Quantifying city-scale carbon emissions of the construction sector based on multi-regional input-output analysis

Cities are open systems that rely heavily on external trade and release carbon dioxide (CO₂)as a predominant by-product. Quantification of trans-boundary emissions is essential, especially for the construction sector, which requires great intermediate inputs from upstream sectors locally and globally. This study investigates the global energy-related CO₂ emissions induced by Hong Kong's construction consumption based on multi-regional input-output analysis for the years 2004, 2007, and 2011. The results showed that the consumption-based CO₂ emissions emitted to sustain the local construction consumption are at least 32.37% higher than those estimated by the conventional approach. The consumption-based CO₂ has slightly declined from 2004 to 2011. This trend was closely tied to decreasing emission intensities of upstream sectors, even with strong growth in construction final demand. 96.61–97.41% of the consumption-based CO₂ were indirect emissions, and 73.50–78.58% were trans-boundary emissions. Utilities, Manufacturing, and Transport & Storage were the main source sectors contributing the most to total CO₂ emissions. Based on the results, extended emission monitoring beyond municipal boundaries, diversification of import origins, implementation of import substitution, use of low carbon-intensive materials, and enhancement in electricity generation towards low-carbon fuels are proposed to mitigate construction-related CO₂ emissions.