Cost of reversing climate change as a CO2 mitigation strategy - using a cost optimization framework in the U.S. electricity sector

Partial reversal of climate change using negative emission technologies such as direct air capture with storage (DAC) is deemed essential to limit global temperature increase below 2⁰C compared to preindustrial levels. We present recent findings on the scale and role of DAC to reduce CO₂ emissions from the U.S. electricity sector by 70% in 2050 compared to 2010. Least-cost technology and emission trajectories are generated with a linear optimization model that minimizes the total cost of installing, operating, and retiring electricity generating units and DAC between 2015 and 2050 to meet the 70% target. Results show that economics-driven natural gas transition under the business-as-usual (BAU) scenario without emission consideration is insufficient to meet the 70% target. More aggressive CO₂ reduction measures including early retirement of older fossil plants and expansion of low-carbon facilities are required. If these measures can take place before 2030, the 70% target could be met without DAC. Continuing BAU trajectories beyond 2030 would necessitate the deployment of DAC. DAC-based strategies are inherently more expensive as the same aggressive measures need to be implemented in an accelerated manner in addition to deploying DAC and further expanding low-carbon capacities to power DAC. DAC-based trajectories would cost additional 580-2,015 billion USD through 2050 compared to starting CO₂ reduction immediately. This translates to about 100-345 million USD of additional cost per day of delay. Further delays in CO₂ reduction beyond 2035 would require so much DAC deployment to be infeasible, making 70% reduction goal out of reach for most uncertainty scenarios we investigated. Hence, minimizing the cost of CO₂ mitigation hinges on the timing of aggressive CO₂ reduction; if the aggressive reduction beyond BAU trajectories can take place early enough, the 70% target could be met without relying on DAC.