Cities and urban areas are critical nodes of societal resource flows, responsible for both global and local sustainability implications. They are complex systems and understanding the implications of potential actions by cities is critical for progress towards sustainability. In this paper the future implications of sustainability strategies are assessed for 10 European cities by comparing two scenarios for 2050: a business-as-usual (BAU) and a post-carbon/sustainability scenario (PC2050) (generated by city stakeholders). The effects of the scenarios are assessed using a mixed methodology: a semi-quantitative sustainability indicator analysis, energy and greenhouse gas (GHG) emissions (both production-based and consumption-based accounting (PBA and CBA)), land-use spatial modelling, and cost–benefit analysis. The paper highlights the clear benefits of PC2050 with improved sustainability indicator results, reduced land sprawl (which averages 16% in BAU) and positive cost–benefit results. Nonetheless, inequality and segregation are a common concern. In addition, whilst PBA indicates a significant decrease (average decrease from 4.7 to 1.3 tCO2eq per capita) CBA demonstrates rising overall emissions from an average of 11 to 14.8 tCO2eq per capita. This is linked to rising affluence and consumption trends despite local improvements in GHG emissions, which highlights a need for cities to address consumption-based emissions.