Stephen Pacala is the Frederick D. Petrie Professor in Ecology and Evolutionary Biology at Princeton University. His research focuses on systems ecology, climate change and the global carbon cycle. He pioneered a mathematical approach to include the Earth’s plant life in climate models, laying the foundation for the “Earth system model” now in use globally. Pacala directs the Carbon Mitigation Initiative, a major Princeton initiative that he founded with Robert Socolow to address the carbon and climate problem. He is founding director of Climate Central, a nongovernmental organization focused on climate change communications. Pacala is a member of the board of directors for the Environmental Defense Fund.