More good news: to achieve this is not a matter of hoping for some technological miracle. The technology we need already exists. It needs refining, and above all it needs applying. But we're well on the way. For instance: photovoltaic panels, which convert the energy of daylight into electricity, have been around since the first communications satellites in the early 1960s. They have steadily got better, and cheaper. They are now close to being a mass-market product. For instance: while wind power is almost as old as humankind itself - think sailing ships and corn-grinding windmills - in recent years there have been huge strides in the efficiency of wind turbines. Increasingly, they will sprout in towns and cities as well as remote moorland and estuaries. For instance: in Seville, Spain, there is already a functioning solar power station, concentrating the sun's rays to drive power-generating steam turbines just as coal, gas and nuclear power stations do. OK, so we're still not too clever when it comes to finding good ways to store such intermittently-produced power. But they're working on it.
Great strides are also being made in developing the more constant wave and tidal energy - invisible undersea power stations powered by pistons responding to the swell of the oceans are now being tested. In the UK, the previously isolated Orkney Islands have become the centre of this emerging technology. All these things will feed clean power to the cities of the near future. But in the cities themselves, is it possible to build a skyscraper that doesn't need outside assistance? That can do everything for itself? Why yes, it is.
This is moving from the realms of science fiction to actuality. A skyscraper can harvest the sun and wind to generate all the power it needs to sustain itself, while around its base can be all you need to store the power, recycle the waste, clean its water and so forth. The trouble is that to do this is incredibly expensive upfront. A true zero-energy 1,000-foot skyscraper could cost as much as ten times as much as a power-hungry, waste-spewing conventional tower of the same size. When you're looking at a build cost of £10 billion rather than £1 billion, you immediately rule out all the world's commercial developers. But if you ease your targets slightly, it becomes affordable. Thus the world's most sustainable skyscraper to date, the Pearl River Tower in Guangzhou, China, is being built right now.
Designed by architects Adrian Smith and Gordon Gill when they were at America's huge design corporation SOM (they have now set up independently), the Pearl River Tower started out as a zero-energy project for a competition to build an HQ for, of all things, a Chinese tobacco company. The project won, and reality then intervened. Expense was one factor, legislation another - the Chinese authorities would not allow the tower its own power plant supplied by waste methane, as intended. Exact costs are confidential but industry experts calculate that by taking a lot of its ideas - such as turning the facades of the building into huge sculpted air intakes for integral wind turbines, and simultaneously making those same facades into a power-generating photovoltaic skin - the Pearl River Tower, to be completed in 2009, will use 60 per cent less energy than its conventional equivalent. Even more remarkably, the extra capital cost of the energy-saving measures will be recouped in lower running costs in a mere five years. The financially-savvy Chinese like the sound of that.
China also knows well enough what the consequences are of all the coal-fired power stations it is building and all the cars that are replacing all the bicycles. It is getting jittery about its international reputation, particularly with the 2008 Olympics about to happen in what threatens to be a toxic atmospheric cocktail of chemicals. Is there hope? Well, possibly, in the form of the planned eco-city of Dongtan at the tip of the huge Chongming Island at the mouth of the Yangtse river.
Dongtan is planned by British engineers Arup, to be the world's first true eco-city, while SOM (again) is involved in the masterplanning of the entire island.The usual buzzword, "sustainable", is taken to mean not just environmentally sustainable, but also socially, environmentally and culturally. So despite the fact that Dongtan will be built on 8,400 hectares of agricultural land amidst sensitive wetlands as an overspill of nearby Shanghai, its impact on the area - and on the globe - will be pretty close to neutral. Or so they say. This is "working towards carbon neutrality" in the official words, rather than claiming to achieve it right away. Dongtan is a prototype for a series of such new cities in China in the years ahead.
