A generation ago, humans eluded nuclear annihilation; with luck, we'll continue to dodge that and other mass terrors. But now we often find ourselves asking whether inadvertently we've poisoned or parboiled the planet, ourselves included. We've also used and abused water and soil so that there's a lot less of each, and trampled thousands of species that probably aren't coming back. Our world, some respected voices warn, could one day degenerate into something resembling a vacant lot, where crows and rats scuttle among weeds, preying on each other. If it comes to that, at what point would things have gone so far that, for all our vaunted superior intelligence, we're not among the hardy survivors?
The truth is, we don't know. Any conjecture gets muddled by our obstinate reluctance to accept that the worst might actually occur. We may be undermined by our survival instincts, honed over aeon to help us deny, defy, or ignore catastrophic portents lest they paralyse us with fright. If those instincts dupe us into waiting until it's too late, that's bad. If they fortify our resistance in the face of mounting omens, that's good. More than once, crazy, stubborn hope has inspired creative strokes that snatched people from ruin. So, let us try a creative experiment: suppose that the worst has happened. Human extinction is a fait accompli.
Picture a world from which we all suddenly vanished. Tomorrow.
Look around you at today's world. Your house, your city, the surrounding land, the pavement underneath, and the soil hidden below that. Leave it all in place, but extract the human beings. Wipe us out, and see what's left. How would the rest of nature respond if it were suddenly relieved of the relentless pressures we heap on it and our fellow organisms? How soon would, or could, the climate return to where it was before we fired up all our engines?
How long would it take to recover lost ground and restore Eden to the way it must have gleamed and smelled the day before Adam, or Homo habilis, appeared? Could nature ever obliterate all our traces?
On the day after humans disappear, nature takes over and immediately begins cleaning house – or houses, that is. Cleans them right off the face of the Earth. They all go.
No matter how hermetically you've sealed your temperature-tuned interior from the weather, invisible spores penetrate anyway, exploding in sudden outbursts of mould – awful when you see it, worse when you don't, because it's hidden behind a painted wall, munching paper sandwiches of gypsum board, rotting studs and floor joists. Or you've been colonised by termites, carpenter ants, roaches, hornets, or even small mammals.
Most of all, though, you are beset by what in other contexts is the veritable stuff of life: water. It always wants in.
After we're gone, nature's revenge for our smug, mechanised superiority arrives waterborne. It starts with wood-frame construction, the most widely used residential building technique in the developed world. It begins on the roof, probably asphalt or slate shingle, warranted to last two or three decades – but that warranty doesn't count around the chimney, where the first leak occurs. As the flashing separates under rain's relentless insistence, water sneaks beneath the shingles. It flows across four-by-eight-foot sheets of sheathing made either of plywood or, if newer, woodchip board composed of three-to-our-inch flakes of timber, bonded together by a resin.
Newer isn't necessarily better. On the one hand, by building things so cheaply and lightly, we use fewer of the world's resources. On the other, the massive trees that yielded the great wooden posts and beams that still support medieval European, Japanese and early American walls are now too precious and rare, and we're left to make do with gluing together smaller boards and scraps.
The resin in your cost-conscious choice of a woodchip roof, a waterproof goo of formaldehyde and phenol polymer, was also applied along the board's exposed edges, but it fails anyway because moisture enters around the nails. Soon they're rusting, and their grip begins to loosen.
That presently leads not only to interior leaks, but to structural mayhem. Besides underlying the roofing, the wooden sheathing secures trusses to one another. The trusses – premanufactured braces held together by metal connection plates – are there to keep the roof from splaying. But when the sheathing goes, structural integrity goes with it. As gravity increases tension on the trusses, the 1/4in pins securing their now-rusting connector plates pull free from the wet wood, which now sports a fuzzy coating of greenish mould. Beneath the mould, threadlike filaments called hyphae are secreting enzymes that break cellulose and lignin down into fungi food. The same thing is happening to the floors inside. When the heat went off, pipes burst if you lived where it freezes, and rain is blowing in where windows have cracked from bird collisions and the stress of sagging walls. Even where the glass is intact, rain and snow mysteriously, inexorably work their way under the sills. As the wood continues to rot, trusses start to collapse against each other. Eventually the walls lean to one side, and finally the roof falls in. That barn roof with the 18-by-18in hole was probably gone inside 10 years. The one on your house lasts 50 years; 100 tops.
