Greenhouse gases
Urban development should be climate-friendly
View of the interior of the new Mainz-Bingen district administration building. The new building has a wooden facade and the interior is also largely made of wood. photo
© Jörg Halisch/dpa
The rapid growth of cities around the world is driving climate change because the construction industry emits large amounts of greenhouse gases. A United Nations report presents a vision of how things could be different.
The construction sector could become climate neutral worldwide by 2050, according to a report. This would be possible if materials were saved, building materials such as concrete and steel were manufactured in a more climate-friendly manner and more renewable raw materials were used. This is emphasized by a report published on Tuesday UN Environment Program (UNEP) and the Center for Ecosystems and Architecture (CEA) at Yale University.
37 percent of CO2 emissions come from the construction sector
According to this, so many new buildings are being built around the world that a city the size of the French capital Paris is added every five days. The construction sector is currently responsible for 37 percent of CO2 emissions. By 2060, it is estimated that the land area and the use of raw materials will almost double.
“Until recently, most buildings were built from locally sourced earth, stone, wood and bamboo. But modern materials such as concrete and steel often only give the illusion of durability, often end up in landfills and contribute to the growing climate crisis,” explained the director UNEP Industry and Economics Department, Sheila Aggarwal-Khan. “Net zero emissions in construction is achievable by 2050 if governments create the right policies, incentives and regulations to spur the industry to act.”
New buildings should be avoided if possible
The experts’ approach is to avoid new buildings as much as possible and to promote the reuse of building materials, to use biological raw materials such as timber, bamboo and biomass from sustainable sources and to produce building materials such as concrete, steel or glass in a more climate-friendly way, for example through the use of renewable energies in manufacturing as well as through recycling and innovative technologies.
So far, the approach to CO2 avoidance in buildings has mainly focused on their function after they have already been built – for example when it comes to heating, cooling or lighting. But while CO2 emissions there will likely decline thanks to renewable energies, they are growing rapidly due to construction activity.
Building materials that store carbon dioxide
The study authors emphasize that it is therefore all the more important for emerging countries to skip the unsustainable construction technologies of the last century. Developed countries should focus more on converting existing buildings and reusing them rather than demolishing and building new ones. Even before construction, it is possible to plan how a building can be taken apart and the elements can then be reused.
If building materials were used that themselves stored carbon dioxide, buildings could even become CO2-negative in the future – i.e. they could mathematically save more greenhouse gases than they emit during their construction. Wood and bamboo also have a significant effect, as they convert carbon dioxide into biomass as they grow and are therefore CO2 stores themselves.
Reduce 40 percent of CO2 emissions with biomaterials
Using biomaterials like wood and bamboo and agricultural byproducts may be “our best hope for radical decarbonization,” the authors say. The shift to bio-based building materials could lead to savings in this sector of up to 40 percent of CO2 emissions by 2050 in many regions, even compared to savings from low-emission production of concrete and steel.
The three materials concrete, steel and aluminum alone are responsible for almost a quarter (23 percent) of greenhouse gas emissions. Concrete use has increased tenfold in the past 65 years, it goes on to say. In 2020, 4.3 billion tons of cement, the most important component of concrete, were produced worldwide.
Alternatives to ordinary Portland cement
In order to achieve climate neutrality in concrete by 2060, ordinary Portland cement must be replaced by regionally available alternatives made from by-products of agriculture, forestry or industry. It is estimated that 140 gigatons (billion tons) of biomass are created as waste products every year and end up in landfills or burned to generate energy. Experts argue that this is a waste of a construction resource that could contribute to CO2 storage.
UNEP report “Building Materials and the Climate: Constructing a New Future”