Greenhouse gas maps

Counting warming at the local scale

What’s making greenhouse gas pollution in your city? Until now, that’s been a gnarly problem: measurement aircraft — even scientific drones — are expensive, and a little data can be dangerous.

Releases of carbon dioxide in Indianapolis

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Credit: Bedrich Benes and Michel Abdul-Massih

Researchers at Arizona State and Purdue University created Hestia, a visualization showing the hourly, building-by-building changes in carbon dioxide emissions in Indianapolis, Ind.

There is data about national and industrial sources, but much less was known at the local level.
Now, we read of a comprehensive survey of carbon dioxide releases in Indianapolis, Indiana, United States. Using a bewildering range of data sources, Kevin Gurney, an associate professor of ecology, evolution and environmental science at Arizona State University, estimated how much each source of carbon dioxide was making, and then mapped it on the square city.

The key data came from city property tax information, says Gurney, “which tells you a lot about every structure: where it is, what it is, the floor area, primary fuel and primary use.” That data — on roughly 100,000 buildings — was poured into a computer program normally used to size air-conditioners and furnaces for individual buildings.

Other data came from at least 20 other sources, including “plain, old solid traffic data,” covering volume, frequencies, and vehicle classes.

Tracking the carbon

The results showed intense carbon dioxide emissions from the city’s power plant, airport, industries and roads, together with a more diffuse but widespread releases at houses and apartments.

Because the study focused on local carbon dioxide releases, it did not account for fossil fuel burned remotely to generate electricity. “The real push is to characterize where carbon is leaving the land surface; we are trying to connect this to measurements of carbon dioxide in the atmosphere,” says Gurney. “The fact that someone puts a plug in the wall is certainly driving activity at a power plant, but the carbon dioxide is leaving at the power plant, not at the plug.”

Measuring the carbon dioxide released to supply a kilowatt hour of electricity for a city is difficult, says Gurney, as the electricity could have originated at a coal or wind plant, which makes “a very big difference” regarding greenhouse gas.

Lights on, its dawn!

By modeling hourly carbon dioxide emissions, the data reflect the mundane details of everyday life, says Gurney. “We all know how we live our lives: most of us get up, get in the car and go to work, and the data really shows almost perfectly: in the morning, residential use goes up, then goes down as the roads light up; it’s a mass movement of human beings through the urban landscape as we go about their business.”

The maps and other data imply that we are all in this together, Gurney says. “I’ve been doing climate science for 25 years, and any time I talk, the public has a variety of understandable reactions. [Many think] it must be somebody else, or the oil companies, but in urban lands, it’s everybody, it’s us, and I think in some ways that is empowering.”

Still, why bother tracking carbon dioxide, block by block, when we know global releases of the gas are surging, to 37 billion metric tons a year in 2010? The goal is to understand the global carbon cycle, the phenomenally complex transfer and transformation of the primary atom of life — which also can form carbon dioxide, the major greenhouse gas. “Cities don’t have a lot of information about how to reduce emissions,” says Gurney, “but a lot of cities are making targets for greenhouse gases,” and they need to know how to reach those goals.

After a previous project cataloged carbon dioxide by county, he says, “People from the cities said, ‘This is great, but we need more detail; we are just a blob on your map.’”

A second motivation is to check adherence to climate treaties. “In some countries, like the U.S. and China, a roadblock to engaging in further international regulation is the inability to verify reductions,” says Gurney. “I would love to trust everyone, but good treaties have verification — look at arms control — and there wasn’t any for greenhouse gases. We are trying to show that this can be done, with independent data, using reproducible scientific techniques.”