Like many Danes of my generation, much of my childhood was spent immersed in the world of Lego. The “City” universe was my absolute favourite. I got to play the role of urban god, carefully piecing together my dream metropolis from the ground up. I had a fire station and an assortment of other buildings but most of my constructions came from my imagination. Gardens were essential, with tiny flowers and soft plastic trees filling the spaces between my buildings. Even back then, I was obsessed with trees – both in my Lego world and the real one.

What I didn’t realise at the time was how much the layout of my pretend city – like so many real ones – was governed by roads. The foundation was always a grid of grey plates directing the flow of traffic and determining how everything else would fit together. If the roads didn’t connect seamlessly, the city simply wouldn’t work. They dictated everything. That’s how I formed my earliest, unconscious definition of a “real city”.

A few decades have passed since then and I now spend most of my time, in my work as an urban designer, rethinking and challenging what a real city could and should be. Despite all the energy and creativity they hold, urban environments are also responsible for making us sick. They pollute the air with heavy metals, trap heat in concrete jungles and surround us with so much noise that our brains and hearts struggle to find peace. Despite being home to much of the world’s population, cities often isolate us more than they connect us.

Let me be clear about one thing: I love cities. I grew up in Copenhagen, and today I live in the heart of the city with my family, right next to a busy road. I thrive on the energy that cities provide – the inspiration, the communities, the culture and the innovation. Cities are where ideas take root and where diverse people come together to create something greater than the sum of their parts. I want my children to experience this richness of life, which is why we’ve chosen to stay in the urban core. But there are aspects I don’t love: the unrelenting traffic just outside our door and the sheer amount of space dominated by black asphalt, covering about 80 per cent of the public area between buildings where I live.

That’s why I began to construct my own little slice of urban life – my garden. When we bought the house, this garden seemed like no more than a parking space. But slowly it evolved into a green oasis. My goal was to create a haven for my family; a place where we could escape the noise and heat of the city. We planted as many trees as we could afford, transforming the area into a biodiversity hub, providing shade, lowering temperatures and absorbing rainwater. More importantly, we created a sanctuary filled with birds whose songs drown out the cacophony of urban life (city birds sing louder than their rural counterparts; nature’s own way of adapting to urban noise). Our garden isn’t just about greenery, though. We also installed a noise-reducing fence made from poplar bark, a sustainable by-product of the furniture industry. The bark absorbs airborne pollutants from car exhausts, which improves air quality around our home and provides a natural, tactile material that passers-by can’t help but touch.

The poplar fence panels came from an exhibition by sla – the studio where I’m design principal – at Copenhagen’s Louisiana Museum of Modern Art. Our exhibition focused on the power of trees and nature in cities. Our fence, like trees, represents a small but effective act of resistance against the problems that urban life can create. Noise pollution, in particular, is a silent killer. It causes stress, disturbs our sleep and contributes to chronic health issues. The simple act of planting trees and installing noise-reducing materials can transform a space and dramatically improve our quality of life. Cities should not be places where we merely survive; they should be places that we truly love.

At the heart of all my work is a desire to improve quality of life – for all life. Our team includes biologists, architects, landscape architects, planners, lighting designers and anthropologists, working together to design cities that don’t just look beautiful but function in a way that makes life better for everyone. We’re also challenging the traditional hierarchy of cities, where roads and cars have always taken precedence. We’re not advocating for their removal but we believe that it’s time they stop ruling the urban landscape. City design needs to change urgently.

One of the most eye-opening experiences I’ve had was working closely with indigenous designers in Canada, whose traditional knowledge, stretching back thousands of years, offers an invaluable perspective. Their principle of considering how every decision will affect the next seven generations forces us to think beyond the short-termism that dominates most modern urban planning. How many recent developments in the city where you live have been designed for two generations after you, let alone seven?

One specific conversation with an indigenous designer left a lasting impression. We were discussing the rather technical term “storm-water management” when he interrupted to suggest we just call it “rain” or “the flow of water that falls from the sky”. This simple reframing, from technical to nature-based, shifted my perspective. Everything in nature is about flow, he reminded me: wind, water, energy, even people. Yet for the past century or so our cities have been built to disrupt these flows. This is why Copenhagen was hit so hard by flooding in 2011 (my own basement was one of thousands filled with water). And now even desert cities such as Dubai, which once laughed off our rainwater-management proposals, are asking for help as they face big water challenges of their own.

Unfortunately, meaningful change in cities only seems to happen when insurance companies and municipalities are forced to act after suffering massive financial losses. But you can’t put a price tag on quality of life. Feeling safe, connected and good are invaluable concepts. Cities should be designed to provide them.

Planting trees is perhaps the simplest and most effective way to improve urban life. Trees change not only the physical environment but also the way people feel and behave in public spaces. Think about where you would rather spend your day – in a park under a tree or in an asphalt car park under a lamppost? Nature has been proven to lower stress levels, make people feel more at ease and encourage social interaction. When we feel connected to nature, we feel more connected to ourselves and to others.

My best memory of this is our collaboration with 1,500 Copenhagen students, helping them to transform their 1960s concrete outdoor space into a social and biological corridor. The composition of their dorm was changed to include 10 per cent set aside for socially disadvantaged individuals. The students took clear social responsibility by inviting their less fortunate peers into their home. They intuitively understood the connection between biological diversity and social equity.

The path forward may be challenging but it’s exciting. We can change the way cities are built and experienced. As someone who started life literally playing with the concept of how a city should look, I now find myself working on how to grow them, for us and for future generations. Cities are often bad for us – but it doesn’t have to be that way.