Exploring the conditions and implications of deploying direct air capture at scale

International audience BECCS has been widely studied in IAMs (Minx et al., 2017), but recent efforts have been made to consider other CDR solutions, including DAC. Our literature review on DAC modelling in IAMs highlights that DAC has been studied for costs below $500/tCO2 essentially, while some have expressed skepticism that DAC can be cheaper than $600/tCO2 (Herzog, 2022). It is also generally unclear how the models consider energy consumption and intermittency, i.e., whether dedicated renewable assets are installed – with or without batteries, or DAC units being connected to the grid. In terms of policy, a global emission trading system (ETS) is generally assumed, but one could expect that it will never happen on a global scale.In view of these shortcoming in DAC modeling, we employ and enhance the MIT Economic Projection and Policy Analysis (EPPA) (Chen et al., 2022) model by implementing different DAC technologies that either generate negative emissions or provide pure CO2 as a raw material for Fischer-Tropsch processes to produce fuels. In this top-down model, DAC can be operated either through grid electricity or dedicated renewables with batteries. With DAC available in 2030, we use a scenario targeting net-zero GHG emissions by 2070, which keeps the increase in global average temperature to below 1.5°C according to the projections of the MESM (MIT Joint Program, 2021). All GHGs are included in this target except land-use CO2 emissions, which fall to near-zero by 2070. We compare two climate policy settings related to the trading of GHGs: (1) GHGs can be traded across regions and across GHGs starting from 2030 (GT) and (2) GHGs are not tradeable across regions but are across GHGs (NoGT).To these climate policy scenarios, we apply sensitivity tests for the cost of DAC and the impact of limited BECCS capacities (BECPen). We set the High, Medium, Low and VeryLow cost cases referring to a cost of DAC approaching respectively $860-1000/tCO2, $420-570/tCO2, ~$250-400/tCO2, and ~$180-330/tCO2. The range display within a cost case refers to regional energy costs.Our results show that DAC is not deployed in the High cost case; the top right figure shows the variations across cost cases.For a medium cost, DACCS is slightly penetrating the generation mix of negative emissions, proving competitive only in Africa and Indonesia and providing 1.3% of total global negative emissions. At this level, DAC is not deployed at scale. Assuming a low cost, DACCS contributes by generating 44% of the cumulative amount of negative emissions, or 435 GtCO2 over the century, especially deploying in Africa and other regions having affordable access to large renewable potentials. For a very low cost of DACCS, it finally overcomes BECCS: 875 GtCO2 of negative emissions are produced through 2100, and Africa clearly dominates the market due to its large and cheap renewable electricity. We observe the same in Indonesia and Brazil. Thus, employing dedicated renewables for DACCS presents and opportunity to generate massive amounts of negative emissions late in the century.Synthetic fuels generation with DAC remains small, even in the very low cost case, utilizing less than 0.7% of the total amount of carbon captured from the air over the century. This represents 6.1 GtCO2 turned into 1 EJ of synthetic fuels, of which 93% is generated between 2095 and 2100.Whether produced by BECCS or DACCS, the trade of negative emissions depends on a high level of international cooperation and the establishment of an emissions trading system (ETS) that is maintained over the century. When turning off the ETS in EPPA with Medium DAC cost (bottom right figure), we observe important changes in the deployment of DACCS, which now appears essential in achieving the climate target, especially for countries like China (CHN), India (IND), Korea (SKO), Japan (JPN), and the Middle East (MES) either because BECCS cannot fulfill their own demand for offsets, or because DACCS is more competitive than BECCS. China and India alone generate 73% of global negative emissions from DACCS in that case, and globally the cumulative amount of negative emissions from DACCS increases significantly (from 12 GtCO2 with international emissions trading to 300 GtCO2 without trading).Moreover, with DAC available for Medium cost case and no GHG trading system (NoGT), big economies like China, India, and Japan, could rely massively on DACCS to reach climate neutrality at a much more affordable price compared to a scenario where global GHG trades are allowed.