Tracking City-Wide Carbon Emissions—Down to Streets and Buildings

Aug 29, 2019

This week scientists at Northern Arizona University published the first-ever map of a megacity’s carbon emissions down to the scale of specific roads and buildings. The animation shows the Los Angeles urban area as carbon emissions rise and ebb over the course of the day. KNAU’s Melissa Sevigny spoke with climate scientist Kevin Gurney about how this data can guide policy decisions about climate change.

Screenshot of visualization of L.A. carbon dioxide emissions
Credit Hestia / Gurney Lab

Climate change is obviously a global issue. Tell me why you think it’s important to quantify carbon emissions at this very specific level?

Yeah, it is a global issue but like a lot of global air pollution-related issues it’s the summation of seven billion little things. Ultimately to do something about it, to change behavior, improve technology, we have to speak to people at the scale at which they cause the emissions…. You know, climate change has long been an abstract problem. But the essence of the problem is the stuff we do every day. It’s me today, getting up in my car, bringing kids to school, coming to work. I think the power of the visualization in cities, it makes that very clear. We see ourselves going about our daily activity. I think until we make that mental link the problem remains abstract.

You put this into a map that’s a real time map; it shows you, for example, the daily cycles?

That’s right. We see people wake up in the morning in their houses, move toward the roads as they commute to work, and then even see the downtown commercial sector begin to emerge through the working portion of the day, and then the rush hour again in the evening. We try to capture all those temporal cycles throughout the day, partly because we want to have the most accurate representation of emissions, and also because policy, were we to reduce emissions in the future, might be best turned to certain times of day verses others.

So if you were looking at your map as a city manager or as a policymaker, what would stand out as maybe the places or activities that are really creating a lot of carbon?

We look at what percentage different entities on the landscape account for how much CO2, so for example, 10 percent of the road surface accounts for 60 percent of the on-road CO2 emissions. It’s similar for buildings, roads, factories, industry: a very small percentage account for most of the emissions. Our point is to guide policymakers to those places where emissions are large.

Cities like Flagstaff and Phoenix have signed these pledges to act on climate change, do you think those kind of policy decisions at a city level are making a difference?

Not yet. I think pledging is the first start. It’s always recognizing the problem, at least making some sort of promise or pledge to do something about it. The next step’s the hardest, that’s doing something. That’s where I think we’re offering information to enable that. Again, Flagstaff matters just as much as Phoenix. As I said, this is the aggregation or summation of seven billion little problems….. Ultimately I’d like to do this for every single city in the United States, make it available to cities, so at least this aspect of the problem is solved. It sort of frees up cities to do the part of the problem that they’re best suited to, which is to figure out what sort of reduction policies they want to engage in.

Kevin Gurney, thank you so much for speaking with me today.

My pleasure.