Global Carbon Emission Pathways and Surface Temperature Projections under Carbon Neutrality Scenarios : A System Dynamics and MAGICC Modeling Approach

Sammanfattning

The Paris Agreement has established the need to limit global warming to well below 2 °C and pursue efforts to limit warming to 1.5 °C above pre-industrial levels. Achieving this goal requires rapid reductions in carbon dioxide and other greenhouse gas (GHG) emissions and the development of pathways toward carbon neutrality (CN). Carbon dioxide emissions are important because they are closely connected to several human activities and processes that contribute to climate change. This study explores global carbon dioxide emissions and surface temperature outcomes under a baseline scenario and three carbon neutrality scenarios for 2050, 2060 and 2070. A system dynamics model was used to simulate emissions from 2000 to 2100, focusing on energy consumption, cement production, land-use and carbon capture. The baseline scenario was based on historical trends and observed data, while the carbon neutrality scenarios were created by adjusting key mitigation parameters. The simulated emission pathways were then used as inputs in the Model for the Assessment of Greenhouse Gas Induced Climate Change (MAGICC) climate response model to project global mean surface temperature outcomes. Since the simulated model focuses on carbon dioxide, non-CO₂ greenhouse gases were represented using exogenous Intergovernmental Panel on Climate Change (IPCC) Shared Socioeconomic Pathway 2-4.5 (SSP2-4.5) trajectories, reflecting a current development pathway. The results show that the baseline scenario does not meet the Paris Agreement’s temperature targets. Instead, carbon emissions continue to increase under current historical trends, leading to a surface temperature outcome of around 3.175 °C by 2100. The results suggest that earlier carbon neutrality pathways are more consistent with limiting warming to around 2 °C, with CN-2050 reaching around 1.848 °C, CN-2060 reaching around 1.938 °C and CN-2070 reaching around 2.046 °C by 2100. The 2 °C target remains within reach in the CN-2050 and CN2060 scenarios, while the CN-2070 scenario slightly exceeds 2 °C by the end of the century. None of the pathways reach the 1.5 °C target, suggesting earlier carbon neutrality leads to lower long-term warming, while delayed carbon neutrality results in higher cumulative emissions and higher temperature outcomes. Reaching carbon neutrality for each of the target years required major expansion of non-fossil energy and carbon capture capacity. The required carbon capture capacity in the modeling reaches approximately 24,955.1 Megaton (Mt) CO₂/year in CN-2050, 27,675.1 Mt CO₂/year in CN-2060 and 30,595.1 Mt CO₂/year in CN-2070. This scenario implies a capacity that is far beyond current and near-term development of carbon capture and should be interpreted as exploratory outputs rather than realistic forecasts. The comparison with SSP1-1.9 and SSP2-4.5 demonstrate that the carbon neutrality scenarios move closer to low-warming pathways. Achieving carbon neutrality for CO₂ alone may not be sufficient to meet the 1.5 °C pathway when non-CO₂ greenhouse gases remain weakly mitigated partly due to continued non-CO2 GHG emissions and differences in land-use emission trajectories. The baseline scenario shares similarities with the SSP2-4.5 scenario until 2060 and then also diverges because of different land-use emission assumptions. Overall, this study shows that combining a system dynamics approach with climate modelling can be used to explore the long-term implications of carbon neutrality pathways for limiting future warming.