The construction industry is one of the largest contributors to global carbon emissions, accounting for 37 % environmental emissionsfrom which 10 % comes directly from building construction. A key, but often overlooked, factor is embodied carbon – emissions that arise from materials extraction, manufacturing, transportation, installation, maintenance and demolition. Although research and regulations have advanced in the area of operational energy efficiency of buildings, there is still a critical gap in understanding the full life cycle of embodied carbon in buildings at the city-wide scale, particularly in developed countries. Addressing the climate crisis and achieving carbon neutrality requires quantifying all carbon emissions from buildings and implementing strategies to reduce them.

New research presents a systematic framework for assessing embodied carbon emissions in buildings at the urban scale. It aims to create a high-resolution dataset of building life cycle emissions for urban areas, evaluate different mitigation strategies, and identify the most influential factors affecting urban embodied carbon emissions. The study focuses on the “cradle to grave” phases (Phases A–C) of the building life cycle, excluding operational carbon from Phase B to focus exclusively on embodied carbon. This research, conducted on the example of the Chicago metropolitan area, simulated over a million buildings and 350,000 iterations, providing deep insight into CO2 emissions under different urban planning scenarios. To achieve the high resolution of the data, “bottom-up” methods were used, which analyze individual buildings, materials, or technologies before expanding them to a broader view of the entire building.

Key findings from the Chicago simulation

A simulation of Chicago, which included 1,010,840 buildings, revealed fundamental insights into embodied carbon emissions. The city's average total changed emissions were 5.49 × 10^9 kg CO2, with a range from 1.93 × 10^9 kg CO2 to 1.62 × 10^10 kg CO2, highlighting the huge difference and the need for informed policy.

The most important conclusions include:

• Lifespan of buildings: The study found that buildings with Over a 50-year lifespan, they emit approximately three times more CO2 such as those with a lifespan of 80 years. Extending the lifespan of a building is associated with reducing the risks associated with expected emissions in urban planning scenarios. This exponential effect of building lifespan on emissions highlights the urgent need for strategies that prioritize building longevity.
• Building area: In addition to the lifespan, the area of a building also has a significant impact on emissions. Changing the area of a building by 20 % may negate the benefits of extended life or mitigate the negative impacts of a short lifespan. This means that hybrid approach to emission mitigation, which includes extending the service life also Reducing the area of buildings is essential.
• Renovation vs. new construction: The impact of new construction in Chicago is on average about 5.42 × 10^5 kg CO2, while the impact of replacement and renovation is about 4.09 × 10^9 kg CO2. This means that new building construction emits 7,500 times more embodied carbon than renovation and reuse existing buildings. Future urban development policies should prioritise the preservation and renovation of existing buildings over the construction of new ones.
• Predictability of strategies: Renovation strategies aimed at extending the life of buildings are not only preferable, but also predictable and associated with lower risk for emission control strategies. In contrast, exchange scenarios are much more prone to higher emissions and have a wider probability band, making them riskier. Currently, only about 1 % buildings are renovated per year.

Recommendations for the future

The simulation and sensitivity analysis results clearly indicate that the optimal solution for minimizing emissions is hybrid approach. This involves the initial use of shorter lifetimes with a smaller built-up area, followed by lifetime extensions through renovations. To successfully mitigate urban emissions, there is an urgent need for city planners to adopt standards and regulations that facilitate building renovations, especially as buildings age. These findings are a valuable tool for city and urban planners, building policy makers, environmental engineers, and the entire civil engineering community to effectively mitigate urban carbon emissions. Spring

The findings are published in the magazine npj Urban Sustainability .