At the center of the Paris Agreement — a text that was the culmination of intense negotiations in the French capital two years ago — is the goal of worldwide net-zero emissions levels over the second half of this century. In the text, it’s referred to as “a balance” between man-made greenhouse gas emissions and various methods of absorbing those emissions.

Expert analysts agree that reaching the goal will require dramatic changes in the world’s infrastructure, whether for energy, structure — or transportation. They also agree that the objective falls a little mire out of reach each passing day.

“We are at a key point for the world, because the infrastructure built today will be in use for the next 30 or 40 years,” Christiana Figueres, a Costa Rican diplomat and founder of Mission 2020, a climate advice group, said in an interview.

Figueres is best known as one of the principle architects behind the 2015 Paris Agreement, the crowning achievement of her six-year stint at the helm of the United Nations Framework Convention on Climate Change, the main U.N. body addressing climate issues. She spoke to Infrastructure Channel from London.

“All told, estimates are that infrastructure changes can do about 75 percent of the work needed to reach our climate related goals,” Figueres said. “But what we need is an integrated approach, one that features low-impact forms of transportation, more localized production of products, energy-efficient buildings, and renewable forms of energy generation.”

The way urban areas are developed — and the ways they are connected — going forward is key, Figueres said. “There are models showing that over the next 20 to 30 years, 80 percent of the world’s population will live in cities,” Figueres said (today the figure is a little more than half). “They have to be efficient so that they do not contribute to climate change, and constructed so that they can withstand the impacts of severe weather that comes from climate change.”

Steve Winkelman, from the U.S.-based Center for Clean Air Policy, said it will be essential to change the way people and products move around. He talked about the successful development of energy efficient transit systems in Colombia, as an example of steps cities can take today in order to make a difference. In Bogota, the TransMilenio system uses a sophisticated network of automated stations built to allow passengers to quickly enter or exit fuel-efficient articulated buses that move around the city on dedicated traffic lanes. Dozens of other cities are either considering similar plans or already starting to work on them.

“The problem is not technology: there are technological breakthroughs happening all the time,” he said. “It’s a question of implementation. Most cities could do something like this with existing technology.”

Paul Chatterton, a professor of Urban Futures at the U.K.’s University of Leeds and director of the university’s Sustainable Cities Group, said any development pathway must connect multiple aspects.

“It’s not just a question of changing bits of the economy, roads, buildings, or whatever, but also looking at how those bits are connected,” he said. “Where people live, where their food comes from, how they move around. We have to look at every aspect, find every advantage. We will have to reinvent the way we do things, and build things, and move things around.”

University of California-Davis professor John Harvey, from the Department of Civil and Environmental Engineering, said that in at least one way cities of the future will look like those of the past: with more green areas and less traffic.

“In cities built after the advent of the automobile, as much as 40 percent of the surface area is paved over,” Harvey said. “Before that, it was 20 or 25 percent. I think that cities in the future will return to that level.”

Harvey mentioned multiple advantages to that kind of reverse trend. Car sharing and localized production will result in less traffic and fewer parking areas as well as less demand for cement and asphalt, all of which will reduce greenhouse gas emissions and air pollution. Reduced amounts of pavement will allow for more natural water flows and drainage; and green areas absorb greenhouse gasses and naturally cool nearby areas.

Such a future will no doubt differ dramatically from the world we live in today: green cities — Figueres remarked about the possibility of incorporating green areas into buildings themselves — connected by low-impact systems of highways and rail effortlessly moving people and products. The entire ecosystem will rely on clean energy; much of it will operate autonomously, without direct human guidance; and will be much more efficient than what exists in most places today.

Not surprisingly, many analysts said the biggest challenges to a low-carbon pathway are probably political. Though leaders of nearly 200 countries agreed to the terms of the Paris Agreement, the specific pledges of action countries voluntarily agreed to will fall far short of the 2050-to-2100 decarbonization goal at the heart of the document.

“It’s a quintessential free-rider problem,” said Massimo Tavoni, a professor of management, economics, and industrial engineering at Politecnico University in Milan. “Every country, every entity, wants others to do more, and the overall effectiveness of action doesn’t really depend on the actions of any one player.”