Net-zero emissions energy systems: What we know and do not know

Addressing climate change requires ambitious transformations, including ambitious transformations of energy systems. This will likely entail the design and implementation of "net-zero emissions systems," which are energy systems that emit no net CO2 and potentially no net greenhouse gases. Interest in net-zero emissions energy systems has grown in recent years as countries, subnational jurisdictions, and other entities set net-zero goals. However, guidance on designing and preparing for these systems, along with their environmental, economic, and social implications, is largely missing. This paper provides a perspective on the current understanding of net-zero emissions systems and guidance for policy- and decision-makers on key characteristics of these systems. We highlight robust insights emerging about net-zero systems and unknowns about technologies, markets, policies, and sociotechnical systems. Although certain characteristics of these systems are common across analyses (e.g., decarbonized power systems, electrification of many end uses, declining fossil fuel consumption), a great deal of uncertainty remains, especially since each country's future system faces challenges with resource availability, cost, scalability, public acceptance, and interactions with other parts of the energy system and society.