Greenhouse gas emissions: How do Nashville, Knoxville stack up to peers around the world?

A new report by international scientists allows people to compare carbon emissions from a broad swath of cities around the world, including in Tennessee.

As the Trump administration adopts policies that encourage fossil fuel usage, cities across the U.S. have made their own efforts to slow the release of greenhouse gas emissions and to temper the pace of climate change.

Not every city measures its emissions, but some — including Knoxville and Nashville — participate in self-reporting programs, and the new study gathers some of their data in one place.

These programs' methods vary, so a group of scientists standardized the information, allowing for an analysis of emissions per-capita. The study was published in the journal Nature. The authors honed in on carbon dioxide emissions from industrial processes, agriculture, waste and wastewater treatment, transportation and emissions from building and other stationary sources.

It's important to note that these cities choose to participate in the reporting programs. That means many cities that don't track their emissions may have worse emissions. Also, cities vary widely by their geography and types of industry, factors that affect the level of emissions.

"The focus on cities is something that is very new,” said Felix Vogel, one of the report's authors, and a research scientist at the government-run Environment and Climate Change Canada.

Vogel hopes that tracking the cities' emissions will show which carbon management actions work which don't.

On a per-capita basis, Nashville and Knoxville have more carbon dioxide emissions compared to the U.S. cities in the sample of peers, except for Cleveland. Their emissions were greater than Austin, Atlanta, Denver, Seattle and others. Most of the cities reported their emissions in 2017, but the underlying data was a few years old in some instances.

The study looked at 64 cities in the United States and 279 from other countries. To narrow the list, USA TODAY NETWORK - Tennessee chose a sample of 15 cities with populations from 150,000 to 1 million.

While Nashville and Knoxville may look high on this list, they are below the national average. The nation's total CO2 emissions were 16.2 metric tons per capita in 2017, the equivalent of greenhouse gases produced by more than three cars driven for a year. Nashville's was 9.3 and Knoxville's was 10.3.

Some cities in Taiwan and Canada outpace both Nashville and Knoxville. 

Nashville has a target of reducing citywide greenhouse gas emissions by 30 percent by 2030, based on a 2017 report produced by the city's Livable Nashville Committee. Metro officials are now working on a plan of action.

Mary Beth Ikard from the Mayor’s Office of Transportation & Sustainability said reducing emissions is dependent on how the Tennessee Valley Authority supplies energy to Nashville. TVA has historically relied on coal-fired power plants — one of the most carbon-intensive sources — but its energy mix is changing dramatically.

Nashville is considering buying renewable energy for Metro operations, Ikard said. Also, Metro officials want to encourage people to walk, bike and use mass transit more.

In Knoxville, city leaders are focusing on emissions from urban agriculture, according to the Carbon Disclosure Project, a repository of city emission information. The city was working on educational materials for home landscaping and gardening.