The next frontier: Human settlements in the marine environment

Human settlements have impacted most terrestrial environments on Earth. With a rapidly growing global population, surging demands for resources, and unprecedented alteration to Earth's ecosystems, the conservation of our only suitable habitat is a contemporary zeitgeist. Moreover, humanity's nature for enterprise and exploitation continuously pushes the frontiers of exploration, while the governance associated with expansion beyond terra firma is uncertain and rife with conflict. Though the notion of human expansion into the oceans is becoming more orthodox, we have largely overlooked Earth's oceans as space for human habitat. Here, we build on the case for humanity's future in the marine environment and discuss how exploring this frontier will result in advances for industries, economies, and exploration. The “Blue Acceleration” could transform the nascent phenomenon of marine cities into reality, and we support this notion with a global marine spatial plan to assess the suitability of marine settlements. Our analysis shows that every oceanic basin supports regions for sustainable human settlements. More broadly, we discuss the implications of a human-marine frontier and the benefits that will ensue for science, humanity and our planet. Finally, we argue that the human-marine frontier should be an immediate steppingstone for future exploration, innovation and discovery.