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The cities of tomorrow, ones we live in today, will look very different to the ones we grew up in. The climate emergency means we will fundamentally change how we live or the inputs to how we live like energy, materials, circularity, ownership vs use and more. We are nature - so how we protect and regenerate the systems that sustain us will be key. And while the majority of non-human nature can be found outside of cities, about now we cross the threshold in time where the majority of people now live in cities. In living memory three in ten people lived in cities, by the end of this decade six in ten will. Our embrace of wider nature will happen in the streets, buildings and parks of dense population centres - sometimes out of sight of grass, trees or birds. Cities are where our future will be created.

What is nature? Beyond just parks or trees and species we enjoy (hey birds are great - we agree) it means spaces where natural ecosystems can operate effectively for the benefit of all. An easy way to imagine nature in this way is to answer the question ‘what would nature do here over time, without our intervention?’

We need to be among it also. Wider nature creates and sustains life in cities, makes us happier and healthier, mitigates the negative affects of transport and industry (GHG, noise, dust, heat) and is both cheaper and more effective than grey infrastructure. But most importantly wider nature reminds us of who we are and to respect and preserve wider nature.

Today we don’t create enough space for nature in cities. The World Health Organisation specifies 15m2 of green space per resident and green space within 300m of every city resident for healthy living. Five of the ten densest urban areas in the EU are in Spain and all of these are in Barcelona or Valencia. If you exclude the hills of Collserola in the city of Barcelona we have 7.5m2 of green space per resident and with some exceptions do not often have green space within 300 metres (less than half of urban Europeans do). Tree-lined streets are useful but on their own do not equate to green space as we need it.

The ideas and attitudes that contributed to the climate emergency will not be the ones that help us meet the emergency and change the equation in our favour. While parks and street trees are vital their potential scope for significantly increasing green space in cities is limited. Most dense cities in Europe have maximised possible space for parks and street trees and only a 10% increase remains possible. We should take this 10%, but it is not nearly enough. If we can shift our thinking to look at other spaces for greenery, our chances to make a difference are improved.

Sixty per cent of our opportunity to increase green spaces in Barcelona lies in the ‘continuous urban fabric’ of the city. This means looking at our sidewalks, carparks, walls, roofs and commercial and public spaces with fresh eyes. Often these places are under-used or significant space is taken by a single use asset or piece of infrastructure. Picture the wide sidewalks in the industrial part of town nobody walks in, the carpark rooftops that bake in the Summer sun or the extensive, plain grey walls of office buildings, government offices and shopping precincts. These pieces of the urban fabric were created with a single use in mind, with cost savings as a significant factor and with low maintenance costs desirable also. They were imagined for their economic use primarily with their environmental and social use of lesser concern.

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When the land titles, buildings regulations and city grids of most urban centres were developed the climate emergency was science fiction or a fringe environmentalist concern. The urban plan Barcelona works to today was approved in 1976 when the Vietnam War was drawing to a close, VHS had just been released and Spain took its first steps toward democracy after Franco. As well as different spaces for green spaces to exist we can find different ways to conceive of land and infrastructure use. It’s important business can flourish for a range of reasons but it shouldn’t be at the expense of our environmental health: now or for future generations.

We can make use of a space for commercial activity but also ask the question: ‘how can this site give back to the local environment as well?’ Should this roof be a green roof? Can our empty land for use in 2040 be turned over for carbon capture in the meantime? Could the carpark be depaved rather than repaired to help the water table and prevent runoff and loss? Questions like these are already part of building and urban planning guidelines for cities around the world and will be here soon also.

Where to start? All nature-based solutions that help are worth consideration but, given the urgency, those with the lowest cost, quickest results and greatest ease are worth a close look now. In Barcelona for example half of the city area today is unbuilt and half of that area is suitable for different use right away. If that land was used for urban nature it could offset 40% of the city’s greenhouse gas emissions. If all unbuilt land was given over to nature use it would nearly offset all emissions in the city. This is directly in line with the stated goals of the climate emergency response policy document and nature plan for 2030.

We could start with the parcels of land laying empty that dot the city in the middle and outer zones like Poblenou, Fabri I Coats and La Sagrera. What were once factories or logistics centres can be urban biodiversity hotspots today, and maybe into the future as well. It could be some time before these pieces of land become new homes, schools, shops or hospitals and they can be useful today in the meantime. Turning wastelands into biodiversity parks that also draw down carbon as an interim or long-term response to the climate emergency supports our city in a range of ways. It addresses the nature imbalance per person, bringing nature within 300m of more people as the WHO asks. It supports biodiversity through habitat increase and creates more bridges between urban species populations and crucially it begins to remove more carbon from the atmosphere than we do today.

The cost to open our empty land to let nature do its work is minimal and the benefits are many and substantial. On such a simple idea now is the time to tots remant en la mateixa direcció.