What is a “carbon sink,” and how can it help us fight climate change? Carbon sinks act like sponges that soak up more carbon from the atmosphere than they release. We define the process by which we remove carbon dioxide from the atmosphere as “carbon sequestration.” The most effective carbon sinks use our natural systems (i.e., forests, wetlands, agricultural lands and coastal ecosystems), but buildings also play an essential role. To achieve net-zero by 2040, we need to consider carbon sinks as a means to amplify our efforts to reduce emissions, and we need to measure the efficacy of carbon sinks because good data supports meaningful policy and design. 
Case in point: the City and County of San Francisco updated its Climate Action Plan in 2021, actively using a data-driven approach to define initiatives to sequester carbon. One key area identified in its Plan to achieve net-zero emissions by 2040 includes healthy ecosystems using nature-based solutions.
I recently met with Lauren Dietrich Chavez (Project Manager with the Recreation and Parks Department at the City & County of San Francisco, Spencer Potter (Natural Resources Regulatory Specialist with the Recreation and Parks Department at the City & County of San Francisco), and Pamela Conrad (Principal of CMG Landscape Architecture and Founder of Climate Positive Design). These experts guided me through the many planning, design and operational considerations contributing to buildings and landscapes that can achieve net-zero targets by 2040.
Carbon Emissions and Sequestration: It’s About Communication
Pamela Conrad believes that you can’t manage what you can’t measure, so it’s essential to develop a feedback loop leading to behavioural change by measuring carbon tools and sequestration. Conrad launched Climate Positive Design (CPD) in 2019 to foster evidence-based research and better understand environmental and carbon impacts through planning design and advocacy leadership. Through an app she developed called Pathfinder, users can determine if their projects are on track to being climate-positive. The CPD challenge targets how many years a project should take to offset its carbon footprint. She noted that a project typically has to cut emissions by half and then double carbon sequestration, adding, “This is the first time we can look in the mirror and have an honest reflection of what those impacts are. We are measuring and developing a feedback loop to change our behaviour and make positive changes, deploying all the tools in our toolkits to increase sequestration.”
Data collected through the CPD challenge continues to yield baseline data, making it easier to establish effective codes and standards for the maximum amounts of carbon a project should emit or the minimum amount it should sequester. Conrad noted that we are a decade behind in finding practical measurement tools for buildings and landscapes. She said, “We should strive for climate-positive landscapes—and provide environments that provide social, economic, health, and ecological co-benefits. And then, someday, we could find a way to expand the Pathfinder tool for biodiversity and other climate-resilient outcomes.” Using a tool like Pathfinder will encourage clients to take the proper steps to improve their projects, and communicate and track progress. “If we include our clients in setting goals at the very beginning and sharing progress along the way, we are designing or creating something that will likely overcome the challenges. Here, everyone is invested in getting a better carbon impact on the built environment,” Conrad explained.
Carbon Emissions and Sequestration: It’s About Communication
Lauren Dietrich Chavez works with the City of San Francisco on various initiatives to address climate change and promote climate-positive design. She is a big-picture thinker who understands the relationship between such aspects as renewable energy that supplies electricity throughout the Bay Area, green roofs and material reuse and recovery in construction. She understands that pushing the needle on climate resilience requires a whole suite of tools, including updating stringent requirements for green building, energy optimization, human health and water conservation. When asked about the cultural shifts required to see the impact of these programs, Dietrich Chavez confirmed the answer to thinking about carbon sinks rests in tracking the data.
San Francisco has developed an embodied carbon checklist so that design teams for all municipal projects have to find a way to reduce the carbon impacts from schematic design to post-construction. To Dietrich Chavez, “The City knows what materials are less carbon-intensive and how they can make choices today that will push the needle forward tomorrow.” Although San Francisco bureaucracy is siloed, nature is not. To her, figuring out how to collaborate across City departments is essential, as is establishing collaborations with public, private, non-profit and research institutions. She cited one project where stormwater collected from an adjacent right-of-way is treated in a City park through rain gardens. Other examples include working with the San Francisco Estuary Institute in the southeast of San Francisco on its Regional Monitoring Program (RMP). This program monitors water contamination in the Estuary and provides water quality regulators with the information they need to manage the Estuary effectively.
Maintaining and Operating Carbon Sinks
Spencer Potter knows that successful climate policies and design guidelines need to be maintained over time. He manages parks and natural landscapes daily with the Recreation and Parks Department at the City and County of San Francisco and acknowledged, “Never before have people looked at our parks and said this will be a carbon sink, but using parks as a means of sequestration should not let carbon emitters off the hook.” Citing the importance of the City’s updated Climate Action Plan’s call for sequestering residual emissions through nature-based solutions that include urban forests, soil health and ecosystem management, Potter added, “We live in a biodiversity hotspot and have an ecological responsibility to preserve biodiversity. The last thing we want to do is plant a monoculture of trees.”
Potter accepts that there is room to get creative regarding managing healthy ecosystems such as the spaces around freeways, empty tree wells or reducing the heat island effect in lower-income neighbourhoods acknowledging the operational challenges of watering and caring for individual street trees, especially during the first three to five years of planting. These challenges only reinforce the value of urban forests as carbon sinks. Urban forests are extraordinary for understanding species threats and survivability during our climate crisis. Potter also recognized the importance of urban forests because “If there is a new pest, wildfire or heat exposure consideration due to climate change, urban forests help integrate science, good design and long-term operational considerations. Trees are a good case study to evaluate how to integrate the various elements.”
Creatively responding to the value of carbon sinks hinges upon our ability to collect valuable data while communicating our evolving knowledge to clients, collaborators and communities. An effective landscape policy leading to landscape design will not only make our cities healthier but also open new pathways to creating a healthier and more equitable ecosystem as we hope to achieve climate-positive cities by 2040.
Lina Al-Dajani is a Senior Associate at SvN Architects + Planners. This op-ed is part of an ongoing series of conversations between SvN, city building, and policy experts leading the way in helping the building industry achieve a net-zero future.