Times Atlas admit a mistake on Greenland press release claim, maintain maps are accurate

Since the Times Atlas claimed last week that the Greenland ice sheet has lost 15% of its ice over the last twelve years, glaciologists who work on Greenland have been in uproar. Well, the Times World Atlas team have now issued a press release which is somewhat of a mea culpa –

The Times Atlas is renowned for its authority and we do our utmost to maintain that reputation. In compiling the content of the atlas, we consult experts in order to depict the world as accurately as possible. For the launch of the latest edition of the atlas (The Times Comprehensive Atlas of the World, 13th edition), 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 (1999 vs 2011) 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 apologize for this and will seek the advice of scientists on any future public statements.  We stand by the accuracy of the maps in this and all other editions of The Times Atlas.

So to be clear, they’re saying that the original press release (which has been removed, but which is archived by Google in HTML form here) was inaccurate. The exact words used in the press release were ‘15% of the permanent ice cover (around 300,000 sq km) of Greenland, the world’s largest island, has melted away’. They are still maintaining that the maps are accurate, despite concerns having been raised by climate scientists about how they represent the boundaries of the ice sheet.

When we spoke to CollinsBartholomew, the subsidiary of Harper Collins who publish the Atlas, they said that the 15% figure had been calculated by comparing Greenland as it was mapped in the Atlas in 1999, based on the data they had available, to Greenland as it is mapped in 2011 – a statement they repeat in today’s update. We asked them for more clarity on what the methodology was, but haven’t yet got a detailed answer.

CollinsBartholomew also told us that the press release, although written by a PR agency, had been ‘looked at’ by the Atlas team. Their statement today appears to make clear that they did not get advice on this issue from the climate science community, who first called attention to the inaccurate claims. The Atlas team had said that they got the information for the maps from US scientists the National Snow and Ice Data Center (NSIDC) – but it now appears that this means that they downloaded the data from the NSIDC’s data archive and interpreted it without consulting with the organisation.

The NSIDC’s Julienne Stroeve put a forthright comment to this effect on the climate skeptic blog Watts up With That:

…we’re trying to get figure out exactly what they did – what data source they used, what processing they did, etc. Obviously we are not too happy about it (and nor or any the glaciologists who study Greenland). I would have thought if they found such a large difference in the extent of the ice sheet that they may have talked to some of the glaciologists who study Greenland to get their feedback before publishing the map. Or have talked to NSIDC aobut their results, or at the very least have done some literature review to see if their map was consistent with other results of changes in the Greenland mass balance. From what I understand, it appears they used the 5-km ice thickness product produced by Dr. Bamber (and distributed by NSIDC) to make their new map but ignored the caveats in the data set as mentioned above by Frank White ( http://nsidc.org/data/docs/daac/nsidc0092_greenland_ice_thickness.gd.html#usageguide).

Apart from the obvious issue of a commercial publisher spinning themselves into a mess, this is an important issue to get right. Melting of the Greenland ice sheet results in sea level rise, and the Met Office estimates that if the whole of the Greenland ice sheet were to melt then global sea level would rise by around 6 metres. So what does the research on the Greenland ice sheet actually show? Here’s a quick summary. First, a rough assessment from Dr Poul Christoffersen, Glaciologist at SPRI and one of the instigators of a letter of complaint to the Times newspaper, who says:

“The volume of ice contained in the Greenland Ice Sheet is approximately 2.9 million cubic kilometres and the current rate whereby ice is lost is roughly 200 cubic kilometres per year. This is on the order of 0.1% by volume [of the ice sheet] over 12 years. Numerous glaciers have retreated over the last decade, capturing the attention of scientists, policymakers and the general public. Because of this retreat, many glaciers are now flowing faster and terrain previously ice-covered is emerging along the coast – but not at the rate suggested in The Times Atlas media release.”

Greenland ice cover is assessed by measurements made on the ice sheet, and by monitoring using satellites (known as ‘remote sensing’), and this estimate is based on Dr Christofferson’s understanding of research into the Greenland ice sheet. Developments in remote sensing have given rise to numerous studies assessing the Greenland ice sheet over recent years, allowing scientists to determine the ‘mass balance’ of the ice sheet – essentially the rate at which snow and ice mass are accumulating on the ice sheet minus the ice mass lost due to meltwater run-off and ice discharge.

An assessment of the Greenland ice sheet mass balance since the 1960s found that it has varied over the decades, losing mass during the 60s and accumulating mass in the 70s and 80s. Through the 1990s, the ice sheet has been losing mass at an accelerating rate, and over the 11 years leading to 2007 ice loss tripled to nearly 270 gigatons per year. (A gigatonne of ice is roughly 1.1 cubic kilometres).

A more recent study confirmed this acceleration, finding that that over the last 18 years ice loss has increased by around 20 gigatons per year. Another study found that between 2002 and 2006 Greenland lost ice at around 250 gigatons of ice per year, which is the equivalent of raising sea level by around 0.5 mm per year. It appears that the ice sheet is growing in its centre, but thinning towards its margins, due to increased meltwater runoff and glaciers at the edge of the ice sheet speeding up, thinning and discharging ice.

250 gigatons of ice loss per year is a lot, but it still puts ice loss in the order of magnitude of 0.1% of the whole Greenland ice sheet over the period, not the 15% claimed by the Times Atlas. The problem with such inflated claims is that they might mean the actual ice loss is viewed as unimportant.

That would be a mistake. At the moment the ice loss only equates to a few mm of sea level change per year. However, if we continue to see Greenland ice loss increasing at the current rate, scientists predict that ice sheet melt will become the dominant cause of sea level rise during this century.

As Professor Liz Morris, SPRI, says in the Telegraph:

“The danger is if people quote these absurd figures the next thing that happens is climate change sceptics say scientists are making daft claims. We are not. It is the publicity people.”

It’s hard to avoid the feeling that by failing to consult with scientists, over-spinning their press release and not responding to criticism openly, the Times World Atlas team may have done a disservice to the scientific community who have be working to understand what’s actually happening to the Greenland ice sheet, and who first pointed out that their claims were suspect.

(Written by Verity and Christian)