When Marika Holland announced the imminent demise of the Arctic ice cap 18 months ago, she was worried.

Her findings, based on predictions from one of the world’s most powerful super-computers, had been double-checked and peer-reviewed – but they still seemed extreme.

“We were suggesting the Arctic ice cap could disappear in a few decades,” said Holland, a senior researcher at America’s National Centre for Atmospheric Research in Boulder, Colorado. “We were confident of our methods but it still felt very dramatic.”

What Holland and her colleagues from the University of Washington and McGill University in Canada had done was analyse the impact of greenhouse gas emissions on the Arctic – and predict that its summertime ice cap could vanish by 2040.

The corollary was that in the longer term it could vanish in winter too. Future explorers would have to use boats rather than sleds.

The idea that the Arctic ice might shrink had been around for a long time but the suggestion that it could disappear, and so quickly, caused a storm.

Pretty soon the climate change sceptics were at work. Holland and her colleagues, they pointed out, had based their work on a computer model – and such models were hardly accurate enough to predict more than a few days of weather. How could they make predictions over decades?

Within just a few months, however, Holland’s findings were borne out even more dramatically than anyone could have expected.

Each year scientists use satellites to measure the area of the Arctic ice cap as it grows and shrinks with the seasons. In winter it normally reaches about 5.8m square miles before receding to about 2.7m square miles in summer.

Last summer, however, things suddenly changed. For day after day the sun shone, raising water temperatures by 4.3C above the average. By September the Arctic ice cap had lost an extra 1.1m square miles, equivalent to more than 12 times the area of Britain.

The melting reduced the summer ice cover to just 1.6m square miles, 43% less than in 1979 when accurate satellite observations began. It left so much open sea that the Northwest Passage, the fabled link between Asia and Europe, became navigable.

For Holland and her team the great melt prompted a great rethink. Their predictions seemed to be coming true, but far earlier than expected. Why?

Holland now wonders whether she and her colleagues had been “too conservative” in their published report.

When they looked at their models again, they found the events of 2007 had indeed been predicted. “We had said this melting process was likely to start around 2025 but the models also showed that there could be periods of very rapid ice melt much earlier,” she said. “Some even showed that the summertime ice cap could start to vanish by 2013.

“Now we are wondering if that is what is happening now. My research points to the possibility that September sea ice will likely undergo periods of dramatic retreat, perhaps beginning as early as 2013."

Holland stressed there was uncertainty over how fast this might happen. She said: "The late summer sea ice could also stabilize for a number of years or even decades before it possibly disappears altogether."

If Holland is right, then the destruction of the Arctic ice cap could become the first great global warming disaster. Why is it happening so fast? And how will it affect the rest of the world?

At the heart of the melting in the Arctic is a simple piece of science. Ice is white, so most of the sunlight hitting it is reflected back into space.

When it melts, however, it leaves behind open ocean which, being darker, absorbs light and so gets warmer. This helps to melt yet more ice. It means that beyond a point, the ice cannot recover. The process keeps accelerating until there is no more ice to melt.

Peter Wadhams, professor of ocean physics at Cambridge University, has been watching this process for two decades, making trips under the polar ice cap in a Royal Navy submarine equipped with radar that can measure the thickness of the ice. Over that period the average thickness has fallen by 40%.

Professor Mark Serreze, from the University of Colorado’s National Snow and Ice Data Centre, who works with Holland, believes that this latest thinning represents a significant change in the destruction of the ice cap. “The key new idea is that as the ice thins it reaches a point where it becomes very vulnerable. It gets so thin that it can get broken up or just melt away very easily. Once that happens it could be very hard for it ever to recover, especially if we get more hot summers. This year is going to be crucial.”

There is some faintly good news. The melting of the Arctic ice cap will not, for example, cause a rise in sea levels – because it is already floating.

In the short term there may even be some economic opportunities. Already the possibility of new shipping routes, as well as access to the wealth of oil and other mineral resources thought to lie under the seabed, has fuelled a flurry of claims and counterclaims from the nations bordering the Arctic.

Russia has been among the most active. Last August it sent a mini-submarine to the seabed to plant a national flag directly on the North Pole. Scientists from Denmark are mapping the seabed around Greenland, a Danish dependency.

Last August, Stephen Harper, the Canadian prime minister, announced plans for an Arctic military training facility and a deep-water port in the Northwest Passage. America has sent armed coastguard cutters to patrol the waters it claims off Alaska.

All are studying the underwater geology to try to increase their claims. Under international law countries have exclusive economic rights to the sea within 200 nautical miles of their coast. If, however, they can prove that the continental shelf extends beyond that limit, the rights can stretch to 350 nautical miles.

Such an extension could be lucrative. The oil and gas fields in the Arctic ice cap are estimated by some geologists to contain very large reserves.

