In 2016, monthly atmospheric CO₂ concentrations passed 400 ppm for the first time in human history. Shortly thereafter, the first CO₂ measurement above 410 ppm was recorded in 2017. As ecologists, how do we adjust and prioritize our research questions and methods in a 400+ ppm world? In this session, we will explore how we evaluate, choose, and rank the ecological processes and questions that are fundamental to Earth’s current and future climate. Speed talks by global change biologists and modelers will review the history and current implementation of ecological processes within Earth system models, including the difficulties involved in translating field data into model improvements. Presenters will also discuss how they prioritize particular ecological processes in global change research and Earth system model development. Following talks, a panel discussion and Q&A with the audience will explore the limits to our current approaches for understanding ecology-global change feedbacks, and what changes we should, or should not, consider making as our world responds to a 400+ ppm atmosphere.