There’s some blogospheric carping about his statement in the JPL press release below regarding Greenland’s ice sheets:“… their cumulative loss could raise sea level by 15 centimeters (5.9 inches) by 2050.”
Well sure, it could be, but as this recent surprise study from GISS’s neighbors at Columbia illustrates, even though we’ve had the GRACE (Gravity Recovery And Climate Experiment) satellite looking at Antarctica, and concluding there’s been ice mass loss there, we have this new study that shows ice being added from underneath due to meltwater refreeze, concluding the models to be wrong.
It goes to demonstrate that we really don’t understand ice sheet mechanics well enough yet to make accurate forecasts, though some people think we can.
Add to that, GRACE has it’s own set of problems. And at least one model conlcusion has been revised post facto because the melt data is overestimated:
The melting of the ice sheets of Greenland and West Antarctica is about twice as slow as previously thought. The study, conducted by TU Delft, SRON and the Jet Propulsion Laboratory. The scientists published their findings in the September issue of Nature Geoscience.
We have concluded that the Greenland and West Antarctica ice caps are melting at approximately half the speed originally predicted.’ The average rise in sea levels as a result of the melting ice caps is also lower.
In fact, errors from GRACE may be quite large. So take this new release from JPL and the squawking about the forecasted sea level rise with a grain of salt. But more importantly, look at what the actual sea-level data is saying, and as Willis Eschenbach points out, natures seems to be Putting the Brakes on Acceleration.
From JPL: NASA Finds Polar Ice Adding More to Rising Seas
Store Glacier, West Greenland. A new NASA funded study finds that the Greenland and Antarctic ice sheets are losing mass at an accelerating pace, three times faster than that of mountain glaciers and ice caps. Image credit: Eric Rignot, NASA JPL
PASADENA, Calif. — The Greenland and Antarctic ice sheets are losing mass at an accelerating pace, according to a new NASA-funded satellite study. The findings of the study — the longest to date of changes in polar ice sheet mass — suggest these ice sheets are overtaking ice loss from Earth’s mountain glaciers and ice caps to become the dominant contributor to global sea level rise, much sooner than model forecasts have predicted.
The nearly 20-year study reveals that in 2006, a year in which comparable results for mass loss in mountain glaciers and ice caps are available from a separate study conducted using other methods, the Greenland and Antarctic ice sheets lost a combined mass of 475 gigatonnes a year on average. That’s enough to raise global sea level by an average of 1.3 millimeters (.05 inches) a year. (A gigatonne is one billion metric tons, or more than 2.2 trillion pounds.)
The pace at which the polar ice sheets are losing mass was found to be accelerating rapidly. Each year over the course of the study, the two ice sheets lost a combined average of 36.3 gigatonnes more than they did the year before. In comparison, the 2006 study of mountain glaciers and ice caps estimated their loss at 402 gigatonnes a year on average, with a year-over-year acceleration rate three times smaller than that of the ice sheets.
“That ice sheets will dominate future sea level rise is not surprising — they hold a lot more ice mass than mountain glaciers,” said lead author Eric Rignot, jointly of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., and the University of California, Irvine. “What is surprising is this increased contribution by the ice sheets is already happening. If present trends continue, sea level is likely to be significantly higher than levels projected by the United Nations Intergovernmental Panel on Climate Change in 2007. Our study helps reduce uncertainties in near-term projections of sea level rise.”
Rignot’s team combined nearly two decades (1992-2009) of monthly satellite measurements with advanced regional atmospheric climate model data to examine changes in ice sheet mass and trends in acceleration of ice loss.
The study compared two independent measurement techniques. The first characterized the difference between two sets of data: interferometric synthetic aperture radar data from European, Canadian and Japanese satellites and radio echo soundings, which were used to measure ice exiting the ice sheets; and regional atmospheric climate model data from Utrecht University, The Netherlands, used to quantify ice being added to the ice sheets. The other technique used eight years of data from the NASA/German Aerospace Center’s Gravity Recovery and Climate Experiment (Grace) satellites, which track minute changes in Earth’s gravity field due to changes in Earth’s mass distribution, including ice movement.
