Nobody would blame you for being pessimistic about the future. After all, if you listen to the media (and, it seems, anybody over 25) we're all going to hell in the proverbial handcart, as the Four Horsemen of the Apocalypse - economic meltdown, climate change, terrorism and, who else, Simon Cowell - bear down on us.

But I have news. Some people are rather fed up of this narrative and are quietly getting on with solving the grand challenges our planet faces, using both new technologies and forgotten wisdom. Their mantra? "Cheer up, it might just happen." I've spent the past 18 months researching a book about these people.

One of them is Tony Lovell, an accountant from Australia, where farming has become synonymous with drought. A decade of low rainfall, heatwaves and wildfires has scorched much of the land. Australians call it "the Big Dry" and it means that when the rains come - as they are doing now on the eastern seaboard - water runs over the parched surface, resulting in devastating floods. Many farms survive on "drought assistance" handed out by the government. Rural suicide is depressingly common.

Lovell thinks he has the answer. At a climate-change conference in Manchester, I find him talking about a new method of farming. "This is a typical ranch in Mexico," he explains, showing an image of a terracotta dust bowl with bare, compacted soil. Then he puts up a second image of lush green vegetation. "This is the ranch next door. Same soil, same rainfall. These pictures were taken on the same day."

I am astounded - it seems too good to be true. Later, I ask his business partner, Bruce Ward, what caused the difference. "Management," he says. "Just management."

To find out more, we travel to New South Wales to a sheep farm owned by Tim and Karen Wright. The Big Dry isn't so big on their land - it looks more like Sussex than the images of the bush that we're used to seeing on TV. The couple have also tripled their sheep stock, with half the labour associated with herds the size of theirs. And yet, Tim says, the rainfall had been low for nine years. What is his secret?

Back to nature

Driving to another farm, Ward and Lovell show me. They point to a paddock by the side of the road that is almost totally bereft of vegetation. "Is that from lack of rain?" I ask. "Look down at the fence," says Lovell. And then I see it, and from that moment on, I see it everywhere we go. Outside the fence there is grass. Indeed, we are standing in it up to our knees. "Things can grow just fine here," says Ward. He bends down and grabs a lump of vegetation. It comes away in his hand. "This is dying, though. That's the other half of the problem."

Back in the car, Lovell tells a story. "If you go back in time, our grasslands were dominated by large herds of grazing animals - bison in America and wildebeest in Africa." There are still a few places where you can witness this. The Serengeti, for instance, is one of the few remaining natural grasslands on the planet and is home to huge migrating herds of wildebeest and zebras. There is no beginning or end to their journey, but a constant clockwise trek in search of water and fresh grass. Every year, two million animals cover 1,800 miles. The herds stay closely packed as a defence against predators.

“What happens is the herd eats the grass but then moves on, looking for the fresh stuff. In the Serengeti, that herd won't be back on the same ground for at least a year," Lovell says. "That's important," says Ward. "There's a natural relationship between grasses and grazing animals. The growing buds are at the base of the plant and they need sunlight. If the plant gets too tall it starts to kill itself by hiding those buds in its own shade. It can't photosynthesise." "That's why that grass came away in my hand," Lovell explains. "It's dead material. In nature, the herd would have come along, eaten the tops off the plants, exposing the growth buds, and moved on. By the time they came back, the grass would have regrown."

“The problem with the way we farm livestock is we don't let them roam," says Ward. "We split up big herds between separate paddocks and keep them there for way too long. With no predators, they can wander where they like in that space. The grass never gets a chance to grow back. An animal will have a go at it as soon as it starts sprouting."

“Why doesn't anybody notice this?" I ask. "Did you?" Lovell replies. It's a fair point.

The effect of such poor land management is a sharp decline in soil carbon levels across grasslands over the past 150 years, directly related to the loss of vegetation. Ward tells me that grass plants grow roughly the same amount of root matter as leaf matter. If the plant gets nibbled by a cow or sheep, it'll slough off a corresponding amount of root matter into the soil in minutes, enriching it with carbon.

“A plant is roughly 58 per cent carbon - from CO2 in the air," says Ward, "and while nearly all of the lost root matter will rot, returning that carbon to the atmosphere, it leaves behind a small amount of residue."

“It's only a small amount of the carbon that makes up the plant," says Lovell, "but a little bit of a bloody big amount soon adds up." He's not wrong. The UN estimates there are 3.5 billion hectares of agricultural grasslands on our planet. Increase the organic carbon content of their soils by just 1 per cent, and this would offset nearly 12 years of global CO2 emissions.

Rotating cows

Some worry about cattle belching methane (another potent greenhouse gas) into the atmosphere and call for us to relinquish meat-eating. But if what Ward and Lovell are saying is right, it's not that we have too many cattle, it's that we have too little grass. Working correctly together, animals and plants are a huge natural "carbon pump" that can take vast quantities of CO2 from the sky. As a bonus, richer soil is far more effective at retaining water, ending the destructive cycle of drought and flood.

What is more exciting is that almost any farmer can adopt the system. All you need is a few fences. Then you build lots of small paddocks, form your cattle into a big herd, and put them in each one for just a day or two.

So why isn't everyone doing it? "The problem is that farming's a traditional business," Ward explains. "Changing the way you farm is the same as saying that what your dad and your grandad did was wrong, which isn't easy when they're still living on the property."

That's why he and Lovell want Australia's government - and other governments - to pay farmers to increase soil carbon. "It's a carrot instead of a stick," Lovell says. "They can tell Dad the change is to bring money in."

It's a wonderful thought - that something as simple as a fence could save the world - and I remembered the words of another farmer I met on my trip, a typically salty Australian called Michael Coughlan. "The thing is, in Australia and America, we've absolutely pillaged our land. We've just fucked the whole thing. But I think we can turn it round really quickly."

“An Optimist's Guide to the Future" by Mark Stevenson is published by Profile Books (£12.99)

Three easy ways to make a difference

Send Klaus Lackner some money

This professor of geophysics at Columbia University has developed a carbon scrubber that removes CO2 from the sky cheaply and efficiently. Now, his team wants to create a commercial prototype - and it needs $20m to do it. Why not help him out by chipping in at giving.columbia.edu?

Create some charcoal

Charcoal has undergone a makeover in recent years. Creating it (and then burying it) is seen as one of the most promising ways to mitigate global warming.

By burning all agricultural waste such as corn and rice stalks, branch and leaf litter (as well as animal dung) in a "low-oxygen" environment to create charcoal, we could "halt the increase and actually decrease the level of atmospheric carbon by 0.7 gigatonnes a year", according to Johannes Lehmann, a soil science expert at Cornell University. The bonus is that charcoal in the soil tends to increase crop yields, too.

Cut your energy bill
Haven't got around to insulating the loft or buying any draft excluder? Energy efficiency is the quickest way to reduce your fossil fuel consumption. Your wallet will appreciate it, too. Just sticking some boards over the beams in your loft will make a difference. And you can use the lovely power tool you got for Christmas.
Mark Stevenson