For much of modern history, climate has been predictable enough to have worked its way into the very culture, industry, and infrastructure of our society. It would make little sense to support a ski industry in Colorado if not for the expectation of snow, and it would make little sense to support a vacation industry in Florida if not for the expectation of sun. Expected climate conditions are the basis for the nation's farming, transportation, and water management practices, among many others.
But Earth's climate system is, in a word, complicated. It incorporates thousands of factors that interact in space and time around the globe and over many generations. For several decades, scientists have used the world's most advanced computers to both simulate climate and predict future climate. Industries such as those mentioned above increasingly rely on information from these models to guide decision making--and with a changing climate, the information is more important than ever.
This site is a primer on how climate models work. The information is based on expert consensus reports from the National Research Council's Board on Atmospheric Sciences and Climate. The most recent is A National Strategy for Advancing Climate Modeling.