Others have a different dream for a warmed-up Arctic – as a new cradle of civilisation. Trausti Valsson, professor of environmental planning at the University of Iceland in Reykjavik, believes that as rising temperatures make many lower latitudes uninhabitable, so the lands around the Arctic will evolve into “the new Mediterranean”, with towns and cities springing up in Arctic Canada, Alaska and Siberia.

Such a scenario may seem unlikely now but an ice-free Arctic would have many attractions – not least being the Northwest Passage itself, which would immediately cut 5,000 miles from shipping routes between Europe and Asia via the Suez canal and whose development would prompt pressure for new ports along Canada’s northern coast.

However, most climate researchers view such thinking with despair. “It is a great irony,” said Serreze, “that the melting of the ice cap could give us access to yet more fossil fuels that will accelerate climate change even further.

“I suspect the only thing that is going to stop humanity wrecking the planet is when we get hit by some serious ecological disasters, and by then it may well be too late.”

Dieter Helm, professor of energy policy at Oxford University, believes most politicians have simply failed to grasp the scale of the problem, let alone face up to the dramatic action needed.

China, for example, plans hundreds more coal-fired power stations by 2030. America is working on plans to triple its aviation industry, a big polluter.

It is in extreme places such as the Arctic and the world’s highest and coldest places that the impact will continue to be seen first, according to scientists.

“There are 150,000-200,000 ice masses around the world and most of them are shrinking,” said Richard Armstrong, a colleague of Serreze’s. “We estimate that between 1961 and 2005 melting glaciers raised global sea levels by 20mm.”

That’s less than an inch – but represents the meltwater from only 4% of the world’s glaciers. Even those amounts are tiny compared with the Greenland ice sheet. It contains enough water to raise global sea levels by 23ft and it too is showing signs of instability.

Some researchers believe the loss of the Arctic ice cap could have profound effects on Greenland and the surrounding Arctic lands. “We can’t be certain of the exact impacts but if temperatures rise then that melts ice and permafrost over a wide area,” said Serreze.

Further south, Europe’s mountain ranges such as the Alps are already feeling the heat. About 9% of the 666 Alpine ski areas are classed as marginal and the 2C global temperature rise predicted by 2050 will put another 200 out of business. For its part, Britain can expect a warmer climate and more extremes in weather events (see panel).

At the other end of the earth, the Antarctic is relatively stable in comparison with its northern equivalent. Most of its ice is insulated by the cold Antarctic circumpolar current that keeps warm water away from its ice sheet. While some melting is occurring, the Eastern ice sheet – which accounts for about 85% of Antarctica’s ice – may even be growing, according to scientists.

In Britain, researchers at the Met Office’s Hadley Centre are more cautious than Holland in predicting how fast the Arctic ice cap will vanish – but accept it is likely to disappear.

“There is a lot of short-term variation so it could grow back for a while,” said Vicky Pope, head of climate change advice.

“The important thing is the long-term trend, which is for temperatures to rise and ice to decline. We know that it is likely to go. What we are discussing is how long it will take.”

Those who have explored the ice cap on foot have noticed the difference.

“The conditions have changed incredibly since I did my solo expedition in 2003,” said the British explorer Pen Hadow. “I have spoken to people up there this year, and the condition of the ice is much, much worse. That is only five years, which is extraordinary.”

He is organising an Arctic survey for next year to assess the problems, but the question is whether the damage is already done. “The projections are rushing towards us at high speed,” he said.

Additional reporting: Holly Watt

Losing an ice cap – what does it mean?

Destruction of wildlife
The Arctic is home to unique wildlife such as the polar bear, Arctic fox, walrus and a variety of marine mammals such as the narwhal. All are declining.

Slowing of the gulf stream
The vast ocean current that gives Britain its temperate climate is powered partly by the cooling and sinking of water under the Arctic ice shelves as they regrow each winter. Recently, however, the shelves have been smaller and thinner than in the past and there are signs the gulf stream is slowing. Such a process could radically change European climates.

A warmer Britain
Britain is cooled by winds that carry Arctic air southwards – so a warmer Arctic would mean a warmer Britain. In some ways Britain might benefit from this, with farmers able to grow a wider range of crops, seaside holidays becoming more attractive and outdoor life taking off. Scotland could be a particular beneficiary.

More storms
The same warming is likely to make summers hotter and drier and winters wetter and a lot stormier. The risk of a true hurricane hitting the UK – now once every 300 years – is likely to increase along with the frequency of other storms.

Squelchy Siberia
The steppes of western Siberia – once made of rock-hard permafrost – are starting to squelch. The region – the size of France and Germany combined – has experienced one of the fastest rates of warming in the world and is now 3C above normal. Western Siberia is full of peat and other organic matter that could release billions of tonnes of greenhouse gases into the atmosphere if they thaw.

The Global Terrestrial Network for Permafrost has found a similar warming trend throughout the permafrost zones of Alaska, Norway and northern Canada.

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