How is this possible? Isn't human settlement always damaging? Well, not necessarily. There is plenty of evidence, for instance, that surprisingly large towns used to dot the waterways of the Amazonian rainforest before the coming of the Colonial invaders with their nasty diseases decimated the local Indian populations. Archaeologiists in Brazil are discovering the remains of relatively sophisticated towns that lived off the fruits of the forest, as it were, cultivating areas of it at the same time without resorting to wholescale clearance. OK, so they didn't have fossil fuels to burn. But then, nor will we in a little while.
At Dongtan, for instance, they will not only generate all their own power from sun, wind, water, biofuels and recycled waste - they are also planning double-decker organic farms. In this way, land lost to agriculture through building will be replaced with what they call, rather disappointingly, "plant factories". Super-intensive agriculture plus organic techniques - now there's a challenge. Meanwhile, public transport will be of the zero-emission hydrogen-powered variety while even the air miles clocked up by the design team before it is built are being carbon-offset: All those flights will result in a new hydro-electric power plant, one hopes of the variety that does not destroy too much wildlife.
Dongtan - which will be well under way by the time the next big World Expo takes place in Shanghai in 2010, and which will grow to hold a population of half a million by 2050 - will be a high-density city, but one that is resolutely low-rise. Buildings will bristle with vegetation. Wind turbines and solar panels will be everywhere. And the area is wet, which helps. Dongtan, with all its waterways, will be a modern Venice, the prototype for a further three such new cities in China. So how much more difficult will it be to build a high-rise eco-city, for instance, in the desert?
This is what is now being considered for the Persian Gulf. We all know about gung-ho Dubai with its mad artificial islands - one an archipelago representing a map of the entire world, named "The World". We know about the world's tallest tower there, the Burj Dubai, now nearly finished. We know that you will find an indoor ski slope with artificial snow out there in the desert. Dubai is a byword for conspicuous, unsustainable consumption. But the next-door Emirate, Abu Dhabi - which has much more oil wealth than Dubai, and huge reserves still - is starting to think ecologically. It turned to the design powerhouse headed by Britain's Norman Foster to design its eco-city. And Foster looked to historical precedent. In the Yemen, for instance, are extraordinary ancient walled cities of tall mud-brick towers, packed close together. Those seem to work - such as Shibam, the conservation of which won an Aga Khan award for architecture in 2007. They form the inspiration for Foster's new planned city of Masdar, which will cover six million square metres.
As with Dongtan, zero-emission public transport is a short walk away from everyone's front door. Even so, a city of that size needs lots of power. Where does that come from? Well, in Abu Dhabi they get a lot of sun and wind. So a vast photovoltaic solar-power plant is planned, plus lots of wind farms. As with the ancient Yemeni cities, the agriculture necessary to sustain the city will take place in surrounding irrigated plantations. Quite where they will get all the water from remains a bit of a mystery. Plus they will have to find ways to store the power generated during the daytime. It's do-able, but nobody is claiming it will be easy.
Foster is not the first to think this way: another international architecture superstar, Rotterdam's Rem Koolhaas, got to the starting-block first with a similarly historically-inspired city for the neighbouring, much less well-known, Emirate of Ras Al Khaimah. The RAK Gateway, as it is known, suggests that there is an alternative to the mad sprawl of Dubai and other Gulf states. More encouragingly, it suggests that the rulers of these desert kingdoms are starting to think long-term, to a time when there will not be oil. The signs are that some of the oil money is going to fund some very interesting experiments in sustainable living.
New eco-settlements are all very well where there is the land, and the will, and the technology, to build them. The fact remains, however, that half the world's population now lives in existing cities, and those - from London to Sao Paulo - are anything but sustainable. We're not going to close those places down. So human ingenuity will have to be applied to improviing them. What's to be done?
There are various degrees of green-ness, starting with existing cities with a well thought-through system of clean, efficient public transport, green space, power generation and recycling techniques. It's a matter of retro-fitting.
The shining example here, because it has been going so long, is Curitiba in Brazil, masterplanned since the late 1960s by a visionary architect-planner (also at various times mayor and state governor) Jaime Lerner. At a time when the rest of the urban world was tearing itself apart with ring roads and motorways, Lerner took an unfashionable, balanced, approach. Cars weren't evil, but maybe if public transport was really good, they wouldn't be so necessary. And maybe where lots of people tended to gather on foot, cars could be excluded. And so it has proved.
