Why is it important to decarbonize construction and achieve net zero

 

Summary The existing climate pledges are inadequate to meet the climate targets. To limit global warming to 1.5°C, greenhouse gas emissions (GHG) have to be reduced by 45% by 2030. Decarbonization of the building sector is essential to meet the climate targets Construction materials such as cement, steel, aluminum, and plastics are major contributors to embodied carbon. In a building, structural elements and finishes are the major contributors to embodied carbon. Introduction to net-zero carbon concepts, drivers, and strategies to achieve it.

 

Alarming emission trends

According to UNEP’s most recent Emissions Gap Report 2022, global GHG emissions must be reduced by 30% and 45% to limit global warming to below 2.0°C and 1.5°C, respectively. For the 1.5°C scenario, the full implementation of unconditional NDCs is estimated to result in a gap of 23 gigatons of carbon dioxide equivalent (GtCO2e). If the conditional NDCs are also fully implemented, the 1.5°C emissions gap is reduced to 20 GtCO2e. 

Fig 1. Current emission trends (Source: UNEP Emissions gap report, 2022)

 

Are the current climate pledges sufficient to stop a climate catastrophe?

Without additional action, current policies lead to global warming of 2.8°C before the end of this century. Implementation of unconditional and conditional Nationally Determined Contributions (NDC) scenarios reduce this to 2.6°C and 2.4°C respectively. Global warming levels only get close to the Paris Agreement temperature goal if net-zero pledges are fully implemented. 

 

Why should we focus on the building sector?

Buildings are responsible for 39% of global carbon emissions, out of which 28% are from operational emissions, and 11% are from construction materials-related emissions. Decarbonization of the building sector is critical in limiting global warming to 1.5°C.

 

Embodied carbon emissions from the building sector

The global building floor area is expected to double by 2060 resulting in 100-200 gigatons of embodied carbon. Unlike operational carbon emissions, embodied carbon is locked in place upon construction. Therefore it is important to address embodied carbon emissions to achieve net zero goals.

Fig 2. Key construction material’s contribution to global emissions (source: https://architecture2030.org/why-the-building-sector/)

The key construction materials concrete, steel, and aluminum are responsible for 23% of total global emissions (see Fig.2). The embodied carbon of these materials can be reduced through policy, design, material selection, and specification. The carbon budget available for key materials is 300Gt for 2100.  Low-carbon energy is not enough to meet this budget. Even with 100% low-carbon energy by 2050, emissions far exceed the available carbon budget (see Fig 3).

Fig 3. Carbon budget for 2100 (source: Circular economy- a powerful tool for climate mitigation)

 

Where do impacts come from in a typical building?

One Click LCA analyzed the distribution of embodied carbon by material category and building elements of approximately 500 Finnish buildings. The four most important construction material categories for embodied carbon are cement, steel, aluminum, and plastics (Fig.4). Of the remaining material categories, insulation, doors, windows, and glass products, and gypsum, cement, and mortar categories also stand out in importance. The results show that superstructural elements are the main contributors to embodied carbon of a building (Fig.5). The substructures and internal finishes are also major contributors.

Fig 4.  A1-A3 carbon footprint by material category (sample of approximately 500 Finnish buildings)

 

Fig 5.  A1-A3 carbon footprint by building element (sample of approximately 500 Finnish buildings)

 

INTRODUCING NET-ZERO CONCEPTS

Net zero carbon definitions

Net zero carbon – construction is achieved when the amount of carbon emissions associated with a building’s product and construction stages up to practical completion is zero or negative, through the use of offsets or the net export of on-site renewable energy.

Net zero carbon – operational energy is achieved when the amount of carbon emissions associated with the building’s operational energy on an annual basis is zero or negative. It is highly energy efficient and powered from on-site and/or off-site renewable energy sources, with any remaining carbon balance offset.

Net zero carbon – whole life is achieved when the number of carbon emissions associated with a building’s embodied and operational impacts over the life of the building, including its disposal, are zero or negative.

Carbon offsetting is the reduction in emissions of carbon dioxide or greenhouse gasses made in order to compensate for or to offset an emission made elsewhere.

 

Various net zero carbon commitments and measures

Many organizations and governments have taken initiatives to reduce carbon and reach their net zero goals. Listed below are a few of the various commitments undertaken to reach net zero carbon of the built environment.

The website Net Zero Tracker provides a summary of Net Zero commitments made by various countries.

How to achieve net zero carbon?

The steps involved in achieving net zero are:

1. Establish a net zero carbon scope: establish if your net zero carbon scope should include Net zero carbon- construction, operational energy, or whole-life carbon.
2. Reduce construction impacts: whole life cycle assessment should be performed to reduce the impacts.
3. Reduce operational energy use: prioritize reduction in operational energy consumption.
4. Increase renewable energy supply: prioritize renewable energy sources.
5. Offset any remaining carbon: remaining carbon should be offset using a recognized framework and publicly disclosed.