[NetBehaviour] Fwd: Imagine Earth without People

[Ryan Griffis]

Begin forwarded message:

> http://www.newscientist.com/channel/life/mg19225731.100
>
> Imagine Earth Without People
>
>     * 12 October 2006
>     * Exclusive from New Scientist Print Edition. Subscribe and get  
> 4 free issues.
>     * Bob Holmes
>
> Humans are undoubtedly the most dominant species the Earth has ever  
> known. In just a few thousand years we have swallowed up more than  
> a third of the planet's land for our cities, farmland and pastures.  
> By some estimates, we now commandeer 40 per cent of all its  
> productivity. And we're leaving quite a mess behind: ploughed-up  
> prairies, razed forests, drained aquifers, nuclear waste, chemical  
> pollution, invasive species, mass extinctions and now the looming  
> spectre of climate change. If they could, the other species we  
> share Earth with would surely vote us off the planet.
>
> "15,589 Number of species threatened with extinction"
>
> Now just suppose they got their wish. Imagine that all the people  
> on Earth - all 6.5 billion of us and counting - could be spirited  
> away tomorrow, transported to a re-education camp in a far-off  
> galaxy. (Let's not invoke the mother of all plagues to wipe us out,  
> if only to avoid complications from all the corpses). Left once  
> more to its own devices, Nature would begin to reclaim the planet,  
> as fields and pastures reverted to prairies and forest, the air and  
> water cleansed themselves of pollutants, and roads and cities  
> crumbled back to dust.
>
> "The sad truth is, once the humans get out of the picture, the  
> outlook starts to get a lot better," says John Orrock, a  
> conservation biologist at the National Center for Ecological  
> Analysis and Synthesis in Santa Barbara, California. But would the  
> footprint of humanity ever fade away completely, or have we so  
> altered the Earth that even a million years from now a visitor  
> would know that an industrial society once ruled the planet?
>
> "9.7 Average eco-footprint of a US citizen, in hectares"
>
> If tomorrow dawns without humans, even from orbit the change will  
> be evident almost immediately, as the blaze of artificial light  
> that brightens the night begins to wink out. Indeed, there are few  
> better ways to grasp just how utterly we dominate the surface of  
> the Earth than to look at the distribution of artificial  
> illumination (see Graphic). By some estimates, 85 per cent of the  
> night sky above the European Union is light-polluted; in the US it  
> is 62 per cent and in Japan 98.5 per cent. In some countries,  
> including Germany, Austria, Belgium and the Netherlands, there is  
> no longer any night sky untainted by light pollution.
> "18.7 Percentage of Earth's surface affected by light pollution"
>
> "Pretty quickly - 24, maybe 48 hours - you'd start to see blackouts  
> because of the lack of fuel added to power stations," says Gordon  
> Masterton, president of the UK's Institution of Civil Engineers in  
> London. Renewable sources such as wind turbines and solar will keep  
> a few automatic lights burning, but lack of maintenance of the  
> distribution grid will scuttle these in weeks or months. The loss  
> of electricity will also quickly silence water pumps, sewage  
> treatment plants and all the other machinery of modern society.
>
> The same lack of maintenance will spell an early demise for  
> buildings, roads, bridges and other structures. Though modern  
> buildings are typically engineered to last 60 years, bridges 120  
> years and dams 250, these lifespans assume someone will keep them  
> clean, fix minor leaks and correct problems with foundations.  
> Without people to do these seemingly minor chores, things go  
> downhill quickly.
>
> The best illustration of this is the city of Pripyat near Chernobyl  
> in Ukraine, which was abandoned after the nuclear disaster 20 years  
> ago and remains deserted. "From a distance, you would still believe  
> that Pripyat is a living city, but the buildings are slowly  
> decaying," says Ronald Chesser, an environmental biologist at Texas  
> Tech University in Lubbock who has worked extensively in the  
> exclusion zone around Chernobyl. "The most pervasive thing you see  
> are plants whose root systems get into the concrete and behind the  
> bricks and into doorframes and so forth, and are rapidly breaking  
> up the structure. You wouldn't think, as you walk around your house  
> every day, that we have a big impact on keeping that from  
> happening, but clearly we do. It's really sobering to see how the  
> plant community invades every nook and cranny of a city."
>
> With no one to make repairs, every storm, flood and frosty night  
> gnaws away at abandoned buildings, and within a few decades roofs  
> will begin to fall in and buildings collapse. This has already  
> begun to happen in Pripyat. Wood-framed houses and other smaller  
> structures, which are built to laxer standards, will be the first  
> to go. Next down may be the glassy, soaring structures that tend to  
> win acclaim these days. "The elegant suspension bridges, the  
> lightweight forms, these are the kinds of structures that would be  
> more vulnerable," says Masterton. "There's less reserve of strength  
> built into the design, unlike solid masonry buildings and those  
> using arches and vaults."
