When Humans Vanish

The moment

It happens between one second and the next. At that instant it is breakfast time in Bucharest, mid-afternoon in Tokyo and late evening in Los Angeles. Around ten thousand aircraft are in the air. Tens of thousands of ships are at sea. Kettles are coming to the boil.

The machines don't notice at first. Autopilots hold their headings. Engines idle in empty cars. Traffic lights keep cycling red, amber, green for streets with nobody on them. For a few hours our world runs on momentum, like a song still playing in an empty room.

Then the fuel runs out. One by one, the airliners drain their tanks and glide down, into oceans, forests and fields. It is the last human noise many places will hear for a very long time.

A power grid is a balancing act. The electricity made has to match the electricity used, second by second, and people steer that balance day and night. Behind them are coal trains, gas contracts and fuel deliveries. Remove the people and the act starts to wobble.

Fossil-fuel plants go first. A frequency swing, an alarm no one answers, a fuel feed that stops: their automatic safety systems trip them offline. Each failure dumps its load onto the next plant, which trips in turn.

The failures cascade across borders and continents. Within a day or two, almost every grid on Earth has gone dark. Hover the map, or switch fuel types on and off in the key, to see what is left.

A few holdouts remain. Some hydroelectric dams run on gravity rather than fuel, and in isolated systems their turbines can keep spinning until debris and mussels clog the intakes. A rooftop solar panel keeps charging a battery for nobody.

Seen from space, the night side of Earth is now as dark as it was in 1800. The only lights are lightning, lava, the aurora, and fires that nobody comes to put out.

When the power fails, the pumps stop. Water collects at the lowest points first, in the tunnels that run beneath the rivers. Within about 36 hours, parts of the network are flooded.

Now the water starts its slow work. The steel columns that hold up the streets stand in it, and begin to rust. London, Paris and Tokyo face the same patient flood beneath their pavements.

Within a couple of decades, the columns give way. Avenues cave in above the tunnels, and streets built along forgotten streams become streams again.

The fuel keeps making heat anyway. Beside each reactor, in deep pools, sit years of spent fuel rods that must be kept under circulating water. Backup diesel generators take over the pumps. Their tanks typically hold enough for about a week.

Then the diesel runs dry. The pools warm, and then boil. Over weeks the water level falls, and once the rods are exposed their zirconium casings can catch fire, releasing radioactive smoke into the wind.

Plumes drift east on the prevailing winds. Around a few hundred sites, including Romania's two reactors at Cernavodă beside the Danube, patches of contaminated land settle, much like the one around Chernobyl.

And yet Chernobyl also shows what comes next. Within three decades of the evacuation, its exclusion zone was full of wolves, elk, boar, lynx and bison. For most wild animals, radiation turned out to be far less dangerous than people.

There is a cruel twist. That haze was shading us, reflecting sunlight back to space. With it gone, the planet warms by a few tenths of a degree within a few years, a hidden bill arriving all at once.

And the night comes back. Today more than a third of humanity cannot see the Milky Way from home. Now it rises again over every city on Earth, for no one. Drag the slider to compare.

Freeze and thaw is a city's oldest enemy. Water seeps into a crack, freezes, grows by nine percent and pries the crack wider. Roofs begin to leak. Once rain gets inside a building, the countdown has started.

Lightning hits a dry roof, and there is no fire brigade. Fires run through the wooden neighbourhoods, fed by a decade of dead leaves in the gutters. Their ash enriches the soil. The first trees are now taller than the lamp posts.

Inside the concrete, the steel reinforcing bars rust. Rust takes up several times more room than steel, so the bars burst the concrete from the inside. Balconies drop. Facades peel away in slabs.

Most wooden houses have collapsed by now. The suburbs go first, because our homes were never built to last without us. Brick chimneys stay standing among the trees, like bookmarks.

