Imaginez un bouton. Ça peut être un gros bouton rouge, entouré de bandes diagonales jaunes et rouges, et avec marqué « Danger » au dessus. Ça peut être un bouton aussi banal que l'interrupteur commandant la lumière dans une pièce. Peu importe, c'est un bouton.

Imaginez qu'en appuyant sur ce bouton, l'humanité disparaisse. Avant, il y avait une humanité, avec ses avantages et ses inconvénients. Après, *pouf*… plus rien… comme ça…

Bon, quelques avions vides s'écraseraient 6000 mètres plus bas, quelques trains et voitures iraient s'encastrer plus ou moins loin dans des machins plus durs qu'eux. Des animaux crèveraient de faim enfermés dans les appartements et maisons. On aurait bien quelques centrales nucléaires qui, faute de régulation humaine, feraient leur intéressante et joueraient à celle qui a la plus grosse (explosion). Bref, rien de bien dramatique dans tout ça. De toute manière, à part quelques ruines éparses, il n'en paraitrait plus rien dans 300 ou 400 ans.

Donc, revenons-en à nos moutons boutons. Vous êtes devant celui-ci. Que faites-vous ?

J'appuie. Sans aucune hésitation.

Sinon, NewScientist.com propose un article sur le sujet : Imagine Earth without people

Morceaux choisis :

Constructions humaines :

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. [...] "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.

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. [...] 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."

Écosystème :

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.

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.

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.

Effet de serre :

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.

Conclusion :

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.

The humbling - and perversely comforting - reality is that the Earth will forget us remarkably quickly.