Can carbon sequestration in urban landscapes form part of a net-zero carbon approach to development?

Humans are responsible for artificially mobilising carbon from ancient biomass reserves and releasing it into the dynamic carbon cycle as atmospheric carbon dioxide. This is the root cause of our current climate crisis. We can slow, and in some cases stop, the rate at which we are releasing carbon into the atmosphere, but are we able to reverse it?

Carbon sequestration refers to the capture and storage of carbon that would otherwise be emitted into, or remain in, the earth’s atmosphere. Nature’s most obvious method of carbon capture is carried out by plants in the process of photosynthesis. Plants store this captured carbon as biomass. When plants die this biomass is decomposed and carbon is transferred into soils where carbon reserves can build up. In this way, plants act as the gateway for carbon to be stored in other non-living components of the ecosystem.

The ambition of achieving “net-zero” is becoming increasingly common in the built environment industry and although meanings differ from project to project, the idea is that a development can achieve an overall balance between carbon released into and removed from the atmosphere.

As we introduce concepts such as the Green Space Factor and net biodiversity gain into planning decisions, should we also create a common methodology to help designers develop carbon sequestering urban landscapes, as part of a net-zero carbon approach?

Quantifying carbon capture and storage of ecosystems is a complex task and currently there is not a simple go-to methodology. Firstly, rates of photosynthesis are very variable and depend on a number of factors relating to the individual plant, such as species and age, as well as the surrounding conditions of the plant, including solar energy input, temperature and moisture levels, nutrient availability and so on. Adding to this complexity, not all carbon that is captured will become stored as some is released back to the atmosphere through natural processes such as respiration of plants and soil dwelling microorganisms, and human factors such as bad practice land management.

There are some tools available on the market that aim to simplify this calculation, using simple data such as tree diameter and species type. Unfortunately, an increase in simplicity often leads to loss of accuracy and results that are highly variable from tool to tool. This simplicity also discourages good green spaces management if the positive effects are not going to be reflected in results. On the other hand, a tool that is too complex is unlikely to be used appropriately, if at all.

There is an opportunity for scientists, consultants and developers to create a tool that that is easy to use and produces accurate and valid results using a standardised methodology. This tool could change the way that built environment professionals view green spaces, not just as somewhere attractive spend time, but as a key player in the climate emergency and a vital component of any development.

KLH are exploring carbon sequestration approaches and strategies with a number of our clients and would love to hear from others that are working in this field - whether you are an academic researcher, a practitioner or simply an interested party, please get in touch!

--KLH Sustainability 09:55, 07 Oct 2020 (BST)