The gods can be boors. Their ways are not ours. They shout a lot. They don't seem as concerned with identity politics or buying things as they might be. Whatever their enthusiasts claim, the risk is that, by now, they have nothing left to say to us. In revenge or desperation we reboot them as science fiction, as monsters of the id, as guest appearances on other shows: gods on skateboards, gods on the autistic spectrum; gods adapted to the needs of ideologies they would never in a billion years have espoused, carrying the baggage of every previous revision. We reappropriate them with more certainty, perhaps, when we do it personally than when we do it as a culture.

AS Byatt's Ragnarok is the latest in the Canongate series of reworked myths (already notable for The Hurricane Party, Klas Ostergren's encounter with the same material). Byatt adds value to the end of everything by adding her own experience of it, as a child in the beleaguered England of the early 1940s. "There was a war on," she says. "Possibly there would always be a war on." This sense of eternal conflict acts as an anchor; while interweaving the stories of the Norse gods with the story of how she first read about them makes a kind of bildungsroman. The story becomes as much hers as theirs. It's a risky strategy, but not as risky as, say, gods on mephedrone. And it preserves a clean, direct contact with the original material, reassembled here from "many stories in many languages".

Evacuated at the age of five to the "ordinary paradise of the English countryside", the "thin child" finds herself walking two miles to school every morning, "across meadows covered with cowslips". She quickly learns to read. One of her favourite books is "a solid volume, bound in green", with a picture of the Wild Hunt myth on the cover; inside she finds the gods waiting for her, in the world they have carved out of their dead precursor's head. Meanwhile she dreams that the Germans are planning to kidnap her parents. She dreams "what she did not know, that her parents were afraid and uncertain". All three of them, mother, father and child, are snagged in the anxieties of their time.

This uncertainty is central to the gods' world too. They know they shouldn't have killed and infested Ymir the giant, shackled and mocked the Fenris wolf, cast Loki's serpent-daughter into the sea, or exiled Hel to her dark halls and cups of poison; they knew all along that these were probably stupid, overconfident acts. Just thinking about it is enough to give Baldur "dreams of real terror, more real than the world the dreamer wakes to". Pretty soon, Frigg, more lobbyist than goddess, is trying to persuade "everything on the earth, in the air, in the ocean" to promise not to harm a hair on fair Baldur's head. Anxiety is winding up like a clock; the clock is ticking down to Ragnarok. The curious blokeishness of the gods, their rowdy but passive game-playing in the face of a disaster they've brought upon themselves, is a clear metaphor for our own destructive behaviour in the world. They celebrate "the cohesion of earth, air, fire and water and all the creatures in and on these elements", but they do everything to make sure that all these things go to hell.

Despite this, Byatt's prose, compact and lyrical, treats them with dignity: Odin, unpredictable, "a god both sinister and dangerous"; Loki the undoer, "putting out waves of glamour" and obsessed with chaos theory; Loki's daughter the World Serpent, "arching herself to swoop down with the white water full of air and light until snake and wave hissed on the sand together and rolled idle". Their world is built from the author's deep concern for ours: "The surface of the earth was like a great embroidered cloth ... with an intricately woven underside of connected threads." The thin child observes the gods' blunders with an impressed yet academic eye. The result is sometimes an enormous pathos, sometimes a recognition that while one knew this or that part of the Midgard narrative, one didn't, until now, understand it so well.

Ragnarok is a clever, lucid, lovely book. But it isn't a novel, or even a story in the usual sense. It's a discourse on myth, woven in and around a polemic about pollution and loss of species diversity: Yggdrasil the World Tree reinscribed as a doomed ecosystem. Byatt's ideas lie close to the surface; moreover, the author herself is waiting patiently at the end of everything, to make sure we take her point.

