Exploring Future Climate Scenarios: CMIP7 Emissions Trajectories and Policy Pathways
Climate modelling groups worldwide conduct coordinated simulations every six to seven years to predict future climate changes. These simulations are crucial for the Intergovernmental Panel on Climate Change (IPCC) reports. The latest set of scenarios for the Coupled Model Intercomparison Project (CMIP7) has been released, replacing the previous shared socioeconomic pathways (SSPs). The new scenarios focus on emissions trajectories, exploring the implications of current policies continuing, strengthening, or weakening. They also revise high-end emissions downward and increase low emissions scenarios to reflect a shift away from coal use.
The new scenarios are named based on emissions trajectories and explore a range of future outcomes. They no longer include "no-climate-policy" baseline scenarios but instead consider policy continuations, strengthening, or weakening. The scenarios range from low-to-negative to high emissions trajectories. The socioeconomic assumptions underlying these scenarios were updated in 2024, projecting a more crowded and less wealthy world per person compared to previous scenarios. The scenarios are based on updated SSP storylines, with population and economic growth assumptions revised.
The new scenarios eliminate baseline scenarios and explore different policy pathways, including strengthening, weakening, or maintaining current policies. The high scenario explores a rollback of current mitigation policies, while the medium scenario extends existing climate policies without assuming countries achieve their Paris Agreement pledges. The low scenario envisions rapid policy strengthening to limit warming to below 2°C, while the very-low scenario aims to limit warming to around 1.5°C by 2100 with some overshoot.
The scenarios also include paths where mitigation is delayed but followed by rapid action later in the century. The scenarios do not have specific likelihoods assigned but are considered plausible futures based on current trends. The new scenarios are designed to be emissions-driven for CO2, matching observations up to 2023, and extended to 2150 to explore long-term warming outcomes. They involve significant carbon dioxide removal (CDR) to achieve emissions reductions, with varying degrees of reliance on engineered and land-based removal methods.
The new scenarios present a narrower range of future CO2 emissions compared to previous scenarios. The high scenario in CMIP7 projects lower warming levels than previous high-end scenarios, reflecting changes in climate policy, technological advancements, and emission trends. The scenarios show a shift towards lower emissions trajectories and explore a range of warming outcomes up to 2150. The scenarios highlight the importance of CDR in achieving emissions reductions and limiting future warming.