Fearless leaders: Indicators of future change

How should we think about indicators that are meant to impart information on future trajectories of the Earth system? There are at least two approaches – first is the use of leading indicators that are measures of current conditions, but for which their change over time is strongly correlated with future directions. The second is the use of model-based indicators. Both have strengths and weaknesses, and we explore how each can be approached in the context of global change.