Catlin Arctic trek to reveal true extent of melting ice caps

The Catlin Arctic Survey will be led by Pen Hadow, the polar explorer famous for trekking alone and unaided by resupply planes, from Canada to the North Pole Photograph: Martin Hartley/Catlin Arctic Survey

Hadow (left) will be accompanied by fellow polar explorers Martin Hartley, an award-winning photographer, and Ann Daniels (right), who helped lead the first British women's team to the South Pole in 2000 Photograph: Catlin Artic Survey

The trio will start from the edge of the permanent sea ice and walk along the line of 140 degrees longitude to the top of the world. If they make their goal they will travel more than 1,000km, a journey of three months Photograph: Catlin Arctic Survey

The survey was prompted by growing alarm over disappearing sea ice. As the ice melts it exposes more dark water, which absorbs more sunlight, perpetuating a cycle of melting and warming Photograph: Martin Hartley/Catlin Arctic Survey

On average the year-round ice is receding by an area the size of Scotland annually, and in 2007 the north-west shipping passage from Europe to Asia opened for the first time since satellite records began three decades ago Photograph: Corbis

What satellites don't show is the depth of snow and ice in the pans and giant ridges and underwater keels which erupt under pressure from wind and ocean currents. Unsure what volume of frozen water is left, experts cannot reliably forecast how long before it melts Photograph: Martin Hartley/Catlin Arctic Survey

Hadow will pull a sled fitted with a specially-designed radar, which will take readings of the depths of snow, ice and sea every 10cm. In total he hopes to make 10m-12m measurements this way Photograph: Martin Hartley/Catlin Arctic Survey

The team will also stop one to three times a day to drill holes in the ice. From this they will take more detailed measurements of cores and the ocean below Photograph: Martin Hartley/Catlin Arctic Survey

Insurance company Catlin and other sponsors have donated nearly £3m – many times the budget of a normal expedition. Costs include trips to northern Canada to test the equipment in the harsh conditions they will have to survive Photograph: Catlin Artic Survey

On the ice, the explorers will experience temperatures as low as -50 degrees Celsius, particularly in the early weeks. With wind-chill this can feel like -90C Photograph: Martin Hartley/Catlin Arctic Survey

As well as walking, the trekkers will swim across “leads” between the ice pans, dragging their floatable sleds to avoid losing time walking around open water Photograph: Martin Hartley/Catlin Arctic Survey

Each sled will weigh up to 100kg. If more money cannot be raised, resupplies might have to be cut from seven to five flights because of rising fuel costs and the falling value of the pound Photograph: Catlin Artic Survey

By day the team will graze from “nosebags” of chocolate, nuts, biscuits and salami. At night they will heat snow to cook freeze-dried meals like Irish stew and chicken korma. To save weight though they will use more calories than they eat, and will lose kilos of muscle and fat Photograph: Martin Hartley/Catlin Arctic Survey

The Arctic is a desolate and beautiful place to live, one moment echoing with the crunching roar of grinding ice, another refracting low sunlight into a rainbow of colours. "It messes with your mind," says Hadow Photograph: Catlin Artic Survey

All three explorers have had tough workout regimes to build up stamina and strength, including sessions on Dartmoor doing circuits and pulling strings of tyres to simulate sledging Photograph: Martin Hartley/Catlin Arctic Survey

To see how their bodies respond to the conditions, they will each wear monitoring equipment from Equivital, constantly measuring their heart rate, breathing capacity and body temperature Photograph: Catlin Artic Survey

As well as cold and exhaustion, polar explorers face more immediate threats – including polar bear attacks. The animals are rarely-seen but highly dangerous Photograph: Jeff Hutchens/Getty Images

As part of the publicity Hadow (and later Hartley) climbed into an icy pool to highlight another deadly risk – falling through the ice. To prepare for such a shock, the team will take cold showers in the days before they leave Photograph: Sophia Evans

It is hoped results will be ready by December, when world leaders meet to discuss a new treaty to cut global warming emissions. “Once they have a figure for how long the Arctic sea ice will be there for, they will have to act,” says Hartley Photograph: Martin Hartley/Catlin Arctic Survey

“Disappearing world: Is this the end of the Arctic?” A special report by Juliette Jowit. This Sunday, in The Observer Magazine Photograph: The Observer Magazine