>
> But even though buildings will crumble, their ruins - especially  
> those made of stone or concrete - are likely to last thousands of  
> years. "We still have records of civilisations that are 3000 years  
> old," notes Masterton. "For many thousands of years there would  
> still be some signs of the civilisations that we created. It's  
> going to take a long time for a concrete road to disappear. It  
> might be severely crumbling in many places, but it'll take a long  
> time to become invisible."
>
> The lack of maintenance will have especially dramatic effects at  
> the 430 or so nuclear power plants now operating worldwide. Nuclear  
> waste already consigned to long-term storage in air-cooled metal  
> and concrete casks should be fine, since the containers are  
> designed to survive thousands of years of neglect, by which time  
> their radioactivity - mostly in the form of caesium-137 and  
> strontium-90 - will have dropped a thousandfold, says Rodney Ewing,  
> a geologist at the University of Michigan who specialises in  
> radioactive waste management. Active reactors will not fare so  
> well. As cooling water evaporates or leaks away, reactor cores are  
> likely to catch fire or melt down, releasing large amounts of  
> radiation. The effects of such releases, however, may be less dire  
> than most people suppose.
>
> The area around Chernobyl has revealed just how fast nature can  
> bounce back. "I really expected to see a nuclear desert there,"  
> says Chesser. "I was quite surprised. When you enter into the  
> exclusion zone, it's a very thriving ecosystem."
>
> The first few years after people evacuated the zone, rats and house  
> mice flourished, and packs of feral dogs roamed the area despite  
> efforts to exterminate them. But the heyday of these vermin proved  
> to be short-lived, and already the native fauna has begun to take  
> over. Wild boar are 10 to 15 times as common within the Chernobyl  
> exclusion zone as outside it, and big predators are making a  
> spectacular comeback. "I've never seen a wolf in the Ukraine  
> outside the exclusion zone. I've seen many of them inside," says  
> Chesser.
>
> The same should be true for most other ecosystems once people  
> disappear, though recovery rates will vary. Warmer, moister  
> regions, where ecosystem processes tend to run more quickly in any  
> case, will bounce back more quickly than cooler, more arid ones.  
> Not surprisingly, areas still rich in native species will recover  
> faster than more severely altered systems. In the boreal forests of  
> northern Alberta, Canada, for example, human impact mostly consists  
> of access roads, pipelines, andother narrow strips cut through the  
> forest. In the absence of human activity, the forest will close  
> over 80 per cent of these within 50 years, and all but 5 per cent  
> within 200, according to simulations by Brad Stelfox, an  
> independent land-use ecologist based in Bragg Creek, Alberta.
>
> In contrast, places where native forests have been replaced by  
> plantations of a single tree species may take several generations  
> of trees - several centuries - to work their way back to a natural  
> state. The vast expanses of rice, wheat and maize that cover the  
> world's grain belts may also take quite some time to revert to  
> mostly native species.
>
> At the extreme, some ecosystems may never return to the way they  
> were before humans interfered, because they have become locked into  
> a new "stable state" that resists returning to the original. In  
> Hawaii, for example, introduced grasses now generate frequent  
> wildfires that would prevent native forests from re-establishing  
> themselves even if given free rein, says David Wilcove, a  
> conservation biologist at Princeton University.
>
> Feral descendants of domestic animals and plants, too, are likely  
> to become permanent additions in many ecosystems, just as wild  
> horses and feral pigs already have in some places. Highly  
> domesticated species such as cattle, dogs and wheat, the products  
> of centuries of artificial selection and inbreeding, will probably  
> evolve back towards hardier, less specialised forms through random  
> breeding. "If man disappears tomorrow, do you expect to see herds  
> of poodles roaming the plains?" asks Chesser. Almost certainly not  
> - but hardy mongrels will probably do just fine. Even cattle and  
> other livestock, bred for meat or milk rather than hardiness, are  
> likely to persist, though in much fewer numbers than today.
>
> "3.3bn Global population of cattle, sheep and goats"
>
> What about genetically modified crops? In August, Jay Reichman and  
> colleagues at the US Environmental Protection Agency's labs in  
> Corvallis, Oregon, reported that a GM version of a perennial called  
> creeping bentgrass had established itself in the wild after  
> escaping from an experimental plot in Oregon. Like most GM crops,  
> however, the bentgrass is engineered to be resistant to a  
> pesticide, which comes at a metabolic cost to the organism, so in  
> the absence of spraying it will be at a disadvantage and will  
> probably die out too.
>
> Nor will our absence mean a reprieve for every species teetering on  
> the brink of extinction. Biologists estimate that habitat loss is  
> pivotal in about 85 per cent of cases where US species become  
> endangered, so most such species will benefit once habitats begin  
> to rebound. However, species in the direst straits may have already  
> passed some critical threshold below which they lack the genetic  
> diversity or the ecological critical mass they need to recover.  
