Are Set to Dominate Climate Change 

Urbanisation is rising and so is the demand for building materials to construct global cities.

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Chapter 1
The Built Environment’s Impact on Global Carbon Emissions
We Used to Build with Low-Carbon Materials
Structure of the Report 

The Built Environment’s Impact on Global Carbon Emissions 

Urbanization is rising and so is the demand for building materials to construct global cities. 

Figure 1.1 Global carbon emissions from the built environment sector, by source, 2021

The built environment sector is responsible for more than a third of global energy-related carbon emissions.

Adapted from UNEP 2022.

The built environment sector is one of the largest contributors to climate change, responsible for more than a third (37 percent) of global energy-related carbon emissions (United Nations  Environment  Programme [UNEP]  2022,  see Figure 1.1). Yet the built environment has received only a small fraction of climate-focused funding for research and development compared to other sectors. Although investments in the energy efficiency of building operations increased 16 per cent among Group of Seven (G7) countries 1 in 2021 (ibid.), such commitments pale in comparison to what is required to decarbonise the built environment. As the largest global industrialised sector, construction also has widespread social impacts; it is at the highest risk of forced labour, with lax environmental and labour regulations tending to coincide (Grace Farms Foundation 2022).

As both population and wealth continue to grow globally, humanity is building more than ever in a quest to secure comfort and well-being. Floorspace worldwide is set to double by 2060, and every five days the world adds enough new buildings to total the size of Paris (UN Environment Programme [UNEP] and International Energy Agency [IEA] 2017). According to a 2019 report from the Organisation for Economic Co-operation and Development (OECD), the global consumption of raw materials will nearly double by 2060 as the world economy expands and living standards rise, doubling the environmental overloading being experienced today. The OECD projects that if we continue“business-as-usual” practices, the biggest increase in resource use by 2060 will be in extractive minerals, particularly in developing economies (OECD2019).

These megatrends are also influenced by rapid urbanisation. In 2020, the 124 countries that dominate the developing world were home to 81 per cent of the world’s population, and this share is projected to reach 87 per cent by the end of the century (Roser and Rodés-Guirao 2013; United Nations Department of Economic and Social Affairs 2020; World Bank n.d.). Much of this future population growth will occur in cities. The World Bank estimates that to meet the rapid increase in urban populations, 300 million additional houses will need to be constructed by 2030 (World Bank 2022a). Enabling this global building boom requires a new agenda for decarbonisation to meet residential needs of developing countries while decarbonizing the full range of building types globally, from formal to informal (see Box 1.1).

In the absence of urgent action, the carbon emissions of common construction materials such as concrete, steel and aluminium are projected to grow to increasingly dangerous levels. Although developed countries have historically contributed the vast majority of global carbon emissions, the world’s top 10 greenhouse gas-emitting countries now include rapidly developing countries such as China, India and Iran (Islamic Republic of) (Nejat et al. 2015). Even with the implementation of widely accepted interventions, emissions from the built environment sector are projected to go far beyond what is allowable to keep global temperature rise within 1.5 degrees Celsius, the target set under the 2015 Paris Agreement on climate change (Cao et al. 2021).

This report outlines concrete pathways to reverse these projections, and even to reach net zero emissions in the built environment sector by mid-century, through the promotion of best available technologies for conventional materials, combined with a major push to advance circular recycling and bio-based materials from forest and agriculture streams.

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Box 1.1


By 2030, 3 billion people worldwide are expected to require access to adequate, affordable and comfortable housing with (United Nations n.d., p.7). Much of this demand will be in the rapidly urbanising developing world. However, most global studies on housing growth to-date have focused on formal buildings, including single-family, multi-family and high-rise types found in developed countries (Marinova et al. 2020).

Recently, growing literature details the additional diversity of buildings in developing countries (Pikholz 1997; de Wet et al. 2011; Malik and Bardhan 2018; Mehrotra, Bardhan, and Ramamritham 2018; Nutkiewicz, Jain and Bardhan 2018). One study defined three categories of building types worldwide – formal, informal and semi-formal – with the most common differing characteristics being in construction materials and style, size, durability and demography of the residents (see Table 1.1) (Iyer, Rao and Hertwich 2023). As of 2016, more than 1 billion people lived in informal housing slums and lacked access to durable housing, along with other basic amenities (UN-Habitat 2016). 

Because formal buildings are typically more durable than the other two types of buildings (Iyer, Rao and Hertwich 2023), many low- and middle-income countries seek to redevelop informal homes and to relocate residents to new, formal constructions (Kharche 2020). However, studies have shown that residents in semi-formal and informal housing often have thriving social lives and a sense of community (Bardhan et al. 2018; Sanyal n.d.), whereas in formal apartment buildings they may be more isolated socially (Debnath, Bardhan and Sunikka-Blank 2019). Resettled inhabitants often end up moving back to informal settlements from their new formal homes, whether for social reasons, to be close to workplaces, to reduce costs or other factors (Debnath, Bardhan and Sunikka-Blank 2019).

Moreover, redeveloped formal buildings are often poorly designed and rarely take into consideration the preferences of relocated residents. Insufficient cooking and outdoor space and poor aesthetics are common issues faced by residents, adding to their motivation to move back to horizontal slums (Debnath, Bardhan and Sunikka-Blank 2019). Based on these findings, policymakers need to ensure stakeholder participation in decision-making processes, especially pertaining to slum redevelopment. Being aware and inclusive of the lifestyle, needs and unique constraints faced by these low-income inhabitants might improve redevelopment success rates.

However, a complete rehabilitation of informal settlements is unlikely. Thus, research needs to focus on improved materials in the building envelope, improving thermal comfort for inhabitants and reducing life-cycle energy demand. Additionally, retrofits with low-cost passive cooling materials must be investigated for informal and semi-formal buildings, to provide thermal comfort in the transition towards more durable homes. This is especially key as these low-income homes perform especially poorly in providing thermal comfort in a heating world, as inhabitants are priced out of common mechanical cooling technologies and appliances.