If you owned a swimming pool, it's now a planter box, filled with either the offspring of ornamental saplings that the developer imported, or with banished natural foliage that was still hovering on the subdivision's fringes, awaiting the chance to retake its territory. If the house's foundation involved a basement, it too is filling with soil and plant life. Brambles and wild grapevines are snaking around steel gas pipes, which will rust away before another century goes by. White plastic PVC plumbing has yellowed and thinned on the side exposed to the light, where its chloride is weathering to hydrochloric acid, dissolving itself and its polyvinyl partners. Only the bathroom tiles, the chemical properties of fired ceramic being not unlike those of fossils, are relatively unchanged, although they now lie in a pile with leaf litter.
After 500 years, what is left depends on where in the world you lived. If the climate was temperate, a forest stands in place of a suburb; minus a few hills, it has begun to resemble what it was before developers, or the farmers they expropriated, first saw it. Amid the trees, half-concealed by a spreading under-story, lie aluminium dishwasher parts and stainless steel cookware, their plastic handles splitting but still solid. Over the coming centuries, although there will be no metallurgists around to measure it, the pace at which aluminium pits and corrodes will finally be revealed: a relatively new material, aluminium was unknown to early humans because its ore must be electrochemically refined to form metal.
The chromium alloys that give stainless steel its resilience, however, will probably continue to do so for millennia, especially if the pots, pans, and carbon-tempered cutlery are buried out of the reach of atmospheric oxygen. One hundred thousand years hence, the intellectual development of whatever creature digs them up might be kicked abruptly to a higher evolutionary plane by the discovery of ready-made tools. Then again, lack of knowledge of how to duplicate them could be a demoralising frustration – or an awe-arousing mystery that ignites religious consciousness.
If you were a desert dweller, the plastic components of modern life flake and peel away faster, as polymer chains crack under an ultraviolet barrage of daily sunshine. With less moisture, wood lasts longer there, though any metal in contact with salty desert soils will corrode more quickly. Still, from Roman ruins we can guess that thick cast iron will be around well into the future's archaeological record, so the odd prospect of fire hydrants sprouting amid cacti may someday be among the few clues that humanity was here. Although adobe and plaster walls will have eroded away, the wrought iron balconies and window grates that once adorned them may still be recognisable, albeit airy as tulle, as corrosion eating through the iron encounters its matrix of indigestible glass slag.
Once, we built structures entirely from the most durable substances we knew: granite block, for instance. The results are still around today to admire, but we don't often emulate them, because quarrying, cutting, transporting and fitting stone requires a patience we no longer possess. No one since the likes of Antoni Gaudí, who began Barcelona's as yet unfinished Sagrada Familia basilica in 1880, contemplates investing in construction that our great-great-grandchildren's grandchildren will complete 250 years hence. Nor, absent the availability of a few thousand slaves, is it cheap, especially compared to another Roman innovation: concrete.
Today, that brew of clay, sand and a paste made of the calcium of ancient seashells hardens into a man-made rock that is increasingly the most affordable option for Homo sapiens urbanus. So what happens to the concrete cities now home to more than half the humans alive?
Before we consider that, there's a matter to address regarding climate. If we were to vanish tomorrow, the momentum of certain forces we've already set in motion will continue until centuries of gravity, chemistry and entropy slow them to an equilibrium that may only partly resemble the one that existed before us. That former equilibrium depended on a sizeable amount of carbon locked away beneath Earth's crust, much of which we've relocated into the atmosphere. Instead of rotting, the wood frames of houses may be preserved like the timbers of Spanish galleons wherever rising seas pickle them in salt water.
In a warmer world, the deserts may grow drier, but the parts where humans dwelled will likely again be visited by what attracted those humans in the first place: flowing water. From Cairo to Phoenix, desert cities rose where rivers made arid soils livable. Then, as populations grew, humans seized control of those aquatic arteries, diverting them in ways that allowed for even more growth. But after people are gone, the diversions will soon follow them. Drier, hotter desert climates will be complemented by wetter, stormier mountain weather systems that will send floods roaring downstream, overwhelming dams, spreading over their former alluvial plains, and entombing whatever was built there in annual layers of silt. Within them, fire hydrants, truck tyres, shattered plate glass, condominia and office buildings may remain indefinitely, but as far from sight as the Carboniferous formation once was. No memorial will mark their burial, though the roots of cottonwoods, willows and palms may occasionally make note of their presence. Only aeon later, when old mountains have worn away and new ones risen, will young streams cutting fresh canyons through sediments reveal what once, briefly, went on here.
