Can a city store as much carbon as a forest? A new tool developed by experts at Aalto University aims to help urban planners ensure that growing cities can remain carbon neutral while harmonising development with climate targets. This innovative solution offers a measurable approach to promote carbon-neutral urban expansion planning, which is essential for achieving carbon emission reduction goals.
Urban growth often leads to the encroachment of forested areas and agricultural lands, resulting in the depletion of carbon sinks. This challenges cities working to reach crucial net-zero emission targets to mitigate climate change. Researchers have introduced a new metric called the carbon storage (CS) factor to address this issue, which estimates the potential for carbon capture in future urban projects. The concept is further elaborated in a paper published in Environmental Research Letters.
Aalto Professor Seppo Junnila, who led the study, explained, “There are many tools available to increase the CS factor. Increasing wooden construction is a good option in some regions, but it’s also possible to store carbon in the soil using biochar and other tools, or to include new fast-growing plants in the landscape, or even through direct carbon capture and storage technologies. We hope planners will adopt this mindset and use the CS factor to help them plan sustainable urban growth.”
The CS factor allows urban planners to assess the impact of new developments on a city’s carbon balance. By comparing the reduction in storage capacity (such as deforestation) to the CS factor of development plans using various methods and technologies, planners can work towards maintaining or improving the region’s natural carbon storage capacity.
Researchers assessed how wooden construction in Finland’s capital region might offset deforestation resulting from urban growth. The study discovered that using suitable wooden construction technologies could allow up to 70% of future construction to maintain the carbon storage capacity of the lost forests. This would require using methods that store substantial amounts of carbon, such as cross-laminated or glue-laminated timber.
The study was carried out in four stages. Firstly, the carbon storage potential of forest areas was estimated using existing literature and databases. Then, researchers collected data on new development and construction projections up to 2050 for the entire metropolitan region in Finland. Next, they conducted scenario analyses to examine different levels of wood demand in planned residential developments. Lastly, they compared the carbon storage potential of the future building stock to the forest areas slated for development.
Data provided by the regional authority showed that the future residential building stock could store between 128 and 733 kt of carbon.
The research also demonstrated that similar results could be achieved using wooden construction in other parts of Europe, Asia, and Oceania. However, the researchers emphasise that increased wooden construction is only sustainable if forests are managed responsibly. Junnila clarified, “Our goal isn’t to encourage cities to expand into new areas but to provide planners with tools to mitigate the impact of development on carbon storage when forest clearing is unavoidable.”