Laurel, Lenny and Silverstream watched the hoarfrost encrusting the elegant petals of a camellia.

Silverstream sighed. Her breath warmed the air and the flower's natural colour returned. Winters here were becoming longer, while equatorial regions now seldom saw rain. With the remorseless change in climate she would not always be there to protect her magical realm of cowslip and bluebell. After each ice age, Nature breathed new life into Silverstream. As the glaciers receded the land slowly sprang back into life, first with scrub, heathers and lichens, followed by birch and willow. But those changes had never been this rapid. They needed time.

Laura and Lenny had no idea that Silverstream was there. Seeing the frost disperse so rapidly was marvellous enough; knowing that the spirit responsible was right beside them would have been too much for their young, practical minds. Which was just as well. A seven-year-old's account of the fantastic was never believed and usually put down by adults to an overactive imagination - apart from one, that is.

Mr Brendan had been watching Silverstream and the children from across the lane. He seemed so ordinary in his tweed suit, too old to be worn by such a young man, and oversized spectacles which made his hazel eyes appear large, like a friendly dog's. Both their mothers commented on how handsome he was and, when they believed younger ears were out of earshot, conjectured on why he hadn't yet married and started a family. He had to be gay, they decided - so where was his partner? Laurel knew why he had no children. She had overheard him tell another teacher that he would not bring them into a world that had no future. Laurel hadn't understood what he meant. Her and Lenny's lives were full of fun and adventure trips with their friends. How could it all end?

The chill returned and Laurel tugged her scarf over her ears before running after Lenny to where his mother was waiting in the car to take them shopping. Mr Brendan waved before turning to stroll up the lane. He had no car and walked everywhere.

Silverstream followed him.

In Laurel and Lenny's classroom, Mr Brendan kept a globe showing the world's climate. The pupils sometimes saw the cloud systems move and the jet stream meanders become deeper. They had no idea how this happened. There was no plug or battery compartment, so it couldn't be electronic. The children were allowed to touch the globe, but none of them tried to until Lulu was dared to poke it with a finger. As soon as she did so the globe lit up and the weather systems danced like the lighting effects in one of their mini discos.

Andrew, who had been fascinated by the globe from a safe distance, claimed the ice of Antarctica and the Arctic was growing. At one time people had believed that it would disappear altogether, but that was a long time ago, before the deep ocean currents that circulated about the planet stopped flowing.

One dark afternoon they were packing their schoolbags, ready to go home. The snow was deep and Mr Brendan was outside with the other teachers trying to clear a path to the front gate. Some pupils had received text and phone messages telling them to wait where they were because their parents' cars were finding it difficult to get through the snow.

So, wrapped up warmly in their coats and scarves ready to leave, there was little to do but sit and watch the globe. Only then did they realise that Andrew had been right. The glowing white ice caps at the planet's poles were growing, while the deserts glowed a furious yellow under an angry sun, its heat scorching the remaining fertile land.

The children were frightened - all except Andrew.

He pointed to a spot in the northern hemisphere.

"Don't touch it!" called Lulu.

Andrew didn't need to be warned. "That's where we are."

"But we're covered by ice. What does it mean?" asked Lenny.

"It's very cold."

"You mean it can get even colder than this?"

"Probably." Andrew backed away from the globe, much preferring it to be a little warmer as well.

A small voice broke the silence. "Why?" asked Amanda.

Andrew sighed. "You'll have to ask a grown-up. They probably caused it."

There was at least one adult who could have answered honestly, but Mr Brendan didn't believe that his pupils were ready for the truth. They should be allowed to enjoy as much of their childhood as they could before the predicament of the Earth's climate was explained to them.

There was a more pressing matter to deal with first. It was his mission to tease a fine thread of hope from the ecological chaos about to engulf the Earth.

Months passed and the changes became more severe. Around the world there were power cuts and famine; billions of people were either freezing or starving.

Silverstream could feel her ability to breathe life back into the land seeping away.

The nature spirit was aware that Mr Brendan had sensed the promise in one of his pupils, but neither could tell which one it was.

Mr Brendan's initial choice was Lenny, or even Andrew, who was so clever at noticing things. Lenny was inquisitive, bright and eager to please. Andrew was thoughtful, serious and self-contained. The two children couldn't have been more different.

Then summer at last arrived.

Laurel no longer played much with her friends, preferring to watch clouds, sketching the way they changed shape as they scudded across the sky. It was as though the seven-year-old caterpillar was building a chrysalis about her in preparation for a transformation.

By the time she was nine, Laurel's sketchbooks were full of flowers, leaves and pine cones. As Mr Brendan looked through its pages one day, he noticed a familiar pattern. In it was the unmistakable figure of Silverstream. He had been watching the wrong children. Lenny and Andrew were now only interested in playing football - weather permitting - in the playground.

He should have been paying more attention to the butterfly that was about to emerge from her infant cocoon. By the time Laurel was due to attend senior school she had grown mature, disciplined and had a profound awareness of things beyond her years.

Mr Brendan immediately obtained a position as a science teacher at the school. His qualifications in everything from history to physics were so impressive its administration could hardly refuse his services.

Laurel suspected that he had secured his new appointment solely for her benefit and was strangely flattered, if not a little intimidated. Mr Brendan had taken great care to prepare projects tailored to her ability and found Laurel so keen to learn she soon surpassed the other students who were more interested in parties and social networking. Even the promising Andrew dwindled into a computer geek reluctant to leave his bedroom, and the bright, outgoing Lenny turned into an adolescent caveman.

The young girl who once thought life was for fun and adventures was now the school's star pupil, her mind filled with ideas on how to solve the problems of a planet being struck by one major disaster after another.

By the time Laurel went to university, food, fuel and other necessities of life were being rationed.

Then Mr Brendan died.

Nobody knew why. He was far too young.

The teacher was found sitting peacefully on a bench overlooking the ancient woodland protesters had long been campaigning to save from the construction of a bypass. By his side was a journal written in a strange language, on his forehead the faint imprint of small fingertips, and in his hand a camellia.

In tribute to the teacher who had given her so much encouragement, Laurel obtained all the qualifications needed to ensure her the position of research technician in a solar energy company. In less than two years her team had developed the efficient energy storage system which had eluded scientists for so long. At last all solar, wind and wave power generated when conditions were ideal could now be stored for the times when they were most needed.

But Silverstream was dying, murmuring as she faded, "Too late Mr Brendan, all too late..."

That spark of hope, Laurel, now had to accept that all things pass. Like those other species humanity had driven to extinction, it was now their turn so the Earth would once again be free to seed her oceans and land with new life.