Robustness metrics: How are they calculated and when should they be used?

Environmental modelers have long considered uncertainty, but this has mostly been focused on quantifiable uncertainty around a single projected future. There is now an understanding that multiple plausible futures must be considered where the relative likelihood of each of these projected futures is unknown. Robustness is a way of measuring the performance across multiple plausible futures, however there are many robustness metrics that reflect different aspects of what makes a decision alternative robust.