Nuances of Climate Change Mitigation: Four Different Goals and Approaches in the Climate Boxes Framework

Author(s): Jackson, Stacy | Advisor(s): Harte, John; Torn, Margaret | Abstract: The Climate Boxes Framework presented in this dissertation provides a structure to discuss and improve the alignment between policy positions and climate goals. I explore the differences in mitigation paths implied by four different mitigation goals ("boxes"): 1) delaying climate change, 2) avoiding a global temperature increase of 1.5-2°C above pre-industrial levels, 3) avoiding a global temperature increase of 3-4°C above pre-industrial levels, or 4) no delay or avoidance of climate change. The topic of delay is particularly under-explored in the literature, and I devote several chapters to calculations of its potential, possible benefits, and arguments for and against different means of achieving it. Throughout the dissertation, the focus is on identifying the physical and technical constraints that set the bounds on the climate goals that can be achieved via different types of mitigation. For Box 1 (Delay), I calculate that maximum technically feasible reductions of short- and medium-lived pollutants have the potential to delay a given temperature increase by 15 years relative to the current trajectory. Elimination of deforestation would delay a 2°C temperature increase by 20 years relative to the current trajectory. There are many pragmatic reasons for delay, but more research is needed to determine whether there would be lasting climate system benefits from a lower rate of temperature change. For Box 2 (Avoid 1.5-2°C), I present a broad range of emission trajectories (peak year, target reduction, plateau year) that would avoid 2°C with various likelihoods, demonstrating the option to leverage an early emissions peak to make relatively smaller reductions for the period through 2050. For both Box 2 (Avoid 1.5-2°C) and Box 3 (Avoid 3-4°C), I calculate the cumulative CO2 budgets that would avoid each temperature increase in the transient and equilibrium time periods. I also highlight the limitations of the carbon budget theory and identify future research needed to make the theory more robust. I find that if CO2 emissions are consistent with an equilibrium goal of avoiding 2°C, then a transient temperature peak above 2°C is unlikely (25-40% likelihood even with elimination of cooling sulfates). Maximum technically feasible reductions of short- and medium-lived warming pollutants could further improve the likelihood of avoiding a transient temperature peak by 8-11 percentage points. For Box 3 (Avoid 3-4°C), I propose a novel policy approach (the Point One Approach) that would be based on the increments of 0.1°C temperature increase that are currently experienced every 7-8 years.Overall, I demonstrate that whether policies are consistent with "addressing climate change" depends materially on which mitigation goal is being pursued; most policy choices are only consistent with a sub-set of the boxes. This applies particularly to policies related to CO2 targets, short- and medium-lived pollutants, offsets, geo-engineering, fossil fuel expansion, forests, and developing world infrastructure.