Summertime 2100, and the living isn't easy

What will London be like a century from now? Seven degrees warmer, with water-absorbent streets and parched public parks. Marek Kohn paints an unnerving picture of metropolitan life in the sweaty grip of a radically changed climate

The year is 2100. Londoners and their guests need a pastiche of Arcadia in the heart of the capital. Peak summer daily temperatures are nearly seven degrees hotter than they were in 2000, and the city is far more crowded. By mid-afternoon the day's heat is starting to hang heavy, and will not disperse until the small hours. Evenings are febrile and nights fitful. Shaded open spaces draw people out of doors like a magnet summoning iron filings.

The natural appearance of St James's Park is the kind of vision that Londoners now crave. They have to shut their eyes and imagine it when they wander between the Mall and Birdcage Walk, though. The features of the park are still in place: the lake, the shade of the trees, the pelican colony, less incongruous now that the climate has warmed. But the glades have shrunk to enclaves no wider than the branches of the trees beneath which they survive. There are wild flowers, but they are confined to beds. It is not that the climate has become too hot and dry for green glades to survive, but that the heat has filled the park with people while starving it of water.

As the summers grew drier and the visitors' footfall heavier, the grass wilted and the open spaces turned to a baked beige. It might have been possible to keep the grass going with irrigation, but that would have involved a great deal of wrangling over limited water supplies. The park's natural appearance also discouraged moves to keep it drizzled and springy underfoot. It was not a bowling green, after all. Public bodies were supposed to set good conservation examples, using water as sparingly as possible. And although it was a Royal Park, it was unquestionably a public space – the London parks were felt to be special precisely because they were open.

In a gesture affirming that even park-keepers can have enough of regulations, children are permitted to splash around in St James's shallow lake once the Met Office has declared a heatwave. Gradually, the park's managers accepted that its visitors overwhelmingly wanted it to be the promenade-ground it had been when Charles II first allowed the public in. The daytime spectacle of the ducks and squirrels had become overshadowed by the buzzing throngs of the new hot evenings. Now that central London had the kind of climate formerly enjoyed in southern Europe, Londoners had developed southern European habits.

The expanses of Hyde Park were left to become bare and dusty, as many of their Continental counterparts had always been. Green Park was left to the same fate, and was renamed Piccadilly Park when the irony became too glaring, but St James's Park was felt to deserve special treatment to make up for the loss of its special character. Large areas are covered with the soft artificial surfaces used to protect paths in nice rural beauty spots, their tones sensitively chosen to respect the remaining vegetation. White furniture offers contrasts and sophistication is added by discreet motifs worked into the surfaces. The park looks as though it has put on a suit.

From above, much of London looks like a mosaic of tiny gardens separated by chalky thoroughfares. The gardens are green roofs, which are as common a covering on flat-topped buildings as tiles are on pitched roofs. The roads look chalky because asphalt has been replaced by new materials that are light in colour, to reflect solar radiation instead of absorbing it and releasing it as heat later. They show up the dirt, but their job is to make the city cooler rather than smarter. Almost all urban surfaces are now pervious to water. Road and pavement surfaces are porous at the edges, creating invisible strips through which rainwater soaks into the ground.

Since the new materials combine strength with elasticity, pavements are springy under foot. With many areas off limits for motor vehicles, older streets now look and feel a little more like they must have done before the roads were surfaced and the pavements raised up, but the new pseudo-organic surface doesn't turn to mud when it rains. Surface flooding is common in winter, though. The porous soakaways cannot drain water away as fast as the old gutters did, but water pooling in the winter streets is the price that has to be paid to save every possible drop in the parched summers. It also does less damage than flash floods from overloaded drains.

Among their other properties, the new surfacing materials lend themselves to colouring and texturing. Streets can be designed as if they were interiors, with shading, patterning and detail. Soft surfaces have encouraged urban planners to explore the possibilities of soft control. Tense neighbourhoods are coated in calming tones, though not necessarily to much effect; avenues and squares are patterned with bright islands of colour that encourage pedestrians to gather, while contrasting shades induce them to keep moving through zones that the planners have decided should be kept clear. Urban designers have seized on the illusion that urban surfaces are organic and intensified it by innervating the streets with fibres that control colour-changing particles. Not only can the authorities alter the surface tones to change the mood of public spaces as they see fit, but they can also send explicit messages that light up on the ground, telling the public what it must and must not do. No longer do the authorities have to rely on standing orders such as "No entry" or "No loitering": now they can issue instructions as they go along, orchestrating public behaviour from minute to minute. This signalling system is exploited with even greater enthusiasm by advertisers. Patterns erupt and sweep in shoals over the skins of busy streets like the evanescent ink-blots that pulse across the skins of squid, illustrating how extravagantly adaptations to climate change can be adapted for other purposes.

