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Grabbing for some hopeful news from Greenland’s shrinking ice sheet

New study adds a layer of complexity without disturbing longer, troubling trend lines.

Iceberg P11-2012, at center, is shown in a July 31 photo as it slides seaward after breaking loose from the Greenland's Petermann Glacier.

The climate-change deniers have gone giddy over an interesting, if narrow, study of recent changes in the Greenland ice sheet.

Yesterday’s edition of The Hockey Shtick blog, for example, read the research this way: “New paper finds climate models wrong, exaggerate sea level rise … The Greenland ice-cap is not melting quicker, but in bursts.”

Over at the National Review, the headline was, “On Second Thought, Maybe Greenland’s Ice Sheet Isn’t Melting as Fast as We Thought.

And closer to home, at the PowerLine, Steven Hayward pitched his post as “More From the Climatefail Files.”

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Hayward sensibly stuck to accurate, if selective, quotations from news reports of the research and concluded that, because they were “no fun at all if you’re a climateer,” the findings would surely be ignored by people like, I guess, me. But in an intellectually honest aside, he also underlined what I, for one, take as the salient central point of the new findings:

“While not departing at all from the standard narrative of global warming, the study concludes with an acknowledgement of the limitations of current forecasting about the new research.”

So what is this new research, and how does it align with earlier work?

Aerial photos and digital modeling

Because the subject is climate change, the first thing to say about this study is that it’s serious, peer-reviewed work, published in the respected journal Science.

Led by Kurt Kjaer of the University of Copenhagen, scientists from Denmark, Britain and the Netherlands examined aerial photographs made since the mid-1980s of glaciers in northwest Greenland. From these images, they produced “digital elevation models” and found “two independent ice loss events” in the periods 1985-1993 and 2005-2010. [A slideshow of the images is here.]

In the dozen years between those events, there wasn’t much melting — but there wasn’t much growth in the ice sheet from new snowfall, either. Their chief conclusion:

Our results suggest that the ice mass changes in this sector were primarily caused by short-lived dynamic ice loss events rather than changes in the surface mass balance. This finding challenges predictions about the future response of the Greenland Ice Sheet to increasing global temperatures.

That’s certainly a cautious statement, especially in comparison to some of the extrapolations it inspired. Similarly cautious, but much more quotable, were these widely lifted lines from a piece Kjaer wrote to accompany his paper:

It is too early to proclaim the ‘ice sheet’s future doom’ caused by climate change … It starts and then it stops. This is a break from thinking that it is something that starts, accelerates and will consume Greenland all at once.” [As quoted by Reuters and several others]

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But how contrarian is this research, really?

Melting of the Greenland ice sheet is a subject that has held the attention not only of scientists but also of the press and public for many years now and with good reason. Calculations are that if the ice should melt fully,  global sea levels would rise to levels that inundate every coastal city on the planet.

There is no doubt that the ice sheet is melting, and at a rapid pace. There is little serious doubt that the recent pace of ice loss is unusual, if not completely unprecedented. But forecasting the future rate of loss is compounded by all kinds of complexity.

I remember, for example, a paper that came out last September from CIRES, the Cooperative Institute for Research in Environmental Sciences, on the subject of how an expanding region of crevasses in a western portion of the ice sheet might affect overall ice loss.

On the one hand, these fissures might accelerate the seaward flow of meltwater at the ice sheet’s surface. On the other hand, they might slow the creation of moulins — little tubes that burrow to the rock beneath the ice sheet, where meltwater can acclerate glacial slide and “calving” of icebergs.

Net impact: Who knows?

So I’m not sure exactly whose thinking Kurt Kjaers is thinking of when he says his research corrects a misimpression that Greenland’s ice sheet is melting at a linear, accelerating pace. Certainly no scientist, nor serious lay student of the subject, sees Greenland as ice cube on hot blacktop.

Nor am I sure that his team’s findings of a start-and-stop pattern in a certain portion of the ice sheet is really good news, though we could certainly use some of that right about now, or even necessarily big news.

For one thing, the quarter-century period of their study is barely a blip in the timescale of Greenland’s glacial record. For another, the images they collected record changes in a limited portion of an ice sheet that still covers more than 650,000 square miles.

Meanwhile, the thawing of Greenland continues to make news of the more common, less encouraging variety:

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A week ago, fresh photographs showed that the 46-square-mile section of the Petermann Glacier that broke loose in mid-July had nearly reached the fjord that will carry it into the sea, having nearly doubled its earlier pace of a kilometer per day. [Other photos from a Bloomberg report here.] And it now appears there is some possibility this big berg may block a shipping channel in the Nares Strait.

Red areas show increase in area of surface melt on the Greenland ice sheet over a four-day period from last July 8 to July 12.
And, of course, there was the flurry of headlines two weeks ago around the NASA photographs of an extraordinary melt event, reported this way in the New York Times:

In a scant four days this month, the surface of Greenland’s ice sheet melted to an extent not witnessed in 30 years of satellite observations, NASA reported on Tuesday.

On average, about half of the surface of the ice sheet melts during the summer. But from July 8 to July 12, the ice melt expanded from 40 percent of the ice sheet to 97 percent, according to scientists who analyzed the data from satellites deployed by NASA and India’s space research institute. …

While scientists described it as an “extreme event” not previously recorded from space, they hastened to add that it was normal in a broader historical context.

Ice core samples taken from the summit of Greenland’s ice sheet that shed light on 10,000 years of its history show that a similar large-scale melting event has happened roughly every 150 years, said Lora Koenig, a glaciologist with NASA’s Goddard Space Flight Center who has also studied the satellite imagery. Because the previous vast melt occurred in 1889, this year’s is more or less on schedule, she said.

Like every new planetary observation that seems related to changing climate, these were seized upon by partisans to prove their point: Greenland is melting faster than ever, which is cause for concern. Or, Greenland is just melting on a normal cycle, so we can all go back to sleep.

For an interesting look behind this particular story, and how it has been used in the climate wars — by deniers Pat Michaels and Roger Pielke Sr., among others — I  commend Jason Samerow’s analysis in the Capital Weather Gang blog.

But if you’re pressed for time, I think it’s fair to say you can read Jason’s long post – and everything else that has been written about Greenland’s shrinking glacial cover — and conclude three things:

  • Ice loss is accelerating generally, if not always steadily, with manmade global warming a significant contributor.
  • No single set of observations can capture the complexity of what’s happening there.
  • While the future may still lie beyond our predictive powers, the trend lines aren’t looking good.