Downscaling the Low-Carbon National Strategy for the Building Activities

Abstract

With buildings responsible for 37% of global energy and process-related CO2 emissions in 2021, their decarbonization is pivotal for mitigating climate change. Positioned at the intersection of significant opportunities for greenhouse gas emission reductions and sectors that are challenging to decarbonize, a comprehensive understanding of their life-cycle emissions and decarbonization potential is crucial. While climate policies such as sectoral carbon budgets provide an essential framework for action, and while various scenarios explore potential decarbonization pathways across different sectors, the accounting framework within which they are embedded lacks flexibility for activities that are international and span multiple sectors. This approach fails to provide a holistic view of emissions, thereby limiting the effectiveness of carbon budgeting and the creation of effective decarbonization strategies and models. The primary objective of this thesis is to develop life-cycle carbon budgets for buildings and model exploratory scenarios for life-cycle emissions trends up to 2050 at different scales—from modeling entire residential activities to detailed performance modeling of new buildings. This work seeks to better align sectoral policies, such as building regulations, with climate policies by leveraging a combination of environmental assessment methods, building stock modeling, prospective techniques, and especially scenario analysis as informed by the latest research. The thesis is structured in three main parts to achieve this goal. The first part establishes a robust methodology that captures the full spectrum of emissions from building activities. This approach facilitates projecting various carbon budgets for different emission scopes, extending beyond traditional sectoral carbon budgets that often limit their scope to direct operational emissions. It also identifies carbon budgets dependent on the decarbonization of upstream sectors, thus reflecting varying decarbonization ambitions. Rather than creating new carbon budgets from scratch, this methodology allows working with existing sectoral carbon budgets while expanding their scope and relevance for policy. The second part models exploratory scenarios for residential activities. Using a building stock database, the goal is to create a modeling framework that supports dynamic projections, enabling the assessment of drivers and the calculation of annual and cumulative life-cycle greenhouse gas emissions (GHGE) up to 2050. In this framework, scenarios for the decarbonization of upstream sectors impacting energy carriers and embodied benchmark values are incorporated to assess their significance in achieving climate objectives. The ultimate aim is to determine how different decarbonization strategies align with the previously defined carbon budgets. The third part delves into building-level analysis, evaluating how scenarios impacting upstream industrial and energy sectors influence the embodied performance of different building types. This part focuses on new construction, using a building Life Cycle Assessment (LCA) database and prospective LCA tools that integrate scenarios from Integrated Assessment Models (IAMs). The goal is to compare the future embodied performance of new building typologies modeled through this approach with proposed future benchmark values. Key findings on accounting and carbon budgeting reveal that the French building stock emitted 162 MtCO2eq in 2019, with embodied GHGE making up 36% of the total. Most embodied GHGE originate from upstream industry and energy sectors, with 20% of emissions occurring outside national borders. By 2040, embodied GHGE are expected to become the dominant source of emissions, taking up a larger share of the carbon budgets for building activities under current decarbonization policies. This underscores the limitations of existing climate policies, which are often too narrow, and suggests the need for more comprehensive inclusion of emissions, particularly as building legislation increasingly requires reductions in life-cycle emissions. Findings on decarbonization pathways for residential activities highlight significant disparities in GHGE outcomes resulting from different strategies. For instance, policies that target fossil fuel use are more effective in reducing operational GHGE compared to those focused solely on energy performance labels. In ambitious scenarios with high renovation rates, embodied GHGE become predominant by 2040. Achieving ambitious carbon budgets will require a combination of sufficiency measures (e.g., reduced square meters per capita) and deep decarbonization of energy carriers and construction materials. Prospective LCA modeling of new construction indicates significant decarbonization potential from upstream sectors, with emissions reductions of approximately 60% in the most ambitious scenarios, measured as emissions per square meter at the building level. However, achieving ambitious targets by 2050 will require additional levers, such as demand-side mitigation. When extrapolated to the national level, these findings suggest that current construction practices, including the market share of various building types, are insufficient to align with ambitious carbon budgets, highlighting the need for further promotion of low-carbon material solutions. Overall, this research contributes to the discourse on carbon budgets for buildings, large-scale life-cycle carbon emission calculations, and scenario analysis tailored for building activities. It provides valuable insights, methodological advancements, and tools to enhance the development of climate policies, building regulations, and forward-looking modeling practices.