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« Hughes bites back | Main | What's a sceptic? »
Monday
Oct222012

New Antarctic ice melt paper

The Age reports a new paper in Nature about the volume of ice in Antarctica (H/T Leo Hickman).

Antarctica is shedding an average of 190 million tonnes of ice every day, according to a landmark study that used satellites to "weigh" the vast land mass.

Although parts of east Antarctica are growing, glaciers in west Antarctica are melting faster, leading to a net loss of ice across the continent, according to the study published in the journal Nature.

However, it's not all bad news:

One result of the findings is that melting ice in Antarctica is not contributing as much to a rise in global sea levels as some other studies have assumed.

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Reader Comments (36)

Is this on the level?

Oct 22, 2012 at 10:18 AM | Registered Commenterjferguson

190 million tonnes sounds like a drop in the ocean. What is the total Antarctic ice mass, and what is the uncertainty in the total mass and in the daily mass loss?

Oct 22, 2012 at 10:48 AM | Registered CommenterPhillip Bratby

Abstract:

Recent estimates of Antarctica’s present-day rate of ice-mass contribution to changes in sea level range from 31 gigatonnes a year (Gt yr−1; ref. 1) to 246 Gt yr−1 (ref. 2), a range that cannot be reconciled within formal errors3. Time-varying rates of mass loss2, 4, 5, 6 contribute to this, but substantial technique-specific systematic errors also exist3. In particular, estimates of secular ice-mass change derived from Gravity Recovery and Climate Experiment (GRACE) satellite data are dominated by significant uncertainty in the accuracy of models of mass change due to glacial isostatic adjustment7, 8 (GIA). Here we adopt a new model of GIA, developed from geological constraints, which produces GIA rates systematically lower than those of previous models, and an improved fit to independent uplift data9. After applying the model to 99 months (from August 2002 to December 2010) of GRACE data, we estimate a continent-wide ice-mass change of −69 ± 18 Gt yr−1 (+0.19 ± 0.05 mm yr−1 sea-level equivalent). This is about a third to a half of the most recently published GRACE estimates2, 5, which cover a similar time period but are based on older GIA models. Plausible GIA model uncertainties, and errors relating to removing longitudinal GRACE artefacts (‘destriping’), confine our estimate to the range −126 Gt yr−1 to −29 Gt yr−1 (0.08–0.35 mm yr−1 sea-level equivalent). We resolve 26 independent drainage basins and find that Antarctic mass loss, and its acceleration, is concentrated in basins along the Amundsen Sea coast. Outside this region, we find that West Antarctica is nearly in balance and that East Antarctica is gaining substantial mass.

Lower satellite-gravimetry estimates of Antarctic sea-level contribution

Oct 22, 2012 at 10:50 AM | Registered Commentermangochutney

Test it with a Hughes-Josh duck...

Oct 22, 2012 at 10:52 AM | Unregistered CommenterRoger Carr

So, let me get this right.
This research, which looks pretty comprehensive to my layman's eyes (admits uncertainty in the models, tries to take account of these, covers a decent time period) comes up with a figure "about a third to a half of the most recently published GRACE estimates", which it says is at most consistent with a rise in sea-level of about one-third of a millimetre a year, and confirms that "Antarctic mass loss, and its acceleration, is concentrated in basins along the Amundsen Sea coast. Outside this region, we find that West Antarctica is nearly in balance and that East Antarctica is gaining substantial mass." [My emphasis]
And the bad news (indeed any news) is what and where exactly?

Oct 22, 2012 at 11:03 AM | Registered CommenterMike Jackson

"Melting"? The Antarctic ice-cap doesn't melt. At -30C ambient, it's way too cold. The change mechanism is an imbalance between ablation via glacier outflow and accumulation due to precipitation. Much more complex than "melting", and quit conceivably due to cooling, rather than warming. Possible mechanism: lower temperatures over the Southern Ocean = less evaporation, drier air, less precipitation over land, a shrinking ice-cap.

Oct 22, 2012 at 11:07 AM | Unregistered CommenterThon Brocket

The organization measuring the rate id decay in planetary rotation, whose name escapes me, have noticed a reduction of the rate of decay. This was put down to increased ice mass at the southern pole. Like an ice skater reducing their spin radius and increasing spin speed.
I can remember back in the 50's a ship reported an iceberg, ''the size of Denmark'' from the western Antarctic ice sheet. So ice breakup seems normal there and nothing to worry about.

Oct 22, 2012 at 11:21 AM | Unregistered CommenterJohn Marshall

Thoughts on the reported figure:

Daily ice loss: 190,000,000 Tonnes = cu m , roughly.
Wow that's a lot of tons, if you're an innumerate liberal-arts grad reading the Age in Starbucks .

And that ice loss is going on 365 days a year. Terrifying
That's 69,350,000,000 cu. m per year.

Antarctic ice cover area, sez Wikipedia 13,720,000 square clicks.
Times a million, for square metres: 13,720,000,000,000 sq. m.

So, annual depth of ice lost: 0.005 m.
That's, yup, five millimetres a year of Antarctic ice, folks. Every year.

WE'RE ALL GOING TO DIE!!!!