The team reconciled the differences between techniques and found them to be in agreement, both for total amount and rate of mass loss, over their data sets’ eight-year overlapping period. This validated the data sets, establishing a consistent record of ice mass changes since 1992.
The team found that for each year over the 18-year study, the Greenland ice sheet lost mass faster than it did the year before, by an average of 21.9 gigatonnes a year. In Antarctica, the year-over-year speedup in ice mass lost averaged 14.5 gigatonnes.
“These are two totally independent techniques, so it is a major achievement that the results agree so well,” said co-author Isabella Velicogna, also jointly with JPL and UC Irvine. “It demonstrates the tremendous progress that’s being made in estimating how much ice the ice sheets are gaining and losing, and in analyzing Grace’s time-variable gravity data.”
The authors conclude that, if current ice sheet melting rates continue for the next four decades, their cumulative loss could raise sea level by 15 centimeters (5.9 inches) by 2050. When this is added to the predicted sea level contribution of 8 centimeters (3.1 inches) from glacial ice caps and 9 centimeters (3.5 inches) from ocean thermal expansion, total sea level rise could reach 32 centimeters (12.6 inches). While this provides one indication of the potential contribution ice sheets could make to sea level in the coming century, the authors caution that considerable uncertainties remain in estimating future ice loss acceleration.
Study results are published this month in Geophysical Research Letters. Other participating institutions include the Institute for Marine and Atmospheric Research, Utrecht University, The Netherlands; and the National Center for Atmospheric Research, Boulder, Colo.
JPL developed Grace and manages the mission for NASA. The University of Texas Center for Space Research in Austin has overall mission responsibility. GeoForschungsZentrum Potsdam (GFZ), Potsdam, Germany, is responsible for German mission elements.
More on Grace is online at http://www.csr.utexas.edu/grace/ and http://grace.jpl.nasa.gov/ .
JPL is managed for NASA by the California Institute of Technology in Pasadena.
===========================================================
Here’s the paper abstract at GRL:
GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L05503, 5 PP., 2011
doi:10.1029/2011GL046583
Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise
E. Rignot
Earth System Science, University of California, Irvine, California, USA
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
I. Velicogna
Earth System Science, University of California, Irvine, California, USA
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
M. R. van den Broeke
Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, Netherlands
A. Monaghan
National Center for Atmospheric Research, Boulder, Colorado, USA
J. Lenaerts
Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, Netherlands
Ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques, over different time periods, and at various levels of spatial detail. Considerable disparity remains between these estimates due to the inherent uncertainties of each method, the lack of detailed comparison between independent estimates, and the effect of temporal modulations in ice sheet surface mass balance. Here, we present a consistent record of mass balance for the Greenland and Antarctic ice sheets over the past two decades, validated by the comparison of two independent techniques over the last 8 years: one differencing perimeter loss from net accumulation, and one using a dense time series of time-variable gravity. We find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss. In 2006, the Greenland and Antarctic ice sheets experienced a combined mass loss of 475 ± 158 Gt/yr, equivalent to 1.3 ± 0.4 mm/yr sea level rise. Notably, the acceleration in ice sheet loss over the last 18 years was 21.9 ± 1 Gt/yr2 for Greenland and 14.5 ± 2 Gt/yr2 for Antarctica, for a combined total of 36.3 ± 2 Gt/yr2. This acceleration is 3 times larger than for mountain glaciers and ice caps (12 ± 6 Gt/yr2). If this trend continues, ice sheets will be the dominant contributor to sea level rise in the 21st century.
Received 4 January 2011; accepted 2 February 2011; published 4 March 2011.
Citation: Rignot, E., I. Velicogna, M. R. van den Broeke, A. Monaghan, and J. Lenaerts (2011), Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise, Geophys. Res. Lett., 38, L05503, doi:10.1029/2011GL046583.
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I like to look at history first. Then ask myself is it part of a natural cycle?
“The temperature and renewal of these waters indicate that they currently cause enhanced submarine melting at the glacier terminus.”
