Are Cities Underestimating Carbon Pollution?

Source: By Camille Squires, Bloomberg • Posted: Monday, March 29, 2021

Greenhouse gas emissions may be worse than we thought. But figuring out the right way to calculate them is complicated.

People take pictures as smoke from California wildfires hangs over the San Francisco skyline in San Francisco. A recent study found that many cities may be under-counting their carbon emissions. The problem is: There’s no one right way to keep track. 

People take pictures as smoke from California wildfires hangs over the San Francisco skyline in San Francisco. A recent study found that many cities may be under-counting their carbon emissions. The problem is: There’s no one right way to keep track.  Photographer: Michael Short/Bloomberg

The city of Los Angeles has been collecting data on its carbon pollution footprint for over a decade as a part of its efforts to fight global climate change. In 2017, the city reported that it had reduced greenhouse gas emissions by 40% from 2008 levels, through various changes such as improving electricity usage in traffic lights, energy efficiency gains in buildings and airport design modifications. It turns out that the city’s emissions measurements were off, though – by more than 50%.

And it wasn’t just L.A.: The city of Cleveland, Ohio, undercounted its emissions by 90%, while Torrance, California, and Blacksburg, Virginia, both miscalculated their cities’ emissions by more than 100% in their respective public reports, according to a study published in the journal Nature Communications in February. Researchers from the Vulcan Project found that U.S. cities overall under-reported their greenhouse gas emissions by nearly 20%. The Vulcan Project is a multi-year effort funded by NASA and the U.S. Department of Energy  to analyze data on carbon emissions over the United States. The major discrepancies Vulcan Project researchers found between their own data  and many cities’ self-reported numbers is now  cities to rethink the way they conduct their own emissions inventories.

U.S. cities typically report their own carbon pollution loads from everyday activities — traffic congestion, electricity usage, waste treatment, as a few examples — and these inventories help direct cities’ efforts at reducing greenhouse gas emissions, whether by planting trees to bolster the tree canopy or reducing food waste. This work, often carried out by a city sustainability office, is an increasingly important aspect of urban planning, as the majority of global carbon emissions come from urban areas. Among the 48 cities included in the study, seven under-counted their numbers by more than 50%. As Bloomberg previously reported, if these results were extrapolated across the country, the under-counted emissions would amount to more than 474 million tons of CO₂ — almost 25% more than California’s total emissions for 2015.

The findings have sparked a discussion among urban emissions experts about the methodologies cities use to measure their carbon pollution, and how to collect data that best supports actionable policy.

It’s not that cities are under-reporting as a way to game the system — there’s no official system to game. Since there is no national mandate for U.S. cities to collect carbon emissions data — and no standard methodology for doing so — cities do this work voluntarily. As a result, there is considerable variability in what each city measures and how, which may help explain why their carbon pollution records don’t match the Vulcan Project’s.

Having both accurate data and actionable policy is essential for cities in the work of understanding and reducing greenhouse gas emissions. The study’s authors say cities need to be working from a more comprehensive dataset to achieve these goals.

How do cities keep track of their GHG emissions?

Most cities have coalesced around one of a few common frameworks for tracking carbon pollution. One widely used system is the U.S. Community Protocol, developed by the ICLEI – Local Governments for Sustainability, an international body of local governments working on climate sustainability policy. It offers a roadmap for local agencies to conduct their own emissions inventories, and has been used by some 700 jurisdictions nationwide, according to Angie Fyfe, executive director of ICLEI USA. Other organizations, such as the World Resource Institute and the Global Covenant of Mayors for Climate and Energy, have developed frameworks for tabulating emissions. California worked with the ICLEI and other organizations to develop its own standard, the Local Government Operations Protocol. These frameworks can vary in the way they categorize different emission sources, but are fundamentally alike in their function of summing up estimates of emissions from different places to get the full picture.

The climate office of King County, Washington, says the ICLEI’s U.S. community protocols make the most sense for the greater Seattle region, given its unique geography and communities. The ICLEI has pushed back against the Vulcan study’s findings, insisting that its current methodologies are suitable and most relevant for developing local policy.

“Local governments know a lot about emissions sources, and what strategies are needed to reduce emissions at this point in time – a couple of decades into local climate action,” says King County Senior Climate Program Manager Matt Kuharic. “Having a good baseline understanding of emissions is important because there is quite a bit of variability from one community to the next.”

In general, ICLEI’s community protocol guides cities in identifying and tabulating emissions that come from three different levels, or “scopes” of human activity. The scopes are organized by the relative level of influence a city has over its emissions sources. The first scope targets direct emissions, such as from vehicle travel, while the second scope targets indirect energy-related emissions, such as from electricity consumption. The third covers emissions from sources outside of a city’s boundaries that are still relevant to city activities, such as from a landfill or solid waste processing.

