PNNL

Abstract

The Paris Agreement is viewed as an important step in establishing a robust, durable and long-term framework to combat climate change1. Indeed, not only did the Agreement bring together countries to articulate near-term emissions reduction strategies through 2025 or 2030 by communicating nationally determined contributions (NDCs), Article 4.19 of the Agreement also invites countries to “to formulate and communicate long-term low greenhouse gas emission development strategies...”2. In response to Article 4.19, many countries have either submitted or are in the process of formulating their mid-century strategies3. In this context, a key question for decision-makers is to what extent the NDCs set the stage for deeper reductions in the future. Most NDCs set high level goals – such as limits on emissions or emissions intensity4 – which do not provide information about the extent to which they lay the foundations of technology, infrastructure and institutions in the near-term to set the stage for deeper reductions in the future. Additional metrics are required to provide that guidance, which is in turn essential in evaluating the challenges of achieving longer-term mid-century goals and their relationship with the near-term NDCs. We illustrate the usefulness of additional metrics beyond emissions alone by considering the U.S. NDC and its mid-century strategy. Using a state-level model of the U.S. embedded within a global integrated assessment model5,6, we demonstrate that although the U.S. NDC lies on a straight-line emissions pathway toward its the mid-century strategy, the resulting energy system transitions involve non-linear transformations. Rates of capacity additions and capital investments in electricity generation beyond 2025 are more than three times the rates during the next decade. Our results demonstrate the need for global stocktaking exercises to evaluate the NDCs using metrics broader than emissions to better illuminate the effectiveness of the NDCs in addressing the Paris Agreement’s long-term goals7,8.