Straneo et. al.
http://www.nature.com/ngeo/journal/v3/n3/abs/ngeo764.html
—
“…the rate of warming in 1920–1930 was about 50% higher than that in 1995–2005.”
Petr Chylek et. al.
http://www.agu.org/pubs/crossref/2006/2006GL026510.shtml
—
“The annual whole ice sheet 1919–32 warming trend is 33% greater in magnitude than the 1994–2007 warming.”
Jason E. Box et. al.
http://journals.ametsoc.org/doi/abs/10.1175/2009JCLI2816.1
—
“We found that northern hemisphere temperature and Greenland temperature changed synchronously at periods of ~20 years and 40–100 years. This quasi-periodic multi-decadal temperature fluctuation persisted throughout the last millennium, and is likely to continue into the future.”
Takuro Kobashi et. al.
http://www.springerlink.com/content/n567324n1n3321h3/
—
“The warmest year in the extended Greenland temperature record is 1941, while the 1930s and 1940s are the warmest decades.”
B. M. Vinther et. al.
http://www.cru.uea.ac.uk/cru/data/greenland/vintheretal2006.pdf [pdf]
—
1937
“Particulars are given regarding the big rise of winter temperatures in Greenland and its more oceanic climate during the last fifteen years.”
http://onlinelibrary.wiley.com/doi/10.1002/qj.49706327108/abstract
—
I’m not worried either. Not long ago we were told to be very worried about Northern Hemisphere snow and cold not returning. A thing of the past if you like.
Well i sort of think that any increase in glacier mass loss should be measurable in increased sea level rise or is there a huge oceanic plug hole?
The real problem with these models is that they are demonstrably wrong. The sea rise in the last 50 years is apparently the slowest in the last 200. Therefore in spite of the claims of catastrophic ice melt, in fact the worlds ice store seems remarkably stable. The modelers are missing something. And they really look stupid. Like a weatherman that does not look outside.
250 Feet Of Ice Accumlated In Greenland Between 1942 And 1992
On July 15, 1942, a flight of six P-38s and two B-17 bombers, with a total of 25 crew members on board, took off from Presque Isle Air Base in Maine headed for the U.K. What followed was a harrowing and life-threatening landing of the entire squadron on a remote ice cap in Greenland. (See photo of downed P-38 from the “Lost Squadron.”) Miraculously, none of the crew was lost and they were all rescued and returned safely home after spending several days on the desolate ice.
Fifty years later a small group of aviation enthusiasts decided to locate that squadron, who had come to be known as “The Lost Squadron,” and to recover one of the lost P-38s. It turned out to be no easy task, as the planes had been buried under 25 stories of ice and drifted over a mile from their original location.
http://p38assn.org/glacier-girl.htm
We seem to be someplace toward the end or at least a rather minimalist phase of this latest transgressive sedimentary phase. Natural, normal and one of those, just the way it is things in nature.
Bad news: we will need hip waders
Good news. No need to get them for about 70,000 years.
Total ice volume is about 33,000,000 km3. At a melt of 475 per year, its nearly 70,000 years.
I am instantly suspicious of any conclusion drawn from the GRACE experiment. Attempting to measure truly minute variations in Earth’s gravity field from space is pushing the limits of noise/signal.
More to the point, gravity is a total-volumetric property, so a “change” cannot be uniquely attributed to a “place” on the planet. Teasing out “conclusions” from GRACE involves horrendous corrections (satellite parameters, lunar effects, ocean and earth tides, etc., etc.) – that is, fiddling – with limited opportunity for independent cross-checks.
To me, GRACE is akin to measuring streamflow underneath a waterfall in an attempt to detect changes in a tributary stream far, far away.
A case of “Just because you can do something doesn’t mean you should”.
Watts says:
“…we have this new study that shows ice being added from underneath due to meltwater refreeze, concluding the models to be wrong……”
but isn’t that a strawman (or red herring?) So what if ice forms underneath the shelfs! The grace satellite will see the shelf floating higher whichever side the water/snow comes from, if mass balance increases, so the new study doesn’t make the models wrong (except that water is always available on the underside, but snow precipitation is limited by low humidity of frigid dry atmosphere.)
