Will the truth brave the cold light of day?

Few places on the planet so catch the imagination as the North West Passage. For 400 years, many of history’s greatest sailors — Cabot, Frobisher, Drake and Cook among them — failed to find a way through the 900-mile-long route (1448km), threading past icy Canadian islands some 500 miles north of the Arctic Circle. Ships disappeared. Crews froze solid, to be discovered years later. In the 1840s, the biggest expedition of them all — two ships commanded by Sir John Franklin — ended with the vessels ice-bound and all 128 men dead.

Another, sent to find out what had happened, had itself to abandon ship after being locked in the ice for three years — and it was not until 1906 that the great Roald Amundsen finally conquered it in a sloop that could sail in coastal waters three-foot deep. A few icebreakers smashed their way through over the next century. However, in September 2007, the once impenetrable passage was suddenly declared “fully navigable”.

Arctic sea ice had unexpectedly shrunk to just 1,600,000 square miles in extent — a full 20 per cent less than its previous record low — reaching a point scientists had not expected until around 2050. A year later, the North East Passage above Russia opened up simultaneously, making it possible to circumnavigate the Arctic for the first time in 125,000 years. Last September set a new record low, with the ice extending just 1,320,000 square miles and some 20 ships lined up to make the journey this summer. But none has got through: The passage remained blocked, as the ice rebounded.

That has been enough to make a mockery of a much-publicised prediction, six years ago, by Prof Wieslaw Maslowski, of the Naval Postgraduate School in Monterey, California, that the Arctic would be entirely ice-free by 2013 — one of a series of alarmist forecasts that include, most notoriously, a statement deep in the last massive report by the Intergovernmental Panel on Climate Change (IPCC) that the glaciers of the Himalayas would melt away by 2035. In fairness, the professor — whose prophecy was contested by most of his peers — later revised his prediction to 2016 “plus or minus three years”, but that also looks far off-beam.

Global-warming sceptics have leapt on his discomfiture — and on the ice’s return — to assert that the world is now cooling, with some even claiming that there is now “record Arctic ice”. But, in truth, they have got it just as wrong. This year’s recovery is only partial and looks good only because last year’s shrinkage was so great. Though much more extensive than in the past two years — or in 2007, for that matter — sea ice is at about the same level as in 2008, 2009 and 2010, far beneath the average of the last three decades and consistent with a steady decline since 1979. When it stops melting in a few days, it will probably bottom out at the sixth or seventh lowest area ever — covering about half as much sea as in the 1950s. Some record! In fact, many climate scientists predicted 12 months ago that such a partial recovery would occur. A straw poll of about 100 at a conference in Bergen, Norway, on August 31 last year showed that four fifths believed that there would be more sea ice this year. Variations in the weather are, of course, responsible.

Last summer, the Arctic sweltered in warm, sunny weather. This one has been cooler. Though, at one stage in July, it looked as if it may be another bad year, with the ice melting twice as fast as usual, the decline slowed down in August, Even so, the North East Passage has remained open, even while its western counterpart closed. By the end of last month, 20 ships carrying 450,000 tonnes of cargo had sailed through it.

And only the other day, a successful test-run by a Chinese merchantman was announced. Besides, looking at the extent of the sea ice is to consider only two of three dimensions, for — as new measurements published last Wednesday showed — it has also been rapidly getting thinner. It is now little more than half as thick as it was in 1980. When its shrinking extent and thinning are both taken into account, it has lost about three quarters of its total volume. Scientists have little doubt that human-induced global warming is overwhelmingly responsible; studies suggest that only between 5 per cent and 30 per cent of the decline over the past 30 years could be due to natural weather cycles.

Indeed some years, like 2009 and 2010, when these cycles should have resulted in lots of sea ice, are among those when it has been at its scarcest. Sceptics retort that there were similar melts in the late 1930s and early 1940s, before global warming took hold. And indeed sea ice did shrink then, through natural variation, but nothing like as much as now. At its lowest, in September 1940, it covered 3,800,000 square miles, about three times as much as last year, before recovering for the best part of three decades. This time, almost all scientists believe that the far greater, more sustained decline will continue until the Arctic is indeed ice-free in late summer, with most placing that epochal event between 2030 and 2050.

The Antarctic, however, is a different story. There — in the present southern winter — sea ice is indeed at record high levels. But at the same time, the land-based Antarctic ice sheets are, overall, melting disconcertingly, suggesting that warming is at work there, too: In total, though regions vary, they have lost some 1,350 billion tonnes over the past two decades. So — when land and sea ice are added together — the Antarctic too has been melting. Meltwater from the land runs off into the sea, making it fresher and thus more liable to freeze — a likely explanation for its rising ice cover. All of this will be discussed in a week’s time, when scientists convene in Stockholm to put the finishing touches to the next big IPCC report. Sceptics this week presented this as a “crisis” meeting “forced” to take place by recent articles questioning global warming in a British Sunday newspaper, with governments “demanding” 1,500 changes to summary of the report. In fact, the meeting is a routine event that takes place before the launch of every major report, and was fixed years ago, under a timetable laid down in November 2009. The number of suggested amendments — 1,800 in fact — is also normal. It is about the same, says the IPCC, as last time it did the exercise seven years ago. But the meeting must address a substantial issue, much raised by sceptics — the decreased rate of warming of temperatures taken on the surface of the Earth over the past 15 years. This has not stopped, as some attest, but it has slowed substantially after increasing rapidly in the 1990s. Nobody knows why, but increasing evidence suggests that the heat may instead be transferred deep into the oceans by changing natural processes. It is important to find out, for, if that were so, it would mean that the planet is still warming rapidly, if in a different way. And that, in turn, will be bad news for the remaining Arctic ice.

— The Telegraph Group Limited, London, 2013