditions that favor methane-oxidizing microorganisms by enhancing moisture retention while maintaining oxygen availability. The effect persisted throughout the five-year study, suggesting that a single biochar application can provide remarkably long-lasting climate benefits. The findings indicate that in addition to supporting stormwater management, cooling buildings and improving urban biodiversity, biochar-amended green roofs can contribute directly to greenhouse gas mitigation.
“As cities invest more in green infrastructure to adapt to climate change, we need to ensure these systems deliver the greatest possible environmental benefits,” says Professor Sean C. Thomas, senior author of the study. “Our findings demonstrate that a simple amendment such as biochar can substantially enhance the climate performance of green roofs by increasing atmospheric methane removal while maintaining or enhancing their other well-established benefits, including stormwater management, urban cooling, and biodiversity support. It also creates an opportunity to transform forestry and urban wood waste into a long-lasting climate solution through a circular bioeconomy.”
The study, “Biochar enhances methane uptake in engineered green roof substrate,” authored by PhD candidate Imrul Kayes, together with Md Abdul Halim, Wenxi Liao, Md Rezaul Karim, Melanie A. Sifton and Sean C. Thomas, was published today in the Journal Carbon Research.
Imrul Kayes