Luckily for the world after humans, not all the big mammals are gone. A continent-sized museum, Africa, still holds a striking collection. Would they spread across the planet after we're gone? Could they replace what we finished off elsewhere, or even evolve to resemble those same lost creatures?
If there were no people left, Africa, which has been occupied by humans longer than any other place, would paradoxically revert to the purest primeval state on Earth. With so much wildlife grazing and browsing, Africa is the only continent where exotic plants haven't
escaped suburban gardens to usurp the countryside. But Africa after people would include some key changes.
Once, North African cattle were wild. But after thousands of years with humans, they've been selected for a gut like an oversized fermentation vat to eat huge amounts of forage during the day, because they can't graze at night. So now they're not very quick. Left on their own, they'd be rather vulnerable prime beef.
And a lot of it. Cattle now account for more than half the live weight of African savanna ecosystems. Without Maasai spears to protect them, they would provide an orgy for bingeing lions and hyenas. Once cows were gone, there would be more than double the feed for everything else.
As for elephants without people: Darwin estimated there were 10 million elephants in Africa. That was actually quite close to what was here before the big ivory trade. At the moment there are half a million.
No people and 20 times more elephants would restore them as the undisputed keystone species in a patchwork mosaic African landscape. By contrast, in North and South America, for 13,000 years nearly no creatures except insects have eaten tree bark and bushes. After mammoths died, enormous forests spread unless farmers cleared them, ranchers burned them, peasants cut them for fuel, or developers bulldozed them. Without humans, American forests represent vast niches awaiting any herbivore big enough to extract their woody nutrients.
In 1996, the British journalist Laura Spinney, writing in New Scientist magazine, envisioned London abandoned 250 years hence, turned back into the swamp it once was. The liberated Thames wandered among the waterlogged foundations of fallen buildings, 1 Canada Square having collapsed under an unbearable tonnage of dripping ivy. The following year, Ronald Wright's novel A Scientific Romance jumped 250 years more, and imagined the same river lined with palms, flowing transparently past Canvey Island into a sweltering mangrove estuary, where it joined a warm North Sea.
Like the entire Earth, the posthuman fate of Britain teeters on the balance of these two visions: a return to temperate foliage, or a lurch into a tropical, super-heated future – or, ironically, into a semblance of something last seen in England's Southwestern moors, where Conan Doyle's Baskerville hound once wailed into chill mist.
Dartmoor, the highest point in southern England, resembles a 900-square-mile bald pate with occasional massive chunks of fractured granite poking through, fringed by farms and patches of woods that exploded from old boundary hedgerows. It formed at the end of the Carboniferous age, when most of Britain lay submerged, with sea creatures dropping shells on what became its buried chalk. Beneath that was granite, which 300 million years ago bulged with underlying magma into a dome-shaped island – which it may be again if seas rise as high as some fear.
Several ice ages froze enough of the planet's water to drop ocean levels and allow today's world to take shape. The last of these sent a mile-high ice sheet right down the Greenwich Meridian. Where it stopped is where Dartmoor begins. Atop its granite hilltops, known as tors, are remnants from those times that may be portents of what awaits if yet a third climatic alternative proves to be the British Isles' destiny.
That fate could occur if meltwater from Greenland's ice cap shuts down, or actually reverses, the oceanic conveyor atop which rides the Gulf Stream, which currently keeps Britain far warmer than Hudson's Bay, Canada, which is at the same latitude. Since that much-debated event would be the direct result of rising global temperatures, probably no ice sheet will form – but permafrost and tundra could.
That happened at Dartmoor 12,700 years ago, the last time the global circulation system nearly slowed to a halt: no ice, but rock-hard ground. What followed is not only instructive, as it shows what the United Kingdom might resemble in coming years, but also hopeful, because these things, too, will pass.
