Coral: a pessimist in paradise, by Steve JonesSix Degrees: our future on a hotter planet, by Mark Lynas

What will nature writers a hundred years hence make of those publishing today? If writers like Steve Jones and Mark Lynas are right, their successors would have to attain a degree of saintliness scarce enough on today's planet to be able to read books like these without suffering acid pangs of envy, if not hatred.

Today's writers enjoy the ability to descend upon far-flung arcadias traditionally associated with the more flamboyant class of deity. Tomorrow's may be able to reach any particular spot on the planet with even greater facility, but those advances will have helped to exterminate the arcadias, the great apes and the great Amazon forests. There may be nearly ten billion people on earth by then, but without the company we have hitherto shared it with, it will be a lonely planet.

And our descendants' own company will not be agreeable, as Mark Lynas foresees all too clearly in Six Degrees. A planet full of peoples clawing desperately for water and coolness, or defending that which they still have, will not be one in which sympathy or generosity will flourish.

It looks as though a century from now, which is where the predictions of the Intergovernmental Panel on Climate Change take us, natural history may be largely history. Writers like Jones and Lynas are thus working in a unique moment, in which their personal opportunities to experience the natural world are maximal, while humankind's collective opportunities to brake before the oncoming catastrophe look as though they are collapsing to minimal. Jones and Lynas are two quite different authorial personalities and they respond to their curious situation in radically different ways; which makes their agreement on the dimensions of the crisis especially impressive.

Having previously "updated" Darwin's Origin of Species (as Almost Like a Whale), Jones has now built a "literary edifice" upon Darwin's earlier work, The Structure and Distribution of Coral Reefs. It concludes with an environmentally pessimistic "Envoi"; and "literary" is le mot juste. Jones positions himself not as a populariser or as a publicist in the campaigning, Continental sense of the word, but as a writer, a real one, as distinct from somebody who merely writes.

He uses coral as the framework for an acrobatic display of narrative powers, like a fish darting this way and that through a reef, revealing strange forms and spaces at every unexpected turn. From Darwin's theories about the origin of coral atolls Jones twists around to sketch Gauguin's romantic vision of tropical isles and Captain Cook's misbegotten attempts to master them.

Then we're on to the nuclear tests of the 20th century, which provided geologists with the opportunity to show that Darwin had been right about how atolls are formed, and off down into the centre of the earth, where we learn among other things about how a Moon-sized blob of terrestrial interior shifted position 400 million years ago, causing the planet to spin faster, as a ballerina does when she brings her arms to her sides. It is surprising, exciting, and so much more interesting than the mechanical simplification that usually passes for popular science.

While the geneticist Jones essays across the sciences and arts, the environment writer Lynas constructs a relentlessly linear narrative almost entirely out of scientific papers. IPCC forecasts suggest that the global average temperature could rise by up to six degrees over the course of the century. Lynas turns the scientific literature into a story of catastrophe, degree by degree. It makes a sunny spring morning look like the edge of an abyss.

The crux of his argument is that the story will follow an inevitable course as the planet warms. Up to two degrees will produce changes that will be profound but containable. Beyond that point, the planet will begin to release vast reserves of carbon, first from Siberian permafrost and then from the ocean floors, which will cause warming to run away beyond any hope of control. Three degrees will lead to four, and four will lead to five. By that stage countless species will be in their evolutionary endgame, and above six degrees it looks like game over for us too.

The result of this analysis is that Six Degrees resembles a Jerry Bruckheimer movie with a conscience, the explosions escalating inexorably to an apocalyptic climax of methane fireballs and a toxic sulphide hell on earth. But alarm, Lynas insists, should not lead to despondency. As he puts it, if your kitchen catches fire, you don't just sit there watching it and getting depressed. Global warming remains a manageable condition, he argues - though we only have eight years to do it, by his reckoning.

Jones also ends by contemplating the extinction of humankind, but admits scant concern whether it occurs imminently or when the Sun has grown old. His subtitle strikes a pretty enough pose, but it would be more accurate to describe his stance as existential indifference with aesthetic leanings.

Or, to put it more plainly, Jones's skills as a man of letters are allowing him to flourish in his natural role as a grumpy old man of science. His voice is artfully oblique, edged, ambivalent, self-conscious and stylised - which to a taxonomist would suggest a highly counter-intuitive evolutionary affinity with camp. It is also profoundly sceptical, which is what makes his pessimistic reading of the scientific literature as ominous in its own way as that of Six Degrees.

Marek Kohn's 'A Reason for Everything: natural selection and the English imagination' is published by Faber & Faber

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