In this introductory textbook chapter, students learn that life on Earth would not be possible without the atmosphere and its greenhouse effect. The history of research on the role of greenhouse gases in the atmosphere is presented, and the concept of contemporary climate change and global warming are introduced. This is the first chapter in the unit, Climate Change, which addresses the question of how human activities are changing Earth's climate. The resource includes a textbook chapter, integrated hands-on and inquiry activities, links to current news articles, and a suite of pre and post unit assessments. A teacher's guide supports classroom use. The resource is part of Global Systems Science (GSS), an interdisciplinary course for high school students that emphasizes how scientists from a wide variety of fields work together to understand significant problems of global impact.