The mile-high club

If birds, with all their lightweight and aerodynamic beauty, evolved from dinosaurs, the progress of skyscrapers over the past 25 years seems to have taken the opposite route. The skypiercing elegance of the art deco Chrysler Building has made way for a plethora of lumpen office towers in New York, while central London's Centre Point Tower, an unfairly derided pop-era provocation, has been succeeded by the lumpen mass of One Canada Square (Canary Wharf Tower) and any number of high-rise commercial blocks. Thumped down gratuitously in our city centres, these immense air-conditioned filing cabinets have all the subtlety of a sledgehammer. Few major cities in the world have escaped from this crushing lumpen skyscraper syndrome.

Norman Foster is not an architect to take this line of argument lying down. In the gilded grandiosity of the old Royal Academy lecture hall, he has done quite the reverse. On a brace of monolithic granite-grey podia, he presents a powerful polemic in favour of the skyscraper: dozens of capitivating models of buildings that, in full-blown concrete and steel form, would reach a mile high.

Sky High: Vertical Architecture is literally the high point in the Royal Academy's Summer Show. Unlike the exhibition of art, which opened to critical hisses and boos last week, Foster's skycraper show is driven, energetic, controlled and pretty convincing. While admitting that far too many skyscrapers have been as leaden as a triceratops, Foster makes the case that the latest generation of tall buildings emerging from computer screens and global building sites is not only relearning the elegance of the Chrysler Building, but is going boldly where no skyscraper has been before.

Take the extraordinary - but as yet uncommissioned - windtower designs by the University of Stuttgart School of Architecture and Foster and Partners. Models reveal fascinating buildings that, using the wind that rushes through close-coupled pairs of towers or across the crest of lone architectural peaks, can produce their own electricity. Giant propellers, like those of the wind turbines seen throughout rural Britain, are set into or on to the towers. As they spin, dynamos generate electricity. These give the proposed skyscrapers a retro-future sci-fi look that Hollywood set designers will surely leap on. The fact that the towers are aerodynamic in form should mean that, for all the wind, pavements, plazas and entrance lobbies down below are calm. Foster and Partners' own Ventiform design shows just how elegant and intriguing such streamlined, self-powered towers might be.

Concrete proof of the skyscraper's progress can be seen in Foster's 30 St Mary Axe building (better known, sadly, as the "gherkin"). Due to open next year, it will feature opening windows (a luxury for all too many city workers) and a greenery of "sky gardens" spiralling up the aerodynamically designed structure. This is one way the contemporary skyscraper is being civilised. Another is represented by a new Bavarian high-rise office, Uptown München, designed by Ingenhoven Overdiek. Here the single glass skin of the tower is punctuated by hundreds of motor-driven portholes that move in and out like silent pistons as they adjust to the weather. On a fine day, they open out; when it rains, they close.

What Foster wants to make clear is that great progress is being made in the design of skyscrapers. But this is only half his case, one he makes well on his West podium at the RA, representing past, present and future skyscrapers of the western world. On his East podium he shows the skyscrapers of the eastern hemisphere, putting the absurdly overblown translations of western models (by 2007, the world's tallest building, at 492 metres, will be the World Trade Centre, Shanghai) alongside new designs, almost impossibly dramatic to British eyes, intended to improve city living.

Among these are huge clusters of low-energy residential towers that should bring relief to Hong Kong (where the population density is about 25 times greater than London's), Singapore and elsewhere. Such developments, Foster believes, contain sprawl, can be connected efficiently to mass public transport networks, resist earthquakes far better than traditional housing or jerry-built apartment blocks, and free up land beneath them that can be laid out as parks. Although tall, they make good urban and environmental sense.

Nothing will stop us reaching for the sky in concrete, steel and glass, and the new skyscraper is quite different from those of recent decades. But in the low(ish) density cities of the western world, we should reject all skyscraper projects that threaten to demean rather than adorn our skylines. In high-density cities like Seoul, Shanghai and Singapore, we should encourage only those that are as gentle as possible on their environments.

Foster's argument, that the only good skyscraper is an inventive one, is true. Just look at the mesmerising ninth-century spiral minaret of the great mosque at Samarra, in what is northern Iraq today; New York's much-loved Chrysler Building, completed at the time of the Great Depression; and Frank Lloyd Wright's audacious scheme for a mile-high city-in-the-sky proposed for Illinois in the mid-1950s - all of which he includes in the show.

We rightly expect skyscrapers to be as thrilling as the ecclesiastical towers and steeples of medieval Europe. But if we cannot match Foster's ambition for the skyscraper, we would be better advised to hug the ground. Few dinosaurs flew well.

· Sky High: Vertical Architecture is at the Royal Academy, London W1, until August 10. Details: 020-7300 8000.