In order for climate literacy assessments to be applicable in large-scale studies, it is essential that they comply with the standards of test administration while maintaining consistency with a comprehensive definition of the concept. In alignment with the different educational frameworks and the Climate Literacy Principles of the U.S. Global Change Research Program, a multidimensional assessment framework was created, and a comprehensive set of items was devised for the first two climate literacy principles, integrating climate knowledge with scientific practices. This paper describes the conceptualization of the climate literacy assessment, the construction of the items, and the investigation of their validity and reliability involving multiple studies with 553 students in grades 10-13. The items presented have been developed for use from the age of 15-16 years and are available from the authors for practitioners to begin assessing climate literacy.