How cities can lead the sustainability transition

Written by Marc Palahí, Stefano Boeri, Maria Chiara Pastore and Vicente Guallart. on 24 September 2019 in Opinion Plus
Opinion Plus

We need to rethink our relationship with nature when building cities, argue Marc Palahí, Stefano Boeri, Maria Chiara Pastore and Vicente Guallart.

Photo credit: Adobe Stock


Human civilisation started with the emergence of the first cities. Since then, cities have in turn shaped human civilisation. Now we need to make our cities sustainable.

The industrial revolution triggered unprecedented urbanisation. Before then, just seven percent of the world’s population lived in urban areas. Two hundred years later, more than half of the world lives in cities.

Industrialisation has radically transformed our economy and made it dependent on fossil resources to meet increasing demand for energy and materials.


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For the last two hundred years, we have relied on burning coal, oil and gas to generate electricity, while steel, concrete and plastics have been used to build our cities. The problem is that this is not sustainable, as it is based on the use of finite resources.

We have now arrived at a tipping point. Our urbanised world, powered by a fossil fuel economy, has become too big for our planet. We are now crossing planetary boundaries caused by climate change, such as the loss of biodiversity and the degradation of our natural capital.

Cities are some of the worst offenders: they consume most of the resources that we use; be it energy, materials or food. They are also responsible for two-thirds of the world’s greenhouse gas emissions. Considering that, by 2050, we expect two-thirds of the global population to be living in urban areas, we clearly need to rethink our model of cities.

Cities need to take the lead in this transformation. The challenge is enormous. It requires a new and holistic approach to rethink cities as living socio-biological systems or ‘biocities’, built and powered using renewable energy and materials as well as green infrastructures.

“Considering that by 2050 we expect two-thirds of the global population to be living in urban areas, we clearly need to rethink our model of cities”

Forests can be our inspiration

Cities emerged because they are the most efficient way to organise ourselves and create social and economic capital while minimising infrastructure costs. The same, from an ecological point of view, is true for forests.

Forests are probably the most “efficient” ecological system on earth to support life and help it adapt to change. They are the most important terrestrial source of oxygen, water and biodiversity and our most important terrestrial carbon sink.

Forests are the “cities” of nature, trees their buildings and wood the most versatile and renewable material on earth. It is reasonable to assume that forests, trees and wood need to become the backbone for our sustainable biocities. But how can we support this biologisation of our cities?

“Forests are the “cities” of nature, trees their buildings and wood the most versatile and renewable material on earth. It is reasonable to assume that forests, trees and wood need to become the backbone for our sustainable biocities”

The importance of wood

Globally, we still need to build 50 percent of the urban fabric that will be required by 2050. But this cannot be built using just steel and concrete. Their production already represents more than 10 percent of global carbon emissions and they are very much responsible for the fact that our currently built urban environment uses 50 percent of the resources that we extract globally (around 85 billion tons).

Wood is the only significant construction material that is renewable and can be grown sustainably. In addition, wood construction is experiencing a revolution due to the use of new wood engineering products such as cross-laminated timber. These new products make it possible now to build skyscrapers out of wood using modern industrial prefabrication methods.

Wood elements are built in factories with only final assembly taking place on site, reducing execution time and waste, and increasing safety and productivity. Wood is also an extraordinary material for building in areas with a high seismic risk, because of its elasticity, lightness and flexibility.

Wood is especially competitive if we look at its environmental benefits compared to steel and concrete. Wood construction is the most effective carbon sequestration and capture technology that we can directly use in our cities. Each 1mᶾ of wood engineering product stores one ton of CO2 and avoids producing more than two tons of CO2 compared to using concrete. These benefits explain why wood is going to be the material of the 21st century.

“We need to rethink our relationship to nature, considering it essential to our daily lives and to the long-term habitability of the planet”

The power of trees

The biologisation of our cities also requires a strategic approach to the use of trees and forests in urban areas. Trees can cool cities by between 2C and 8C. They can also substantially a building’s energy consumption when cooling by around 30 percent, or heating by 20 to 50 percent, depending on the climate and buildings.

Urban forests clean the air and offer important health benefits to citizens, like lowering stress levels. Orbital forests around our urban areas are also important for recreation, biodiversity and improving micro-climates. Furthermore, one-third of the world’s largest cities get a significant proportion of their drinking water from forested areas.

We need to rethink our relationship to nature, considering it essential to our daily lives and to the long-term habitability of the planet. A new approach is needed for our cities, whether they are planned or unplanned, newly founded or long-established. We must demineralise and regenerate already built cities with forest surfaces and plants, while building new forest cities in those parts of the world where we still need to tackle new urbanisation. Only then can our cities begin to shape a sustainable future.

About the author

Marc Palahí is director of the European Forest Institute, Stefano Boeri and Maria Chiara Pastore are architects at Stefano Boeri Architetti, Vicente Guallart is the founder of the Institute for Advanced Architecture of Catalonia

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