Across the globe, cities account for the majority of our carbon emissions and energy use. Although they only cover 3% of the earth’s land surface, cities create more than 70% of all carbon emissions – mainly from buildings, energy and transport. They also consume 78% of the world’s primary energy.
Yet the effect of cities on the planet is set to get even worse. More than half of the world’s population currently lives in cities – but this figure is expected to rise to nearer 70% by the middle of the century. As urban populations continue to grow, so will new construction – resulting in even higher energy consumption and carbon emissions.
The production and use of the materials that make up the foundation of modern cities – such as cement, steel and glass – need to be transformed in order for a zero-carbon future to become reality. These materials are responsible for 20% of global emissions and demand is growing.
Optimizing plant operations is a good start. Improving cement plant efficiency, for example, can reduce fuel-derived emissions by as much as a fifth – simply by fine-tuning operations, taking into account all the variables such as fuel efficiency, kiln feed rate, fan speed and precalciner temperature.
But zero-carbon cities will also require new methods of production and novel materials. The production and transformation of these materials involves complex physical and chemical processes that interact together over time. This is why Carbon Re is focused on artificial intelligence (AI) models to accelerate the necessary transition at scale.
Electric plant machinery and vehicles can also be introduced to reduce fossil fuel consumption. And this can be extended to passenger vehicles too. Advances in electric heavy-duty vehicles have expanded the availability of medium and heavy-duty trucks in recent years with more than 110 new models introduced in 2022.
Off-site construction is another approach that can help address environmental challenges. Prefabricated modular units can range from flat-pack components, such as walls, to complex three-dimensional building sections, such as fully-built bathrooms. Advances in digital technology have taken complex planning and accurate manufacturing to a new level – and helped to optimise module design, workflows and delivery logistics.
Prefabrication helps reduce waste by optimizing material use and enabling offcut reuse or recycling. As prefabricated components are manufactured in a controlled, moisture-free environment, it is easier to use sustainable materials for some of the components. And constructing large parts of a building off-site means less material needs to be transported to the construction site – which results in fewer emissions.
Building design also has a part to play – more new buildings need to be designed in ways that respond to the local climate and reduce the demand for heating, cooling, ventilation and lighting. By making careful design decisions regarding building orientation, shading, natural ventilation, daylight and so on, much of the building energy demand can be reduced. Combined with efficient mechanical and electrical systems, this can make a big difference – potentially with on-site renewable energy generation to help offset the remaining energy use.
Reusing buildings instead of constructing new ones can typically save between 50% and 75% of the embodied carbon emissions compared with constructing a new building. This is particularly true if the foundations and structure are preserved, as that is where most embodied carbon can be found.
And reusing materials can also make a significant difference. Salvaged materials – such as bricks, metal, broken concrete or wood – usually have a much lower embodied carbon footprint than newly manufactured materials, as the carbon to manufacture them has already been spent. With reclaimed wood, in particular, there is not only the saving of energy that would have been spent in cutting down the tree, transporting it to the mill and processing it – but the tree that is not cut down is still doing the work of sequestering carbon.
Integrating materials such as biochar within buildings can also help reduce carbon emissions by capturing them at source. Combining this with a system of carbon capture, usage and storage (CCUS) means direct air capture can literally suck up emissions.
Cities have a vital role to play in our transition to a net-zero future. The right approach now will not only improve the quality of life of our urban populations but help safeguard the future of the planet for all of us.