Buildings towering over polluted city are unlike all others across skyline

For years, one solution to tackling human-created climate change has been to plant more trees, and one architect decided to take the concept a step further and build an entire forest.

Roughly 800 trees, 5,000 shrubs and 15,000 perennials and ground-covering plants make up a forest equivalent to 322,000 square feet in the Porta Nuova district of Milan, Italy. Only, this forest stretches up into the sky and covers two residential towers.

In this picture taken on Aug. 3, 2017, a partial view of the vertical forest residential towers at the Porta Nuova district, in Milan, Italy. If Italy's fashion capital has a predominant color, it is gray not only because of the blocks of uninterrupted neoclassical stone buildings for which the city is celebrated, but also due to the often-gray sky that traps in pollution. The city has ambitious plans to plant 3 million new trees by 2030 -- a move that experts say could offer relief to the city's muggy and sometimes tropical weather. (AP Photo/Luca Bruno)

"We are building a forest in the city," Stefano Boeri, the architect of the Bosco Verticale, or Vertical Forest, project, told The Discovery Channel as the towers were under construction.

The two residential buildings, 260 feet and 360 feet in height, respectively, were built from 2007 to 2014, and merge natural and industrial environments. The project was "a device for limiting the sprawl of cities through greenery," according to Stefano Boeri Architetti's website, and it comes along with a few environmental benefits as well.

In this picture taken on Thursday, Nov. 15, 2018, architect Stefano Boeri gestures during an interview with the Associated Press as the vertical forest residential towers are visible in the background, in Milan, Italy. (AP Photo/Luca Bruno)

With foliage shielding the building's structure, the leaves filter the sun's rays rather than allowing the building's facade to absorb or reflect them. When the latter happens during a heat wave, it can create a warmer microclimate within the area, a phenomenon known as the urban heat island effect. This doesn't just mean a warmer area, but also an increased risk for people vulnerable to extreme heat.

In one of the most extreme cases of sunlight interacting with architecture, the reflection of sunbeams off of a building in London once reportedly melted the bodywork of a Jaguar that had unknowingly been parked in the fry zone. The building was the 20 Fenchurch Street skyscraper, also referred to as The Walkie-Talkie due to its shape. Unfortunately, that shape acts as a concave mirror, focusing sunlight onto nearby streets to the south. A permanent awning has since been built to intercept the rays.

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In addition to shielding the structures from adding to the heat island effect, the green curtain "regulates" humidity and absorbs carbon dioxide and microparticles while producing oxygen.

Cities worldwide produce roughly 70% of the carbon dioxide in the atmosphere, though forests and wooded areas are able to absorb more than half of those emissions, according to a press release issued by Stefano Boeri Architetti in May of 2021. The Italian firm is hoping that increasing forested areas within and around cities would bolster the areas' abilities to both mitigate climate change impacts and reduce the production of carbon dioxide.

"Nature-based solutions can favor sustainable urbanization, restore degraded ecosystems, improve climate change adaptation and mitigation and help risk management and resilience," architect Francesca Cesa Bianchi, partner of Boeri, said in the press release.

Pollution has long since plagued Milan, if not the entirety of Northern Italy's Po Valley. Out of a list of 323 European cities that the European Environment Agency (EEA) had collected air quality data from during 2019 and 2020, Milan ranked 303rd on the list with some of the continent's worst air quality. Other northern Italian cities also occupied the 300-ranks alongside, mostly, cities from Poland. In the most recent report on air quality in Europe, published in 2020, data from 2018 found that Italy saw some of the highest pollution-related deaths on the continent, according to the EEA.

To be able to have a positive impact on the city, Boeri had to ensure that the lofted plants wouldn't do more harm than good. Storms and strong winds can significantly damage trees. Add in the factor of being grown on the side of a skyscraper, and any branches or boughs knocked about have a bit more of a distance to fall. They could also impact the actual structure, so experts from engineers to botanists were consulted on the matter.

"It's been a challenging work because I'm a structure engineer and in this particular project I didn't have only to deal with proper structure but also with trees. The trees are transferring loads to the structure because they are taking wind in some way and they are transferring wind to the structure," one structural engineer told The Discovery Channel.

The team had to test the stability of the trees in a wind tunnel.

"All the trees are on the terraces, which are typically a place where you don't want to have big loads, but that's the best place for them to live so in some way we had to provide a very efficient structure providing enough strength for the trees," the engineer said.

The design is not without its critics, however. Journalist Tim De Chant voiced his concerns not just over logistics and safety, but also how sustainable the buildings were compared to investing in planting more trees on the streets that lack them, which would negate both pollution and the heat island effect just as well as placing them on a skyscraper.

Since the completion of Milan's Bosco Verticale, Boeri has undertaken similar projects, such as the Nanjing Vertical Forest in China's Nanjing Pukou District, the planning of the Smart Forest City in Cancún, Mexico, and the Wonderwoods and Trudo Vertical Forest in Utrecht and Eindhoven, Netherlands. The Trudo Vertical Forest, when completed, will be the firm's first project aimed at social housing. Others of its kind by Stefano Boeri Architetti have been exclusively high-end residential projects.

"Furthermore, by reshaping the urban environment, Nature-based Solutions can enhance inclusivity, equitability and livability, regenerate deprived districts, improve citizens' mental and physical health and quality of life, reduce violence and decrease social tensions through better social cohesion, particularly for the most vulnerable groups e.g. children, elderly and people of low socio-economic income status," Bianchi said.

Construction on the residential tower began in 2017 and remains ongoing. With 19 floors of apartments with affordable rents, the project is intended to accommodate predominantly low-income users, especially young couples, while providing a space with a high quality of life, according to the project's website.

Climate change has had, and continues to have, an impact on affordable housing at least in the United States, as the frequency and reoccurrence of climate-related disasters exacerbates the affordable housing crisis in areas prone to disaster, according to the Aspen Institute.

The housing crisis in the Netherlands, specifically in large cities, has particularly hit young people, according to the Dutch Review. The nation's Central Bureau of Statistics in 2019 found that over the course of a decade, the number of people experiencing homelessness in the Netherlands has more than doubled. The figures showed that the number of people between 18 and 65 who did not have a permanent home had gone from 17,800 in 2009 to 39,300 in 2018, according to the Nederlandse Omroep Stichting (NOS), a local broadcasting organization. At the time, one in three people experiencing homelessness were between the ages of 18 and 30, more than three times the estimates from 2009.

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