Cities, major contributors to greenhouse gas emissions in recent years, could improve their balance by becoming more densely populated.

This is according to the latest report on climate change from the United Nations Intergovernmental Panel on Climate Change. Among other findings, he notes that encouraging more people to live in cities with walkable access to necessities could reduce carbon emissions worldwide.

Where to start? And what would a dense, green city look like? “Marketplace” host Amy Scott sat down with Karen Seto, a Yale urbanization and geography professor and one of the lead coordinating authors of the IPCC report, and started by asking Seto what he would be needed to design new cities that respect the environment.

Karen Seto: Cities that have not been built are actually, at present, mostly small towns and smaller towns. So when you think about all these new developments, they don’t come out of nowhere, do they? For cities that are already compact and walkable, it will be important to ensure that there are high densities of housing and employment. The other is for cities to nurture the green spaces and ecosystems they have, because one of the ways urban expansion affects emissions is by taking over green spaces and changing land cover. It affects the local climate by building roads and sealed surfaces.

Amy Scott: The report makes it clear that upgrading existing cities, especially cities like LA and Houston that were designed around cars, can be very difficult – and, I imagine, very expensive. Is there hope that we can actually do this on a large scale?

Seto: Absolutely. I mean, it’s not about having to completely redesign the city. And most of us live in neighborhoods, don’t we? And so, it’s about making sure that we build, for example, a supermarket very close to where there’s a lot of housing. It makes the streets more passable, and you can make the streets more passable by planting more street trees, creating green spaces. It is also about modernizing existing buildings, putting in place green roofs and green walls.

Scott: Density had kind of a setback, really, during the pandemic, when a lot of people who lived in cities wanted to move to the suburbs, wanted more space. In the US, at least, homes are getting bigger again. Do you think it’s temporary?

Seto: Oh, that’s a very good question. You know, what’s interesting is that people are leaving the big cities, but it’s not that people are moving, you know, to the countryside and adopting an agrarian lifestyle. Overall, people still live in cities, but they are moving from big cities to small towns. But there’s no doubt that people still want to live in cities because that’s where the services are – that’s where the amenities that people want are, like restaurants, culture, museums , etc.

Scott: Many people have interpreted these reports as a warning that we are close to the point of no return from the severe consequences of climate change. And as someone who helped write it and lived in that data, what, if anything, gives you hope?

Seto: Well, I think the biggest source of hope is that two-thirds of carbon emissions come from cities and towns. And so if we develop solutions for cities, and if they were adopted by cities, that could eventually solve two-thirds of the problem, so that’s pretty exciting. I’m also optimistic because we’re going to add 2.5 billion people to cities and towns over the next 30 years, and those are places that haven’t been built. So we can use science to affect all these unbuilt cities of tomorrow, how they are designed and how they are operated. So we can do a lot of things.

Scott: What change have you made as a result of your work on this subject?

Seto: Oh, well, we’re making those changes at home right now. We have just switched to electric vehicles. We just ripped out our driveway, which was an asphalt driveway that contributes to storm water and doesn’t allow groundwater ingress and we ripped it out and put in a permeable driveway.

Scott: I started composting. It was my small but significant step.

Seto: Yes, they are small. I mean, I come from a family of devoted carnivores. And I will say that I’m not going to go vegetarian tomorrow, but we’re completely reassessing and trying to eat more sustainably, and really being aware of food waste and minimizing it. So we can do a lot of things at home.