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

NASA
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.”

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]

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:

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.

NASA
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.

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Comments (6)

  1. Submitted by Neal Rovick on 08/07/2012 - 09:52 am.

    (quote)….I’ve now heard

    (quote)

    ….I’ve now heard that according to ice core records, epic melting years like this one seem to occur in Greenland about every 150 years or so. I’m sure back home there will be much debate about whether this year’s high melt was part of a natural cycle or if it is yet another symptom of global warming. The answer to that question doesn’t actually matter. The fact remains that during this year, like every other year in the past decade, more ice will be lost than created. It’s the trend that matters and this year’s melting will accentuate the ice-loss trend. I think it’s safe to say that at this point, it would take decades of cold, snowy weather to reverse course in Greenland…..

    …….Next time you take a flight, look out the window. What do you see? Are there vast tracts of wilderness, old-growth forests munching away at CO2 through photosynthesis? Or have people changed the landscape everywhere you look? If you fly from New York to Los Angeles, how much of the land is covered in old growth forest and how much of it has been cleared for farms, roads and towns? Ask yourself why, if we can change the land so much, why not the climate?….

    http://blogs.scientificamerican.com/expeditions/2012/08/06/following-the-ice-8-epic-melting/

    (end quote)

    That last point is a very good point. Minnesota is an entirely different place than it was 200 years ago. Old-growth forests from one end of the state to the other are gone, with only a few square miles never affected by human activity remaining. If we can change the face of the earth so much, how is it so inconceivable that we are also changing the way the system of the world work? Virtually every square mile of the world that are arable and/or habitable have been changed.

    And not just the surface has been changed. Hundreds of millions of years of carbon that were trapped in the ground as oil or coal or gas have been released in the last 100 years. Two hundred years ago 1 billion people lived on the planet. It’s now 7 billion, all pulling more carbon from the ground, pumping it into the air.

    What arrogance–we are reversing the chemistry and physics that took place over millions of years in a few decades–and pretending that it all doesn’t matter or that the world is a very different place than it used to be.

  2. Submitted by Mike Downing on 08/07/2012 - 02:46 pm.

    Please read the article before commenting!

    Neal Rovick needs either a remedial class in reading or use the facts in an article to prepare a comment. Why cannot someone comment on this fact in the article: ” the previous vast melt occurred in 1889″?

    Were there cars producing CO2? Were there coal fired power plants producing CO2? What caused the “previous vast melt” in Greenland in 1889?

    For that matter, what caused the medieval warm period?

    • Submitted by Joel Fischer on 08/07/2012 - 11:32 pm.

      It’s YOUR reading comprehension

      that needs some work. He addresses that very point in his first paragraph.

      RE: Medieval Warm Period. I don’t know. What do the climate scientists say?

    • Submitted by Neal Rovick on 08/08/2012 - 08:29 am.

      Medieval warm period?

      (quote)

      Since that early century warming, temperatures have risen well-beyond those achieved during the Medieval Warm Period across most of the Globe. This has been confirmed by the National Academy of Sciences Report on Climate Reconstructions. Further evidence (Figure 1) suggests that even in the Northern Hemisphere where the Medieval Warm Period was the most visible, temperatures are now beyond those experienced during Medieval times.

      Secondly, the Medieval Warm Period has known causes which explain both the scale of the warmth and the pattern. It has now become clear to scientists that the Medieval Warm Period occurred during a time which had higher than average solar radiation and less volcanic activity (both resulting in warming). New evidence is also suggesting that changes in ocean circulation patterns played a very important role in bringing warmer seawater into the North Atlantic. This explains much of the extraordinary warmth in that region. These causes of warming contrast significantly with today’s warming, which we know cannot be caused by the same mechanisms.

      Overall, our conclusions are:
      a) Globally temperatures are warmer than they have been during the last 2000 years, and
      b) the causes of Medieval warming are not the same as those causing late 20th century warming.

      http://www.skepticalscience.com/medieval-warm-period.htm
      (end quote)

  3. Submitted by rolf westgard on 08/09/2012 - 10:01 am.

    Sea level rise is steady but very slow.

    Good article on a complicated subject.
    The estimated global temperatures of the Medieval Warm Period(when Greenland got named) were probably just a fraction of a degreeC cooler than current global land temperatures. But sea temperatures were probably higher in the MWP.
    Greenland is just one source of rising sea levels which have been rising at a little over an inch a decade during the past forty years when we started to get satellite data. Florida is not going under water by 2100, altho some world low areas will have real problems. Greenland contributes because its melt is land ice. Antarctica is bigger, but its melt is mostly shelf ice on water and there is an interior ice buildup.

  4. Submitted by rolf westgard on 08/11/2012 - 12:38 pm.

    Solar luminosity – no big changes in recorded history

    Over geologic time, our sun’s radiation is slowly increasing. In a billion years or so it will evaporate our oceans. 500 million years ago, solar luminosity was about 30% less than today, but things like more atmosphere CO2 kept earth temps up.
    There is a slight solar intensity cycle consistent with the 12 year sunspot cycle. With more spots there are solar bright areas(faculae) which put out more radiation. The sunspot cycle is not perfect, and a few hundred years ago there was a 40-50 year period(Maunder Minimum) with few sun spots consistent with the Northern Hemisphere Little Ice Age. At present we are experiencing a slightly extended period of low sun spots which should have been rising by now.

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