By Rebecca Morelle
Science reporter, BBC News
It was a feat many thought was utterly impossible.
To trek alone, without re-supply, from Canada to the North Pole was deemed so difficult experts said it was an endurance act too far.
But in 2003, Briton Pen Hadow made history by becoming the first person to do just that, and next year he plans to return. However, this time he has more on his mind than just adventure.
I met him at the Royal Geographical Society in London where he told me about his concerns for the Arctic.
Research shows that for three decades, sea ice cover in the region has been shrinking; and this summer, figures revealed a record withdrawal - the smallest area covered by sea ice since the beginning of the satellite age.
Scientists are now in a race to work out just how long it will be before we see completely ice-free summers in the Arctic.
"I realised one of the biggest environmental questions of our time was how long the North Pole icecap could survive the onslaught of global warming," said Mr Hadow.
"And the only way to get a more accurate figure... is by doing a direct surface survey; and I find myself in the wonderful and unexpected position of being able to do that."
Next February, Mr Hadow, along with Ann Daniels and Martin Hartley, will set out on an 2,000km (1,200 miles) trek from Point Barrow, Alaska, to the geographic North Pole; a journey that will take approximately 100 days.
As they walk - and at times swim - across the hostile landscape, they will be towing a sledge carrying a host of scientific instruments.
Mr Hadow said: "I feel like a bit of a donkey to be honest; all I'm really going to be doing is pulling this hugely heavy sledge with this incredibly hi-tech gadgetry which can measure the exact thickness of the icecap."
Although there is very good data on the extent of Arctic sea ice, the data on thickness is relatively poor. And if scientists are going to make the best forecasts on ice longevity, they need both types of measurement.
To date, most information on thickness has come from submarines.
Professor Peter Wadhams, head of the Polar Ocean Physics Group at the University of Cambridge, said: "The role of submarines has been vital.
"The very first measurements of ice were done from the Nautilus, the American submarine in 1958, and every year since then a submarine, either British or American, has gone to the Arctic.
"In fact, [submarines] have been the only way of mapping how the ice thickness has changed over the last 40 years."
The vessels use an upward-looking echo sounder to probe the ice thickness, and recent technological advances mean they can even produce 3D maps of the terrain above.
However, there are drawbacks.
The missions are dependent on time aboard military vessels or the use of expensive remotely operated vehicles (Rovs), meaning they are limited to a few weeks, just once or twice a year, in specific locations. In other words, the submarine picture is an incomplete one.
So scientists use another technology to get around this problem, measuring the ice from above using satellites.
Earth from above
Seymour Laxon, a climate physicist at the Centre for Polar Observation and Modelling, University College London, said: "[Satellites] are monitoring the Arctic ice day and night, all throughout the year."
While satellites are able to measure the area of ice cover directly, probing its thickness is trickier.
Satellites estimate the ice thickness by measuring the top layer of ice
Dr Laxon explained: "We can't measure ice thickness directly, but what we can do is to measure the amount of ice sticking up above the water surface.
"As most people know, nine-tenths of ice is below the water, so you can measure the one-tenth that is above and then use that to estimate how thick the ice is.
"We do that using either a radar or a laser."
Currently, the European Space Agency's satellite Envisat makes the bulk of these measurements. However, said Dr Laxon, it was not designed with ice measurements nor the polar regions in mind.
Nasa's Icesat and Esa's forthcoming Cryosat 2 satellites are set to improve data accuracy and coverage, but some problems persisted, said Dr Laxon.
One of these is snow cover. Satellites have trouble discerning the difference between snow and ice.
Pen Hadow believes his Vanco Arctic Survey will make a huge contribution.
As the team traverses the region, every few centimetres, a ground-penetrating radar will be probing the ice as it is towed behind the sledge.
Crucially, the radar will be able to distinguish between the base ice-layer and any overlying snow layer.
The explorer said: "In predicting the lifespan of the ice, it's the ice layer that is critical.
The radar can distinguish between snow and ice
"The snow is almost irrelevant, so we need to strip that layer out in our measurement process."
Every 20km, the team will also be drilling ice cores to calibrate the radars and investigate snow and ice density.
And a raft of communications technology will enable the radar's findings to be transmitted back to the "base camp" in the UK, as well as footage, environmental, biological and meteorological data, which can also be accessed via the team's website.
Julienne Stroeve of the National Snow and Ice Data Center in Boulder, Colorado, US, commented: "If we can just start compiling a big database of any observations that people make, it will certainly help us to understand the changes that are happening in terms of ice thickness in the Arctic."
And this, she said, would be vital for those trying to forecast when the ice might disappear. However even when scientists have worked out a timetable, other uncertainties remain.
She said: "Obviously we know that everything is connected on the planet, so if we change one part of the globe such as the Arctic, the rest of the system is going to have to respond. But we don't really know exactly how this is going to pan out."
And this, says Pen Hadow, is the driving force behind this latest expedition.
"To start with, the Arctic represented personal challenges: I saw the whole thing as me against it.
"Now my level of knowledge, interest and commitment has moved me away from the adventure, and now I feel it is my social responsibility to represent her - the Arctic Ocean - as best as I am able; because she needs friends right now."