The typical way to measure carbon emissions is to think about it in terms of geography. You pick a particular place, such as a country or a city. You add up all the emissions that are taking place within its boundaries. And you're then left with a territorial carbon footprint. If you've done any research on carbon emissions or climate change, you've likely encountered this method of accounting for carbon.
But there's a flaw with this logic.
The problem with this method is that it considers each geography to being more or less independent. For example, let's say you live in Philadelphia and you happen to be the owner of something called a computer. With territorial accounting, the carbon emissions associated with you powering your computer would get attributed to Philadelphia and the emissions associated with the actual production of the computer would get attributed to wherever it was made. Let's say it was China.
One of the problems with this approach is that it penalizes the places that make a lot of stuff and it privileges the places that don't make as much stuff, even if they may actually be the consumers of far more stuff. This might make you feel better about your life decisions if you happen to live in a dense urban knowledge economy that doesn't really make anything physical -- but is it entirely accurate?
An alternative measurement approach is consumption-based carbon accounting. The goal here is to capture all lifecycle emissions associated with a particular good or service, and then attribute it back to the consumer that arguably triggered the emissions. In the case of our Philadelphia computer example, the emissions associated with the production, transportation, and consumption of the computer would also get attributed locally to Philadelphia, instead of to China.
This more complex method of carbon accounting -- which is something that the University of Pennsylvania has been working on over here (hence the Philadelphia computer example) -- can be instructive for a whole host of reasons. It also has some relevance to city building.
It is widely understood that building up is more sustainable than building out. Because when you build out, you end up doing things like forcing people into cars. But the other side of this equation is that cities tend to also house a lot of rich people, and household wealth is a massive driver of carbon emissions when you account for them based on consumption. Some would argue it is more important than urban density.
In my opinion, none of this is to suggest that dense urban environments are bad. The point here is that territorial carbon emissions don't fully capture the emissions caused by high consumers who might happen to live in an otherwise efficient urban environment. You can live in a compact apartment and walk to work, but what else are you consuming? And how might these consumption patterns change based on built form?
For more on this topic, check out this report by Daniel Cohen and Kevin Ummel (of the University of Pennsylvania) called, "The case for neighborhood-level carbon footprints."
Photo by Chris Henry on Unsplash
Building height and density are not one and the same. You can have tall buildings configured in a low-density way (think post-war towers in the park). And you can have low/mid-rise buildings configured in a high-density way (think Paris and Barcelona). This is one of the reasons why it is important to decouple density and tallness when thinking about our cities.
This line of thinking is the approach that a recent study took when trying to determine the optimal built form for minimizing climate impact. In the study they define four building typologies: 1) high density, high-rise, 2) low density, high-rise, 3) high density, low-rise, and 4) low density, low-rise.
What they found was that taller environments tend to have higher life cycle GHG emissions, but that lower-density environments are (obviously) far more land consumptive. To determine life cycle GHG emissions they looked at both embodied and operating emissions, which is why the taller stuff didn't score as well under their methodology. There's typically a lot of concrete and steel in tall buildings.
This lead the team to conclude that if you want to optimize around climate impact, you should probably aim for that perfect middle ground: dense, but not super tall.
But as Joe Cortright (City Observatory) rightly pointed out in his email newsletter, one of the big limitations of this analysis is that it does not consider transportation-related impacts. And since we know that transportation is one of if not the largest source of GHG emissions and that how we get around is heavily dependent on land use patterns, it is probably an important piece to consider.
Photo by Alfons Taekema on Unsplash
Image: Financial District, Downtown Toronto, Canada by Yeonju SEONG on 500px
Today I learned about something new called 2030 Districts. They are: “designated urban areas committed to meeting the energy, water, and transportation emissions reduction targets of the 2030 Challenge for Planning.”
Toronto’s new 2030 District is downtown, which is bound by the lake in the south, Bathurst Street in the west, Dupont Street and Rosedale Valley in the north, and the Don Valley in the east.
It’s the first district outside of the US. The other established districts are in Seattle, Pittsburgh, Los Angeles, Denver, Stamford, San Francisco, and Dallas.
The goals for Toronto’s district are as follows (quoted from 2030 Districts):
To cut district-wide emissions in half, including zero-emissions from new buildings by 2030.
Support a better understanding of where and why energy use, water use, and GHG emissions occur across the District.
Work in partnership with building owners, service providers and conservation groups to accelerate the adoption of best practices for building design and management.
Facilitate broad stakeholder dialogues to uncover and overcome systemic barriers to long term reductions in energy use, water use and GHG emissions.
I’m looking forward to following and learning more about this initiative. I think many of us can agree that producing less, not more, GHG emissions in the future would be preferable. And we know that the bulk of it comes from both buildings and transportation.