Carbon neutral cities: Can we fight climate change without them?Chatham House Associate Fellow and chartered member of the Royal Institute of British Architects, Karim Elgendy explores the role of buildings in the race to net zero cities.
Cities play a central and critical role in global decarbonization efforts. Although the physical footprint of them only amounts to 2% of the world’s total land area, cities still account for two-thirds of energy consumption and generate 70% of greenhouse gas emissions.
Carbon neutrality or net zero carbon, is about striking a balance between the carbon emitted into the atmosphere, and the carbon removed from it. If the world is to collectively reach net zero by 2050 then our cities, the very hearts of the global economies, will need to proactively transform themselves into low carbon, or even zero carbon, cities.
A carbon-neutral, or zero carbon city, is one that reduces the majority of carbon emissions and offsets residual emissions, to the point that its operations do not result in a net increase in emissions. Currently, 708 cities have joined the Race to Zero, committed to eliminating their emissions by 2050.
However, despite an increasing number of cities navigating a path to carbon neutrality, it’s important to note that cities do not share equal starting points. Some cities are in a better position as they have carbon emissions that are already low compared to others, and therefore they are far more able to quickly transition to zero carbon.
Cities that currently use renewable energy sources to generate most of their energy are also at an advantage. In 2018, 42 cities, including Addis Ababa, Brasilia and Basel, achieved 100% of their electricity from renewable sources. While an additional 59 cities, including Stockholm, Zurich, Dar-es-Salam, Montreal and Seattle, were able to generate at least 70% of their energy from these sources.
But even cities, such as London, that have a higher building density, and good public transportation networks, have the potential to become zero carbon. The city has committed to become carbon neutral by 2050 and, among other targets, is working to decarbonize its energy supply as well as become a zero carbon transport and zero waste city.
However, one of the key challenges facing cities around the world, including London, are energy inefficient buildings and the need for more energy efficient building stock.
The operational carbon emissions of buildings, such as through heating, cooling, and lighting account for 19% of all emissions in the UK. The embodied carbon of buildings is also crucial to consider, as it accounts for the carbon emitted during the manufacturing of materials and the construction process, and this is a significant portion of a building’s carbon footprint.
Buildings that operate at net zero carbon, by reducing emissions associated with their energy use and offsetting all residual emissions, are often referred to as net zero carbon buildings. However, a truly net zero building, is one that also reduces embodied carbon emissions.
When appropriately designed and thoughtfully considered, buildings can be one of the most impactful ways to achieve emissions reduction targets. And while designing and building new net zero buildings can have a substantial and positive impact on emissions in growing cities, retrofitting existing buildings in cities with stable populations, as in London, is deemed to have the most impact on reducing city emissions.
Some cities are choosing to take climate action through their pursuit of low emissions buildings. 28 cities, for instance, have already signed the Zero Carbon Buildings Commitment, organized by the World Green Building Council and C40. These cities have committed to ensuring that all their new buildings are designed to operate at net zero by 2030, and that all existing buildings are to achieve net zero by 2050.
When appropriately designed and thoughtfully considered, buildings can be one of the most impactful ways to achieve emissions reduction targets.
In recent years, there has been a rise in the number of ground-breaking buildings that have achieved net zero building operations’ emissions, with some claiming to be truly net zero through reduced embodied carbon.
There has also been an emergence of new voluntary energy standards for buildings, such as the US ‘LEED Zero Carbon’ and the ‘2022 Zero Code” in California. The development of these energy standards, when used as a framework, can help guide and pave a path for developers and designers to work together to create new net zero buildings that have reduced operational carbon emissions.
In order for this to be achieved, designers first need to design new buildings in ways that respond to the local climate and reduce energy needs and demands for heating, cooling, ventilation, and lighting. By making careful design decisions regarding building orientation, shading, natural ventilation, day-lighting, and other design measures, much of the building energy demand can be reduced. Once these initial design steps have been set in place, they then need to design efficient mechanical and electrical systems. Finally, they can also consider on-site renewable energy generation to help offset the remaining energy use.
Those who seek to push the boundaries further, and to push to reduce embodied carbon, may need to challenge their assumptions regarding the need for new buildings and to consider ways in which they can build less by retrofitting buildings that already exist, build simpler and with lighter materials, reuse materials from existing buildings, and select new materials with low embodied carbon.
Ultimately, no building can be built without a carbon footprint of some measure, and some offsetting is almost always required to reduce carbon emissions to zero. With the emissions that are remaining, these need to be offset by renewable energy, and also through carbon sequestration.
The pursuit of carbon neutral cities is not just a matter for national and city policymakers. Planning, design and construction industries play a critical role in this transformation. As evident by the mainstreaming of sustainability and green buildings in these industries in recent years, we are encouraged that carbon neutral buildings in cities can become the norm by the end of the decade.
Karim Elgendy is a sustainability consultant based in London. He is an associate with Dar, an Associate Fellow with Chatham House, and the founder of Carboun, an advocacy initiative promoting sustainability in cities of the MENA region. Karim is the recipient of the 2013 Global Green Building Entrepreneurship Award by the World Green Building Council, and is a chartered member of the Royal Institute of British Architects.
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