Evaluating the near- and long-term role of carbon dioxide removal in meeting global climate objectives

The paper addresses a key gap in the IPCC AR6 assessment: incomplete information on total carbon dioxide removal (CDR) deployment due to inconsistent reporting methodologies for land-sector removals and a lack of separation between gross emissions and removals. Prior analyses often omitted scenarios lacking explicit land removals or used net-negative AFOLU emissions as a proxy, obscuring current removals and near-term land dynamics. To close this gap, the authors compile a comprehensive global and regional assessment of total CDR from AR6 scenarios using a novel dataset of land-based carbon fluxes. They evaluate contributions of gross CO2 and non-CO2 emission cuts, resulting residual emissions, and total CDR across IPCC pathway categories: C1 (limit warming to 1.5 °C with limited overshoot), C2 (return to 1.5 °C after high overshoot), and C3 (limit warming to 2 °C). They distinguish between conventional CDR on land (afforestation and reforestation, currently around 2 GtCO2/yr) and novel CDR (e.g., BECCS, DACCS, enhanced weathering, currently ~2 MtCO2/yr), to quantify their near- and long-term roles in meeting climate objectives and assess regional distributions and fairness/sustainability considerations.

The authors highlight that AR6 did not comprehensively assess total CDR because integrated assessment models reported land CDR inconsistently or did not separate gross land-sector emissions from removals. Existing publications analyzing AR6 scenarios either exclude scenarios without explicit land removals or rely on net-negative AFOLU emissions as a proxy, neglecting current removals and near-term land dynamics. This creates a data and knowledge gap for understanding the mitigation solution space and the trade-offs between gross emission reductions and CDR. The study builds on and contrasts with recent work quantifying CDR deployment and residual emissions and ties into broader discussions on costs, feasibility, and fairness in mitigation portfolios.

The analysis combines two datasets: (1) the IPCC AR6 scenarios database of mitigation pathways, and (2) a new reanalysis dataset that estimates gross land-based carbon dioxide removals by driving the compact Earth system model OSCAR v3.2 with selected scenario variables. Inputs include reported CO2 emissions from AFOLU (Emissions CO2|AFOLU), land cover variables (Land Cover Cropland, Forest, Pasture), and climate assessment information from the simple climate model MAGICC v7.5.3. The reanalysis yields estimates of total CDR on land consistent across scenarios. Results are assessed at the IPCC R5 regional aggregation due to land-cover data availability: OECD90+EU (OECD and EU), REF (Reforming Economies), ASIA, MAF (Middle East and Africa), and LAM (Latin America and Caribbean). The authors categorize scenarios by climate outcomes into three groups used by the IPCC: C1 (limit warming to 1.5 °C (>50%) with limited overshoot), C2 (return to 1.5 °C (>50%) after high overshoot), and C3 (limit warming to 2 °C (>67%)). They decompose mitigation into contributions from gross CO2 reductions, non-CO2 reductions, and total CDR (split into conventional land CDR and novel CDR such as BECCS, DACCS, and enhanced weathering). They evaluate timeframes from 2020 to 2030, to 2050, at global net zero CO2, and to 2100, reporting medians and interquartile ranges. Delayed mitigation is characterized along two dimensions: time to halve net CO2 emissions from 2020 levels and years until global net zero CO2 is achieved. Regional analyses include cumulative gross emissions and CDR pre- and post-net-zero, and relationships with global bioenergy demand at net zero (with 100 EJ/yr discussed as a sustainability threshold). Modelled 2020 values are used, and results reflect model-based LULUCF accounting conventions.

