Research team breaks the ice with new estimate of glacier melt

Mar 02, 2010
Northern Arizona University geographer Erik Schiefer surveys a debris-covered glacier margin. Credit: Photo by Amanda Stan

The melting of glaciers is well documented, but when looking at the rate at which they have been retreating, a team of international researchers steps back and says not so fast.

Previous studies have largely overestimated mass loss from Alaskan glaciers over the past 40-plus years, according to Erik Schiefer, a Northern Arizona University geographer who coauthored a paper in the February issue of that recalculates glacier melt in Alaska.

The research team, led by Étienne Berthier of the Laboratory for Space Studies in Geophysics and Oceanography at the Université de Toulouse in France, says that glacier melt in Alaska between 1962 and 2006 contributed about one-third less to sea-level rise than previously estimated.

Schiefer said melting glaciers in Alaska originally were thought to contribute about .0067 inches to sea-level rise per year. The team's new calculations put that number closer to .0047 inches per year. The numbers sound small, but as Schiefer said, "It adds up over the decades."

While the team looked at three-fourths of all the in Alaska, Schiefer noted, "We're also talking about a small proportion of ice on the planet. When massive ice sheets (such as in the Antarctic and Greenland) are added in, you're looking at significantly greater rates of sea-level rise."

Schiefer said the team plans to use the same methodologies from the Alaskan study in other glacial regions to determine if further recalibrations of ice melt are in order. These techniques use satellite imagery that spans vast areas of ice cover.

Previous methods estimated melt for a smaller subset of individual glaciers. The most comprehensive technique previously available used planes that flew along the centerlines of selected glaciers to measure ice surface elevations. These elevations were then compared to those mapped in the 1950s and 1960s. From this, researchers inferred elevation changes and then extrapolated this to other glaciers.

This is a 3-D view of the Barnard glacier in Alaska showing significant quantities of debris that cover the lower parts of the glacier. Credit: Imagery courtesy of CNRS -- French National Center for Scientific Research

Two factors led to the original overestimation of with this method, Schiefer said. One is the impact of thick deposits of rock debris that offer protection from solar radiation and, thus, melting. The other was not accounting for the thinner ice along the edges of that also resulted in less ice melt.

Schiefer and his colleagues used data from the SPOT 5 French satellite and the NASA/Japanese ASTER satellite and converted the optical imagery to elevation information. They then compared this information to the topographical series maps of glacial elevations dating back to the 1950s.

While the team determined a lower rate of glacial melt during a greater than 40-year span, Schiefer said other studies have demonstrated the rate of ice loss has more than doubled in just the last two decades.

"With current projections of climate change, we expect that acceleration to continue," Schiefer said. This substantial increase in ice loss since the 1990s is now pushing up the rise in sea level to between .0098 inches and .0118 inches per year—more than double the average rate for the last 40 years.

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Provided by Northern Arizona University

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joefarah
3.7 / 5 (3) Mar 02, 2010
Tell me. How much ice will one colder than average winter add as compared to the net melt?
Scalziand
2.8 / 5 (4) Mar 02, 2010
Here's another thing I wonder: Do studies like this take into account how much the the bedrock under the glacier is being eroded by the glacier?
axemaster
2.6 / 5 (5) Mar 02, 2010
"Tell me. How much ice will one colder than average winter add as compared to the net melt?"

Do you know the meaning of "net melt"?

Then you know how meaningless your question was.
JayK
1.9 / 5 (9) Mar 02, 2010
joefarah: Do you want a real answer, or are you just trolling, as usual? If you don't understand volume, then go away.
Sean_W
2.2 / 5 (6) Mar 02, 2010
Let the average ice gain for several years be 1 unit. Let the extra ice gain in the cold year be 1 unit. Total ice gain that year equals 2 units. Let the total ice lose in that year equals 4 units. Net melt then equals 2 units. Compare extra ice that year with net melt equals 1/2. So in this case "meaningless" equals 0.5 units of ice. The higher the net melt the smaller "meaningless" becomes. The larger the extra ice value is the greater "meaningless" is.

It is called a ratio.

As for measuring elevation of ice to calculate volume and extrapolating loss to other glaciers - it makes me wonder whether they used the same methodology for choosing which glaciers to use as they did for deciding which tree ring samples to use.

O/T Have people like Al Gore started selling their coastal properties due to all this sea level rising yet? Just curious.
JayK
2 / 5 (8) Mar 02, 2010
@Sean_W: Do you have a real dispute with tree-ring proxies? Do you have a citation or do you have a professional publication that you will be submitting your peer-reviewed article to?
fixer
3 / 5 (2) Mar 02, 2010
Or are you just a bit smarter than most and worked it out for yourself?
At least your answer provided information,unlike some others here.
Parsec
2.3 / 5 (3) Mar 02, 2010
I suppose the only answer that AGW deniers will accept is either 0 net loss, or net gain.

