On 11 March 2011 the sea runs into a narrow valley on the coast of Iwate. It tears away the small harbour of Aneyoshi. It strips trees and soil from the slopes until only bare rock remains. Nowhere in Japan does the wave climb higher that day. Survey teams later measure almost 39 metres.

Then the water stops. Some 90 metres below a stone by the side of the road. Above it stand the houses of the village. Not one of them is damaged.

The stone reads, in translation: Do not build your homes below this point. High dwellings are the peace and harmony of our descendants. Remember the calamity of the great tsunamis.

The Village That Already Knew

The stone is not old. Nor was it the first attempt.

In 1896 a tsunami destroys Aneyoshi. Two people survive. The village moves uphill. A few years later it is settled again, back at the shore. In 1933 the next wave comes. This time four survive. The houses stood down by the water because that was where the boats lay. It was reasonable, every single day. Until the one day when it no longer was.

Only after the second loss do the survivors set the stone. They had understood what their parents had missed. Knowledge alone does not hold. It has to stand in a place no one can walk past.

The disaster researcher Fumihiko Imamura of Tohoku University reckons with about three generations. That is how long it takes a society to forget what it lived through itself. On this coast the gaps between great tsunamis are often longer than a human life. Memory does not reach as far as the next wave. The stone does.

The Wall and the Stone

Aneyoshi was the exception. Hundreds of such stones stand along the Japanese coast, some more than six hundred years old. In the boom years after the war, many towns grew towards the sea regardless. Even communities that had once moved uphill returned to the water.

Something else had taken the place of the stone. Concrete walls along the coast promised protection where restraint had once been needed. People could build low again. The places that relied on their walls were hit hard in 2011.

The wall was not bad engineering. It held back smaller floods for decades. That was exactly its effect on people. Whoever lives behind a wall no longer needs to know how high the sea can rise. They only need to trust the wall. The limit had moved out of people's heads and into the concrete.

Freiberg, 1713

Almost two centuries before the first wave at Aneyoshi, at the other end of Eurasia, a man stood before a different limit. Hans Carl von Carlowitz had been chief mining administrator in Freiberg since 1711, the highest office in Saxon mining. Silver mining needed wood. Wood for the tunnels, for the smelting furnaces, for charcoal. The forests around the mines were shrinking faster than they grew back.

At the Easter fair of 1713 his book appeared in Leipzig, the Sylvicultura oeconomica. In it he calls for wood to be tended so that there would be a "continuous, steady and sustaining use". Wood, he wrote, was an indispensable thing without which the land could not endure.

The word he used, nachhaltend, the root of the German word for sustainability, slipped out almost in passing. It was one synonym among several, next to steady and continuous. Carlowitz did not set out to coin a term. He wanted Freiberg to still be mining silver in a hundred years. His restraint was not a sacrifice to nature. It was the condition for mining to have a future at all.

The stone at Aneyoshi says where not to go. Carlowitz says how much may be taken. Both ask the same thing: to do less today than one could. For people one will never know.

Where Limits Wander

In the end, Carlowitz's wood shortage was not solved by forestry. It was solved by coal. In the nineteenth century hard coal freed Europe from its dependence on the forest. The limit Carlowitz had calculated against disappeared.

But it disappeared only from the edge of the forest. It resurfaced in a place where for a long time no one was looking. The carbon that gathered in the atmosphere over two centuries was the bill for the lifted wood limit.

This is the pattern of a humanity that lives by its technology. Technology rarely abolishes limits. It relocates them, usually to a place that lies further away or falls due later. In Japan the limit moved from the hillside into the wall. In Europe it moved from the forest into the air.

Today the Haber-Bosch process draws nitrogen from the air for fertiliser. By common estimates, the food of roughly half of humanity depends on it. The limit of the soil has not vanished. It now sits in factories, in natural gas, in supply chains.

With every such shift, humanity grows stronger. It also grows more dependent. Whoever moves a limit into a machine must keep that machine running for good. They must also remember why it stands there.

Where Nothing Grows Back

The strictest form of this pattern waits where humanity wants to go. Beyond Earth no forest grows back. No rain falls. Every breath and every litre of water comes from a machine.

On 14 September 2026, Martin Elvis of the Smithsonian Astrophysical Observatory and Jonathan McDowell of Durham University published a calculation on exactly this, under the title "No cities on the Moon". Water ice lies in the permanently dark craters at the lunar poles. Some of these craters have not seen direct sunlight for about four billion years. Elvis and McDowell generously assume one billion tonnes. An analysis from 2022 put the combined total of the eight richest craters at about 34 million.

Even the billion would last a city of one million people only about two and a half years without recovery. With the recycling rate of the International Space Station, 98 percent, it lasts around a century. At 99.9 percent it would be about two thousand years.

On the Moon, Carlowitz's rule becomes exact. Nothing grows back there except what is recovered. The loss in the cycle is the real felling of the forest. Two percent or one per mille: this digit after the decimal point decides whether a settlement lasts one century or twenty.

This is not a verdict against the Moon. By their calculation, a settlement of one thousand to ten thousand people with rigorous recycling remains viable for centuries. The calculation sets an upper bound. Elvis also calls on China, the United States and their respective partners to manage the water together instead of racing for it.

The Settlers After Us

Whoever is born on the Moon or on Mars has signed nothing. They inherit a loss rate. They inherit installations whose limits someone set before them. They inherit rules whose reasons perhaps no one remembers.

There is more water on Mars. But Earth lies further away. A radio signal takes up to 22 minutes. A journey takes months. What the settlers need to know cannot stay stored on Earth. It has to stand on site.

Three generations are enough to forget. On Mars the third generation might be the first never to have known a world without machines. The systems that give them air and water are to them what rain is to us. That is exactly when the wall is most dangerous. Not because it was badly built. But because no one knows anymore how high the sea can rise.

This condition does not begin on distant planets. We already live inside systems of power, satellites, fertiliser and data centres. They run so reliably that we hardly see their limits anymore. The settlers after us are not only people in distant craters. They are also our grandchildren on Earth.

So Aneyoshi and Freiberg do not teach distrust of technology. Carlowitz did not abandon mining, he secured it. The fishermen of Aneyoshi still go out to sea. What sets both apart is something else. They fixed the limit before scarcity forced it on them. They wrote down the reason along with it.

A limit without a reason will one day be read as harassment and abolished. A reason without a limit remains a warning that keeps being postponed. Only the two together last across generations. For the first settlements beyond Earth this means: the permitted loss rate belongs in the founding order. So does the upper bound of a settlement. So does the shared management of a supply that does not grow back. Not as an amendment once scarcity becomes visible. But on the first day.

Somewhere at the Moon's south pole, one day, someone will set the first stone. They will inscribe it for people they will never meet.

Homepage: https://planet-future.org