CO2 can be a bit of an enigma. It's an essential component of our planet's life cycle, yet in excess, it's a potent greenhouse gas (GHG) that contributes to global warming and climate change. While the need to reduce our carbon footprint is clear if we are to remain within the 1.5° threshold, talking about CO2 can be difficult at times. Since at standard temperatures and pressures CO2 is an invisible gas, numbers are the only way for us to put it into perspective. It makes up around 0.04% of the air we breathe in and around 4% of the one we breathe out. CO2 is all around us, and yet its intangible nature makes it difficult to truly grasp its significance. Unlike plastics or fossil fuels, consumers usually don’t come in contact with it on a daily basis. And yet, CO2 is one of the main culprits of the current climate change crisis, representing almost 80% of the greenhouse gases in our atmosphere. 

But how is CO2 related to the construction industry?

There are two main types of GHG emissions connected to the construction industry: operational and embodied.

Operational carbon emissions refer to the CO2 released during the use of a building, mainly through energy consumption for heating, cooling, lighting, and other electrical needs. These emissions can be substantial, especially with older buildings that are not as energy efficient, and operational carbon still represents the majority of the emissions of the sector.

Embodied carbon emissions, also known as embedded or 'hidden' carbon, refer to the CO2 emissions associated with the entire lifecycle of a building. This includes the extraction, processing, and transportation of raw materials, construction, maintenance, and eventually, demolition and disposal. Embodied carbon is a major component of the total carbon footprint of a building. In fact, as operational efficiencies improve, embodied carbon becomes a more significant proportion of a building's overall carbon impact.

Most worldwide regulations focus on operational carbon, as it’s easier to tackle with policies favouring renovations and upgrades to cooling and heating systems. Embodied carbon on the other hand remains largely unresolved. The strategies to mitigate embodied carbon quantities are not so straightforward, and require an industry-wide sensibilization to low-carbon building materials.

Overall, our built environment contributes to the emission of CO2 for nearly 40% of global energy-related CO2 emissions. This includes everything from the construction materials used to the energy required to heat, cool, and light up the spaces we inhabit. The production of cement alone is responsible for about 8% of the world's CO2 emissions. These percentages can feel arbitrary especially when related to something as impalpable as GHG emissions. 

So how can we put them more into perspective?

If the cement industry were a country, it would be the third-largest emitter of CO2, coming only after China and the US. This is because producing just one tonne of cement releases around 2.1 tonnes of CO2, enough to nearly fill 13 double-decker buses with CO2 gas. And in 2022 a staggering 4.1 billion tonnes of cement were produced to meet the rising demand. Meanwhile, the average carbon footprint per capita in the European Union is 8.2 tCO2eq/year, which includes the burning of fossil fuels for heat, the use of electricity, and transportation. Considering that one kilogram of carbon dioxide at standard atmospheric pressure occupies about 0.54 cubic metres, the average European contributes roughly 4500 cubic metres of CO2 equivalents every year. To give a sense of scale, that is around the same volume as 2 Olympic swimming pools or more than 150 standard shipping containers. 

All these figures can now seem a bit intimidating so let’s backtrack for a moment. Isn’t CO2 only a tiny fraction of our atmosphere after all?  Yes, in absolute numbers the CO2 concentration is around 420 ppm, which is equivalent to a football stadium with 100,000 seats but only 42 people in it. But but absolute numbers only tell half of the story. This miniscule amount is sufficient to cause a drastic 1.1°C increase in the temperature of our entire planet. That is why it's so crucial to keep the levels of greenhouse gases in check, as even a tiny amount can have a massive impact. These levels of CO2 had not been witnessed for 800.000 years according to ice core data and the built environment –  with its high operational and embodied carbon emissions –  has played a shameful role in their drastic rise.

What can we do then?

Tackling the emission problem in the built environment is vital to avoid irreversible climate-related effects. The key to achieving this lies in leveraging accurate and comprehensive data to understand our current state and guide our future actions.  Data-driven support for low-embodied-carbon building materials can catalyse a shift away from traditional carbon-intensive production processes. This includes promoting the use of responsibly sourced timber, recycled boards, and biomaterials. The climate crisis presents a formidable challenge, but it also unveils an unprecedented opportunity. By rethinking how we design, construct, and use our buildings, we can drastically reduce our carbon footprint and reshape the building industry for the better.