He is the doyen of fantasy and one of the most widely read authors in Britain. She is the Booker prize-winning queen of the literary novel, famous for her uncompromising erudition.

But, speaking at the Edinburgh international book festival, AS Byatt has declared Terry Pratchett her hero, for having "caused more people to read books than anyone else – because he tells them something they want to know, that they can laugh at, and because he writes really good English".

Indeed, the author of Possession and, most recently, the Man Booker-shortlisted The Children's Book, suggested that a free distribution of Pratchett to all 12-year-olds would "have a very good effect" on getting young people to read.

Byatt was speaking at the launch of her new book, a retelling of the Norse Ragnarok myth, in which, after a succession of natural disasters, the world ends: a story she has found compelling since her childhood during the war.

Byatt said that, while she had not wished to present an allegory or a polemic, the story was impelled by a profound sense of gloom about the environment and indeed about all human endeavours.

"I didn't want to write a parable," she said. "I didn't want to say: 'We are like these stupid Norse gods and we are destroying the world.' I wanted to hurt people's imaginations."

She added: "We are into the world of Ragnarok, where whatever we do we cannot stop the doom that is coming. The scientist Steve Jones, for whom I have a huge respect, said he once thought we had about 150 years before we blew things up, but now thinks we have about 50.

"The image in Ragnarok that most moved me as a child was the ship of the dead that comes up to the last battle. It's made out of dead men's fingernails. When I was very little I saw it as an 18th-century schooner. Later I realised it was a longship.

"This colour, of the dead and slightly translucent thing, moved me. And then I saw what the modern image was: we have created in the Pacific an area of plastic as big as Texas, just stuff, dead, semi-translucent, in the middle of the ocean; and no one knows what to do.

"I am a profound pessimist both about life and about human relations and about politics and ecology. Humans are inadequate and stupid creatures who sooner or later make a mess, and those who are trying to do good do a lot more damage than those who are muddling along. This is something George Eliot understood: there is a grimness about her that I rather approve of."

There is one area of life, however, about which Byatt is upbeat: the state of the novel. "Novels are fine at the moment. For about the last 15 years people have been able to write what they want, and somebody will understand what they have done.

"The critics are various, and mostly quite flexible. And there is a great number of novel forms that people are using and in all kinds of countries and cultures.

"Our main problem is that there are too many; we cannot read all the good novels that there are."