- In 1.5 °C limited-overshoot pathways (C1), 2020–2030 mitigation is dominated by gross CO2 reductions (70% [64, 77] of net GHG reductions) and non-CO2 reductions (20% [16, 24]), with conventional land CDR contributing 10% [5, 14], nearly doubling CDR volumes this decade. - Novel CDR scales by mid-century to around 4 GtCO2/yr [2, 6] by 2050 in C1 pathways to help achieve net zero CO2. - Between 2020 and global net zero CO2 in C1, gross CO2 reductions account for 71% [66, 74] of net GHG reductions; CDR contributes 15% [12, 21]. Across C1–C3, over 80% of net GHG reductions to net zero come from cuts in gross CO2 and non-CO2 emissions. - At the year of global net zero CO2, gross GHG emissions are 18 [16, 21] GtCO2e/yr across scenarios. - Delaying mitigation increases total CDR required before net zero: for net zero by mid-century, cumulative CDR is 166 GtCO2 [149, 193]; for net zero between 2050–2075, 251 GtCO2 [203, 320]; for later than 2075, 445 GtCO2 [345, 524]. Conventional land CDR rises faster when net zero is 2050–2075, while novel CDR rises faster when net zero is 2075–2100. - Beyond global net zero CO2, CDR volumes by 2100 are >3× 2020 levels in C1 pathways and >6× and >4× higher in C2 and C3, respectively. Post-net-zero to 2100, in C1 about 55% [44, 91] (342 GtCO2 [245, 426]) of total CDR balances residual gross CO2; in C2 about 50% [40, 60] (298 GtCO2 [236, 384]). CDR deployed to reverse overshoot is higher in C2 (309 GtCO2 [221, 424]) than in C1 (184 GtCO2 [26, 418]). Novel CDR constitutes about two-thirds of total CDR post-net-zero (66% [58, 79]). - Regional (2020 to net zero): Asia has the highest cumulative gross GHG emissions (410 [351, 443] GtCO2e in C1) and cumulative CDR (66 [53, 100] GtCO2). OECD+EU is second in gross emissions (225 [205, 253] GtCO2e). Median gross CO2/non-CO2 shares are ~70/30 in Asia, OECD+EU, and Reforming Economies; ~60/40 in Latin America and Middle East & Africa. - Regional (post-net-zero to 2100): Middle East & Africa becomes the second-highest gross emitter (160 [121, 190] GtCO2e in C1), slightly above its 2020–net-zero gross emissions (156 [128, 176] GtCO2e). Asia remains highest (255 [203, 328] GtCO2e). Latin America is typically net negative (median) and has a roughly even split of conventional vs novel CDR post-net-zero (conventional shares: 49% [38, 56] in C1; 41% [29, 49] in C2; 45% [32, 57] in C3). - Time-varying regional roles: In Asia (C1), gross CO2 reductions contribute about 80% (median) of mitigation across time periods; in C2/C3, CDR exceeds 20% beyond 2050. In OECD+EU, removals after 2050 contribute medians of ~43% (C1), 48% (C2), and 35% (C3). In Latin America (C1), CDR contributions are 18% [14, 28.5] (2020–2030), 32% [22, 42] (2030–2050), and 79.5% [49, 136] (2050–2100). - Sustainability constraints influence deployment: lower global bioenergy demand at net zero is associated with slightly higher conventional land CDR and markedly lower novel CDR before net zero. There is a weak correlation between global bioenergy demand at net zero and cumulative total CDR, especially above 100 EJ/yr, partly because IAMs assume rising yields for second-generation biofuel crops. - Cost and feasibility: Novel CDR options have high costs and long lead times (e.g., capital and OPEX for DACCS; mining/transport for enhanced weathering), while conventional land CDR has higher near-term potential but faces land competition and permanence risks under climate change.

The findings demonstrate that achieving near-term climate objectives primarily relies on deep cuts in gross CO2 and non-CO2 emissions, with conventional land CDR providing a meaningful but secondary contribution before global net zero. Delays in mitigation increase both the volume of CDR required and the reliance on novel, currently unproven technologies, raising intergenerational fairness and feasibility concerns. After global net zero CO2, CDR becomes the dominant lever to balance residual emissions and to deliver post-peak cooling, with novel CDR comprising about two-thirds of total removals. Regional assessments reveal heterogeneous portfolios: Asia and OECD+EU bear large gross emissions and CDR contributions pre-net-zero, Middle East & Africa emerges as a major post-net-zero emitter, and Latin America often provides net-negative emissions with sizable shares of conventional and novel CDR. The study underscores the importance of balancing portfolios across conventional and novel CDR options while integrating broader sustainability and equity considerations, since cost-effective allocations in models may not align with principles of fairness and common but differentiated responsibilities. These insights refine understanding of the mitigation solution space by consistently quantifying total CDR alongside gross emission reductions across pathways and regions.

This work provides the first comprehensive assessment of gross emission reductions and total CDR in AR6 mitigation scenarios using a dataset that separates land-use sector net emissions into gross emissions and removals. Over 80% of net GHG reductions between 2020 and global net zero CO2 come from deep cuts in current emission sources, with conventional land CDR playing an important near-term role, especially in Latin America and Asia. In the medium to long term, novel CDR becomes more important, but remains nascent, costly, and unevenly deployed across regions, raising fairness concerns. Results align with model-based LULUCF accounting and may differ under UNFCCC accounting, highlighting the need to translate between conventions. Addressing sustainability limits and equity requires rapid scaling of mitigation investments and assessments of fair shares of mitigation finance consistent with Paris Agreement principles.

- Scenario literature and this assessment may not comprehensively represent climate-related feedbacks and risks (e.g., sink strength changes, droughts, wildfires) that could reduce land-based CDR potentials. - Results follow model-based LULUCF accounting conventions; outcomes may differ from UNFCCC Party accounting conventions. - Regional analysis is constrained to coarse R5 regions; findings should be interpreted cautiously when applied to individual countries. - Novel CDR options are at early stages, expensive, and face deployment uncertainties; conventional land CDR faces land competition and permanence risks under future climate change. - Cost-effective scenario allocations do not incorporate equity and responsibility considerations, potentially misaligning modeled deployments with fairness principles.