Marc Barra

Marc Barra is an urban ecologist, and he will tell you himself that the job is hard to translate. In French his title is "écologue", which is not the same word as the political "écologiste", and on the show he admitted he always struggles to render it in English, settling on "ecologist" or "ecology scientist". What he actually does is steadier than the label: since 2009 he has worked at the Paris region's biodiversity agency, today the ARB îdF, the biodiversity department of L'Institut Paris Région, producing the science-based evidence that tells cities how to bring nature back into how they are built.

Marc Barra's one big argument is that nature-based solutions are real engineering. Nature-based solutions, often shortened to NBS, are things like green roofs, restored rivers and constructed wetlands used to do a job that a pipe or a wall used to do, and you can see how they fit the wider water-tech picture. The usual knock on them is that they are soft, vague, a bit hippie. Marc Barra's answer is that his own training is literally called ecological engineering, which he describes as using living organisms, plants, earthworms, soils and rocks, to build a system that works and delivers a service. As he put it, if you look closely at how nature actually functions, there is a lot of technology in it.

Marc Barra is also clear about why cities still pour concrete, and it is not the price. He points out that a nature-based solution is usually cheaper than the grey alternative, a bioswale instead of pipes and tanks, and the literature backs that up once you set aside the cost of the land it needs. The real blocker, he says, is cultural confidence: cities are comfortable paying for the hard engineering they know, and they will not spend a euro on green infrastructure they quietly fear is not efficient. So the work is less about inventing technology and more about earning trust, which is also why he led the EU H2020 REGREEN project, a four-year effort across Europe and China to put hard evidence behind what nature-based solutions can do.

Marc Barra carries the argument all the way out to economics, which is rarer than it sounds for an ecologist, and he is honest that he had to go and learn the economics to do it. He wrote a book on producing and consuming within the limits of the biosphere, and on the microphone he framed it as a transition toward an economy of limits, where the economy is embedded in the health of ecosystems rather than the other way round. He is also refreshingly skeptical of the easy fix: the carbon market has run for years, he notes, and atmospheric carbon has not actually come down, so he trusts planning and regulation as much as he trusts a price signal.

“If you look closer at the nature processes, the nature functions, you understand that there is a lot of technology in it actually, and there's a lot of engineering. My training is called Ecological Engineering, and that means using living organisms such as plants, such as earthworms, and using the environment such as the soil, such as the rocks, to build a system that is working and that creates some advantage and some services.”

Marc Barra is, in the end, the ecologist who refuses to let nature be the soft option: he wants the green choice held to the same engineering standard as the grey one, and measured on the evidence rather than the mood. You can hear the full conversation in my Nature-Based Solutions series below.