Designing the mid‐transition: A review of medium‐term challenges for coordinated decarbonization in the United States

Decarbonizing the energy system is critical for addressing climate change. Given the dominance of fossil fuels in the energy system, decarbonization requires rapid and significant industrial transition of the energy supply at scale. This includes explicit and coordinated plans not only for zero carbon phase‐in, but for fossil carbon phase‐out. Even very rapid decarbonization will likely take decades, leading to a medium‐term future where the conventional, fossil‐based energy system coexists with a new, zero‐carbon energy system. Each imposes operational constraints on the other: what we call the mid‐transition. Notably, this coexistence means that the new, zero‐carbon system will develop under fossil carbon system constraints. The mid‐transition will therefore likely require specific analytical metrics designed to support decision making under dynamic and uncertain conditions. Many aspects of transition will be felt, and shaped, directly by individuals because of our direct interactions with energy systems. Even rare missteps are likely to have significant and potentially system design‐relevant impacts on perception, political support, and implementation. Comparisons of the new system to the old system are likely to rest on experience of a world less affected by climate change, such that concerns about lower reliability, higher costs, and other challenges might be perceived as inherent to zero‐carbon systems, versus energy systems facing consequences of climate change and long‐term underinvestment. This review assesses and evaluates medium‐term challenges associated with the mid‐transition in the United States, emphasizing the need for explicit planning for joint and coordinated phase‐in and phase‐out.