The deep freeze lasted 1,300 years. During that time, water trapped in fissures in Dartmoor's granite bedrock froze, cracking apart huge rocks below the surface. Then the Pleistocene ended. The permafrost thawed; its runoff exposed the shattered granite that became Dartmoor's tors, and the moor bloomed. Across the land bridge that for another 2,000 years connected England to the rest of Europe, pine moved in, then birch, then oak. Deer, bears, beavers, badgers, horses, rabbits, red squirrels and aurochs (an extinct type of cattle) crossed with them. So did a few significant predators: foxes, wolves, and the ancestors of many of today's Britons.
As Americans, and Australians did long before, Britons used fire to clear trees, making it easier to find game. Except for the highest tors, the barren Dartmoor prized by local environmental groups is another human artifact. It is a former forest repeatedly burned, then waterlogged by more than 100 inches of annual rainfall into a blanket of peat where trees no longer grow. Only charcoal remnants in peat cores attest that once they did.
The artifact was shaped further as humans pushed hunks of granite into circles that became foundations for their huts. They spread them into long, low unmortared stone reaves that crossed and hatched the landscape, and remain vivid even today.
The reaves divided the land into pastures for cows, sheep, and Dartmoor's famous hardy ponies. Recent attempts to emulate Scotland's picturesque heaths by removing livestock proved futile, as bracken and prickly gorse appeared rather than purple heather. But gorse befits a former tundra, whose frozen surfaces melt to spongy peat familiar to anyone who walks these moors. Tundra this may be again, whether humans are here or not.
Between global warming and ocean-conveyor cooling (if the dominant system is partly muted by the other, as some models propose), Europe's meticulous mechanised farmlands would, without humans, fill with brome and fescue grass, lupine, plumed thistle, flowering rapeseed, and wild mustard. Within a few decades oak shoots would sprout from the acidic former fields of wheat, rye, and barley. Boars, hedgehogs, lynx, bison, and beaver would spread, with wolves moving up from Romania and, if Europe is cooler, reindeer coming down from Norway.
The British Isles would be somewhat biologically marooned, as rising seas batter the already-receding chalk cliffs of Dover and widen the 21- mile gap that separates England from France. Dwarf elephants and hippopotamuses once may have swum almost double that distance to reach Cyprus, so presumably something might try. Caribou, buoyed by their insulating hollow hair, cross northern Canadian lakes, so their reindeer siblings might just make it to England.
Should some impetuous animal attempt the journey via the Channel Tunnel after human traffic ceases, it might actually make it. Even without maintenance, the Chunnel wouldn't quickly flood like many of the world's subways, because it was dug within a single geologic layer, a bed of chalk marl with minimal filtration.
Whether an animal would actually try is another matter. All three Chunnel tubes – one each for westbound and eastbound trains, and a parallel central corridor to service them – are swaddled in concrete. For 35 miles there would be no food or water – just pitch darkness. Still, it's not impossible that some continental species might recolonise Britain that way: The capacity of organisms to ensconce themselves in the world's most inhospitable places – from lichens on Antarctic glaciers to sea worms in 80C vents – may symbolise the meaning of life itself. Surely, as small, curious creatures like voles or the inevitable Norway rats slither down the Chunnel, some brash young wolf will follow their scent.
One day, perhaps, we will learn to control our appetites, or our duplication rates. But suppose that before we do, something implausible swoops in to do that for us. In just decades, with no new chlorine and bromine leaking skyward, the ozone layer would replenish and ultraviolet levels subside.
Within a few centuries, as most of our excess industrial CO2 dissipated, the atmosphere and shallows would cool. Heavy metals and toxins would dilute and gradually flush from the system. After PCBs and plastic fibres recycled a few thousand or million times, anything truly intractable would end up buried, to one day be metamorphosed or subsumed into the planet's mantle.
Long before that – in far less time than it took us to run out of cod and passenger pigeons – every dam on Earth would silt up and spill over. Rivers would again carry nutrients to the sea, where most life would still be, as it was long before we vertebrates first crawled onto these shores. Eventually, we'd try that again. Our world would start over.
This is an edited extract from 'The World Without Us', by Alan Weisman (£20), published by Virgin Books tomorrow. To order a copy for the special price of £18 (free P&P) call Independent Books Direct on 0870 079 8897, or visit www.independentbooksdirect.co.ukReuse content