Forests regulate climate through exchanges of energy and materials with the atmosphere. The idea that forests affect climate is not new. A vigorous debate about deforestation, reforestation, and climate change began during European settlement of the Americas, spreading to all regions of the world before collapsing in the early 1900s. The story of forests and climate change is told as being scientifically wrong and advanced for political, economic, or cultural reasons, but it has not been told from a modern scientific perspective. In fact, it represents the foundation for the interdisciplinary study of Earth as a system. Many of the questions posed in today’s study of climate change and climate solutions have their origins in the forest-climate question. The multicentury controversy over forests and climate change is a narrative in which purposeful modification of climate is longstanding, but by felling or planting trees. Earth system science is a centuries old idea, conceived in the long-held belief that forests influence climate and doomed to fail by the disciplinary specialization of the sciences. Narrow-mindedness prevented a vision of the world as an interconnected system.