Bushy says:
March 10, 2011 at 8:19 am
Well i sort of think that any increase in glacier mass loss should be measurable in increased sea level rise or is there a huge oceanic plug hole?
Sea level may drop in 2010
Posted on January 17, 2011 by Anthony Watts
Guest post by John Kehr
“2010 could likely show a significant drop global sea level.”
“Since the data has not been updated since August it is difficult to guess more precisely,…..”
“If the drop does show up as expected it is possible that 2010 will show the largest drop in sea level ever recorded.”
“The best source of sea level data is The University of Colorado”
Has the data for 2010 since August been posted?
Is there anybody else tracking sea levels?
Do we need another Berkley’s BEST?
Notice how published “glacier” pics are always taken on sunny days, never on a cloudy or snowy one.
Another point: Is ice loss due to melting or is it due to estivation? If the latter, it shouldn’t have much of an impact of sea levels, should it?
In one of those articles on the ice mass loss, the said the ice was “leaving the Antarctic and Greenland ice sheets.”
http://sciencedude.ocregister.com/2011/03/09/uci-study-ice-sheet-melting-speeding-up/123115/
That sounds to me like ice breaking off the edges and floating away.
I know this will seem utterly trivial and of course it is but with respect (how dare I!), this does need correction because some folk may consider it’s correct usage. I am referring to “Add to that, GRACE has it’s own set of problems. ”
“It’s” always, without exception, in every case can only be an abbreviation for “It is”.
In other words, “GRACE has its own problems.”
I’m not worried in the least about sea level rise, because I know it can’t happen. I have a theory which my computer model has proven correct (even though I have no empirical evidence at all). I call it
The Hydraulic Theory.
It says simply that as the sea level rises, it pushes on the land masses much like squeezing a pimple, forcing them up from increasing pressures. We know that land is in fact malleable, and can flow in a plastic manner under certain conditions. The earth’s oceans account for more mass than exposed land, so if the water pressure is increased by a rising sea level, then the exposed land will be forced to go where there is the least resistance. Up.
This theory is beyond reproach, and I think I read it in a peer reviewed Weekly World News journal (after I had the idea first, of course).
is there a huge oceanic plug hole?
didn’t you see the last episode of “Lost?”
everyone sing along…
there’s a rock- in a hole- in a pond- in a cave- in a stream- in a jungle- on an island- in the middle of the sea…
I would have thought that The Jet Propulsion Laboratory would spend more time on, I don’t know……. jet propulsion.
The general trend of both Greenland and Antarctic continental ice, as well as most the major glaciers of the world is not in question…they are losing mass. Yes, there are minor tweeks that need to made to the general understanding of certain dynamics (such as the growth of ice from the bottom, etc.), but the trend is not in dispute. Furthermore, the fingerprints of anthropogenic warming get harder and harder to simply ignore, causing skeptics to stick their collective heads further and further into the sand:
http://www.physorg.com/news/2011-03-earth-core-climate-insights.html
Combine the shrinking year-to-year arctic sea ice, to ice mass loss in Greenland, Antarctica, and the majority (though not all) major glaciers around the world the 40% rise in CO2 since the 1700’s, and studies such as the one referenced above, and it would seem to get harder and harder to maintain a skeptics position. Reminds of the last hold-outs who doubted that smoking caused lung cancer…
“their cumulative loss could raise sea level by 15 centimeters (5.9 inches) by 2050”
And the problem is? 6 inches in 40 years. the smallest and slowest tsunami every recorded. about the same size as the male organ and similarly exaggerated.
If all of these glaciers and ice sheets are melting faster and faster…
Why has NOAA’s Climate Indicator for Glacier Mass Balance show that glacier mass balance has been growing since 2003?
Did the glaciers not get the memo from Amazing GRACE?
None of this modeling or predicting or remote sensing matters one iota. All one has to do is measure the actual trend in rising sea levels. There is no acceleration. And sea levels are supposed to be rising. We are in an interglacial and they ALWAYS rise in an interglacial. If you don’t like rising sea levels you will certainly not like the alternative–much of the Northen Hemisphere covered with a half mile thick sheet of ice! Everyone enjoy the interglacial while it lasts.
