The European Union (EU) aims for net-zero greenhouse gas (GHG) emissions by 2050, as outlined in the European Green Deal and the EU Long-term strategy. While the goal is accepted, implementation remains debated. Policy measures for emission reductions vary across member states and can include bans, taxes, subsidies, or standards. The availability of crucial technologies (CCS, wind, nuclear, bioenergy) depends on technological progress, social acceptance, and political feasibility. While the impact of individual technology options on climate mitigation is well-studied, comprehensive analyses integrating technology options, policy measures, and behavioral changes across sectors are less common. This study addresses this gap by examining the interplay of these three dimensions in achieving net-zero emissions. The study employed an iterative stakeholder dialogue process involving representatives from business, government, civil society, and science to identify relevant transformation measures in key sectors (buildings, industry, transport, and land). These measures were grouped into three dimensions: (i) technology and innovation, (ii) political coordination, and (iii) behavioral change. These dimensions represent different perspectives emphasized by various stakeholders. This process led to a set of scenarios agreed upon by stakeholders, representing diverse approaches to the transformation challenge.

The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) highlights the importance of multi-sectoral approaches in achieving net-zero CO2 emissions consistent with a 1.5°C warming limit. Existing literature extensively explores the impacts of technology options on climate change mitigation strategies. However, studies comprehensively integrating the interplay of different policies and behavioral changes across all sectors are less frequent. This study aims to address this research gap by combining technology options, policy measures, and behavioral changes within a coherent scenario framework. The importance of multi-stakeholder engagement in climate change mitigation is also highlighted in the literature, with improved stakeholder dialogues being crucial for creating realistic and politically feasible scenarios.

The study uses the REMIND-MAgPIE model, a state-of-the-art multi-regional energy-economy-land model with global coverage. The model was extended to represent the transformations and derive deep decarbonization pathways for the EU, consistent with the net-zero strategy and a global 1.5°C limit. Five scenarios were developed in collaboration with stakeholders based on two possible realizations for each of the three dimensions: 1. **Technology and Innovation:** "Focus on GHG mitigation" (all mitigation technologies available) vs. "Focus on social acceptance" (technologies with limited public support restricted). 2. **Political Coordination:** "Market-oriented" (cross-sector CO2 price) vs. "Sector-oriented" (CO2 price plus targeted sector policies). 3. **Behavioral Change:** "Price-oriented" (behavior driven by price signals) vs. "Value-oriented" (shift towards sustainable consumption). These combinations yielded five scenarios: Policy Steering, Behavior-Oriented, Technology-Oriented, Acceptance-Oriented, and Market Economy. The scenarios were designed to be globally consistent with the 1.5°C target and the EU's net-zero goal. The REMIND model represents 15 sub-regions, including a detailed EU region. The MaGPIE model, coupled with REMIND, models land use and agricultural systems, considering biophysical and socio-economic constraints. The models account for various technologies, including carbon capture and storage (CCS) and bioenergy, and their respective costs and limitations. The model also accounts for sector-specific policies, such as bans on internal combustion engines and changes in dietary habits. The models are iteratively run to ensure consistency between bioenergy demand and supply and emissions.

The study's key findings include: * **High Carbon Prices are Necessary:** Across all scenarios, achieving GHG neutrality requires significant and immediate emission reductions. However, scenarios without behavioral change and with technology restrictions (e.g., limiting CCS) are unable to reach the net-zero target, even with a relaxed target of 200 Mt CO2/yr in 2030. Achieving this relaxed target necessitates CO2 prices ranging from €125/tCO2 to over €450/tCO2 in 2030. * **Impact of Sector Policies:** Scenarios with targeted sector policies (e.g., banning internal combustion engines) show significantly lower carbon prices compared to market-oriented scenarios relying solely on carbon pricing. These policies accelerate the uptake of electro-mobility and phase out fossil fuels in the transport and buildings sectors, leading to more direct electrification. * **Technology Availability Reduces Carbon Prices:** Limiting technologies with perceived low public support (e.g., CCS, nuclear) increases the necessary CO2 price substantially. The availability of CCS is crucial for managing residual emissions and reducing the required carbon price. Increasing CCS deployment and bioenergy production (requiring land) reduces the CO2 price, highlighting a trade-off between technology acceptance and land use. * **Behavioral Change is Crucial:** Incorporating value-oriented behavioral changes (shifts towards sustainable consumption) significantly reduces the required carbon price and residual emissions, particularly non-CO2 gases. This leads to lower energy demand and positive environmental impacts. However, influencing consumer behavior broadly remains a challenge. * **Carbon Dioxide Removal (CDR) is Essential:** None of the scenarios achieve the climate target without CDR. Residual emissions require significant CDR (740-1180 MtCO2eq/yr by 2050), primarily through BECCS and DACCS. Limitations on CCS constrain CDR options, increasing the need for emission reductions from other sources, such as through behavioral changes. * **Trade-offs Exist:** Policymakers face trade-offs between technology acceptance (e.g., CCS), high carbon prices, behavioral changes, and the extent of CDR deployment. The study highlights the complexities of balancing economic costs, environmental targets, and social acceptance.

The study's findings underscore the critical interplay between technology availability, policy design, and behavioral changes in achieving net-zero emissions. The results demonstrate that relying solely on carbon pricing is insufficient; complementary policy measures and significant behavioral shifts are crucial for achieving climate targets without exceptionally high carbon prices, which could have negative socio-economic consequences. The significant impact of value-oriented behavioral changes highlights the potential for societal shifts in consumption patterns to contribute significantly to emission reductions. The model's trade-off analysis illuminates the challenges in balancing technological choices with land-use implications and public acceptance. The study contributes significantly to the understanding of the complexities inherent in designing effective climate policies and suggests that achieving net-zero emissions requires a multifaceted strategy involving technological innovation, robust policies, and widespread behavioral transformation.

This research demonstrates the complementary nature of technology availability, sector policies, and behavioral changes in achieving net-zero emissions in the EU. The results highlight the necessity of a multi-pronged approach, acknowledging trade-offs between costs, technology choices, and social acceptance. Future research could focus on more detailed analysis of the distributional effects of various policy options and further exploration of methods to incentivize large-scale behavioral changes.

The study uses a global model with limited spatial resolution; thus, findings represent aggregate EU values, lacking country-level detail. The model assumes a first-best solution without market failures. Technology costs and future price developments are subject to uncertainty. Further research could explore these aspects in more detail.