London is run as a tight ship in other ways. Air conditioning was banned decades ago, in a belated and ineffectual attempt to reduce greenhouse-gas emissions, and remains prohibited in order to help maintain energy discipline.

Buildings are expected to rely on their own resources to cool themselves. Some householders do flout the ban, often concealing the illegal equipment behind shrubs on their green roofs, but the thermal surveillance satellites generally find them out. There are separate arrangements for the rich, as always. The wealthiest residents are able to have their rooms at whatever temperature they please, usually by securing privileged access to groundwater sources, or living by the Thames. Many of them have apartments in a belt of skyscrapers that has sprung up along the north bank, which offers both the water supply and the south- facing riverside frontage that can absorb maximum sunlight without any other buildings getting in the way.

Elsewhere, the drive for density has created forests of tall buildings that shade each other out, reducing their ability to make use of solar surfaces. As buildings have risen taller and sunlight has become an increasingly fundamental source of energy, litigation over access to light has become increasingly common. Although London's thirst is more gargantuan than ever, because of increased temperatures and increased population, its residents consume a small fraction per head of the water that their predecessors got through at the turn of the millennium.

Most of the population of London is comfortably off by anybody's standards, but there are still districts that defy stability. The places where the social fabric is frayed are also gaps in the city's environmental fabric, consuming water and mains electricity at unusually high rates: solar films are coated with grime, windows are boarded up after breakages or against intruders, roofs that were once green are now more like pocket deserts, clods of electronic circuitry lie discarded and unreplaced. The packaging that insulates homes from heat and cold is tattered. '

In summer people sit out the night heat on steps and roofs, simmering and never far from boiling over. The blighted districts are the ones to which the most desperate climate refugees have found their way. Decades of struggle to build up the resources of the belt that runs across Africa south of the Sahara withered as growing seasons shortened or failed altogether. Though most migrants remain within their countries or regions, the numbers are so huge that the ripples of all crises reach the British Isles: even Central Americans driven off the land by drought and South-east Asians driven off their coasts by flood have found refuge here.

These climate ghettoes are also found in other large cities, and London no longer stands out from the rest of the country for its ethnic diversity. Towns and villages throughout the British Isles are world towns and villages, some as ethnically varied as any inner-city district. When people in many English villages talk about their heritage, they are more likely to be referring to ancestors from distant continents than to the church steeple or the duck-pond on the green. Diversity comes in different forms, though. Among wide swathes of the middle classes it is largely a matter of appearances. People look different but behave and think similarly, sharing a common, cosmopolitan culture. Those who have retained traditional beliefs and moral codes mostly find sufficient evidence of shared values in the mainstream for them to feel able to take part in it.

Among the servants of the middle classes, it is largely a personal matter. Many of the migrants from poor regions of the world earn their living in service, caring and cleaning for the affluent and the infirm. Dispersed around the country to wherever they can find jobs, they rarely have compatriots for neighbours. When they encounter hostility and resentment, as they frequently do, they have to face it as individuals. The most visible tensions are those that arise between different ethnic communities, into which much of what used to be known as the working class is now divided. Urban politics has become a contest between different ethnic groups over resources. The bourgeois of the world have united; the workers have Balkanised.

Traditional landmarks still decorate the political scene. Parliament is opened by the monarch with as much attendant pomp as ever, and elections are held to choose a proportion of its members. But although political life goes through the old motions, a different order has evolved. Parties continue to exist in name but no longer figure as real forces. Their place has been taken by transient factions that coalesce and fly apart like fish in a tank.

The sea these shoals swim in is one of consensus. At the national level, efforts to build consensus on major initiatives help to hold the nation together. The more difficult it becomes to define a national identity based on shared traditions, the more valuable it becomes to reach agreements on a case-by-case basis.

Achieving consensus does not necessarily resolve contradictions. On climatic migration there is a consensus of ambivalence. People know that they need the migrants, prosperous and destitute alike, who have come in search of a kinder climate. At the same time, they feel threatened by them and fear them.

In the old days, these contradictions would be fought out by opposing political parties, some trading on xenophobia, others making a case for immigration and closer ties with other countries. Nowadays people feel that they themselves are in two minds. This inclines them to leave politics to the politicians, but they can be roused now and again by the temporary formations that sweep on to the scene in pursuit of one demand or another. These campaigns focus on issues; they do not project visions. It is not done to call either for a world without borders or one in which foreigners go back where they came from, because people feel that both these options would cause the country to fall apart. Instead, every so often a group of bewildered Asian or African migrants will find itself facing levies to pay for the treatment of diseases that occur more frequently among them than in the population as a whole, or curfew punishments for going out in the traditional clothes they brought from the old country. The limits of Europe are defined generously, but there the generosity ends.

