Author's Summary: Many modeling studies depend on direct air capture (DAC) in their 1.5°C stabilization scenarios. These studies rely on assumptions that are overly optimistic regarding the cost and scaling-up of DAC systems. This can lead to highly misleading results that can ultimately impact the ability to reach climate stabilization goals.

Abstract: Despite the commitments to the Paris Agreement’s goal of pursuing efforts to limit the global temperature increase to 1.5°C, the world exceeded this target for most if not all of 2023, raising questions about its longer-term feasibility. Most modeling studies rely on carbon dioxide removal (CDR) or negative emission technologies, such as direct air capture (DAC), bioenergy with carbon capture and storage (BECCS) and afforestation/reforestation, to keep long-term temperature targets in reach.1 DAC, in particular, has drawn substantial interest in recent years because it can generate high-quality carbon removal credits. Specifically, (1) the removal is immediate as opposed to over time as in, for example, afforestation/reforestation projects, (2) it is straightforward to measure and verify the “net” amount of carbon removed, and (3) when coupled with geologic storage, the CO2 will remain out of the atmosphere for millennia or more. 

While these advantages are compelling, there are also many practical challenges associated with real-world deployment of DAC that affect its cost and potential deployment, including challenges related to scaling-up, energy usage and siting. However, many modeling studies diminish or neglect these challenges, assuming costs of DAC deployment that do not align with the engineering realities of the technology.

Overly simplified or optimistic consideration of these challenges can lead to highly misleading results related to mitigation and adaptation strategies and their associated costs, and ultimately impact the ability to reach climate stabilization goals.