Assessing the Need for Direct Air Capture in the Context of the Shared Socioeconomic Pathways

Abstract:

Limiting warming to 1.5 or 2°C by 2100 will require drastic emissions reductions, combined with large-scale CO₂ removal to reach net-zero or net-negative emissions globally. Here, we use the Global Change Assessment Model (GCAM) to evaluate the impact of shared socioeconomic pathway (SSP) assumptions on the need for direct air capture and other negative emissions technologies in deep decarbonization (i.e., 1.5 or 2°C compliant) pathways. We demonstrate that direct air capture with carbon storage (DACCS) can begin contributing to climate mitigation at Gt-CO₂ scales before mid-century, preconditioned upon policies consistent with actually meeting the long-term warming targets. DACCS can reduce the sharpest tradeoffs of land-intensive negative emissions technologies such as bioenergy with carbon capture and storage and afforestation, but drives large additional energy and water demand. Much of the requirement for negative emissions is driven by the need to offset emissions from difficult-to-decarbonize sectors such as long-distance shipping and aviation, which currently rely on liquid hydrocarbon fuels and are difficult to electrify. We therefore incorporate a new technology into GCAM: direct air capture with carbon utilization (DACCU), in which CO₂ captured from the atmosphere is used to produce ultra-low carbon hydrocarbon fuels, and harmonize the assumptions regarding its future adoption with the SSPs. We find that under more sustainable development pathways (e.g., SSP1), the need for DACCS and other negative emissions can be substantially reduced. Scenarios with higher reliance on fossil-fueled development (e,g., SSP5) and/or lesser degrees of international cooperation (e.g., SSP3) see much higher reliance on DACCS to meet the long-term warming targets. When constraints are imposed on the use of DACCS and bioenergy for negative emissions, DACCU could play an important role in meeting the 1.5 and 2 °C goals.