In 1980, the US Department of Energy created the Human Interference Task Force to investigate the problem of human intrusion into waste repositories. What was the best way to prevent people many thousands of years in the future from entering a repository and either coming into direct contact with the waste or damaging the repository, leading to environmental contamination?

Over the next 15 years a wide variety of experts were involved in this and subsequent projects, including materials scientists, anthropologists, architects, archaeologists, philosophers and semioticians – social scientists who study signs, symbols and their use or interpretation.

Science fiction author Stanislaw Lem suggested growing plants with warning messages about the repository encoded in their DNA. Biologist Françoise Bastide and semiotician Paolo Fabbri developed what they called the “ray cat solution” – cats genetically altered to glow when in the presence of radiation.

Quite apart from the technological challenges and ethical issues these solutions present, both have one major drawback: to be successful they rely on external, uncontrollable factors. How could the knowledge required to interpret these things be guaranteed to last?

Semiotician Thomas Sebeok recommended the creation of a so-called Atomic Priesthood. Members of the priesthood would preserve information about the waste repositories and hand it on to newly initiated members, ensuring a transfer of knowledge through the generations.

Considered one way, this is not too different from our current system of atomic science, where a senior scientist passes on their knowledge to a PhD candidate. But still, putting such knowledge, and therefore power, into the hands of one small, elite group of people is a high-risk strategy easily open to abuse.

Perhaps a better way to warn our descendants about the waste is to talk to them directly, in the form of a message.

At Andra’s headquarters outside of Paris, Jean-Noël Dumont, head of Andra’s memory programme, shows me a box. Inside, fixed in plastic cases, are two transparent discs, each around 20 centimetres in diameter. “These are the sapphire discs,” he says. The brainchild of Dumont’s predecessor, Patrick Charton, each disc is made of transparent industrial sapphire, inside which information is engraved using platinum.

Costing around 25,000 euros per disc, the sapphire (chosen for its durability and resistance to weathering and scratching) could last for nearly 2 million years – though one disc already has a crack in it, the result of a clumsy visitor on one of Andra’s open days.

In the very long term, though, these plans also have a major drawback: how can we know that anyone living one million years in the future will understand any of the languages spoken today?

© Emily Graham for Mosaic

Think of the differences between modern and Old English. Who of us can understand “Ðunor cymð of hætan & of wætan”? (Thunder comes from heat and from moisture.) That – meaning “Thunder comes from heat and from moisture” – is a mere thousand years old.

Languages also have a habit of disappearing. Around 4,000 years ago in the Indus Valley in what is now Pakistan and north-west India, for example, people were writing in a script that remains completely indecipherable to modern researchers. In one million years it is unlikely that any language spoken today will still exist.

In the early 1990s, architectural theorist Michael Brill sought a way to side-step the issue of language. He imagined deterrent landscapes, “non-natural, ominous, and repulsive”, constructed of giant, menacing earthworks in the shape of jagged lightning bolts or other shapes that “suggest danger to the body... wounding forms, like thorns and spikes”.

Anyone venturing further into the complex would then discover a series of standing stones with warning information about the radioactive waste written in seven different languages – but even if these proved unreadable, the landscape itself should act as a warning. To help convey a sense of danger there would be carvings of human faces expressing horror and terror. One idea was to base them on Edvard Munch’s The Scream.

The drawback is that such a landscape – a strange, disturbing wonder – would probably attract rather than repel visitors. “We are adventurers. We are drawn to conquer forbidding environments,” says Florian Blanquer, a semiotician hired by Andra. “Think about Antarctica, Mount Everest.”

Or think about the 20th-century European archaeologists, people not noticeably hesitant when it came to opening up the tombs of Egyptian kings, despite the warnings and curses inscribed on their walls.