These are reputable scientists publishing in a peer reviewed journal reporting that the overall net loss as previously been overestimated. That means less ice being lost that previously estimated. But ice is being lost overall.
Caliban
3.3 / 5 (7) Mar 02, 2010
@Scalziand,
I think that you are asking if perhaps some of the mass of the glacier is "hidden" by their possibly digging out a deeper channel in softer strata, and therefore somehow their true extent is being missed? The short answer is no. The depth can be measured with great accuracy by any number of methods.
@SeanW,
Obviously, it would be nearly impossible to measure each and every glacier. So, much like in any other data collection, you take a representative sample. There isn't much likelihood that there will be any statistically significant variation in samples taken at the same Altitude/Latitude.
jonnyboy
1 / 5 (2) Mar 03, 2010
@caliban
Did you even bother to look at the picture before you made just an obviously inaccurate comment to Sean?
Caliban
3.4 / 5 (5) Mar 03, 2010
@jonnyboy,
Did you bother to remove the pipe from your lips before you typed your obviously hallucinatory comment to me?
DachpyarviIe
1.7 / 5 (6) Mar 03, 2010
So alarmists was wrong when they stated that Alaskan ice melt will raise global sea levels by 30 feet by 2030!
We now know that the globe has been cooling for the last 70+ years (1934 was warmest year globally on record) and it has been warmer before (the vikings grew pineapples in Greenland).More lies from the communist AGW alarmists :)
Ronan
5 / 5 (2) Mar 03, 2010
Dachpyarvile, is that an intentional or accidental straw man? No one has EVER predicted that Alaskan ice melt would cause a rise of thirty feet, by 2030 or by any other time. There physically is not enough ice in Alaska to have that effect. I'm sure you're intelligent enough to realize that fact, and also to realize that no one else is ignorant enough to seriously make that claim.

Also, um, 1934 was one of the warmest years (still not the warmest; if I recall correctly 2005 beat it) for the 2% of the Earth's surface that is the US, not for the world. And...wait, pineapples in Greenland?

Pineapple? The South American plant?

(Edit): Ah, never mind. DachpyarviIe with an "I," then; a mimic of dachpyarvile. That...would explain much.
PRADYUMNA
2 / 5 (2) Mar 03, 2010
With Global warming, just as glaciers would melt, sea water would evaporate faster as air RH falls. so sea level would be the cobined effect of melting ice and faster evaporation near equator. I suspect, that on the whole we will have more water in the sky as clouds. You see the same in hotter planets like jupiter. Obviouslt rains will pour like hell. whenever that happens
PRADYUMNA
2.3 / 5 (3) Mar 03, 2010
Any icebergs, ice floating on sea near poles will not affect sea level even if all melt. Just take a glass of water, put some ice and mark the level. wait till ice melts. you will see no change in level.
JayK
2 / 5 (4) Mar 03, 2010
Actually, Pradyumna, the equator isn't going to warm as much as the poles, so the assumed increase in evaporation won't be as great an offset as you might think. Actually modelling the evaporation and cloud cover effect is a major effort right now within climate science.
Loodt
1 / 5 (5) Mar 03, 2010
JayK,

Why should we believe you when you state that ...the equator isn't going to warm as much as the poles...

I don't believe that statement and challenge you to site real observations that demonstrate beyond doubt, and manipulation of the date, that point.

Or is this just another Mickey Mouse Play Station Model!

At least this article is reporting real science, actual observations, and not some results from another stupid model!
JayK
3 / 5 (4) Mar 03, 2010
How many citations would you like, Loodt?

http://webarchive...ndex.cfm

http://www.spring...fqghlvk/

http://www.spring...6505620/

The IPCC AR3, AR4 both have those conclusions and it has basically become a fundamental understanding in climate science that the poles will warm faster than the equator.
jet
1 / 5 (1) Mar 03, 2010
Hmm..did not account for SHADE! thats Comedy...

*apologies to slappy squirrel.
JayK
1.7 / 5 (3) Mar 03, 2010
If you just prefer pretty graphs:

http://colli239.f...ge-2008/

Scalziand
3 / 5 (1) Mar 03, 2010
@Caliban:
Cool beans. Thanks for the response.
Loodt
1 / 5 (4) Mar 03, 2010
JayK,

Wow, what an impressive list!

IPCC AR3, Boys Own Action Manual, Rock Climbing & Glacier Wartching Annual..

Quoting anything produced by the IPCC carries absolutely no GRAVITAS in the post-Climategate era. Whereas you could have impressed the gang at the tea-trolley with quotes from that document last year, find something more substantial and reliable this year!

The train has left station and you are standing on the platform!
JayK
2.5 / 5 (4) Mar 03, 2010
Wow, what an incredible come back, I'm humbled by your knowledge in these weighty manners, sir.
Caliban
2 / 5 (4) Mar 03, 2010
Any icebergs, ice floating on sea near poles will not affect sea level even if all melt. Just take a glass of water, put some ice and mark the level. wait till ice melts. you will see no change in level.


PRADYUMNA,
Everyone did this experiment in school. You mark the water level in the container BEFORE adding the ice, silly!
operator
3 / 5 (2) Mar 06, 2010
loodt kind of jumping the band wagon with your "climate gate" aspertions ain't you, the inquiries havn't finished as yet but already we're seeing the summary findings from the institute of physicists to the commons committee come under scrutany. seems we have a little problem with oil backed members getting on the IOP boards and casting aspertions about the CRU wihtout its members backing.

so until the inqueries are in, maybe your rubishing of the CRU's data and its methords are a little misplaced, to say the least. but those with a predefined agenda proberly wont be swayed by any of the science.

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