This sounds like good science being done. When you are trying to predict something like carbon emissions, standard practice is to run a few different scenarios. If you run 5 models, one with predicted CO2, and the others with higher and lower values, of course some of your scenarios will be unlikely. You're doing that on purpose so that you have a ability to see how wide the range of possible results is even with uncertainty in CO2.
"Correspondingly, the authors “recommend establishing a process for regular updates” to the scenarios and recommend that key variables in the scenarios “be updated now to be consistent with new historical data.”"
So the author is explicitly saying different scenarios should be used, just that they should be updated regularly.
