The potential of syngas as a central mediator for a carbon-agnostic circular economy.

Carbon is the foundation of life and industrial production, but the current use of fossil-based carbon in a linear economy leads to climate breakdown with global ecological consequences. To mitigate the effects of the climate catastrophe, transitioning from a fossil-based linear economy to a circular carbon economy requires scalable strategies that do not compete with arable land resources. Accordingly, processes for the utilization of waste streams from various sources including CO2 must be established to enable circularity. Here, we propose synthesis gas (syngas; CO, H2 and CO2) as a universal, homogenized hub feedstock that decouples upstream waste heterogeneity from downstream chemical and biotechnological manufacturing. We review established and emerging routes for syngas production from biogenic and fossil-derived wastes and discuss their integration with thermocatalytic upgrading and biological gas fermentation. Advances in aerobic and anaerobic microbial assimilation and hybrid abiotic-biotic systems enable the selective conversion of syngas and syngas-derived intermediates such as methanol, acetate and ethanol into a broad spectrum of fuels, chemicals and materials. We argue that syngas-based value chains provide a flexible, carbon-agnostic platform for closing carbon loops across sectors and geographies. Realizing this vision will require (i) further quantitative exploration to identify optimal waste-to-product strategies; (ii) continued innovation in catalyst and bioprocess engineering, continuous operation concepts; and (iii) supportive policy frameworks that incentivize chemical recycling and gas-based carbon utilization as core pillars of the circular economy.