Life cycle GHG emissions of the Austrian building stock: A combined bottom-up and top-down approach

Construction and operation of buildings are responsible for 37% of global greenhouse gas (GHG) emissions. In contrast, the Austria's National Inventory Report attributes a mere 10% of national emissions to buildings - including only direct operational emissions of residential and service sector buildings. This narrow definition of the buildings sector neglects important environmental hotspots attributable to building-related life cycle emissions and calls for a comprehensive analysis of GHG emissions of Austrian buildings. In this study, we assess annual building related GHG emissions for the Austrian building stock from a full life cycle perspective (i.e. including operational and embodied emissions). For embodied emissions, we model emissions using both a process-based and an input-output based life cycle assessment (LCA) approach. Building LCA case studies and statistical building stock data are used to estimate embodied emissions from a bottom-up perspective, which are complemented by estimated emissions from the input-output based LCA approach. Our work illustrates the importance of adopting a life-cycle perspective on building-related emissions to inform the different stakeholders and advance climate action in the built environment. While both the chosen system boundaries and methods significantly determine the results, we argue that emission reduction measures should be based on a comprehensive system boundary of building-related emissions to contribute towards the achievement of a climate-neutral built environment and the stringent climate targets. By adding indirect emissions and non-residential buildings to the officially reported building emissions, the operational emissions alone increase by a factor of 2.4. As expected, the process-based LCA yields lower embodied emissions than the input-output based approach. Depending on the method, they can be responsible for up to 40% of total buildings related emissions. Summing up, total buildings related emissions rise by a factor of 3 to 4 when extending the system boundaries to comprise the whole area of action buildings, and go from 7 Mt CO2-eq/a (direct operational emissions, 10% of national emissions), to 22-31 Mt CO2-eq/a for the case of Austria.