We examine how science, conservation, and management of park resources have changed over the past century since the birth of the US National Park Service, and how climate change may require shifts to conservation and management paradigms during the second century of national parks. We first review the state of science and conservation at the time the Organic Act was passed in 1916. Within a month of passage, Grinnell and Storer argued for science-based management of national parks and for parks to be free from human impacts on nature. Nevertheless, Mather chose to invest in infrastructure and no park scientists would be hired until 1928. The fall and rise of science in the US National Parks would be repeated several times during the 20th century before expansion in the 21st century. We then examine the key issue facing the future of parks throughout the world: how to steward them through the rapid environmental and cultural changes taking place. Success may require the dominant paradigm of 20th century conservation—“manage to maintain current and historic baseline conditions”—to be co-mingled with two other paradigms: “manage for natural processes and trajectories of change” and “manage proactively for projected future conditions.”