When writer Gareth E Rees stands on the muddy foreshore at Pett Level in East Sussex, his mind turns to the Mesolithic peoples who hunted, lit fires and dreamed their very human dreams on the lands now subsumed by the steel grey swell of the English Channel.

It’s low tide at Pett Level and, as at every low tide, the withdrawing waters have exposed a landscape of twisted and pocked tree trunks that is illegible to many of today’s brisk dog-walkers and young families out on the migrating shingle.

It is one of many sunken lands around the world that Rees has become fascinated by – places where people used to live that have been lost beneath the waves throughout history – areas from the past that may tell us something about our own climate-change induced predicament of today.

“What I love about this place is that I get such a buzz from seeing the layers of history open out,” Rees tells me as we brave a southerly wind that whips scarves about our cheeks. Rees, a trim 50-year-old dressed in a band T-shirt and jaunty tartan scarf, is, for his part, fired up.

“Standing here, I imagine the forest of birch and oak that once stretched from here to France,” he explains, casting a wide arc with his arm. “Over there, near to the nuclear reactors of Dungeness power station, I can see the bustling streets of Old Winchelsea port, which was inundated by a flood in 1287.”

In 1980, David Bowie and director David Mallet chose Pett Level as the location for the video for Ashes to Ashes. Its conceit was the artist’s rebirth at the dawn of a new decade, with lyrics referencing his 1969 hit Space Oddity and Bowie striding through the beach’s damp boughs with a funereal parade of New Romantics in the shallows, awaiting regeneration.

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Pett Level was the perfect choice, Rees says of the video: “Here, ancient forests have turned to marshes, marshes to fields, fields back into marshes and marshes to sea.” He pauses, then adds: “You see, as humans we are born from amniotic fluid, but we are also children of the flood.”

Rees’s latest book, Sunken Lands, follows his 2013 book Marshland, which explored the history and folklore of east London’s marshes as stretches of its wild meadows were bulldozed for the 2012 Olympics, and Unofficial Britain (2020) which rhapsodised about sundry British civic furniture, from industrial estates to flyovers.

Sunken Lands was inspired by Rees’s pandemic, during which he took to parking his dented Peugeot at Pett Level, which is near his Hastings home, and poking about this storied stretch of coastline with his two young daughters and cocker spaniel, Hendrix.

In those strange months he would enjoin his daughters to push their fingers into the soft wooden matter of these ancient fallen trees, touching the same spot that other children may also have touched long ago, before Jesus was born. “My kids thought it was a bit strange at first, but then they got it,” he says.

The book is a lyrical, light-historical excavation of lands lost to encroaching waves throughout human history. It recounts stories passed down to us of these deluges, ranging from the familiar – the tale of Atlantis – to the less well known, such as the fable of the land that lives below the Irish Sea, known to the Welsh as the kingdom of Cantre’r Gwaelod, and the English as the Lowland Hundred.

As a project, Sunken Lands follows in the tradition of Robert Macfarlane’s The Old Ways (2012), in which the academic follows the ancient tracks, holloways and drove roads that crisscross the British landscape; and of historian Matthew Green’s Shadowlands (2023), which explores the archaeological and historical traces of British settlements lost to natural forces, war, plague and economic shifts.

Rees’s approach is a psychogeographer’s rather than a historian’s: a conversation between landscape and our emotions. It is inspired by 19th-century flâneurism and 20th-century situationists such as Guy Debord, who argued for playful exploration of spaces guided by our responses to them. Yet unlike its companion pieces in the emergent “lost lands” travel-writing canon, Sunken Lands is also a manifesto. It’s a call to action for a planet that’s currently projected to see sea level rises of up to a metre by 2050, submerging cities including Amsterdam, Venice, Kolkata and New Orleans.

“I’m a hypochondriac turned climate-catastrophising dad,” Rees laughs. Partly then, the book is a way of grappling with Gen X’s rabid consumption patterns, worse in some ways than the Boomers often inculpated in the generational blame game. “What with climate change, deforestation and microplastics, our kids are inheriting a mess, frankly,” Rees says as we crunch across Pett’s shingle, passing a shuttered beach café where signs from 2021 still advertise deals on burgers. “How do we talk to them about it?” he asks. “Can and should we sugar-coat it?”

The book sees him visit long-lost and about-to-be-lost lands around the world. It travels from Sussex to Wales and Cardigan Bay, where at low tide on the beaches of Ynyslas and Borth stumps of birch and pine ghost forests emerge. It moves on to the Fens, which he depicts as a terrain stripped bare by centuries of profit-driven land reclamation; and the Scilly Isles, which are due to be our islands’ first loss to the rising seas.

In Italy, he dives on the remains of Baia in the Bay of Naples, once a holiday resort for upper-class Romans, now submerged after a volcanic eruption; and in Louisiana in the US he visits the communities clinging on in a low-lying state that is thrashed by storm surges, yet in thrall to fossil-fuel extraction.

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Before we met, I’d wondered about the risks of telling stories about the many floods humanity has endured in the guise of environmentalism. If humans have always contended with waters that ebbed and swelled and claimed ancestral lands and civilisations, was this not playing to the climate-change sceptics’ contention that climate change is cyclical, and that human beings should be staunch in the face of its threats? Think of plucky Noah packing up his menageries, or the merchants resuming their trade in cloves and claret at New Winchelsea.

Rees stops abruptly on the shingle. “No! No! No!” His aim in telling stories about the loss of lands to flood is to snap us out of our fever dreams of mindless consumption, not to make us feel impotent and gloomy.

