Why it matters
Urban CDR strategies reduce urban heat and improve air quality, thereby enhancing adaptation and resilience in cities. Furthermore, integrating CDR into urban planning can promote climate justice by ensuring that benefits such as healthier living conditions and reduced pollution are shared across communities.
With the aim of supporting the path to achieving net-zero emissions in cities, the study by Rodriguez-Mendez et al., 2024 assesses the existing literature on CDR at the urban scale. The study seeks to quantify the potential negative emissions contribution of cities globally.
Deploying urban CDR could substantially contribute to local and global climate mitigation efforts
Short summary
Cities, home to over half of the world’s population and responsible for more than 75% of global CO₂ emissions, are at the forefront of the climate crisis. Urban CDR strategies, such as storing carbon in vegetation, soils and built environments, as well as indoor air capture, could play a key role in helping cities reach net-zero emissions, while also supporting global climate goals. However, scaling up these solutions is hindered by uncertainties, economic barriers and governance challenges.
Brief description of Methods
The study involved a comprehensive review of existing literature on urban carbon sequestration, supplemented by expert consultations. The team assessed the global potential for carbon storage in different CDR methods.
These options include:
- storing carbon in urban vegetation, such as street trees, parks and green roofs
- soils, through biochar addition
- built environments, such as construction materials
- indoor environments, through ventilation systems
The authors also qualitatively evaluated the co-benefits and implementation barriers of each CDR option. Furthermore, the study examined the potential of enhancing urban surface albedo (e.g. reflective roofs and pavements) in mitigating urban heat islands and reducing building energy consumption, despite the fact that it does not directly sequester carbon.
Key results
A portfolio of urban CDR options could collectively store up to1 GtCO₂ per year worldwide.
The highest potential for carbon storage is achieved by storing C in the built environment using biogenic construction materials. Separate figures are provided for wood in construction (0.1–0.5 GtCO2/year) and for biochar additions to cement-based materials (0.2–0.7 GtCO2/year). Storing C in urban vegetation (0.1–0.3 GtCO2/year) offers the greatest potential for co-benefits, whereas capturing C from indoor environments (0.02–0.13 GtCO2, potential for capture, disregarding of CO₂ transportation) faces the greatest implementation barriers. Soils could store 0.007–0.05 GtCO2/year. While increasing surface albedo provides co-benefits, it does not contribute to C storage.
Co-benefits & barriers
Urban CDR also offers significant additional benefits, such as improved human health, better air quality, and enhanced waste management. Urban CDR also offers significant additional benefits, such as improved human health, better air quality and more efficient waste management. Of all the options, urban vegetation provides the greatest co-benefits, for example through vegetative cooling, UHI mitigation, and its support for biodiversity conservation.
However, the study identified several major barriers to implementation. These include uncertainties regarding the long-term storage of carbon, the potential for adverse environmental impacts such as water scarcity, economic challenges, and the absence of governance structures to ensure sustainable and equitable practices. Indoor air capture faces the most barriers, for example due to the costs and mechanisms of transport and storage of captured CO2 and increased energy requirements.
Future directions
The study highlights several knowledge gaps and recommends a research agenda to make urban CDR more viable and accessible. Future work should focus on additional field deployments that consider the unique characteristics of different urban areas and socio-economic contexts. It should also focus on developing robust carbon accounting methodologies that span multiple economic sectors. It is also critical to expand the scope to include more urban CDR options and improve the scalability of these solutions from local to national levels.
Read the full article here: Rodriguez Mendez, Q., Fuss, S., Lück, S. et al. Assessing global urban CO2 removal. Nat Cities 1, 413–423 (2024). https://doi.org/10.1038/s44284-024-00069-x