What’s the Difference Between a Tree and a Building? Sometimes Nothing.

Dickson Despommier

The New City: How to Build Our Urban Sustainable Future is about the urban environment and how to make it a safer place for us to live in and, at the same time, dramatically reduce its effects on rapid climate change. I base all my proposed changes to our cities on the concept of biomimicry—how cities could be repurposed to a sustainable endeavor by emulating the essential features of a forest that enable it to sustain itself and thrive over long periods. In our current cities, construction sites, traffic, air and water pollution, infectious diseases (such as the latest pandemic), and various occupational hazards contribute to their lack of sustainability. This situation is grounded in history: the urban environment was explicitly designed to accommodate the invention of commerce at the beginning of agriculture. The perils of living in a city became even more acute shortly after the Industrial Revolution.

Today, cities contribute 60 percent of the total greenhouse gases in our atmosphere and are a significant player in rapid climate change. The construction materials currently used to build skyscrapers—concrete, steel, and glass—are responsible for nearly 20 percent of the total greenhouse gases that cities generate. It is no wonder that the United Nations Committee on the Environment strongly suggests rethinking how we construct and live in cities.

The natural world has also suffered the effects of urbanization.

The natural world has also suffered the effects of urbanization. Deforestation continues to outpace reforestation because of an ever-increasing demand for farm products as our population continues to increase. Cutting down whole swaths of forest in favor of agriculture deprives our planet of one of its primary mechanisms of managing the carbon budget: trees. Trees are nature’s air conditioner. At one time in Earth’s history, there were over 6 trillion of them. We have removed half of them in favor of soil-based agriculture. All this needs to change if we are to restore the ecological balance between us and the rest of the biological world.

We can have practical solutions to our environmental problems, and there is no better source for answers than those found in nature—specifically in trees. Howard Odum, a widely respected ecologist, once remarked: “Nature has all the answers. What’s your question?” I chose the temperate zone forests of the world as my source of inspiration because the survival characteristics found in trees and forests can be applied to the built environment of cities. Emulating natural processes—biomimicry—has been incredibly useful for generating thousands of new inventions based on knowing how nature accomplishes a similar task. In the case of cities, every building in the new metropolis can, like trees, sequester carbon, harvest rainwater, generate food, and use passive renewable energy sources to make all that happen. This is precisely what trees in a forest do every day. In addition, like trees in a forest, the buildings in the sustainable city will communicate with one another and share resources such as water, energy, and food.

Rainwater harvesting is another feature of trees that the sustainable city must embrace.

Carbon sequestration is critical to restoring the Earth’s atmosphere to its state before the mass exploitation of fossil fuels. So how could a city possibly help to store carbon simply by choosing a different construction material? It sounds improbable, but everything changed with the invention of cross-laminated timber (CLT), which can now be used to construct a building. CLT has the same density as a tree trunk and thus is resistant to destruction by fire. Proof of concept—check out the aftermath of a forest fire, and what do you see? The trunks of trees are still standing. That is because fire needs oxygen, and the high density of the trunk stops the flame in its tracks. Trees char but do not burn to the ground. For that reason and many others, CLT is gaining in popularity worldwide as a renewable, abundant construction material. In addition, mass plywood and mass bamboo have emerged as CLT-like building materials. CLT is twice as light and twice as strong as concrete and can be easily repurposed. It is cut to shape off-site and delivered to the construction site for rapid deployment. The increased use of CLT will rejuvenate a stagnant lumber industry and add economic and biological value to the regeneration of damaged, fragmented forests. In this way, city buildings made of CLT will contribute to reversing climate change by sequestering carbon.

Rainwater harvesting is another feature of trees that the sustainable city must embrace. For example, with a physical footprint of some 300 square miles, New York City gets an average of 47 inches of rain each year, equivalent to nearly 250 billion gallons of freshwater. That is half of what New York consumes in a year, and yet none of the rainwater that falls on the Big Apple is captured. If it were, there would never be any water shortages. In Bermuda, 63 thousand people live the good life dependent solely on rain for all their water needs. Many other countries are now demanding rainwater capture as a way of augmenting their annual water budgets.

…indoor farming within each building of the new city could supply enough fresh produce to feed its entire population.

Food production by trees supports various forest-dwelling wildlife with fruits, nuts, and leaves. Similarly, indoor farming within each building of the new city could supply enough fresh produce to feed its entire population. There might even be a surplus for export, depending upon the choice of food items grown. Now a 7-billion-dollar industry with an annual growth rate of 20 percent, vertical farming is becoming commonplace throughout the world and has the potential to allow each city to become its own food supplier.

Finally, the energy needs of a city must be solved without the consumption of fossil fuels if we are to make them a net-carbon-negative enterprise. There is real hope that this can be accomplished with existing technologies. For example, recent progress in photovoltaics has introduced the concept of converting clear glass windows into functional energy-producing photovoltaic cells. The technology has advanced so quickly that some transparent photovoltaic cells are now commercially available, with more examples soon to follow. If this breakthrough continues to be developed into a practical, affordable product, then imagine how much power a modern city filled with glass and steel skyscrapers could generate just by capturing the energy of the sun each morning, just as trees do when they convert sunlight into chemical energy via photosynthesis. Energy industry experts estimate that such an outcome could happen in the foreseeable future. There are already commercial buildings clad in traditional photovoltaics that produce excess energy, and it’s just a matter of time before this could become available throughout the built environment of the new city. Another addition to the renewable energy platform is the hydrogen fuel cell. Perhaps this is the one that will eventually win the day since its “waste product” is pure drinkable water.

The future of cities is bright if we can mimic nature, discard what is not working, and instead incorporate integrated new approaches inspired by something as wonderful and nurturing as a woodland environment.

Dickson D. Despommier is emeritus professor of public health and microbiology at Columbia University and the author of The New City: How to Build Our Urban Sustainable Future.