sentence1: Rather they are assessments of how the future might unfold compared to a previously defined reference case - given a national commitment to achieve the emission reductions, and given the mix of technology and policy assumptions embodied in each of the scenarios.
sentence2: Given a national commitment to achieve the emission reductions, and given the mix of technology and policy assumptions embodied in each of the scenarios, they are rather assessments of how the future might unfold compared to a previously defined reference case.