The DOE Parallel Climate Model (PCM) is used to simulate the earth’s climate system and has been used to study the climate of the 20^th century and to project possible climate changes into the 21^st century and beyond. It was designed for use on distributed memory, highly parallel, architectures. The computational requirements and design of the model are discussed, as well as its performance and scalability characteristics. A method for port validation is demonstrated. The shortcomings of the current model are summarized and future design plans are presented.