[SustainableTompkins] New Scientist article: Imagine Earth without people

[GayNicholson at aol.com]

Disquieting thought experiment on how quickly the Earth would  heal itself of 
us....
 
 
http://www.newscientist.com/channel/life/mg19225731.100  
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Imagine Earth  without people

* 12 October 2006
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* 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.

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?

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.

"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.

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.

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.

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 CO_2 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 CO_2 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 CO_2 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 CO_2  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 CO_2 . 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 CF_4 , 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
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Printed on Mon  Oct 16 05:30:01 BST 2006