The humiliating climbdown for HarperCollins – part of Rupert Murdoch's publishing empire – came after key sources of data on the Greenland ice denied that their research, cited by the Times Atlas, warranted the claims. Despite criticism of the claim by scientists, a spokeswoman for the atlas had, as recently as Monday, issued a robust defence of the claim, saying: "We are the best there is ... Our data shows that it has reduced by 15%. That's categorical."
But HarperCollins put out a statement on Tuesday saying: "For the launch of the latest edition of the atlas we issued a press release which unfortunately has been misleading with regard to the Greenland statistics. We came to these statistics by comparing the extent of the ice cap between the 10th and 13th editions of the atlas. The conclusion that was drawn from this, that 15% of Greenland's once permanent ice cover has had to be erased, was highlighted in the press release not in the atlas itself. This was done without consulting the scientific community and was incorrect. We apologise for this and will seek the advice of scientists on any future public statements."
Experts at the US's main research body for the Arctic, the National Snow and Ice Data Centre, said their estimates showed that the Times Atlas was wrong. In a statement, NSIDC said: "[We have] never released a specific number for Greenland ice loss over the past decade...The loss of ice from Greenland is far less than the Times Atlas brochure indicates." They joined experts from the UK's Scott Polar Institute in Cambridge, who criticised the Times Atlas for failing to consult researchers before publishing the claims.
However, the publishers' statement was not enough to settle the controversy, as the company puzzled scientists by continuing to insist the maps were correct, even though they show as clear of ice some areas of land around the edges of Greenland that glaciologists say retain ice cover. HarperCollins said: "We stand by the accuracy of the maps in this and all other editions of The Times Atlas."
Scientists said that the maps showed some coastal areas of Greenland to be clear of ice, when they were in fact still ice covered.
A new edition of the Times Atlas – one of the biggest selling reference books, billed as being "the most authoritative" – is published every few years, but the changes tend to be relatively small. For this, the 13th edition, the publishers raised a fanfare of publicity, centred on the claim that their surveys of the Greenland ice cap showed it had diminished in extent by about 15% since 1999, when the 10th edition of the stlas was published.
But claims about ice can be slippery – although Greenland has been losing ice mass, and the area covered by ice is gauged to be smaller than in past decades, to put a precise figure on the loss is difficult, as ice cover can change from year to year and seasonally, and depends on the volume of ice as well as its extent. Although the amount of ice lost is likely to be about 200 cubic kilometres per year, this is still tiny compared with the enormous extent of the ice, at about 2.9m cubic kilometres in total, according to data from the Scott Polar Research Institute. Although ice loss is accelerating, it could still take centuries for the Greenland ice cap to melt away – if a 15% loss in 10 years were true, it would mean that all of the key climate change models would have to be drastically redrawn.
Scientists are confident that the observed loss of Arctic ice – which can be graphically illustrated in the retreat of some of the island's biggest glaciers and the break-up of thinning sea ice, for instance – is a result of the observed warming temperatures of the past decades.
However, glaciologists are wary of making sweeping claims about ice loss. Such a claim landed the Intergovernmental Panel on Climate Change in hot water nearly two years ago, when a prediction in its 2007 report on climate science suggested that the Himalayan glaciers could have largely disappeared by 2035. This was subsequently found to be incorrect, and severely damaged the IPCC's reputation.
Poul Christoffersen, glaciologist at the Scott Polar Research Institute, said he and fellow researchers had examined the atlas and found that "a sizeable portion of the area mapped as ice-free in the Atlas is clearly still ice-covered". He added that there was "to our knowledge no support for [the 15% ice reduction] claim in the published scientific literature.
Christoffersen said: "A close inspection of the new map of Greenland shows that elevation contours are noticeably different to the contours in an older map. My colleague Toby Benham, a scientist at the Scott Polar Research Institute, was able to reproduce these contours using ice thickness data. It appears that the Times Comprehensive Atlas of the World may have used 500m ice thickness to map the ice sheet margin. If so, it is obviously an incorrect and flawed procedure."
He said the previous Times Atlas maps appeared to show a truer picture of the ice extent. "I would by far rather use the old maps for education and for students."
He added that HarperCollins was cooperating in sharing the data and methods used for the maps.
Although a loss of 0.1 per cent of Greenland ice in total over more than a decade might seem a small proportion, he said it was still enough to cause a problematic rise in sea levels in future years, because of the huge scale of the Greenland ice sheet. "A small percentage of a very big number is still a big number," he said.
Prof J Graham Cogley, professor of geography at Trent University in Canada, said: "What may have happened is that somebody has examined a satellite image and mistaken the snowline for the ice margin. Snow is much brighter than bare ground, but it is also a good deal brighter than bare ice, of which there is quite a lot in summer around the margin of the Greenland ice sheet."