As our climate continues to change, we need to make decisions and design for an uncertain future. Climate projections based on a variety of scenarios can help in that process. A scenario is a postulated course of events. It is not a prediction.
Scenarios are used in a wide variety of planning activities, from infrastructure design to health care, because they enable planners to consider a range of possible futures and minimize risk. For the same reasons, emissions scenarios are used in climate models.
Choosing what emissions scenarios to examine depends on a variety of factors. In many situations, it makes sense to “stress test” a system by looking at the highest plausible scenario. As experience with various crises demonstrates, preparing for low-probability, high-impact, worst-case scenarios is just smart planning.
The three RCPs – Representative Concentration Pathways – illustrate three levels of warming and their impacts. Comparing impacts from the lowest and highest of these helps us understand the choices that will determine our future.