> These "dead species walking" - cheetahs and California condors, for  
> example - are likely to slip away regardless.
>
> "784 Number of species that have gone extinct in the wild since  
> 1500 AD"
>
> Other causes of species becoming endangered may be harder to  
> reverse than habitat loss. For example, about half of all  
> endangered species are in trouble at least partly because of  
> predation or competition from invasive introduced species. Some of  
> these introduced species - house sparrows, for example, which are  
> native to Eurasia but now dominate many cities in North America -  
> will dwindle away once the gardens and bird feeders of suburban  
> civilisation vanish. Others though, such as rabbits in Australia  
> and cheat grass in the American west, do not need human help and  
> will likely be around for the long haul and continue to edge out  
> imperilled native species.
>
> "388 Number of species listed on the invasive species database"
>
> Ironically, a few endangered species - those charismatic enough to  
> have attracted serious help from conservationists - will actually  
> fare worse with people no longer around to protect them. Kirtland's  
> warbler - one of the rarest birds in North America, once down to  
> just a few hundred birds - suffers not only because of habitat loss  
> near its Great Lakes breeding grounds but also thanks to brown- 
> headed cowbirds, which lay their eggs in the warblers' nests and  
> trick them into raising cowbird chicks instead of their own. Thanks  
> to an aggressive programme to trap cowbirds, warbler numbers have  
> rebounded, but once people disappear, the warblers could be in  
> trouble, says Wilcove.
>
> On the whole, though, a humanless Earth will likely be a safer  
> place for threatened biodiversity. "I would expect the number of  
> species that benefit to significantly exceed the number that  
> suffer, at least globally," Wilcove says.
>
> On the rebound
>
> In the oceans, too, fish populations will gradually recover from  
> drastic overfishing. The last time fishing more or less stopped -  
> during the second world war, when few fishing vessels ventured far  
> from port - cod populations in the North Sea skyrocketed. Today,  
> however, populations of cod and other economically important fish  
> have slumped much further than they did in the 1930s, and recovery  
> may take significantly longer than five or so years.
>
> The problem is that there are now so few cod and other large  
> predatory fish that they can no longer keep populations of smaller  
> fish such as gurnards in check. Instead, the smaller fish turn the  
> tables and outcompete or eat tiny juvenile cod, thus keeping their  
> erstwhile predators in check. The problem will only get worse in  
> the first few years after fishing ceases, as populations of  
> smaller, faster-breeding fish flourish like weeds in an abandoned  
> field. Eventually, though, in the absence of fishing, enough large  
> predators will reach maturity to restore the normal balance. Such a  
> transition might take anywhere from a few years to a few decades,  
> says Daniel Pauly, a fisheries biologist at the University of  
> British Columbia in Vancouver.
>
> With trawlers no longer churning up nutrients from the ocean floor,  
> near-shore ecosystems will return to a relatively nutrient-poor  
> state. This will be most apparent as a drop in the frequency of  
> harmful algal blooms such as the red tides that often plague  
> coastal areas today. Meanwhile, the tall, graceful corals and other  
> bottom-dwelling organisms on deep-water reefs will gradually begin  
> to regrow, restoring complex three-dimensional structure to ocean- 
> floor habitats that are now largely flattened, featureless wastelands.
>
> Long before any of this, however - in fact, the instant humans  
> vanish from the Earth - pollutants will cease spewing from  
> automobile tailpipes and the smokestacks and waste outlets of our  
> factories. What happens next will depend on the chemistry of each  
> particular pollutant. A few, such as oxides of nitrogen and sulphur  
> and ozone (the ground-level pollutant, not the protective layer  
> high in the stratosphere), will wash out of the atmosphere in a  
> matter of a few weeks. Others, such as chlorofluorocarbons, dioxins  
> and the pesticide DDT, take longer to break down. Some will last a  
> few decades.
>
> The excess nitrates and phosphates that can turn lakes and rivers  
> into algae-choked soups will also clear away within a few decades,  
> at least for surface waters. A little excess nitrate may persist  
> for much longer within groundwater, where it is less subject to  
> microbial conversion into atmospheric nitrogen. "Groundwater is the  
> long-term memory in the system," says Kenneth Potter, a hydrologist  
> at the University of Wisconsin at Madison.
