Residual Emissions Requiring Carbon Removal

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.

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#00062Carbon Mineralization in Construction Materials

Permanently store captured CO2 by mineralizing it into concrete and other construction materials. The CO2 reacts with calcium and magnesium compounds and becomes rock — permanently sequestered. Neustark, a Swiss ETH spin-off, operates 19+ plants across Switzerland, Austria, Liechtenstein, and Germany doing exactly this, with over 2,500 tonnes of CO2 removed to date and a target of 1 million tonnes by 2030. The resulting concrete performs equivalently to conventional products, creating a circular economy link between carbon removal and construction.

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Elena Popescu

#00061CCS at Municipal Waste-to-Energy Plants

Retrofit waste-to-energy incineration plants with post-combustion carbon capture, transporting captured CO2 for geological storage or industrial use. Since waste incineration produces roughly 50% biogenic CO2 (from organic waste), capturing it achieves net-negative emissions (BECCS). KVA Linth in Switzerland will be the first such facility, designed for 100,000 tonnes CO2/year. Copenhagen's experience shows the technology is not yet proven at municipal scale — cities should pursue this as one element of a portfolio, not as a single solution.

Basel-Stadt, Switzerlandcity

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Marcus Johnson

#00063Diversified Negative Emissions Portfolio Strategy

Instead of betting on a single carbon removal technology, build a portfolio combining CCS at point sources, direct air capture procurement contracts, carbon mineralization in construction, and potentially enhanced weathering or biochar. Set intermediate milestones requiring each technology to demonstrate progress, with fallback provisions to scale alternatives if one fails. Copenhagen's collapse after relying solely on CCS at one waste-to-energy facility is the definitive argument for diversification. The Swiss federal Climate and Innovation Act provides CHF 200 million per year (2025–2030) that cities can leverage for portfolio development.

Basel-Stadt, Switzerlandcity

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Leo Martinez