How much water in a litre of milk?
The obvious answer is “about a litre”, but it’s a lot more complicated once we factor in the water used to produce the milk. Every drop we pump from rivers or dams, plus every drop that falls as rain from the sky and is used to grow grass or grain crops to feed cows, as well as that used in production processes, needs to be counted. Turns out that actually, it takes around 1000 litres of water to produce a litre of milk. So that little milk carton on the supermarket shelf is considered to “embody” 1000 litres of water.
The concept of “embodied carbon” laid out in a new report from the World Green Building Council (WorldGBC), Bringing Embodied Carbon Upfront, is similar. Right now, when we consider the emissions produced by a building, we’re mostly focused on those it produces once it’s built. These emissions, generated by the energy used to heat, cool, light or power the building, are referred to as ‘operational emissions’. But according to the report, 11% of all a building’s emissions are not generated by powering it during its lifetime, but by the carbon produced by manufacturing materials, transporting them to sites, and disposing of them once they have ended their useful life. Like a fly trapped in amber, the emissions are “embodied”, or given tangible form, by the steel girder or the concrete floor.
Around the world, buildings are responsible for 39% of all carbon emissions. That’s a lot, but buildings also give us a uniquely cheap and effective way to lower our emissions in the face of the climate emergency. That’s because so many of them haven’t yet been built. As the global population heads towards a peak of 10 billion, the floor space of earth’s buildings is set to double. Here in Australia, around than half of the buildings that will be standing in 2050 are yet to be constructed. If we choose to build sustainably, we can reduce the emissions required to run our buildings over, saving emissions over the long term.
In Australia, we’re already moving towards net zero carbon buildings. Industry sees the writing on the wall; the Australian Sustainable Built Environment Council (ASBEC)’s Built to Perform lays out an industry-led pathway to improving the minimum standards for the energy performance of new buildings, while the more recent Growing the market for sustainable homes shows how sustainable homes can meet Australian homebuyers’ desire for healthy, attractive homes whilst delivering jobs and growth to the construction sector. Government is also heading in that direction – for example the state and federal government ministers who make up the Council of Australian Governments (COAG) Energy Council’s Trajectory for Low Energy Buildings shows that we are already on the road towards net zero buildings.
But even the most energy efficient building can’t claim to be truly ‘net zero carbon’ if huge emissions have been created by producing the materials it is made of. What’s more, with operational carbon steadily reducing, embodied carbon is set to grow as a percentage of each building’s emissions.
In our globalised, interconnected world, supply chains are incredibly complex. But if we fail to map out and understand the carbon implications of these complexities, we could favour processes that generate needlessly high emissions. By measuring embodied carbon using standardised tools, we will be creating the conditions to favour those that generate the least emissions.
It’s often said that climate change is a truly global problem, but in fact it’s a problem that exists at all levels, from the intensely personal to the local, state, national and international. To address embodied carbon, we need to understand and address the way all these levels interact.
Reducing embodied carbon in our buildings marks another key stage as we progress towards a low carbon future. We’ll get to zero net carbon when we use low carbon materials and practices throughout the entire building process. If we can do this, our commitment to combat climate change will be embodied in everything we build.