The protocol asks cities to identify five emissions sources that collectively cover all three scopes, though cities may measure additional emission sources where relevant. A port city, for example, may include the emissions of the local marine shipping industry, as it may be considered part of that community’s activities.

“The protocol is very focused on action, control, ownership and influence that local governments have,” says Fyfe. “It’s very policy driven.”

So, have cities been doing inventories all wrong?

The way cities have been tracking their emissions isn’t necessarily wrong. Instead, the Vulcan Project’s study indicates that while the ICLEI’s methodology and others like it are sound, there may be issues with the qualityof the data that cities are collecting.

The Vulcan Project takes a broad geographic approach to measuring carbon pollution: It makes use of multiple publicly available government  datasets to evaluate fossil fuel emissions at a given location, be that a single factory, or an entire city. It then aggregates all emissions sources for that location and cross-references them against data on the amount of CO₂ in the atmosphere (sourced from public agencies such as NOAA) to confirm accuracy.

However, the Vulcan method only captures emissions that come directly from sources, such as a fuel-burning plant. For the study, the Vulcan Project then compared that data to the cities’ data, which is how it spotted significant discrepancies. Vulcan study author Kevin Gurney attributes much of this to the way that cities collect and interpret their own data.

“We’re really not criticizing the protocols,” says Gurney, a professor at Northern Arizona University and lead author of the study. “We’re worried about the hard part, which is collecting data, managing, manipulating, cleaning the data — to turn it into the useful bit of information.”

On the one hand, self-reporting gives cities the ability to be more flexible and adapt their inventories to local needs and policy levers — for example, it helps cities understand whether they should prioritize energy efficiency with programs to help homeowners reduce electricity consumption, or reduce on-road emissions by greening a public bus fleet. However, it also leaves open the possibility for cities to miss critical information, or to store incomplete datasets. Fyfe at ICLEI says that its staff offers cities resources and support in verifying the data they collect for their inventories, but ultimately the inaccuracies may be a matter of perspective.

Data on liquid fuel emissions from an industrial sector, for example, may prove difficult for an individual city to inventory. The process of collecting and interpreting that data is difficult to make sense of with few data points, such as a singular steel mill on the outskirts of a city. By looking at things at a national scale using EPA datasets, Gurney says, the Vulcan Project is able to better interpret this data and more accurately capture the emissions generated by various sources.

Gurney also says that collecting emissions data can be costly for cities, in terms of time, money and resources. It’s for that reason that many places, like King County, Washington, conduct inventories periodically, but not every year. The infrequent inventorying alone may affect the quality of the data, but according to Kuharic, the emissions data doesn’t change often enough to warrant that.

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Gurney counters that if mitigation is the goal, then more frequent inventories are necessary to understand how a city is making progress towards that goal. Gurney hopes that large-scale datasets like the Vulcan Project’s can be a reliable measure for cities to check against — a free tool at city leaders’ disposal to strengthen their inventories. Fyfe agrees, but maintains that policy influence must be a central driver of how inventories are conducted. Even if Vulcan data shows much higher emissions levels in the railroad sector than self-reported numbers, as was the case in Boulder, Colorado, for example, that may not immediately translate to a local ordinance to reduce emissions.

What can cities be doing to better meet their climate targets?

While collecting and accessing direct-source emissions data can be difficult for cities, recording emissions for the other scopes — consumption and outside sources — can be even tougher. The greenhouse gas impact of all of the goods and materials manufactured, imported and used to meet local consumer demands — regardless of where they are produced — is still difficult to tabulate accurately.

In King County’s most recent emissions report, it found that consumption-based emissions accounted for some 58.2 million metric tons of greenhouse gases, the equivalent of some 12.5 million passenger vehicles on the road in one year.

As more local governments evaluate consumption-based emissions, strategies for reducing them will inevitably require more collaboration across cities and regions. Much of this collaboration is already taking place; King County participates in the King County Cities Climate Collaboration, a regional effort among the county and 17 city governments across Washington state to coordinate mitigation strategies and sustainability work. Experts have recognized, however, the need for more support from the state and federal governments in order to enact successful large-scale mitigation efforts.

Kuharic emphasizes that all of these evaluation strategies must work in service of real, incremental action on climate, not just future plans. Accurate data, and relevant data, are only going to become more important as climate change compels cities to more drastically reduce carbon emissions.

“You bake a cake —  you can have a great recipe, written by a chef who knows everything about baking cakes, and you can still make a mess of the end product,” said Gurney. “And that’s really what I think matters, the ingredients, and how you carry out interpreting the recipe. That’s where the challenges lie. I don’t doubt that cities are absolutely trying to do the right thing, but we think cities shouldn’t have to do this alone.”