There’s something comforting in the realisation we are tiny and fleeting in the cosmic and geological scale of things

“People of the early Holocene who saw their ancestral homes and hunting grounds slip beneath the waves were just like us: human beings with complex thoughts and emotions and real fear about what was happening to lands where they had lived, hunted and loved.” Looking back into “the deep time of human history”, Rees believes, can give us solace. “There’s something comforting in the realisation that we are tiny and fleeting in the cosmic and geological scale of things,” he says.

Not that this gives us any excuses. Then as now, we are dependent on a fragile world that we exploit at our peril – and we need to understand that although this has happened before, what is taking place now is so much worse. The people in these ancient stories were just like us, and we will be just like them if we don’t take action. This reality isn’t someone else’s reality, far away in Tuvalu or Bangladesh, “It’s right here and now,” says Rees. “The Scilly Isles are on track to be underwater in a century and Rhyl by 2050.”

It was on a walk from Hastings to Pett Level in 2015 that Rees realised his marriage had ended. At Pett Level, land and sea are in constant motion and never the same from day to day or minute to minute. Spiritually, maybe, we are all in hock to its inexorable forces. Rees believes this is one of the reasons we are drawn as humans to storytelling: to make meaning from nature’s bamboozling idiosyncrasies and to make sense of our swept-away lands and drowned homes.

There are more than 200 known global flood myths, with stories of catastrophic inundation colouring our oral histories and major religions. It’s not just Noah: Deucalion is gifted with foresight of a great flood by Zeus, and in Hindu texts from the sixth century BC, Vishnu takes the form of a fish and tells the first man, Manu, to build a boat before the deluge. The myriad Celtish myths of sunken kingdoms include Lyonesse, a prosperous kingdom supposed to have been between Cornwall and Scilly, and Ys off the coast of Brittany.

It struck Rees in researching this rich hinterland of flood mythology, that we humans never win when the floods come, as we won’t win in the face of climate-change-wrought flooding, however much hope, or hard cash, we throw at those prayers and levees. “Eventually these people all had to adapt and move,” Rees says simply. “That’s the only story in all of these stories. There wasn’t any grand conclusion where they engineer their way out of disaster – a magical fable where someone closes the sluice gates and all is well.”

We are the children of the flood. More recently, these stories have once more bobbed to the surface of our collective consciousness. In 2011 a bell was installed below the pier in Aberdyfi in Wales, designed to be rung by the movement of the tide. It’s a tribute to the legend of the church bells of the Lowland Hundred – the tinkling said to be heard across the waves when winter storms blow – and to the fact that such legends are capturing our folk imagination anew.

Rees is also a singer-songwriter and makes various references to stirring music in Sunken Lands – from Hawkwind’s We Took the Wrong Step Years Ago, to the blaring trumpets and rolling piano keys of New Orleans jazz. An album of Rees’s own music will accompany the book, as well as a Spotify playlist of his road trip music. “Music and spoken word can reach people where literary projects can seem a bit for the initiated,” he says.

Back to that manifesto, and Rees wants to give the oil men two barrels of their own noxious extrusions. The big oil brigade, he tells me, “are the big tobacco magnates of today”, funding partisan reports, initiating new drilling projects in fragile wetlands, encouraging nations such as Guyana, where most of the population lives below sea level, to extract seabed oil reserves; and, just as risibly, peddling the concept of the “carbon footprint” to shift the responsibility for climate change on to individuals like you and I, rather than corporations or governments. “I don’t think anyone is inherently evil,” Rees says of these fossilcrats, “though you do have to wonder what their basic plan is: use the world’s resources when I’m alive and let everybody burn when I’m gone?”

In Rees’s view, big oil will become the baddies of stories whispered around campfires of the future, with Greenpeace and Extinction Rebellion the heroes of the tale rather than characters of Celtic myths such as Seithenyn and Mererid.

Sunken Lands concludes in Louisiana, a “hardcore industrial landscape” of gas-processing plants, drilling rigs and swampland, where the twisted tops of telegraph poles and leafless trees are all that’s visible above polluted, encroaching marshwaters. “Isle de Jean Charles in Louisiana was the toughest moment for me,” Rees says of one of the Louisiana communities he visited. “This was once a thriving community, where the Biloxi-Chitimacha-Choctaw tribe lived with and on the watery land for generations, but it’s on the verge of disappearing off the map entirely thanks to oil companies’ drilling.” A weathered sign at Isle de Jean Charles reads: “Isle de Jean Charles is not dead. Climate change sucks.”

In his book, Rees recounts how he comes a cropper in Louisiana in his hire car, and is thrown on to a raised shingle bank where he briefly imagines he’ll be lost to the filthy floods. He laughs about this moment as we get into his battered Peugeot and leave Pett Level’s ancient arboreal souvenirs and rockpooling families in peace. “It was really just a puddle, looking back.”

We are children of the flood, but we’re kids who need hope, too. In Sunken Lands, Rees dives into the abysses of our flooded worlds past and present and emerges an optimist. Gone for Rees, these days, is all the “disaster-scrolling and paralysing climate terror”. He’s turned from catastrophising dad to post-doomer and advises us to do so, too.

“As humans we all have powerful shared stories to tell, of survival and solace,” he says, as a light rain patters on the Peugeot windscreen, “and we all have the power to change things for the better”.

Sunken Lands by Gareth E Rees is published by Elliott & Thompson, £16.99 (guardianbookshop.com, £14.95)