Given the limited potential for renewable energy and high population density of South Korea, nuclear has been an essential electricity generation option for supply of reliable power whilst reducing greenhouse-gas emissions and mitigating air pollution. However, the recently elected (2017) South Korean government has a policy committing them to a phase-out of nuclear and coal, offset by an increase in the share of variable renewables. However, the main component of the power transition is set to be liquefied natural gas (LNG), due to technical and economic barriers facing large-scale renewables. It is therefore critical for South Korea to develop an evidence-based perspective on the details of the transition, before any future energy policy is decided. Here we review: i) the national role of renewable sources given technical and economic limitations in South Korea; ii) potential environmental and economic issues with gas; and iii) potential barriers of and benefits to a nuclear pathway. Our conclusion is that, given the geographical and economic limitations facing South Korea, and the need to reduce carbon emissions cost effectively, a nuclear pathway coupled with a moderate renewable share offers the most viable policy, with a gas-focused energy future being neither environmentally friendly nor economic.