As climate change inflicted shocks and strains on the economies of regions around the world, Europe's political and business elites pursued security through the expansion of the continent's internal markets. The more disruptions that floods and failed harvests caused to global trade, the more important it was to have as large a European market as possible. And the larger the bloc, the more resources it can count on. Many European politicians have thanked the Union's lucky stars that the great breadbasket of Ukraine's wheat fields is on Europe's table. Within the Union, the rules of the internal market guaranteed that countries could buy what they needed from each other, while more distant countries were becoming increasingly nervous about allowing unrestricted food exports for fear that poor harvests could leave them struggling to feed themselves.

While they are nowadays diffident about politics in general, citizens are often ardent in their devotion to civic duties on their own doorsteps. Having accepted that environmental responsibility demands self-sacrifice, they watch their neighbours like hawks for signs of slacking or self-indulgence. Believing also that in crowded communities, harmony depends on the suppression of disturbance or inconvenience, they are ever ready to explain this to neighbours who have left toys in their front gardens or music playing with windows open. New arrivals from overseas receive extensive guidance about local customs, to which they rapidly learn to conform.

Family values have come under the influence of the climate, too. When, in the earlier part of the century, it looked as though the pursuit of emotional wellbeing through spending had reached the end of the road, people were left facing each other and wondering about the quality of the relationships on which, they reflected, their happiness had really depended all along.

People move around less altogether. Fuel is expensive and routes congested. Railways have regained a good deal of the importance they had in transport before motorways displaced them in the second half of the 20th century. Motorways themselves have become more like railways, and what were once drivers are now passengers. Cars drive themselves, and when they reach major roads, traffic-management computers slot them into columns of synchronised vehicles that hurtle along together, bumper to bumper, like trains. Speeds are set by the system, whose programs are configured to keep fuel consumption down, and by the weight of traffic, which is usually about as much as the system can bear. Automation and central control keep the roads moving, but even the most sophisticated software cannot make them go fast. On the other hand, electronically chauffeured cars make cosy little offices, and commuters jovially remark that they get more done on the way to work than when they get there.

The London area has become an employment island within the south-east. It has had to reorganise itself, dotting itself evenly with focal points to minimise the distances people travel to work, and to relieve the pressure on the central zone. The old radial Underground system, built to bring commuters from different directions into the centre, still survives as a relic of how the Victorians and Edwardians made the capital work, but it can no longer cope with either the demand or the climate. Deep-level Tube lines with trains running every few minutes would be impossible to keep cool in London summers.

The Tube system has become a seasonal railway, changing from a metro stopping service in winter to a pseudo-express line for a limited selection of stations in summer. Its inability to adapt to modern conditions has tipped the capital's transport balance in the opposite direction to the rest of the country.

London's railways have lost their grip, and London relies for its transport on the automated vehicles that its traffic system routes as if they were phone calls. For those who still hanker after the freedom that wheels can bring, who still want to be in charge of their vehicles, there is a mazy proliferation of cycle lanes.

When it comes to climate change, London leads the country. Although the Thames Valley is generally a touch cooler than the coast to its south, London's heat island makes the capital hotter than Solentside, the conurbation that has swallowed up Portsmouth, Southampton, Bournemouth and Poole. London is more than half a century ahead of Manchester, which by the 2080s was about as warm as London had been in the 2020s.

This temperature gradient has had a marked effect on how people in different parts of Britain see their relationship to each other and to the rest of the world. Watching the rest of the world's climate go by, the Scots count their climatic isolation as another good reason for going it alone. In north Britain and Ireland, distant regions are not easy to see through the Atlantic mists. People in the north are inclined to feel that they certainly could detach themselves, or at least semi-detach themselves, from a Europe that no longer feels much like a common home. To them, the Continent seems like a vast park whose grass has dried to dust, while their Celtic fringe survives like one last flowerbed on the edge.

There once was a time when funds for Europe's poorer regions found their way to the outer parts of the British Isles, but that was long ago. European funds now flow southwards and eastwards. The north and west of the British Isles feel that historically the south has prospered at their expense, and that they continue to be at a disadvantage. People in the north see that the impacts of climate change are falling mainly on the south. As far as many northerners are concerned, the southerners have got the money, so they can pay for it.

© Marek Kohn 2010 (Faber and Faber). This is an edited extract from 'Turned Out Nice' (Faber, £14.99) by Marek Kohn, published on Thursday.