It was 38 years ago after he got lost in the Sahara desert that photographer Mark Edwards got the idea. The Tuareg nomad who rescued him produced a cassette machine and played a bootlegged version of Bob Dylan's prophetic song about global decay, "A Hard Rain's A-Gonna Fall".
In the decades since Edwards has roamed the world taking and collecting pictures to illustrate every image-laden line of the song. The result is an arresting display of 44 photographs now on show at the Royal Botanic Garden in Edinburgh, as part of the festival (see below).
Climate chaos, global poverty and environmental collapse are all strikingly illustrated with images that echo Dylan's lyric, originally written during the Cuban missile crisis in 1962. It is said to have been penned in just half an hour.
The song, like much of Dylan's work, has intrigued fans and scholars ever since, with its biblical, almost apocalyptic, visions of a world gone wrong. "I'll stand on the ocean until I start sinkin'", it ends. "But I'll know my song well before I start singin'".
Edwards has also published an accompanying book and written to world leaders demanding action. Environmental degradation and human poverty reinforce and feed off one another, he told them. "Yet you – and we – do little or nothing."
Research showed that most of the planet's ecosystems are losing their ability to service human needs, Edwards said. "More than one billion people live in absolute poverty, a poverty that kills many of them, including the 1.7 million children who die each year from preventable diseases."
The book has already prompted a welter of supportive responses, including messages from the former Prime Minister, Tony Blair, the Tory leader David Cameron, the Libdem leader Menzies Campbell, and the Governor of California, Arnold Schwarzenegger.
The Indian writer, Arundhati Roy, said: "Your book is a piece of sustained beauty. I treasure it." Achim Steiner, the executive director of the United Nations Environment Programme described it as a "powerful call for action".
A portion of the proceeds from the book are being donated to the ecological centre, the Eden Project, in Cornwall. The project's co-founder and chief executive, Tim Smit, regards the exhibition as disturbing and moving.
"It is a masterpiece that summons up the ghosts of our past and a vision of the future that was ours to change," he said. "Regret and optimism make strange bedfellows, but great artists have always known this."
"I've stumbled on the side of twelve misty mountains."
"I've walked and I've crawled on six crooked highways"
"I've stepped in the middle of seven sad forests"
"And it's a hard rain's a-gonna fall"