In a mediated age, this effect extends beyond the book. I know, for instance, that the "thin child" is probably AS Byatt herself, because before I opened Ragnarok I read her recent piece in this newspaper. Between that and a precision-crafted afterword, she is able to control, to a much greater degree than was possible in the early 1940s, the way the reader receives and interprets the text. I'm in a sense grateful for that, I feel in safe hands; after all, Byatt knows a great deal more about these myths  and myth in general  than I ever will. In another sense I'm disappointed that she doesn't leave me alone to discover what she's made. The young Byatt could allow the stories of Midgard to roll over her, "not as pleasures but as encounters with the inapprehensible"; whereas her older self's "rescue" of them won't quite permit us to do that.

M John Harrison's Pearlant will be published next year by Gollancz.

Stories begin when characters set out on their travels and end when they arrive at a destination or return wearily home, but what matters to the storyteller is the middle of the journey with its middle-aged complexities  divided loyalties, tormenting decisions about which way to turn. Myths are simpler, starker and more abrupt. They ignore the median region and its middling conflicts; their province is a beginning we can't remember and an end we may not be alive to experience. How did the world originate, and who, if anyone, made it? And how will its conclusion come about  a firestorm or a blizzard, inundation by black waters, or an angry deity's brusque decision to stop the show?
When AS Byatt agreed to contribute to Canongate's series of updated myths, she chose as her subject the ultimate end, the Scandinavian legend of Ragnarok. This is what Richard Wagner, in the last instalment of his Ring cycle, called the twilight of the gods, who give up regulating nature and allow the world to destroy itself. Because apocalypse overwhelms individual fates, Byatt could hardly follow the example of previous writers in the series, who have extracted characters from the myths and probed their minds: Margaret Atwood in The Penelopiad asks why Odysseus slew his wife Penelope's maids, while David Grossman in Lion's Honey investigates the motives of the temple-toppling Samson, whom he likens to a contemporary suicide bomber. Byatt chose to deal with elemental forces, personifications of the weather, resistant to the novelist's insights and empathy. Unlike the inhabitants of Mount Olympus, the Norse gods whose murderous squabbles and vindictive wars bring about the final catastrophe "did not have faces, they were not persons".
Despite its brevity, Ragnarok is three books in one, and none of them is anything like a novel. It starts as fictionalised autobiography, with Byatt remembering herself in the third person, as a "thin child", encountering the myth 70 years ago. Next, and alternating with the autobiographical passages, comes her personal version of the legend, forcefully dramatic and moodily poetic. Having sentenced the world to death, she exchanges creativity for criticism, and concludes with a self-aware essay on the ancient source and its modern relevance.
Although Byatt doesn't believe in the biblical Eden  in her view a mere fairytale, not even a myth  she begins by wistfully reviving a lost paradise. Early in the war she was evacuated from Sheffield. Sent to live in the nearby countryside, she roamed through a wild garden that consisted both of flowers and the equally florid words that named them: "Daisies. Day's eyes, she learned with a frisson of pleasure Dandelion, dent-de-lion, lionstooth, her mother told her." This golden world clouded over when her mother presented her with a volume of Nordic religious lore. Its gloom served as a grimly truthful antidote to the cheery Christianity that kept people's spirits up and assured them that they'd see their uniformed loved ones again, in heaven if not on earth. The version of the universal narrative that Byatt found in Asgard and the Gods was unremittingly violent, its outcome inconsolably bleak.
She pored over it as her parents stoically soldiered through what seemed to be the end of the world they knew. What transfixed her was an image or a vision. She spent hours peering at an engraving of some anthropomorphic rocks in the Riesengebirge, boulders that looked like helmeted giants with thick, belligerent arms. The stone was formless, inert until it was animated by "the reading eye". Byatt found metaphorical beasts lurking in the crosshatched murk of the illustration: a bush impersonating a crouched dog, a branch that might be seen as the lethal licking tongue of a snake. Having learned how to bring about this small miracle, she had her first precocious experience of the power that uniquely belongs to the artist. This  she remembers feeling  is why she wanted to write, and this was what a writer could achieve. A human being can create superhuman beings, giants or even gods; customised microcosms come into existence in response to our magical commands.
