Deployment expectations of multi-gigatonne scale carbon removal could have adverse impacts on Asia's energy-water-land nexus

The Paris Agreement's 1.5°C warming limit is at risk due to current emission rates. Immediate decarbonization (renewables, electrification, energy efficiency) is crucial, but insufficient to achieve net-zero emissions. Carbon dioxide removal (CDR) technologies, such as bioenergy with carbon capture and storage (BECCS) and direct air capture with carbon storage (DACCS), are gaining importance as a method to achieve net-zero emissions. While CDR is vital for net-zero targets, over-reliance could negatively impact the global energy-land-water system. BECCS is land and water-intensive, while DACCS is energy-intensive and may increase emissions. Studies suggest over 10 GtCO2yr-1 of gross CDR might be needed by mid-century to limit warming to below 1.5°C. This study quantitatively assesses the potential damage to Asia's energy-land-water system from a multi-gigatonne CDR deployment by mid-century. Four scenarios are modeled using a modified Global Change Assessment Model (GCAM-TJU): HIGH (high CDR reliance), MODERATE (moderate CDR reliance with BECCS limited to 1.8 GtCO2yr-1), LOW (low CDR reliance with only afforestation/reforestation), and REFERENCE (no new climate policies). The study addresses the scarcity of quantitative studies on the energy-land-water trade-offs of varying CDR reliance levels, the treatment of emission reduction and CDR as interchangeable, the lack of focus on the Asian region, and the limited analysis of land and water implications under various CDR scenarios.

The literature on the adverse impacts of high reliance on CDR has primarily been philosophical, theoretical, and qualitative. Policy formulation often treats conventional emission reduction and CDR as equivalent, delaying urgent emission cuts. There are calls to separate CDR and emission reduction targets, a strategy this study adopts by modeling pathways where CDR scales only to the specified amount without undermining emission cuts. Previous studies limiting CDR often decreased carbon capture and storage (CCS) or biomass supply; this study explicitly sets caps on CDR without affecting CCS and biomass supply for other activities. Existing quantitative studies on the impact of high CDR are mostly global and primarily focus on the energy system, with limited analysis of land and water implications in specific regions like Asia, where a significant share of future CDR could be concentrated without equity considerations. Previous studies predominantly model land-based CDR approaches globally, overlooking limitations in countries with land and biomass constraints.

This study uses a modified version of the Global Change Assessment Model (GCAM-TJU), incorporating six CDR approaches (afforestation/reforestation (AR), biochar, BECCS, DACCS, direct ocean removal and carbon storage (DORCS), and enhanced rock weathering (ERW)). Four scenarios are explored: HIGH (all six CDR approaches deployed without limits), MODERATE (BECCS and AR deployed, with BECCS limited to an annual average of 1.8 GtCO2yr-1), LOW (only AR deployed), and REFERENCE (no new climate policies). The central pathway targets net-zero GHG emissions in Asia by mid-century, with 2030 GHG emissions 45% lower than 2019 levels. The model assesses impacts on energy demand (primary and final), abatement costs, emissions (positive and negative), net-zero timing, air pollutants, land allocation, water consumption, and fertilizer demand. The SSP2 baseline (middle-of-the-road scenario) is used. The study modified the core version of GCAM to include three additional CDR methods beyond those included in the standard version. The selection of BECCS in the MODERATE scenario is due to its prominence in IAM studies, low cost, high technological readiness, and ability to provide low-carbon energy. The study includes a sensitivity analysis to validate the robustness of the findings. The study's rationale for focusing on Asia stems from the region's significant population, primary energy consumption, GHG emissions, and potential role in global CDR deployment, particularly in the context of the Paris Agreement's 1.5°C target and the existing net-zero emission deadlines announced by various Asian countries.

High CDR reliance risks perpetuating fossil fuel consumption, delaying the transition to cleaner alternatives. By 2050, unabated fossil fuel consumption in Asia could exceed 30% under the HIGH scenario, compared to less than 10% under MODERATE and LOW scenarios. Additional coal and natural gas consumption is projected under HIGH CDR. Final energy consumption is only 5% lower in the HIGH CDR scenario than in the REFERENCE scenario in 2050. Under MODERATE and LOW CDR scenarios, final energy consumption shows reductions of 35% compared to the REFERENCE scenario. The marginal abatement cost of carbon is higher in MODERATE and LOW scenarios than in the HIGH scenario, indicating that while CDR technologies are expensive, they delay the urgent need for emission reductions. Spatially, countries like China and India could have 17% and 27% of their primary energy from renewables under the HIGH CDR scenario, compared to 33% and 45% under the MODERATE scenario, respectively. Electrified transport share is significantly lower under HIGH CDR, especially in China and India. Total positive GHG emissions in 2050 are lower in MODERATE and LOW CDR scenarios than in the HIGH CDR scenario. Under the HIGH CDR scenario, significant residual fossil fuel and industry emissions remain by 2050. The HIGH CDR scenario leads to higher air pollutants. The choice of CDR approaches varies across Asia: DACCS may be favored in resource-rich, fossil fuel-intensive economies, while BECCS might be more suitable in countries with abundant biomass. Under the HIGH CDR scenario, several Asian countries might opt for purchasing foreign CDR instead of achieving domestic net-zero emissions before 2050; this is economically less attractive under MODERATE and LOW CDR scenarios. High CDR reliance increases annual bioenergy crop-land allocation but reduces other agro-land allocation (excluding biomass), increasing water consumption and fertilizer demands. South Korea exhibits the highest change in land allocation for cultivating bioenergy crops, while Taiwan shows the lowest change. Cumulative stranded capacity of fossil fuel power plants is higher under LOW and MODERATE CDR scenarios (1260 GW and 1305 GW respectively) than under HIGH CDR (1100 GW). Coal power plants face the highest risk of stranding, while solar power shows the highest percentage in newly installed capacity.

Over-reliance on CDR in Asia delays decarbonization, leading to continued carbon lock-in and higher residual emissions. Achieving domestic net-zero becomes more expensive under high CDR reliance, leading some countries to consider purchasing foreign CDR. Lower CDR reliance makes domestic net-zero more economically attractive. Minimizing CDR reliance offers co-benefits for air pollutant reduction. High CDR reliance increases land allocation for bioenergy, reduces other agro-land, and raises water and fertilizer demands. While some CDR is essential for hard-to-abate sectors, prioritization of decarbonization is paramount. Conventional methods like afforestation should be prioritized before scaling up novel CDR options. The study underscores the need for ambitious policies that prioritize near-term decarbonization while strategically integrating moderate CDR to offset residual emissions, adhering to ethical principles and development goals.

The study emphasizes the risks of over-reliance on CDR, advocating for policies that prioritize emission reduction strategies while viewing CDR as a complementary approach. Separate CDR and emission reduction targets are recommended to prevent substitution. While decarbonization is the primary focus, moderate CDR integration can offset residual emissions, provided the deployment aligns with ethical considerations and development goals. Further research should focus on the equity implications of CDR deployment in Asia and on the development of robust policy frameworks to encourage both decarbonization and responsible CDR implementation.

The study relies on a specific model (GCAM-TJU) with its inherent assumptions and limitations. The scenarios are stylized representations of potential future pathways, and actual CDR deployment might differ. The analysis focuses on Asia, and results may not be directly generalizable to other regions. The model's representation of societal and technological changes might not fully capture the complexity of real-world transitions. Uncertainties around the scalability and cost-effectiveness of various CDR technologies are acknowledged.