Tackling Scope 3 Emissions In the Construction Sector Using Hybrid Lifecycle Assessment.

Companies in many sectors are trying to estimate and reduce their carbon footprint. This is essential for meeting the UK's legislative carbon budgets, and for achieving the global Paris Agreement on climate change. Construction is one of the sectors that is receiving attention and change, because the carbon footprint of buildings and infrastructure represents 42% of global greenhouse gas emissions [1].

At a company level, carbon footprints are usually broken down into Scope 1, Scope 2 and Scope 3 emissions. Scope 1 and 2 relate to the energy use by the company, which is relatively easy to measure. Scope 3 is 'everything else', including all the emissions caused upstream in a company's supply chain.

Scope 3 emissions are notoriously difficult to estimate but can dominate a company's carbon footprint, including in construction. There are two main approaches for estimating Scope 3 supply chain emissions: "top-down" (based on economic input-output tables) or "bottom-up" (based on engineering and emissions data for individual processes, such as manufacturing or transport).

Top-down approaches are more complete, but they are broad averages for whole sectors and they are not necessarily representative of specific companies or products. Bottom-up approaches provide much better specificity but suffer from incompleteness or poor data availability.

A hybrid life cycle assessment (LCA) seeks to make the most of each approach by combining the two. However, while there is a long history of hybrid methods, they have not yet been widely used, and are not used at all in UK construction.

This PhD will therefore develop a hybrid LCA method for the UK construction sector. This will produce novel academic research with potential for significant use within the construction sector and beyond. References

[1] Global Alliance for Buildings and Construction, Global Status Report, 2019: Towards a zero-emission, efficient and resilient buildings and construction sector.