A global carbon budget, as defined by the IPCC, is derived by subtracting the emissions released since 1850 from total permissible emissions, based on the Paris Agreement’s 1.5°C target. The IPCC’s global reduction pathway defines the required emissions reductions and their timeline. However, translating this budget into national and sectoral targets is challenging due to country-specific differences and methodological uncertainties. For example, most studies and statistics in Germany are based on the Climate Protection Act (KSG), which only accounts for direct emissions in relation to specific sectors. As a result, there is no uniform and cross-sectoral system boundary for the German construction and real estate industry, which includes direct and indirect emissions as well as embodied emissions. This contribution develops an integrative approach combining top-down and bottom-up methods to identify gaps in existing statistics and studies that primarily focus on the KSG-defined building sector. The top-down approach applies macroeconomic data and multiregional input-output (MRIO) models to quantify consumption-based emissions and cross-sectoral linkages. The bottom-up approach combines disaggregated life cycle data from environmental product declarations (EPDs) for construction products and processes and national production statistics to assess material- and activity-specific emissions along the entire building life cycle. Simultaneously, identified gaps in the opening balance and emissions trajectories are addressed by integrating disaggregated bottom-up data into the overarching top-down structure. The objective is to develop a hybrid conceptual model that bridges both approaches and enables a harmonized, phase-specific attribution of greenhouse gas emissions. This paper focuses on a conceptual approach rather than presenting quantitative results. It supports German authorities in closing gaps in national statistics and regulation. The outcome demonstrates how emissions should be quantified to define a reduction pathway for the construction and real estate industry in accordance with the requirements of the European Energy Performance of Buildings Directive (EPBD) and guiding future integration into dynamic, scenario-based modelling to support compliance with carbon budgets.
Kaya et al. (Wed,) studied this question.