Grey Carbon—A New Nature-Positive Carbon Removal Technology for the Built World

Humanity is in a race to reduce carbon dioxide levels in the atmosphere. Emissions must be reduced while also accelerating net carbon dioxide removal (CDR). Historically, carbon removal has been shouldered by “green” and “blue” nature—land, coastal areas, and ocean. With the world’s growing population, impacts from climate change, and increasing urbanization, it is clear nature cannot handle all the CDR needed. Natural systems are under threat, risking their ability to maintain the same rate of carbon sequestration. Man-made technology must deliver more. The IPCC Assessment Report 6 (AR6) highlights a mix of nature- and technology-based CDR solutions that will be needed. Here, we look at a new CDR solution for the construction industry, which is responsible for 38% of global CO2 emissions. Since climate change is only increasing demand for construction, we must reimagine how and what we build with. We need building technologies that can help keep their own industry’s emissions in check while also reducing CO2 from the atmosphere. This is where “grey carbon” comes in. Like its blue and green cousins, grey carbon offers net carbon removal from man-made technology and presents a pathway that delinks pollution and development. Here, we use a case example of how the Bahamas is turning to a grey carbon building product to respond to housing demand and climate adaptation. We describe the science behind this CDR technology and apply financial valuation techniques to calculate the monetary value that could be derived from the grey carbon credits. We show how grey carbon delivers climate, nature, and community benefits from the following: CO2 avoidance and removal during production, longer-term carbon removal as the materials continue to weather, ocean protection through reduced brine waste, and social benefits from the sale of grey carbon credits. We show that a 1250 ft2 home built with this cement can deliver 170.94 tCO2e credits over 20 years for a present value of $38,145 per home and $57.22 million for 1500 homes. We conclude that grey carbon can mitigate emissions from the built world while also helping to deliver a future in which the biosphere and Technosphere, blue, green, and grey climate solutions, coexist as allies for human well-being and climate stabilization.