As always, there are many exhibitions showing in Edinburgh at Festival time but I want to write about just one of them, a display of images laid out on in the open air, on a triangular grass site next to the palmhouses in the Royal Botanic Garden.

It was last Saturday, on a dreich evening when what R L Stevenson called Edinburgh's shifty and uncongenial summer weather was at its most fickle, that I stumbled quite by chance on this extraordinary exhibition. I saw a few visitors, mainly German, staring at the series of images laid out on the ground and discussing them with a hushed intensity.

Within a few seconds I, too, was hooked, and about 30 minutes later, having devoured the most powerful indictment of our mistreatment of our beautiful planet I've ever come across, I wandered off, shocked and intending to return the next day to have a second look and see if my initial awestruck reaction was justified. It was.

The concept of the exhibition, starkly called Hard Rain, is devastatingly simple. Environmental photographer Mark Edwards takes the words of Bob Dylan's apocalyptic 1962 song, A Hard Rain's A Gonna Fall, and illustrates each line of that amazing lyric with a single image. Most of the pictures are by Edwards himself; a few are by other photographers or from agencies. There is also a succinct commentary, calmly condemning "wilful, inane and immoral carelessness towards people and planet by both our leaders and ourselves". And that's it.

The result is a harrowing onslaught on our shared responsibility for climate change, for poverty (both spiritual and material), for habitat loss and for the abuse of basic human rights. The message is that environmental and human poverty reinforce each other. Many sensitive and informed people are aware, to at least some extent, that if only through their consumption patterns they contribute to the raping of our environment and to appalling mistreatment of our fellow beings, human and non-human. These images, from many countries and many contexts, must heighten that awareness, and bring it into acute focus. They illustrate a world gone desperately wrong.

On a personal level the exhibition was revelatory for me because for some time I've been worried about the overuse, and potential manipulation, of images. I've always preferred words, though, of course, words can be manipulated, too. But here was a brilliant fusion of powerful, prophetic words and, if anything, even more powerful images. Edwards is a superb photographer. He is aware that in our daily lives, and through our democratic political systems, "we pay attention only to the short term, the visible and the nearby". It is as if he, and the songwriter Dylan, take us by the hand and lead us to the many dark places we prefer not to know about.

The image which first hit me was from Agra. In the background is the Taj Mahal, the world's most grandiose and extravagant tomb, with tourists walking along the balustrades. In the foreground, by the edge of the River Yamuna, lies a human corpse, half silted over, with a scabby dog nosing it. Just beyond the dog, on a sandbank, stand three vultures, waiting.

My first reaction was that this picture was stunted. I thought the juxtaposition was too neat, too horrific. But the more I looked at it and the other pictures I realised that was cynical. This exhibition is true in the best sense, and burning with sincerity.

My only caveat is that, although Dylan's lines are printed clearly, we could do with hearing the song, too. Dylan wrote it, originally as a poem, at the time of the Cuban missile crisis in September 1962. Then, taking the structure of the old ballad Lord Randall, he turned his poem into a song. He first performed it at the Gaslight Club in Greenwich Village; a few days later he sang it at the Carnegie Hall, before what was then the largest audience of his career.

Dylan always emphasised that the song was about more than the Cuban crisis, when the world was on the brink of nuclear war. He called it a song of terror, but made clear that it referred to more than a specific historical moment. Edwards's pictures are about the destruction of people, animals, plants, forests, oceans, rivers and communities. And about the destruction of dignity and hope as well as of life. That is why they are so disturbing.

What'll we do now? That's the obvious and necessary question. We can't leave it to the leaders and politicians. Edwards wisely quotes the always apposite words of Edmund Burke: "Nobody made a greater mistake than he who did nothing because he could do only a little." First awareness, and then action. It doesn't matter if the actions are small. Gathered together, they could save our planet and ourselves.