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Study into Greenland’s speeding glaciers prompts yet more confusion

  • 04 May 2012, 11:50
  • Verity Payne

Greenland's glaciers melting faster, say scientists according to one headline. Greenland glaciers may be melting slower according to another. Once again new glacier research is making headlines, and once again they are contradictory.

Confused? Here's what's going on.

New research, published in the journal Science this week, finds that on average glaciers on Greenland sped up over the first decade of the 21st century. The researchers from the University of Washington analysed data from satellites monitoring over 200 glaciers around the margins of the Greenland ice sheet between 2000 and 2010. They found that how fast the glaciers moved varied from region to region, and that different types of glacier grow and shrink at different rates - echoing previous studies.

Despite what it an obviously complicated picture of regional ice loss, the study finds that on average Greenland's glaciers sped up by around 30 per cent between 2000 and 2010. Since faster-moving glaciers are associated with increased meltwater and ice loss, the contribution of Greenland's glaciers to sea level rise probably continued to increase over that period, as satellite measurements suggest it has over the last couple of decades.

The research has led to a range of wildly different interpretations in the media. News agencies Reuters and AFP, for example plump for almost directly opposing headlines, leading with Greenland glaciers speed up, swelling rising seas: reports, (Reuters) and Greenland glaciers may melt slower than thought: study (AFP) respectively. The Guardian go for the more revealing Sea-level rises 'may not be as high as worst-case scenarios have predicted'.

So how have the media reached such different interpretations of the same piece of work? As is often the case, it's the details of the paper which matter.

It's pretty clear where the 'Greenland glaciers getting faster' headlines come from, after all the paper finds that on average Greenland's glaciers sped up over the study period.

Why can you argue the paper shows the glaciers may melt slower than thought? Whilst the study focuses on how fast Greenland's glaciers have flowed over the past decade, in the concluding paragraph Moon and colleagues consider how this might change in the future and impact sea levels.

They reference previous research from William Pfeffer, University of Colorado Boulder, and colleagues, that aimed to give a "'most likely' starting point for refinements in sea-level forecasts". Pfeffer and colleagues estimated the range of how much Greenland might contribute to sea level by 2100 as between 0.8 and 2 metres.

The 2 metre estimate assumed that Greenland's glaciers "quickly accelerated to extremely high limits", whereas 0.8 metres - which the authors said was more plausible - assumed less glacier acceleration.

Moon and colleagues write that the increase in average Greenland glacier speed they measured does not match the acceleration assumed by Pfeffer and colleagues to reach their upper bounds, therefore:

"sea level rise from Greenland may fall well below proposed upper bounds."

Moon explains further:

"We found we are certainly not on the worst-case scenario, but the glaciers are speeding up and we see no sign of that stopping."

However, the possibility of a larger Greenland contribution to sea level rise still remains, as co-author  Ian Howat, Ohio State University, explains:

"There's the caveat that this 10-year time series is too short to really understand long-term behavior [...] So there still may be future events - tipping points - that could cause large increases in glacier speed to continue. Or perhaps some of the big glaciers in the north of Greenland that haven't yet exhibited any changes may begin to speed up, which would greatly increase the rate of sea level rise."

Clearly, the nuanced conclusions reached by Moon and colleagues are not the same as saying that all previous sea level forecasts are wrong, as some headlines seem to indicate.

The scientific community have made an effort to point this out, saying that Pfeffer and colleagues' paper was not intended to be realistic, and was "a thought experiment, or a 'what if' scenario."

Glaciers and sea level: a recipe for confusion

This isn't the first time that we've seen a flurry of confusing headlines about research into glaciers and global sea level. New analysis earlier this year of the amount of ice lost from global glaciers prompted some seemingly conflicting headlines. They ranged from the Independent's Billions of tons of water lost from world's glaciers, satellite reveals through to the Guardian's The Himalayas and nearby peaks have lost no ice in past 10 years, study shows.

The trouble is that putting new findings about melting ice and sea level into the context of previous findings is a pretty nuanced affair. Capturing these nuances in a headline is pretty difficult. In our experience it's easier to make headlines snappy or accurate - getting both is somewhat harder.

Interestingly the Mail, eschewing its recent trend for fundamentally misleading climate stories, has written a pretty accurate article. Although this might be because it seems - to us at least - to be nearly identical to the article from Associated Press science writer Seth Borenstein. At least for once the Mail didn't plump for yet another ' Forget global warming...' headline. Well done that paper.

 

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