Environment and Society, Data Science for the 21st Century (DS421) is a new National Science Foundation Research Traineeship interdisciplinary graduate training program at UC Berkeley at the interface of data, social, and natural sciences. Environmental change is accelerating, driven by growth in population and consumption and the inexorable impact of CO2 emissions on global climate. At the same time, advances in technology are generating an explosive flood of data, fueling the emerging field of data science and the need for all researchers and educators to become fluent with new concepts and tools that are driving discovery. The DS421 program will train a new generation of scientists to tackle grand challenges at the intersection of natural, social, and data sciences, translating data into evidence-based analysis of impacts and solutions in the face of rapid environmental change.