Erroneous data about how much ice is vanishing due to climate change are once more at the heart of an explosive controversy. This time, it's not the Intergovernmental Panel on Climate Change, but the venerable Times Comprehensive Atlas of the World that is in the line of fire. Journalists across the UK received glossy press packs last week for the launch of a new edition. It included a press release declaring that: "For the first time, the new edition […] has had to erase 15 per cent of Greenland's once permanent ice cover – turning an area the size of the UK and Ireland 'green' and ice-free. This is concrete evidence of how climate change is altering the face of the planet forever."
Today glaciologists have been crying foul, saying that the 15 per cent figure is wildly inaccurate.
When New Scientist contacted the Times Atlas team last week to find out where they had obtained the number, they cited the National Snow and Ice Data Centre (NSIDC) in Boulder, Colorado, but were unable to be more precise. Little rise, big mistake
Ted Scambos, the NSIDC's expert on the Greenland ice sheet, says neither he nor his colleagues were consulted in person. "Graduate students would not have made a mistake like this," he told New Scientist. "If what The Times has said were true, something like a metre of sea level rise would have occurred in the past decade."
That is nowhere near what measurements show. "Currently, Greenland is losing mass at about a rate of 150 billion tonnes per year, or about one-third of a millimetre of sea level rise per year," says Scambos. That means in the 12-year period from 1999 to 2011 that the Times Atlas analysed, meltwater from the Greenland ice sheet has contributed roughly 3 mm to global sea level rise – not 1 metre.
In total, the Greenland ice sheet holds enough ice to raise global sea level by about 7 metres, so the loss since 1999 has been less than 0.05 per cent. Thickness, not surface area
Those numbers correspond to the mass of ice that has been lost, not how much the surface extent has shrunk, as seen from space or in a map. Mass loss is the preferred measurement for glaciologists as it takes into account the thickness of the ice. Scambos says the decrease in surface extent would have been "similarly tiny".
So what went wrong? Today, the Times Atlas team were unable to say whether they had spoken directly to the NSIDC. The team say they downloaded records of ice thickness directly from the NSIDC website, used them to extrapolate the surface extent of the ice that needed to be mapped, and then compared it to what they had published in 1999. When they did so, they found their dramatic ice loss.
But Scambos says the thickness records are not intended to show the edge of the ice sheet, so it's likely that without consulting a glaciologist directly, the cartographers misinterpreted the data.
"We are still trying to catch up on what went wrong," says Mark Serreze, adding that the datasets are very complex. "Clearly whoever did this analysis made their own interpretation of the data. At NSIDC we made no statement of a 15 per cent ice loss. We do not know where that number has come from. There has been some kind of error, or some kind of mis-assessment of the data. We're not sure. We're trying to track it down."
The error is doubly unfortunate, says Scambos, because the public may look at the smaller but real numbers and deem them insignificant. But the rate at which Greenland is losing ice is accelerating. The ice sheet will have made a substantial contribution to sea level rise before the end of the century, he says, and the implications are "very serious if it keeps going at the rate that we're seeing".
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Poster Comment:
More dis-info from the "sky-is-falling" crowd - though one of the scientists quoted (Scambos) tries to redeem himself (translation: not risk losing funding) at the end of the article.
