The scale, and the rate of increase, of our consumption of resources, and the pollution it inflicts, is catastrophic. In these lectures, I will show that the same key trends that drive environmental decline are also generating disastrous social instability.
Yet cities, which are now failing to provide the most basic needs of society, can provide a healthy and civilising environment for our citizens. I passionately believe that the art of city building has never been so crucial to our future.
My cause for optimism in the face of grim evidence comes from the growing acceptance of ecological thought worldwide. Scientists, philosophers, economists, architects, and artists, often working with local communities, are now using a global perspective to explore strategies to sustain our future.
The classic statement of this approach is the United Nations report "Our Common Future", which laid down the concept of sustainable development as the backbone of a global economic policy. The core of this approach is a new notion of wealth, incorporating environmental elements previously considered limitless and free - clean air, fresh water, fertile land and sea. The ultimate aim of sustainable economic development is to leave to future generations a stock of environmental wealth that equals or exceeds our own inheritance.
I believe environmental "sustainability" needs to become the guiding law of modern urban design - an innovation that would have an impact on the 21st-century city as radical as that of the industrial revolution on its 19th-century counterpart.
As it stands, cities and buildings are the most important destroyers of the ecosystem. In London, for example, massive traffic congestion causes more air pollution today than there was before the Clean Air Act banned the burning of coal in 1956. Foul air is blamed for the fact that one in seven city children in Britain now suffers from asthma.
In Japan, Tokyo alone dumps an estimated 20 million tonnes of waste every year. The city has already saturated its bay with waste, and is now running out of sites on land.
But although cities are breeding environmental disaster, there is nothing in the nature of city living that makes this inevitable. On the contrary, I believe that cities can be transformed into the most environmentally balanced form of modern settlement. In future lectures, I shall talk about how cities, and city living, can be designed to be more efficient and environmentally sustainable.
The social aspects of city life are vital to a city's sustainability. It is only if our cities offer a vibrant, healthy and secure urban life that we can dissuade people from fleeing to the suburbs, with all the problems - environmental and social - that this exodus continues to create.
Cities have grown and changed so much that it is hard to remember they exist first and foremost for people. They are the cradle of civilisation, a place for societies to come together and exchange ideas. They concentrate physical, intellectual and creative energy.
I am passionate about the choice and diversity of city life. I love the combination of ages, races, cultures, and activities, the mix of community with the unknown, familiarity and surprise - even the sense of dangerous excitement they can generate. I enjoy the animation that pavement cafs bring to the street, the informal liveliness of the public square, the mixture of shops, offices and homes, that makes a living neighbourhood.
One of the exhilarating moments of my career was when the Parisian authorities agreed to give half the site they had set aside for the Pompidou Centre to a public piazza. Today, to my great delight, the Place Beaubourg and the Pompidou Centre teem with life, and this has led to a wholesale renewal of the areas around it.
I have been talking about the importance of a vibrant urban life - to my mind, the essential ingredient of a good city. And yet today this quality is increasingly missing.
Just ask anybody what they think of city life now. He or she will more likely talk about congestion, pollution and fear of crime, than community, animation, or beauty.
The essential problem is that cities have been viewed in instrumental or consumerist terms. Those responsible for them have tended to see it as their role to design cities to meet private material needs, rather than to foster public life.
The central distinction here is between what the American political theorist Michael Walzer has called "single-minded" and "open-minded" spaces. The first is designed by planners and developers with only one purpose in view. The second caters for a variety of uses in which everyone can participate. The residential suburb, the housing estate, the business district and the industrial zone, the car-park, underpass, ring road, supermarket, and shopping mall are all "single-minded spaces". But the busy square, the lively street, the market, the park, the pavement caf, are "open-minded".
Both types of space have a role to play in the city. Single-minded spaces cater to our very modern craving for private consumption, for autonomy, and intimacy. They are, admittedly, very efficient. By contrast, "open- minded places" give us something in common: they bring diverse sections of society together, and breed a sense of toleration, identity, and mutual respect.
Yet we have seen the first eclipsing the second. "Open-mindedness" has given way to "single-mindedness". The emphasis is on selfishness and separation rather than on contact and community. As public spaces decline, we lose the natural policing of streets that comes from the very presence of people going about their business. Spaces in cities become territorial. Now they are perceived not merely as inhospitable but as dangerous.
It is in the sprawling cities of the United States - with their ingrown ghettos, heavily policed middle-class dormitories, shopping centres and business parks - that the tendencies I have identified are most clearly seen.
In its time Los Angeles has provoked as much enthusiasm as any city on Earth. But the Californian writer Mike Davis has described how LA has grown more and more segregated and militarised. Starting at the outskirts, there is the Toxic Rim - a circle of giant garbage landfills, radioactive waste dumps and polluting industries.
