Residual Emissions Requiring Carbon Removal
#00059
Even with aggressive decarbonization, cities face residual emissions from waste incineration, industrial processes, and hard-to-abate sectors that cannot be eliminated by 2030–2040 deadlines. Reaching net-zero therefore requires negative emission technologies — carbon capture at point sources, direct air capture, or carbon mineralization — that are expensive, unproven at scale, and carry the risk of becoming an excuse to delay emission reductions.
Parent issue
#00046 Urban Carbon Neutrality
Sustainable Development Goals
Location
global
Description
Every city pursuing carbon neutrality confronts the same arithmetic: after maximizing energy efficiency, electrifying heating and transport, and switching to renewable electricity, a stubborn 5–15% of emissions remains. These come primarily from waste incineration (which cannot stop processing waste), certain industrial processes, and residual fossil fuel use in hard-to-convert applications.
Carbon capture and storage (CCS) at waste-to-energy plants is the most commonly proposed solution. Since roughly half of waste incineration CO2 is biogenic (from organic waste), capturing it can produce genuine negative emissions (BECCS). Switzerland alone has 29 waste-to-energy plants emitting approximately 4.5 million tonnes of CO2 annually.
However, Copenhagen's experience is a stark warning. The city's entire 2025 carbon neutrality strategy depended on CCS at its Amager Bakke waste-to-energy plant. When the project failed due to bureaucratic obstacles and financial disputes, the entire target was abandoned. The lesson: never bet everything on a single unproven technology.
Direct air capture (DAC) works — Climeworks' Mammoth plant in Iceland captures up to 36,000 tonnes per year — but at costs exceeding $900/tonne, it remains prohibitively expensive for municipal-scale deployment. Carbon mineralization, where CO2 is permanently stored in concrete and construction materials, is more affordable and creates circular economy benefits. Swiss startup Neustark operates 19+ such plants across Europe.
The responsible approach is a diversified portfolio: CCS at point sources where feasible, mineralization for near-term offsets, and DAC contracts for the remainder, with intermediate milestones and fallback provisions if any technology underdelivers.