Accelerated and Delayed Climate Action for Energy Transition under Carbon Budgets

First iteration of modelling to support CCAC CBWG

CORE SCENARIO ASSUMPTIONS

Two different Carbon Budgets (CB) for the period 2021-2050 are modelled based on the IPCC assessment of the global Remaining Carbon Budget (RCB). The analysis focuses on the RCBs aligned with global temperature increases of up to 2°C. These CBs for Ireland are as follows:

• 400Mt aligned with 67% likelihood of limiting global warming to 2.0°C (IPCC AR6 1150Gt CO2 RCB)
• 315Mt aligned with 50% likelihood of limiting global warming to 1.7°C (IPCC AR6 900Gt CO2 RCB)

Two distinct demand projection scenarios are also considered:

• Business as Usual (BAU)
• Low Energy Demand (LED)

Combining the CO2 budgets and demand projection pathways generates four following scenarios:

• 400Mt_BAU: This scenario involves a generous 400 Mt carbon budget aligned with 2°C target and represents a demand projection in line with BAU projections.
• 400Mt_LED: It involves a 400 Mt carbon budget and represents a demand projection in line with LED projections.
• 315Mt_BAU: This scenario involves a more stringent 315 Mt carbon budget aligned with a 1.7°C target, reflecting demand projections associated with BAU practices.
• 315Mt_LED: With a 315 Mt carbon budget, it reflects LED scenario.

Accelerated versus Delayed Action

12 additional cases for each core scenario are defined. These alternative cases involve overshooting the carbon budget within the first two periods of 2021-2025 and 2026-2030, with increments of 2.5%. These 12 sensitivity cases investigate overshoot scenarios ranging from 2.5% to 30% during these periods. Consequently, the study investigates four core scenarios, including two carbon budgets and two demand projections. For each of these scenarios, 12 sensitivity cases are also conducted, resulting in a total of 52 pathways. The below figure illustrates the distribution of two carbon budgets across various time periods. For instance, in the 400Mt scenarios with a 15% overshoot, there is a 15% higher carbon budget until 2030, followed by a reduction in the post-2030 period. Conversely, the base 400Mt scenario (i.e., with a 0% overshoot) represents a more constrained budget in pre-2030 periods, offering an accelerated action pathway. As the permissible overshoot increases in the sensitivity cases, expanding the budget for the pre-2030 period, the model allows for more emissions in the initial periods, suggesting a delayed action pathway.