According to the Icelandic Edda, our planet was made by excavating the corpse of the dead giant Ymir. His flesh became earth, his bones made mountains, his blood decanted oceans, and his hollowed-out head formed the sky. "The created world," Byatt comments, "was the skull"  or that at least was where the creative power, not confined to God as in the Bible, had its headquarters. Byatt therefore says that her purpose here is "to write a myth", not merely to retell one. It is a proud and dangerous claim, which she triumphantly justifies when she summons up the thronging landscape of the sagas.
Wagner's texts for the four operas in his Ring cycle mimicked the alliteration of ancient Nordic verse: he believed that those recurring sounds at the beginning of words kick-started his lines rather than closing them off in predictable endings as rhyme does. In the same way, the alliterative patterns in Byatt's style make the myth's events vividly audible. When she notes that "Odin dealt death at a distance to those whose displeased him" the concussive repetition sounds like Wagner's Wotan as he cues thunderclaps by banging his spear on the ground. Describing an amphibious tree that nurtures aquatic life in its wet roots, Byatt almost makes you feel seasick: "Things swayed, and slid, and sailed through the sea-forest, hunting and hunted", while "pallid prawns flicker glassy feelers". Like an abracadabra, her verbal images make live things materialise before our eyes. "A mackerel's skin," she remarks, "is a vanishing trick," after which she brilliantly traces the montage of reflections that ripple along its scales before it disappears in the water. As the metaphors germinate, we watch nature itself evolving. The ravenous snake Jörmungandr gobbles up the contents of the sea and becomes "as long as an estuary", sinuously unravelling like "a marching army on land".
When Odin's son Baldur is killed, everything that remains alive laments, and Byatt's lyrical elegy  with stalactites dripping, boulders exuding moisture, humid tropical forests steaming, and the lidless eyes of fish brimming to add water to the oceans  turns the earth into a vale of tears. But the myth, as she says, is "ineluctable", and this mournful outpouring cannot avert the end. Ragnarok follows, taking the form of climate change.
Wagner trusted in a cyclical return of life, which is why when Valhalla burns and the Rhine overflows at the end of Götterdämmerung, the orchestra assures us with one of its recurrent motifs that the world has been cleansed and redeemed by love. Byatt offers no such compensation. Hurricanes  like the one that flattened southern England in 1987, and supplied her with the climax of her novel Possession  alternate with droughts. The declining sun emits a light that is "dull red, sullen, like embers". A funeral ship loaded with coagulated rot sets sail: this is Byatt's nightmarish reimagining of the trash vortex, an archipelago of undecaying plastic that swirls in the middle of the Atlantic.
In Byatt's view, the saga's villain is Loki, Wagner's Loge, the trickster whom she turns into a connoisseur of chaos, destructive because of his slippery analytical intelligence. Wagner thought that the abdication of the gods would liberate humanity, but Byatt, professing a kind of cosmic Toryism, laments our assault on the divinities who once set limits to our ambitions and held the world together with their sanctimonious "bonds and fetters". Freed from such prohibitions, we have overrun and eaten up "the world we were born into", eroding the land, depleting the seas, burning irreparable holes in the sky. Wagner rounded up a few human witnesses to watch in amazement as the world ends. For Byatt, there can be no such audience: humanity itself is doomed.
This polyphonic book has different voices for the stages of Byatt's life and the phases of the world's history. Childhood is recreated in a tone of naive wonder: a "glossy parliament" of rooks in the treetops, the bud of a poppy with its "secret, scarlet, creased and frilly flower-flesh". When the myth takes over, Byatt adopts a voice that is entranced and oracular, like a witch reciting spells or one of the Norns who recall the beginning and foresee the end in Götterdämmerung. The epilogue, consulting scientists to establish the contemporary relevance of Ragnarok, settles down into a cooler, wintrier, more academic manner, as if she had both used up her reserves of infantile delight and retired from her commanding role as a fabulist.
The three voices match Byatt's belief that writing a book is a three-dimensional activity, an exercise, as she once said, in "making a thing". What she has made in this case  thanks to a rare fusion of imagination and intellect, sensual poetry and cerebral prose, youthful joy and elderly wisdom  is an entire world, compressed but energetically alive in all its details. When we have artists like this, who needs gods?