It’s no surprise that after President Trump withdrew from the Paris Agreement, that states and cities stepped up to the plate and said, “Climate change is real, and no amount of fake news can stop it.” A number of mayors and governors across the political spectrum have pledged to take action about climate change on their own, and have already been starting to do so.

Those mayors and governors could benefit from a new study from MIT that shows how cities can fight climate change most effectively.

The study analyzes how local planning policies could either complement the Obama administration’s Clean Power Plan of 2015 or compensate for its absence. The researchers analyzed 11 major U.S. cities—Atlanta, Boston, Chicago, Cleveland, Denver, Houston, Los Angeles, Miami, Philadelphia, Phoenix, and Seattle—and developed models projecting emissions through the year 2030, based on several different policy scenarios.

What the researchers found was that it will be easier to reduce emissions from residential energy use rather than from local transportation. And that reduction will happen mostly because of better building practices rather than greater housing density.

Requiring newly built homes to be more energy-efficient would reduce residential emissions by an average of 6 percent through 2030, the researchers said, but requiring existing homes to be retrofitted to increase efficiency would cause a further 19 percent reduction in residential energy emissions.

The researchers were surprised to see that there was less benefit from reducing the number of single-family homes and replacing them with multi-family residences.

“Shifting people to multifamily buildings is what planners have always wanted to do, but that’s actually not as effective as most advocates would have thought,” said David Hsu of MIT, one of three co-authors of the paper summarizing the study’s results.

The greater housing density “would have virtually no incremental benefit in terms of reduced residential energy use and CO2 emissions,” the paper states.

The reason for this, the researchers found, is that as new homes become more energy-efficient, the energy use differences between larger single-family homes and homes in multi-family dwellings will shrink.

Hsu said the impact of policies related to construction standards and retrofitting alone is significant. “You can do a lot of things at the local level to affect housing stock that are basically equivalent or even more aggressive than the Clean Power Plan,” he said.

On the other hand, transportation is what the researchers referred to as a moving target, although a federal mandate increasing vehicle fuel efficiency to 54.5 miles per gallon would reduce auto-based emissions in the 11 cities studied by 38 percent. And that’s without any additional mass transit or density programs. That number could increase to 46 percent if cities adopted robust transit and density policies.

“The results for increasing the average fuel efficiency of the U.S. fleet are still stronger than what we can do on the planning side,” Hsu said. But he did note that this is a relative outcome, and incremental emissions reductions from increased use of mass transit and other traffic-related policies could be worth pursuing at the municipal level.

“We’re trying to be hopeful,” Hsu concluded. “It’s really just [about] getting planners to think about what makes sense in their market. There’s not going to be a policy idea that works everywhere equally…if you have a fixed amount of time and political capital and focus, you should do the most efficient thing.”

So, there’s a lot that cities can do at the municipal level to combat climate change, but the political will has to exist in order to do these things. Oftentimes, increasing available public transportation, for example, is a long-term goal that requires tax levies. But tax levies (or bond issues, as they’re called in some states) are not very popular, even though they may be for the greater good.

What do you think? What can cities do to combat climate change in an efficient and practical way? Please share your thoughts in the comments.

Photo: A city street in Boston. Photo via Pixabay