This document provides an introduction to climate change science. It discusses that climate change is a large multi-disciplinary issue that affects all sectors of society and the economy. It then summarizes the key components of the climate system and how human activities have changed the composition of the air and land use. The document reviews evidence of climate change from increasing greenhouse gas concentrations and global temperature rise. It discusses climate modeling and projections for further warming and impacts. The conclusion emphasizes that human influence on climate is clear and emissions reductions are needed to limit climate change risks.