In Salt Lake City, suburban sprawl is bad news for climate change

In Salt Lake City, suburban sprawl is bad news for climate change
CO2 sensors detail surprises about urban growth
SALT LAKE CITY — Multiple carbon dioxide sensors strategically scattered throughout Salt Lake Valley reveal the impacts of urban growth and suburban sprawl on greenhouse gas emissions, offering unique insight to metropolitan planners and city leaders trying to reduce their carbon footprint. In findings published this month in the Proceedings of the National Academy of Sciences, a University of Utah-led research team determined suburban sprawl causes more carbon dioxide emissions than an already-established urban core. “Youre taking an area that had nothing and adding something to it,” said Logan Mitchell, a research associate with the U.s Department of Atmospheric Sciences. The U. started what is now the worlds oldest network of carbon dioxide sensors in 2001, collecting a steady stream of data on greenhouse gas emissions for a decade. The research projects first sensor went on top of the William Browning Building on campus, with more that followed in Rose Park, Murray, Sugar House and in 2004 in southwest Salt Lake County, an area dominated by open fields. The sensor placed in the southwestern section of Salt Lake County was intended to measure greenhouse gas emissions in rural areas, but over the study period, development exploded in the area, adding another 13,000 people. Even though Salt Lake Citys metropolitan area added about the same number of people, the carbon dioxide emissions footprint was less, researchers said. “With urban growth, you are putting more people into an existing area. They dont have to drive as far to get to their jobs. Youre replacing a house with an apartment building. It is not associated with that much more carbon dioxide emissions,” Mitchell said. The southwest sensor allowed researchers to examine the effects of population growth on carbon dioxide emissions, and particularly how land use decisions might shape outcomes.

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CO2 sensors detail surprises about urban growth

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Meanwhile, lawmakers decided to change the name of the Utah Transit Authority to the Transit District of Utah because, well, no one knows why, exactly. Apparently, the Ministry of Trains, Buses and Junk Like That was too long to fit on a sign.

Jays Jokes: An inland port is great, but how do we get the ships to Salt Lake City?

Over the past few years, momentum has been building to make cities a focus of climate change action. Although they cover less than 2 percent of the earths surface, cities consume 78 percent of the worlds energy, reports the UN, and produce more than 60 percent of all carbon dioxide and significant amounts of other greenhouse gas emissions.

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But theres a problem: theres a lot we dont know about emissions in cities, because the ability to detect emissions on local, fine-grained scales is a relatively recent development. This technology is improving steadily, and this week, a paper in PNAS reports results from a detailed analysis of Salt Lake City. Its findings add to growing evidence that dense urban populations, rather than suburban sprawl, has an important role to play in climate action.

Salt Lake City has an emissions sensor network that is ahead of the game. There have been urban CO2 monitoring projects in Pasadena and Heidelberg (Germany) for more than 10 years, but only at a single location in each city. That makes it impossible to get a multi-faceted picture of how emissions vary across the different spaces in the city.

State lawmakers gave up on the idea of renaming a highway in southern Utah after Trump. They were worried too many drivers would start out on the road but quickly resign or get into legal trouble.

More sensor networks that cover multiple sites within a city are springing up, but they are relatively recent, with no data going back past a few years. But the network in Salt Lake City circumvents both of these disadvantages: it has data going back all the way to 2004 from multiple sites across the city as well as a non-urban, mountainous control zone.

This network allowed a team of researchers led by Logan Mitchell at the University of Utah to monitor the differences in carbon levels as theyve changed over time. Mitchell and his colleagues took readings every five minutes, comparing the excess CO2 within the city to the CO2 levels found in the control zone. This painted a picture of how much higher emissions were at different locations in the city compared to a background level in the atmosphere.

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There are non-human factors influencing the amount of CO2 that the sensors would be detecting. On both daily and seasonal timescales, patterns of temperature and air movement would cause relatively predictable changes. To focus just on the changes brought about by human activity, the researchers had to account for these rhythms. Once they were accounted for, a clear trend emerged.

The data showed that the increase in emissions across the sites was dependent on population density. There was population growth throughout the Salt Lake City area, but that growth had a higher impact in rural areas. In areas with fewer than 1,000 people per square mile, new housing developments brought more people out into the sprawl, and these population increases brought big increases in emissions.

In dense urban areas with more than 5,000 people per square mile, and in existing suburbs, there had also been population growth—but the increase in emissions wasnt as high as the population growth would suggest. Traffic, the authors note, plays a large role in this difference: on-road emissions increased when rural areas were developed into suburban areas, they write. But per-person on-road emissions, they explain, decline at higher population densities.

Maybe the first act of the new port authority will be to dig a trench to the Pacific Ocean.

It might not be too surprising that building housing in previously rural areas comes with a spike in emissions, but theres still an important insight here: the car traffic associated with new suburbs is an emissions force to be reckoned with, as are the energy requirements of standalone dwellings. If cities are looking to reduce emissions, population density is an important consideration.

Conor Gately, who researches changes in emissions across time and space and wasnt involved in this research, told Ars that the researchers success in drawing strong evidence from the Salt Lake City network was an important result. What really excites me here, he said, is that this is one of the first studies to show that with a reasonably-sized observing network (5-6 sites), it is possible to accurately detect annual and decadal trends in CO2 emissions at the urban scale.

Gately cautioned that it may not be possible to extrapolate perfectly from Salt Lake Citys suburban sprawl to other cities. The relationships [between population density and emissions are] very complex and site-specific, he explained. It is unclear whether their findings can be extended to other cities.

As cities become the focus for climate action, getting this kind of data becomes all the more important. There are a lot of cities in the US and around the world that are making bold commitments to reduce their CO2 emissions over the next 15-30 years, said Gately. But our ability to actually monitor their progress toward meeting these commitments is going to require exactly this type of observation. We should be discussing how to expand these sorts of systems in a way that best supports our climate goals.

In honor of the 50th anniversary of the beginning of the Apollo Program, Ars Technica brings you an in depth look at the Apollo missions through the eyes of the participants.

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