Why A Carbon Budget?
As we learn more about greenhouse (GHG) pollution and global warming we’re getting better at understanding cause and effect. There’s lots of complexity, obviously. However, the variables are slowly being identified, tested, and fed back into the models. Last year the media latched onto a story that global warming had ceased. I wish the stories indeed did debunk climate theory. Unfortunately not. We’re just in a period of warmer oceans and cooler atmosphere. Will Steffen explained this in a very objective manner when questioned in the Senate Committee on Extreme Weather Events (see page 12 of this transcript). Anyway, all the scientific research into climate change now enables us to make predictions of warming based on the volume of GHG we release into the atmosphere. And we’re even able to make predictions about what effects this may have. The below infographic is an incredibly good summary of these predictions, and the background data is rock solid if you’re interesting in looking into this further.
It’s pretty clear we need to try to limit warming to two degrees. The big reason for this is that there are tipping points for our climate, which trigger events that force more warming. Some examples include melting of arctic tundra and stored methane, release of methane from sea bed methane clathrates or the collapse of the amazon due to drought and fire. We don’t actually know at what point these events will happen and they may even happen before we get to two degrees warming. What we do know, is that it’s highly likely they will happen if we keep warming the planet. Even without these events occurring, we’re on track for four degrees of warming by the end of the century. Four degrees will probably put so much pressure on food resources there’ll be major global conflict. Not over land, or oil, but over food. It could get very messy.
A Per Capita Carbon Budget
So, we need to work out how much more carbon we can release to avoid these events, we need to set a budget. There is actually a level of GHG pollution that the planet can happily cope with naturally through chemical and biological sequestration. It’s a rubbery number, but sits at about 2.0 tCO2e per person. In 2050, accounting for population growth, we really need to be aiming for approximately 1.0 t CO2e per person per year which would actually enable us to reduce the GHG in the atmosphere. This, then, is our sustainable level of GHG emissions on a per capita basis. Some calculations on this here and here (with slightly different results).
Apportioning to Economic Sectors
Relating this to buildings is a little difficult because we don’t really know how the economy is going to decarbonise. There might be breakthroughs in certain sectors that enable it to effectively zero its GHG emissions, whilst others may find it very hard to shake the existing thirst for fossil fuels (or land use change). If however, we assume that all major sectors of the economy decarbonize together, then we can essentially take each sector’s current percentage of GHG emissions and multiply it by 1.0 t CO2e to yield the per capita budget for each sector. This is one of the best diagrams I have come across to explain GHG flows through the economy. It’s taken from a great publication called Navigating the Numbers.
In the diagram, the column “end use activity” is what we need to focus on to determine how current GHGs are apportioned across our economy. Directly, buildings are responsible for 15.3% of GHGs. However, there are a lot of indirect emissions that relate to buildings if you take a life cycle approach to measuring an impact of a building. These include transportation of materials to the site, transportation of equipment and labour, construction energy, emissions relating to materials production, further transport, and equipment use to maintain the building. Then deconstruction, demolition and landfill emissions. There may also be land use change emissions associated with some building products, or urbanisation as well. If we make the below assumptions regarding the allocation of these indirect emissions to buildings (which are not based on research, but I believe are reasonable), we land at a number of 26% of total GHG emissions relating to buildings.
- 60% of building energy use relates to electricity to determine distribution and transmission losses
- 70% of coal is used for electricity or downstream processes attributed to buildings
- 30% of oil and gas gets used for electricity or downstream processes that can be attributed to buildings
- Unallocated fuel combustion is proportionally attributed to all end uses
- 1% of air transport and 10% of all other transport relates to building construction, maintenance, design or management.
- 50% of iron, steel and cement is used in building construction or maintenance
- 10% of chemicals are used in building construction or maintenance
- 25% of aluminium and non ferrous metals are used in building construction or maintenance
- 10% of other industries are providing materials or services to building construction or maintenance
- 25% of land use change emissions due to harvest and management of forests relate to construction and maintenance of buildings
- 15% of all landfill gas emissions relate to disposal of construction waste
- 75% of waste water treatment emissions relate to building waste water
These assumptions and calculations at this point are moving pretty quickly towards “back of the envelope”. The only way I can really justify this is that there are no numbers out there telling us what is a sustainable level of GHG emissions for buildings. So don’t hang your hat on these numbers, however, in lieu of more robust calculations, here’s a starting point.
A Carbon Budget For Buildings
We can now set a rough carbon footprint for environmentally sustainable buildings at 260kgCO2e per year per capita. This will be split between residential dwellings and other buildings. If we assume the split is the same as the direct GHG split in the “Navigating the Numbers” flow chart, that gives us a budget of 168kgCO2e per year per capita for residences, with the remainder of building related GHG distributed to workplaces, hospitals, civic buildings etc. We haven’t done any work on how to distribute the remainder amongst these other buildings as it gets pretty complex but watch this space. For residential buildings in Australia, we have a lot of work to do to achieve this budget. See the below chart for a visual on that.
Although these numbers require more work to confirm, they provide some guidance in lieu of other sources. They display the extent of the challenge. In particular, note in the last chart that the target is many times less than even the embodied GHG of current “average” buildings in Australia. I extend on this topic in this post, exploring some lateral thinking to solving the challenge of hitting our carbon budget for buildings. Note, this is an update on the video attached to the next post so you may spot a difference in the figures.