Technical Abstract: In the past three decades, climate change has become a pronounced driver of ecosystem change. Changes in phenology, range shift of species, and increases in disturbances such as wildfires have all reflected ecosystem scales responses to a warming biosphere. There have also been abrupt, nonlinear changes in ecosystems where the level of response to incremental increases in temperature have suddenly changed trajectories. These thresholds of ecosystem change are not well understood but are potentially critical to adaptation strategies for managing natural resources in a rapidly changing world. This synthesis is intended to evaluate the current state of understanding of thresholds and to recommend possible actions to improve knowledge and adjust management priorities even with incomplete understanding of what drives thresholds of change and when they will occur.