How will we look back at 2009 and the Copenhagen climate conference 50 years from now? Will this month's summit between world leaders and senior environmental scientists be seen as a pivotal moment that saved the planet from apocalyptic scenes of destruction? Or will it, as tidal waves wash over Piccadilly, be seen as the greatest lost opportunity in human history? Or will we simply look back with an indulgent smile at the doom-mongering headlines, and file climate change away with the nuclear arms race and the Millennium bug as another forgotten media scare story?
Whichever scenario emerges will determine the future estimation of the works specially commissioned for Earth, an exhibition at the Royal Academy timed to coincide with the Copenhagen summit. Imagining what future generations might make of contemporary art is a fascinating game, even more so when the work is so closely linked to the great political issue of the day.
But for now this show feels a little earnest, and the heart sinks slightly as we make our way past the eco pop-up café and pick up our catalogue bearing the Earth logo, where the letters "art" stand out in bold – geddit? Perhaps it's the heavy-handed corporate sponsorship from GlaxoSmithKline that makes one wary: "Creativity and innovation are critical to our business of improving health and well-being," says the blurb, "so we want this year's topic, Earth, to encourage debate, discussion and creative thinking and the role art can play on the relevance that climate change has on our daily lives." Sorry, but can't we leave our artists to get on with the noble pursuit of truth and beauty?
Fortunately, these emerge as by-products from many of the works, especially those which take the wonder of nature as their subject. Take for example Keith Tyson's three giant Nature Paintings, each a fanfare of bold colours and swirling patterns, inspired by an accident in his studio when some chemicals got mixed up with a pigment, forming an extraordinary display that he recreates here. At first glance they are just visually rewarding, vibrant bursts of energy leaping out of the rigid edges of an aluminium panel. But once armed with the knowledge of how they were made, we become awed by the mysteries of science and the unexpected beauty of a chemical reaction.
The work of Ackroyd and Harvey makes a similar point – they take the humble acorn and in two different works show how life can explode out of such an unpromising little brown kernel. Beuys's Acorns is an installation of saplings outside one of the gallery windows: we gaze out into the cold London landscape, a backdrop of drab grey buildings, and here in front of us is an army of young trees pulsating with life, perhaps a foot or two high at most, looking in all their different rag-tag heights like a class of schoolchildren. They are like the thousands of clay figurines that stare up at us in Antony Gormley's Amazonian Field, his popular work of 1992 which has been installed here, filling a whole room, reason enough to visit if you didn't see it first time round. Ackroyd and Harvey's other acorn work is simply a photo of a more advanced sapling removed from the soil – brilliant green leaves above, a tangle of roots below, and at its heart still the little brown acorn.
Finding striking imagery in nature is hardly a challenge, nor does it take much to snap an emotive image of a melting glacier or dried river bed. One suspects many of the 35 artists were, perhaps rightly, determined to steer clear of anything that would fit too comfortably in the pages of National Geographic. So Tracey Emin has made a tapestry, embroidered with birds, insects and flowers, and, as is her habit, places herself in the middle of her work, adorning it with lines of her writing. But here it doesn't quite work: her trademark scrawlings made no sense to this viewer. And I wonder how much thought went into her other piece, an energy-consuming neon sign.
Where the artists do attempt to induce climate-change-guilt in the spectator it is done with subtlety and style. Cornelia Parker's Heart of Darkness consists of pieces of charred wood taken from the site of a forest fire in Florida: they are suspended from the ceiling in a block in the middle of a white room. Looked at from afar this creates a pleasing black-and-white pattern, like a charcoal drawing; up close, the hanging pieces of charcoal are, in their bleak stillness, a haunting embodiment of death.
Another memorable piece dwelling on destruction is Tracey Moffatt's 10- minute video Doomed, which splices together movie disaster scenes to a pounding soundtrack. Gruesome car, plane and train crashes rush before your eyes in a blizzard of explosions. It is at first mesmerising, playing on our fascination with disaster; then you start to feel sick and have to look away.
Emerging from an exhibition highlighting man's destruction of his habitat should be a depressing experience, but the Royal Academy has done something more subtle with Earth. It is a thoughtful, varied and at times surprising show which left me strangely uplifted, more confident that we can overcome whatever natural disasters we face. Copenhagen will determine what the planet looks like in 2059, and if Burlington House isn't ankle-deep in seawater by then, this exhibition might merit a revival.
'Earth: GSK Contemporary (020-7300 8027) to 31 Jan