With their windows gone and rain pouring in, steel-framed towers start to buckle. Some fall. Others stand as hollow cliffs where peregrine falcons nest, as they already do today. The streets below are a forest.

The great suspension bridges, unpainted for three centuries, drop into the rivers they once crossed. In Panama, the canal has long since silted up, and the two Americas are joined again.

After a thousand years, a city is a cluster of wooded hills, oddly straight-edged, with rubble under the moss. Only what was made of stone, glass and very thick concrete still shows through.

The Carpathians

Romania holds Europe's largest brown bear population outside Russia, around 8,000 animals, along with wolves and lynx. With the guns silent and the orchards of abandoned villages dropping fruit, the bears move downhill. They already visit the edges of Brașov. Within decades, its streets belong to them.

Transfăgărășan

Nobody clears the road in spring. Within a few winters, rockfalls and avalanches cut it. Within a century, the most famous hairpins in Europe are a faint zig-zag of young forest on the mountainside.

The Danube Delta

In the 1960s to 80s, dykes turned large parts of the delta into farms and fish ponds. Unmaintained, those dykes fail one flood at a time, and the river takes its marshes back. Europe's largest reed beds spread, and pelicans, among more than 300 bird species, come back to nest in them.

The Iron Gates

The Porțile de Fier dam, one of Europe's largest hydropower plants, may keep a few lights burning longer than almost anywhere in the Balkans. The dam itself should stand for centuries, while its lake slowly fills with the silt of half a continent.

The Bărăgan

Not everything turns into forest. The plains of the south-east were steppe long before the plough, and they go back to grass. Wild horses from abandoned farms graze where the wheat was.

Bucharest

The Palace of the Parliament weighs around four million tonnes, one of the heaviest buildings on Earth. Long after the apartment blocks around it have fallen, it will still be there. In a thousand years it will be a great wooded hill in the middle of a forest, with marble underneath.

Chernobyl, the rehearsal

Some 2,600 square kilometres of Ukraine have been almost empty of people since 1986. Scientists counting animals there found wolf numbers up to seven times higher than in nearby nature reserves. It is the closest thing we have to a preview of this story.

The oceans and new forests start drinking it back. It is fast at first, then slow. A century on, the level is still higher than at any point in the two million years before us.

After the oceans have had their fill, roughly a quarter of our carbon remains, and the planet stays warmer than in 1850. Ice sheets keep melting for centuries, and the seas keep rising for thousands of years.

The last of it is removed by rain, slowly dissolving rock and washing the carbon into the sea, where it becomes limestone. That takes a few hundred thousand years. Our exhaust, it turns out, is one of the longest-lasting things we left behind.

After 24,100 years, half of the plutonium-239 present at the start remains. Another 24,100 years would halve that remainder.

Then the ice comes back. Earth's orbit drifts, northern summers cool, and the ice sheets grow. If this one matches the last, it will bulldoze Chicago, Toronto, Stockholm and Berlin into gravel. Bucharest, far to the south, is spared. Our lingering carbon may have delayed it by tens of thousands of years.

After a million years, the faces on Mount Rushmore, eroding about 2.5 cm every ten thousand years, are still recognisable. Most of the species alive today are still around too. New ones are appearing on islands.

Buried and squeezed, it becomes rock. Concrete turns into an odd conglomerate. Aluminium, which nature almost never makes pure, stays as glinting flecks. Plastics thin into black films of carbon, like the fossil outlines of leaves.

A geologist of the far future would find a band a few centimetres thick. It is full of strange minerals, carbon with the wrong isotopes, and bones, billions upon billions of chicken bones. Hover the rock to read its layers.

By then, the variety of life has recovered from the extinctions we started, as it did after the asteroid, in roughly ten million years. The creatures of that world will walk over the line without knowing what it means.

Its makers expected the record to survive a billion years. By then the slowly brightening Sun will have begun to boil away Earth's oceans. The record will still be drifting between the stars, playing to no one, a letter with no return address.