Moving inwards, you pass so-called "gated" or privately patrolled residential suburbs and a zone of self-policing lower middle-class homes, until you reach a "free-fire" downtown area of ghettos and gangs. Here, the Ramparts Division of Los Angeles Police regularly investigates more murders than any other police department in the country.
Finally, beyond this "no-go area" lies the business district itself. In parts of this area, television cameras and security devices screen almost every passing pedestrian. At the touch of a button, access is blocked, bullet-proof screens are activated, bomb-proof shutters roll down. The appearance of the "wrong sort of person" triggers a quiet panic. A new type of citadel has emerged.
Our own cities are not yet like this, but many display the same characteristics writ small. We, too, have seen a retreat from the city and growing inner- city poverty, an increasing reliance on private security and private transport, the proliferation of one-dimensional spaces, and the explosion of riots.
What I have been describing reflects the fundamental dichotomy of the city: its potential to civilise and its potential to brutalise.
But if we lament the recent transformations of our cities, we should acknowledge that cities can only reflect the values and character of the societies they contain. This relationship is well explored in the long tradition of attempts to make cities reflect society's ideals. Vitruvius, Leonardo da Vinci, Thomas Jefferson, Ebenezer Howard, Le Corbusier, Buckminster Fuller and others have proposed ideal urban forms to propel society through its traumas.
These architectural and social utopias exert a constant and profound influence on our great architects and patrons, and filter through to developers and city builders. In a democratic age, you might expect contemporary architecture to express democratic ideals and egalitarian values.
But recent transformations of cities reflect the workings of businesses committed to short-term profit, where the pursuit of wealth has become an end in itself, rather than a means to achieve broader goals. City planning world-wide is dominated by market forces, and short-term financial imperatives - an approach most spectacularly illustrated by the chaotic and office- dominated development on the Isle of Dogs in London. Not only have such developments eliminated variety of function from our city centres, but in this single-minded search for profit, we have ignored the needs of the wider community.
Putting cities back on the political agenda is now fundamental. What's needed is greater emphasis on citizens' participation in city design and planning. We must put communal objectives centre-stage. And should people doubt the possibility of regaining democratic control of our cities, examples from around the world prove them wrong. In France, for example, President Mitterrand has stated that "culture" - and first of all architecture - is the fourth highest voting issue. I dread to imagine where our politicians would rank culture here.
Educating our children is a necessary first step towards the participation of communities in decision-making. It is on this that we must focus our National Curriculum. Teaching children about biology and history, but not about their actual environment - the built one - leaves them ill-equipped to participate in the process of respecting and improving the city that so critically affects their lives. We must teach citizenship and listen to citizens.
Any type of close citizen involvement in city design requires us to make funds available to interest and inform the public. San Francisco has gone further and integrated the whole concept of public participation in urban planning into their electoral system. In local elections, you don't just choose a candidate, you have the opportunity to decide your own surroundings. How much office space should be allowed? Which dockside plan is the best?
Closer to home, Rotterdam is a good example of government-sponsored but community-led development. Here, much of the land is publicly-owned and can be given to the community when and where the need arises rather than when someone can afford to buy a site. The city grows in cell-like fashion, splitting and replicating into coherent neighbourhoods of between three and five thousand people, rather than sprawling and dividing into dormitory and work zones.
What these examples prove is that we can transform the fabric and environment of our cities through greater, genuine, public participation and committed government initiative.
Technology can also play a critical role. I find it amazing, that only 70 70-year lifespans separate our own epoch, which has the ability to build a city in space, from the first mud cities along the Euphrates. The prospects that technology offers now are greater still. Only two 70-year lifespans separate the invention of the bicycle from the sinister perfection of the Stealth bomber. Less than one lifespan separates the first electronic computer from the uncharted horizons of the information superhighway.
The problem is not with technology, but with its application. Today technology destabilises and transforms the modern age - as Marx famously said, "All that is solid melts into air". Caught in this endless upheaval, technology can, however, be used to positive ends to advance social justice - one of modernity's greatest ideals. Perhaps we can say that when technology is used to secure the fundamentally modern principles of universal human rights - for shelter, food, health care, education and freedom - that the modern age attains its full potential. It is here that the spirit of modernity finds its very expression.
And that, I suppose, is at the heart of my concept of sustainability. The critical application of creative thinking and technology to secure our future on this small planet.
This is an edited extract of the first of Sir Richard Rogers' six Reith Lectures. The second will be broadcast on Radio 4 next Sunday at 7.30pm and published in the Independent next Monday.