Mark Williams and Jan Zalasiewicz of the University of Leicester embark on a fascinating exploration of the potential for cities of the future.
Picture the building you live or work in. On the ground floor there is a temperate deciduous forest biome that connects directly with the external environment in the street, which itself is lined with trees that stretch off into the distance to the edge of the city, where flourishing deciduous forests are home to a diversity of life. This forest biome has been developing for several decades now, in a natural process towards its climax state. As you walk into the building in the morning you are met by calls of birds that populate the tree canopy, whilst a bee whizzes past your nose as you head for the lift. The colours, sounds and smell of the building uplift your soul as you head to work. In this world there is no tangible ‘boundary’ between your building and the biosphere, and the edge of the great city that you live in – now with more than 30 million people, but with even more non-human inhabitants, is a diffuse and intricate mix between the concrete, glass and steel constructs and the biosphere. Life is thriving in this city, colonising the spaces engineered by humans, the living assemblages changing rapidly to fill the spaces around the human ecologies. Now reflect on the world that you really live in, where the boundary between the concrete and brick ecological wasteland that you inhabit and the remaining woodlands and fields outside are so visibly demarcated by the giant tarmac ring road that surrounds your city.
Our planet is an old planet, one-third of the entire age of the cosmos. It sustains a remarkable diversity of life, fed by the energy of its local star and sustained by the liquid water that exists at its surface. For four billion years the biophere has been evolving its increasing complexity – albeit with occasional setbacks in mass extinctions, to produce the wonderful variety of animals, plants, fungi and microbes that form the modern biosphere. Each stage of life’s story has helped engineer the next. Thus, the evolution of microbes that used light, water and air to build their tiny bodies – through the process of photosynthesis, helped spread the biosphere across the entire surface of the Earth more than 2 billion years ago, sowing the seeds for the oxygen-rich atmosphere that was vital for the evolution of animals.
Another major stage in our planet’s evolution came half a billion years ago, when the empire of the microbes was superceded by one dominated by multicellular organisms, as the ‘Cambrian explosion’ of such complex life brought, in a few (geologically) brief tens of millions of years, worms, crustaceans, corals, sponges and other such animals to our world. Evolving into predators and prey, they built complex ecosystems. When they fed, these organisms churned through the sediment of the sea floors, and filtered the seawater too, to allow oxygen to reach greater parts of our planet.
A couple of hundred million years later, this complex ecosystem spread from the ocean realm that had been its exclusive home, to clothe the land in forests, with insects, fish and amphibians accompanying the plants as they transformed the landscape, forming deep rich soils and changing river patterns.
Now humans too – in their short geological history, have learned to bioengineer their planet. But can humans engineer a future that enhances biological diversity or will they push a diminished biosphere to the fringes of our world?
Homo sapiens is a geologically recent species, extending back just some 195,000 years, with a time-span of less than half that for ‘culturally modern’ humans that could live, hunt – and create art, too – within complex social structures. For much of that time human influence was limited to muscle power magnified through the use of various stone implements. As these tools grew in their complexity, reflecting changes in ways of thinking, humans began to re-engineer the biosphere around them. At first, the change was likely so slow as would have seemed almost imperceptible to people living 50,000 years ago. But it shows in the disappearance of certain large mammals, called the ‘megafauna’, those ‘fossil’ animals like the mastodon or mammoth, that began to disappear from the landscape as humans extended their range across the world. Later, human engineering spread domestication and agriculture from multiple sources across the planet from 14 millennia ago, and in the past few centuries has transitioned into an industrial age. Human activities now shift more sediment than all of Earth’s rivers combined, control much of the production of plants to feed us and our captive animals, and build technological systems so intimately interconnected that neither human society or its technology can exist without the other. In engineering this Anthropocene world, humans have had a tremendous impact on biodiversity, one that now threatens the stability of the biosphere in its present form.
So what can we do as a species to prevent a potentially calamitous human impact on biodiversity? We need to look to our old friend the biosphere. It is an extraordinary repository of information, acquired over billions of years and preserved in the geological record. What might it tell us about engineering a sustainable future? We could look to those structures in nature that foster biodiversity, for example the carbonate reef systems of the oceans. They cover less than 0.2% of the ocean surface but sustain perhaps as much as 35% of marine species biodiversity. Likely, reefs have helped foster biodiversity for half a billion years on Earth. Reefs are made of many different organisms, but at the core of modern reefs are corals that have fostered a symbiotic relationship with tiny dinoflagellates that live within them: this sustains the reef in zones where nutrient supply is poor and the reef can then provide a myriad array of microhabitats in which other animals can live and feed, and thrive (and in fact, the reef zone needs to be kept nutrient-poor, otherwise the life-supporting corals are overwhelmed by seaweed, and the reef ecology collapses).
So why don’t humans engineer structures that mimic this diversity? In fact we do engineer structures that are host to fabulous diversity. It’s just that it’s the wrong kind of diversity. We build hugely complex structures called cities with their immense steel, glass and concrete buildings above ground, the roads that connect these at the surface, and the underground systems of trains, drains and power cables that sustain them. These structures provide many unique ‘ecologies’ that are rapidly colonised by a huge diversity of technology. Chairs, tables, computers, sinks, toilets, chocolate bars, mobile phones and many other artefacts all evolve rapidly to fill the space of an office block. It is a diversity that mirrors in shapes and forms the biodiversity in nature. There are, for example, billions of mobile phones occupying this human ecospace. Humans have engineered environments in which these technological artefacts evolve, thrive and proliferate, but it’s a kind of ‘bioengineering’ where these structures and spaces do not foster biological diversity. There may, for example, be many ‘species’ of mobile phone in a modern city skyscraper, but how many species of animals and plants live in the building where you are reading this?
Can we engineer biodiverse buildings? In a recent scientific paper assessing the 252 miles of the New York Subway over one thousand microorganism types were identified from their genetic material. Evidently microbes are colonising human structures apace, but plants, fungi and animals need the space and resources to allow them to thrive, and our current city-structures mostly do not allow this. As cities continue to grow, the pressure to house people in concrete structures looks set to continue unabated: between 2011 and 2014 China alone used more concrete than the United States used in the whole 20th century. And while there are many good examples of ‘green buildings’ whose design, construction, use, and eventual demolition is predicated on the efficient and sustainable use of resources, perhaps we need to go a stage further, and engineer spaces – akin to a coral reef – in which complex organisms other than ourselves can live, adapt to and, with sufficient time, co-evolve with our human-made structures into new kinds of biological communities. This might sound a little crazy. A modern building’s lifespan might be just a few hundred years, not sufficient time to provide a habitat for organisms to flourish, interact, bioengineer and evolve into. But perhaps such spaces could be viewed as continua that future buildings would evolve into and around: such spaces could provide a long-term habitat for life where it could flourish and evolve, rather like the reef systems of the oceans. This might sound prohibitively expensive – and even prescriptive – but then the alternative might literally cost the Earth.
So here is a final thought. To allow us to thrive, the cities of the future will need to be green and biodiverse, like the building we began our journey in. The alternative is that they will simply become a new kind of desert, impoverished of all species, including of our own. As human population grows, we must, of course, continue to build our cities and engineer the landscape. Our collective decisions and actions of the coming decades will, though, determine what kind of planetary system we are building.