Dear Zero: Please accept my apology and my explanation of why I hate AI images of buildings covered in trees

We have a carbon problem with construction, but putting trees on tall buildings solves nothing and could make it worse, and these images are everywhere now.

Zero is “a global community that raises awareness, shares knowledge and empowers its members to meet our vision of a zero carbon construction industry.” Its mission:

ZERO is our answer to construction’s big 5 billion tonnes of CO₂ per year problem. As a global community of professionals, we have a common goal to make construction a zero carbon industry. We want to work with more than just leaders and decision makers because we are all responsible to answer the challenge and to support those who have to make decisions on change.

ZERO has created a valuable playbook that is “a foundation to many ideas, concepts, and routes to reducing carbon in your construction projects.” I am going to join ZERO and will introduce my sustainable design students to it, along with their Zero Next Program, where they “aim to unite young people around the world to champion sustainability and reduce embodied carbon for a cleaner planet.”

All good stuff, which is why I owe ZERO an apology.

ZERO used this image on a post on Linkedin, and these always trigger me. I did my own Linkedin post, writing:

“I know this organization is just looking for an image for their post, but this is like Portlandia's "just put a bird on it" except with trees. Planting trees on giant buildings does not make them green or reduce carbon emissions, it takes tonnes of extra structure to support them. Study after study shows that we want lower buildings closer together! That is how you drive carbon reduction in construction.”

My post got all kinds of comments, and the poor ZERO people got dragged in. But I feel that I have to explain that these kinds of images are really problematic, especially when they are used by organizations that know a thing or two about building.

It is a mission I have been on ever since Stefano Boeri designed and built the Bosco Verticale (vertical forest) in Milan. It has been the poster child for “green building” ever since, even for affordable housing, which it certainly isn’t. It is a wonderful, glorious building that deserves to be celebrated. But it is also a distraction.

Architectural renderings are powerful things. This rendering of the Bosco Verticale launched a thousand blog posts that actually helped get it built; Boeri writes in his book on the building:

To convince my clients, I asked a journalist friend to publish a picture in an Italian newspaper showing the two towers covered with trees and a compelling title: The first ecological and sustainable tower to be created in Milan." ...I added in that article, which was so successful as to push my clients to take this little "quirk" seriously- that in addition to carbon dioxide, the leaves of the trees would also absorb the pollutant micro-particles created as a result of urban traffic and so would help clean the air in Milan, as well as producing oxygen in turn.

But it is a stretch to call it ecological and sustainable.

Look at Bosco Verticale under construction and at the amount of concrete that is cantilevered out to support the trees in giant planters. Boeri explains:

“From an architectural standpoint, the balconies are the most important element of the vertical forest.... in their final configuration, they all extend out for a distance of three meters and 25 centimeters. This solution has allowed an expansion of the inhabited spaces in the open air and at the same time the creation of plant pots with a greater depth (up to 110 centimeters) The overall surface of the balconies is approximately 8,900 square meters. [95,798 square feet]”

It takes a lot of concrete to support cantilevers that deep, especially when you load a planter onto the end of it. I don’t have hard numbers, but I suspect the trees will never absorb a fraction of the upfront CO2 emitted, making the concrete for them. And, of course, we shouldn’t be building out of concrete in the first place.

There are other problems with the image that ZERO used, basically a bunch of tall buildings in a park. We have seen it before, a hundred years ago from Le Corbusier. There are many reasons why this concept has been challenged, but with our new obsession with embodied or upfront carbon, the problem today is that tall buildings are not carbon efficient. In my post How tall should a building be: How not to build in a climate crisis I quoted the UK branch of Architects Declare, which wrote an open letter about them:

The unavoidable fact is that, in terms of resource efficiency, the embodied carbon in their construction and energy consumption in use, skyscrapers are an absurdity. The amount of steel required to resist high windspeeds, the energy required to pump water hundreds of metres above ground and the amount of floorspace taken up by lifts and services make them one of the most inefficient building types in a modern metropolis. It could also be argued that skyscrapers further detach us from any meaningful relationship with the natural world. Above about ten storeys, balconies don’t work because it is simply too windy, so high-rise apartments are hermetically sealed – as isolated from nature as possible.

Yet all these renderings of buildings have them covered in “nature.” Can it live above ten storeys? Author Tim de Chant wondered about this back in 2013, before Bosco Verticale was finished.

Want to make a skyscraper look trendy and sustainable? Put a tree on it. Or better yet, dozens. Many high-concept skyscraper proposals are festooned with trees. On the rooftop, on terraces, in nooks and crannies, on absurdly large balconies.

He didn’t think it would work.

There are plenty of scientific reasons why skyscrapers don’t—and probably won’t—have trees, at least not to the heights which many architects propose. Life sucks up there. For you, for me, for trees, and just about everything else except peregrine falcons. It’s hot, cold, windy, the rain lashes at you, and the snow and sleet pelt you at high velocity. Life for city trees is hard enough on the ground. I can’t imagine what it’s like at 500 feet, where nearly every climate variable is more extreme than at street level."

Bosco Verticale works because it has a squad of flying gardeners, hardly an economical and sustainable model.

Every four months, they fly around the Vertical Forest. They hang by rope from the edge of the roof and descend by jumping between balconies. Botanists and climbers, only they have the consciousness of the richness of the lives that the Forest hosts in the Milan sky.

Now everybody is doing it, like Heatherwick’s ridiculous 1,000 trees project in Shanghai, with trees in giant concrete pots, another poster child for greenwrapping.

I tried to find the source of ZERO’s image through Google and got “green city with alienesque architecture.” I didn’t find theirs, but I did get served a thousand towers covered in plants and trees. This is now the stock image of the future of architecture. And it scares me.

This is why I owe ZERO an apology. They are doing important work and are not trying to greenwash or greenwrap anything, they just want a nice green image for their post. I am the one with the problem: these images drive me nuts.

I love the Bosco Verticale, but every time I see it used to illustrate building a better world, I feel compelled to point out that it is not a green and sustainable model in a world where we worry about upfront carbon emissions. And every time I see an AI rendering of buildings covered in green stuff, I have to point out that it is pure greenwrapping, putting a bunch of trees on a built environment that we would be appalled by if it was grey instead of green. Poor ZERO has a twofer going here, with both Bosco Verticale and a tree-covered AI-generated Voisin plan.

Matthew Jackson, co-founder of Zero, responded to all the comments with:

Thank you for the engagement but a fantastic example of a bunch of comments who haven’t read the post just looked at a picture. Which could be trees or maybe crawlers? Who knows?! I suppose all attention to ZERO is positive though so I thank everyone for their engagement (even if it’s a reaction to a picture rather than the actual importance of uniting efforts in reducing carbon across construction)

Yes, it is a bunch of comments from people who just looked at the picture, including me. The content of the post, and Zero’s work, are critical and important.

But images matter, especially for architects! It is why we start our blog and Linkedin posts with them; they grab the reader’s attention. But they are as important as the words that follow. It’s why, especially in the age of AI, we have to be so careful with our choice of them, to ensure that they reflect our values and our message, and are not just another pretty picture of buildings covered in green stuff.