“Why has NOAA’s Climate Indicator for Glacier Mass Balance show that glacier mass balance has been growing since 2003?”
The glacial mass balance is not actually growing… The annual value is becoming less negative (recovering toward zero).
So they measured part of warm AMO cycle and extended it until 2050. Based on today’s temperature which warmed by 15°C between 6AM and 14PM, I can also estimate what temperature will be during the weekend. Just my work will not be funded by NASA.
When this scientific masturbation on the 30-year warm AMo/POD trend will come to the end?
Actually if there is a lot of refrozen ice in Antarctica it will affect GRACE results. Ordinary glacier ice is about 10% less dense than “ordinary ice” since it is created from compacted snow and contains a lot of atmospherig gases. Refrozen ice will presumably have “ordinary ice” density. This will make the gravity field over the icecap slightly stronger.
Greenland’s ice sheets:“… their cumulative loss could raise sea level by 15 centimeters (5.9 inches) by 2050.”
Assuming the recently decreasing rise rate resumes its historic satellite rate of 3.2 mm/year, that gives 12.48 centimeters by 2050. Given the error margin, 15 cm is in the ball park, but it would take a rate of 3.8 mm/year. Since my house is 90 ft above sea level, that’s 7200 years before I have a beach. We’ll be in the next ice age by then, so it’s nothing to count on.
“It goes to demonstrate that we really don’t understand ice sheet mechanics well enough yet to make accurate forecasts, though some people think we can.”
~ ~ ~
More heat in the system, ice melts, dynamics of heat distribution makes for interesting localized conditions, both in space and time. But still add heat to a virtually closed system (our planet) that was residing within a relatively steady state and we should expect boundary ice/permafrost to melts.
As is being observed.
~ ~ ~ ~ ~ ~ ~
“I’m not worried either. Not long ago we were told to be very worried about Northern Hemisphere snow and cold not returning. A thing of the past if you like.”
~ ~ ~
The Northern Hemisphere is much more than the East Coast.
Not sure how you can say “(AGW? is a) thing of the past?” What about the real Earth Observation data?
GISS Surface Temperature Analysis (GISTEMP)
http://data.giss.nasa.gov/gistemp/
~ ~ ~ ~ ~ ~ ~
“Well i sort of think that any increase in glacier mass loss should be measurable in increased sea level rise or is there a huge oceanic plug hole?”
~ ~ ~
Well they are measuring that, and yes the signal fluctuates, but the trend… trajectory is uphill.
http://sealevel.colorado.edu/
~ ~ ~ ~ ~ ~ ~
“The real problem with these models is that they are demonstrably wrong. The sea rise in the last 50 years is apparently the slowest in the last 200.”
~ ~ ~
Can you share any citation – reference?
What about the information at: “Sea Level Rise – Understanding the past – improving projections for the future”
http://www.cmar.csiro.au/sealevel/sl_hist_intro.html#fewthousand
~ ~ ~ ~ ~ ~ ~
“That sounds to me like ice breaking off the edges and floating away.”
~ ~ ~
and most the time that ice finds itself getting sucked along by currents and melting off, though not always… they do have seasons up there.
~ ~ ~ ~ ~ ~ ~
“In other words, “GRACE has its own problems.”
~ ~ ~
These “problems” you’re talking about are part and parcel of any scientific endeavor. Those kinds of “Problems” are indispensable to the learning process. Scientists are well aware of these “problems” and devote a good deal of their time delineating, understanding and quantifying these complexities.
Here check out this interesting paper: “Validation of GOCE and GOCE/GRASE Data Products, Prelaunch support …”? http://earth.esa.int/goce04/first_igw/papers/Shum_etal.pdf
What about independent lines of evidence?
Accelerating uplift in the North Atlantic region as an indicator of ice loss
http://www.nature.com/ngeo/journal/v3/n6/abs/ngeo845.html
~ ~ ~ ~ ~ ~ ~
DJ (@March 10, 2011 at 10:48 am)
Cool post. 😉