The value of the Curitiba experiment - which also promotes other things, such as making it worthwhile for the young and otherwise unemployed to look after their city rather than vandalising it, while simultaneously providing a high standard of education - is the pioneering way it anticipated the needs of all cities in the early 21st century. While it is easier to plan a new city with marvellous public transport than it is to graft a new system onto a city that has lost the knack, Curitiba shows that it's never too late. The city could not afford expensive metro networks, for instance: so it came up with imaginative ways of making buses so frequent and regular that they might as well be trains.
Those places that - doh! - somehow missed out on the whole public-transport thing - here I would nominate Astana, new capital of Kazakhstan, already gridlocked at peak times - might well be able to retro-fit the Curitiba model and become a whole lot greener as a consequence. It even happens on a small scale in Britain. We've been able to build small zero-carbon developments, such as Surrey's famous BedZed housing scheme by architect Bill Dunster, for some time. Sure, there's doubt about how zero zero really is - plenty of the residents have cars, after all - but compared to a conventional housing estate, BedZed is saintly.
Other architects are working fruitfully in this area. David Marks and Julia Barrfield, inventors of the London Eye, have come up with a neat urban wind-generating device, "The Beacon" which they see as being dotted around on virtually every street corner. The idea is that such micro-generating stations would become so commonplace as to pass without notice. Meanwhile, we could all save ourselves shedloads of money and carbon if we could afford to fit solar water heaters and electricity-generating photovoltaic panels to all our existing houses. If our government was serious about its carbon targets, it would immediately introduce far more generous tax breaks to encourage us to do just that. Instead of spending the same sort of money on nuclear power stations, say.
There are two pictures you can paint when it comes to the urban future. One is to point to the examples above - straws in the wind, if you like - and say - that's the way it's going. Technology will provide the answers. These prototype settlements will show everyone the way forward, we'll crack that business of using the sun and wind and sea to effectively generate and store power, we can all still have cars because they'll be hydrogen-powered, oh, and we'll find some clever way of making hydrogen that doesn't itself use huge amounts of energy. As it does at present.
The other picture is rather darker. It shows a world which is only just starting to wake up to the problem of unbridled expansion and consumption. These are good examples, but why are there so few of them? And how serious are the various governments in promoting and funding them? Dongtan will very probably happen, but at the same time that is being built, city sprawl of many times its size, and none of its eco-credentials, will continue to mushroom all round Shanghai and a thousand cities like it. In India, which is rather crucial to the future of the industrialized world, they haven't even got as far as China or the Gulf. There's a bit of an eco-city initiative under way in Bangalore, mostly concerned with water conservation. That seems to be it, for an entire continent. And what is Russia doing? While even the United States is now taking some public-transport lessons from Curitiba, Putin-land, rich in oil and gas, is more concerned with plonking down conventional skyscrapers to rival Dubai.
So we've got a way to go. If there's ever going to be a tipping-point that gets everyone designing new kinds of sustainable cities, it will come when the conventional alternative just gets too awful and expensive to contemplate. Here's a thought: it seems to me that eco-cities will be a lot nicer places to live in. Given which, when they are built we'll all want to flock there and they will be huge successes. In the end, consumers as much as politicians may demand truly green cities.
Dongtan background from engineers Arup: http://www.arup.com/eastasia/project.cfm?pageid=7047
Pearl River tower: http://www.som.com/content.cfm/pearl_river_tower
Lost eco-cities of Amazonia: http://www.hughpearman.com/articles2/amazon.html
The Masdar initiative: http://www.masdaruae.com
RAK Gateway eco-city by Rem Koolhaas: http://www.oma.eu/index.php?option=com_projects&view=portal&id=443&Itemid=10
The Curitiba experiment: http://www.pbs.org/frontlineworld/fellows/brazil1203/
via Gabion: Hugh Pearman