>
> Carbon dioxide, the biggest worry in today's world because of its  
> leading role in global warming, will have a more complex fate. Most  
> of the CO2 emitted from burning fossil fuels is eventually absorbed  
> into the ocean. This happens relatively quickly for surface waters  
> - just a few decades - but the ocean depths will take about a  
> thousand years to soak up their full share. Even when that  
> equilibrium has been reached, though, about 15 per cent of the CO2  
> from burning fossil fuels will remain in the atmosphere, leaving  
> its concentration at about 300 parts per million compared with pre- 
> industrial levels of 280 ppm. "There will be CO2 left in the  
> atmosphere, continuing to influence the climate, more than 1000  
> years after humans stop emitting it," says Susan Solomon, an  
> atmospheric chemist with the US National Oceanic and Atmospheric  
> Administration (NOAA) in Boulder, Colorado. Eventually calcium ions  
> released from sea-bottom sediments will allow the sea to mop up the  
> remaining excess over the next 20, 000 years or so.
>
> Even if CO2 emissions stop tomorrow, though, global warming will  
> continue for another century, boosting average temperatures by a  
> further few tenths of a degree. Atmospheric scientists call this  
> "committed warming", and it happens because the oceans take so long  
> to warm up compared with the atmosphere. In essence, the oceans are  
> acting as a giant air conditioner, keeping the atmosphere cooler  
> than it would otherwise be for the present level of CO2. Most  
> policy-makers fail to take this committed warming into account,  
> says Gerald Meehl, a climate modeller at the National Center for  
> Atmospheric Research, also in Boulder. "They think if it gets bad  
> enough we'll just put the brakes on, but we can't just stop and  
> expect everything to be OK, because we're already committed to this  
> warming."
>
> That extra warming we have already ordered lends some uncertainty  
> to the fate of another important greenhouse gas, methane, which  
> produces about 20 per cent of our current global warming. Methane's  
> chemical lifetime in the atmosphere is only about 10 years, so its  
> concentration could rapidly return to pre-industrial levels if  
> emissions cease. The wild card, though, is that there are massive  
> reserves of methane in the form of methane hydrates on the sea  
> floor and frozen into permafrost. Further temperature rises may  
> destabilise these reserves and dump much of the methane into the  
> atmosphere. "We may stop emitting methane ourselves, but we may  
> already have triggered climate change to the point where methane  
> may be released through other processes that we have no control  
> over," says Pieter Tans, an atmospheric scientist at NOAA in Boulder.
>
> No one knows how close the Earth is to that threshold. "We don't  
> notice it yet in our global measurement network, but there is local  
> evidence that there is some destabilisation going on of permafrost  
> soils, and methane is being released," says Tans. Solomon, on the  
> other hand, sees little evidence that a sharp global threshold is  
> near.
>
> All things considered, it will only take a few tens of thousands of  
> years at most before almost every trace of our present dominance  
> has vanished completely. Alien visitors coming to Earth 100,000  
> years hence will find no obvious signs that an advanced  
> civilisation ever lived here.
>
> Yet if the aliens had good enough scientific tools they could still  
> find a few hints of our presence. For a start, the fossil record  
> would show a mass extinction centred on the present day, including  
> the sudden disappearance of large mammals across North America at  
> the end of the last ice age. A little digging might also turn up  
> intriguing signs of a long-lost intelligent civilisation, such as  
> dense concentrations of skeletons of a large bipedal ape, clearly  
> deliberately buried, some with gold teeth or grave goods such as  
> jewellery.
>
> And if the visitors chanced across one of today's landfills, they  
> might still find fragments of glass and plastic - and maybe even  
> paper - to bear witness to our presence. "I would virtually  
> guarantee that there would be some," says William Rathje, an  
> archaeologist at Stanford University in California who has  
> excavated many landfills. "The preservation of things is really  
> pretty amazing. We think of artefacts as being so impermanent, but  
> in certain cases things are going to last a long time."
>
> Ocean sediment cores will show a brief period during which massive  
> amounts of heavy metals such as mercury were deposited, a relic of  
> our fleeting industrial society. The same sediment band will also  
> show a concentration of radioactive isotopes left by reactor  
> meltdowns after our disappearance. The atmosphere will bear traces  
> of a few gases that don't occur in nature, especially  
> perfluorocarbons such as CF4, which have a half-life of tens of  
> thousands of years. Finally a brief, century-long pulse of radio  
> waves will forever radiate out across the galaxy and beyond, proof  
> - for anything that cares and is able to listen - that we once had  
> something to say and a way to say it.
>
> But these will be flimsy souvenirs, almost pathetic reminders of a  
> civilisation that once thought itself the pinnacle of achievement.  
> Within a few million years, erosion and possibly another ice age or  
> two will have obliterated most of even these faint traces. If  
> another intelligent species ever evolves on the Earth - and that is  
> by no means certain, given how long life flourished before we came  
> along - it may well have no inkling that we were ever here save for  
> a few peculiar fossils and ossified relics. The humbling - and  
> perversely comforting - reality is that the Earth will forget us  
> remarkably quickly.
>
>
> From issue 2573 of New Scientist magazine, 12 October 2006, page 36-41
>
> © Copyright Reed Business Information Ltd.
>
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