The Earth System Science (ESS) department at the University of California, Irvine, aims to improve undergraduate recruitment and retention in a strategic and data-driven way. The department goals are to increase the overall recruitment of students into our majors, increase the retention of students within our majors, and improve the applicability of the curriculum for students within the department. ESS offers two majors: a BS in Earth System Science and a BA in Environmental Science and Policy, both focused on different aspects of the climate system and sustainability. Our department therefore provides a unique opportunity to study the population of students that chooses a BS degree over a BA, as well as to track the success of individuals that choose each degree type. In doing so, we hope to better understand the population of students that comprise the ESS department, develop courses and major requirements based on our student's interests and future career goals, and increase the accessibility of our major to students traditionally underrepresented in the STEM fields. In this work we present analyses of the influence of demographic factors, such as gender, socio-economic status, ethnicity, and first-generation status, on major choice and retention We also present research on career-self efficacy and address specific changes to curriculum and career readiness training, aimed to improve the accessibility and relevance of our majors to all students, with particular emphasis on those who are traditionally underrepresented in the STEM fields.