Oct 22, 2012 at 11:31 AM | Unregistered CommenterThon Brocket

mangochutney's link to Nature's paywalled paper allows you to download the supplementary info, which is considerable.

http://www.nature.com/nature/journal/vaop/ncurrent/extref/nature11621-s1.pdf

Oct 22, 2012 at 11:34 AM | Registered CommenterPharos

I notice they don't mention how much is being added BACK into the ice mass on the continent. So a little bit of melting is something to shriek about, but massive amounts of new ice being added, are ignored?

Oct 22, 2012 at 11:37 AM | Unregistered CommenterOtter

"east Antarctica"

Is there such a place? I thought everywhere was North... :-)

Oct 22, 2012 at 11:49 AM | Registered Commenterjamesp

But if East is where you go when you've been travelling North and turn right, everywhere is East.

Oct 22, 2012 at 11:55 AM | Unregistered CommenterRichard Drake

Thank you Thon,

Amazing how the bleedin' obvious can bring you up short. So used am I to the alarm surrounding ice "melt" that I have allowed my own thinking to become lazy about this (an "eye off the ball" situation if you like) - "melting" of course being an inappropriate word for what might be going on. Ablation/accumulation of course seems to be the correct description.

I wonder why the professor refers to "the melt".

Unless someone is (kindly) able to educate me as to why the word "melting" is accurate here, I am going to use this example in a Law class I teach as a means of identifying the need to be precise in language.

Oct 22, 2012 at 12:06 PM | Unregistered CommenterRB

Depends what is meant by melting. If it is temperature induced then it may be something to be worried about but if it is just the normal glacial process of water production due to very high pressures within the ice then that is normal because that is how glaciers flow.

Oct 22, 2012 at 12:11 PM | Unregistered CommenterPhysics

Well said Mr Brocket! You did forget to add in the additional ice from extra snow coverage, which would make the loss even more insignificant & meaningless than you had already amply demonstrated. I thought the most omenous term in the article was the word "model" & making satellite data match the ground observations! That's models for you, infinitely tunable & able to produce any answer your paymasters desire! Oh & as to measuring to 1/100th of a millimetre, yeah right, as if that's has any real-world meaning whatsoever! Don't they just love scary numbers!!!!

Oct 22, 2012 at 12:32 PM | Unregistered CommenterAlan the Brit

I'm still not losing any sleep.

Oct 22, 2012 at 12:35 PM | Unregistered CommenterJimmy Haigh

We have had hundrerds of such reports picked up by the media and debunked, without being reported by the same media) a few weeks later. The most recent beinmg the record melting ASrctic ice one which NASA later admitted was die to increased wind breaking up the ice.

Lets see how this stands 6 weeks from now.
I am also suspicious of the "East Antarctica/West Antarctica phrasing. One is a relatively small volcanically active peninsula and the other is a continent with ice piled up to 3 km high, containing 90% of the planet's ice..

Oct 22, 2012 at 12:37 PM | Unregistered CommenterNeil Craig

Another giggle from the numbers:
Antarctic ice-cap area : 13.7 m sq. km
World's ocean area: 360 m sq. km
Rate of ice-loss in Antarctica (see my last post): 5 mm / year

Therefore rate of sea-level rise due to loss of Antarctic ice:
13.7 / 360 x 5 = 0.20 mm / year
So if this report is correct, we need five years to see raise sea-levels rise by one millimetre due to Antarctic ice loss. This rate of SLR is in fact way lower than what we've been used to (2 mm to 3 mm / year, measured over the last century) and certainly very much lower than what the screamers have been screaming at us. So it seems to me that this report is no advertisement at all for CAGW, and can in fact be wielded with effect on the skeptic side of the debate : "Scientists say that Antarctic melting (heh!) only adds one mil to sea-level every five years!"

Oct 22, 2012 at 1:10 PM | Unregistered CommenterThon Brocket

Is that the same Antartica about which the "experts" were telling us two weeks ago that "Global Warming means more Antarctic ice"? What happened to that "wall of wind" that was keeping all the coldness "bottled up in Antarctica". Gone with the Wind?

Looks like Drs. Maksym, Scambos, Vaughan and Serreze have some more 'splainin' to do.

Oct 22, 2012 at 1:47 PM | Unregistered CommenterGeoff

Thon -
There's an easier way to reach your answer (of the 1:10 PM comment): the abstract says that the authors "estimate a continent-wide ice-mass change of −69 ± 18 Gt yr−1 (+0.19 ± 0.05 mm yr−1 sea-level equivalent)."

However, all GRACE studies need to be viewed with a certain amount of caution. E.g. Velicogna (2009) used GRACE to estimate 143 Gt yr-1 over the period 2002-2009. The difference is largely in the assumptions used for glacial isostatic rebound, which is quantified in Velicogna as "176 ± 76 Gt/yr." When correction terms are of the same order of magnitude as the quantities being measured, caution is advised.

GIA corrections affect the estimate of rate but not of acceleration. So to me, the more significant result is that King et al.'s estimate of mass loss acceleration is only -4.4 Gt yr-2, contrasted with Velicogna's estimate of -26 Gt yr-2. [I note in passing that The Age article does not mention this.]

Oct 22, 2012 at 1:51 PM | Registered CommenterHaroldW

3 to 4 weeks ago Antarctica was adding large amounts of ice...measured in the old reliable cubic measurements known as "Manhattans".

This was happening at the same time that global Warming/Climate Change was melting the Artic ice, although later it was admitted that the Artic loss of ice was caused by typhoons

See this: Antarctica gains 2,400 Manhattans worth of ice overnight
iceagenow.info/.../antarctica-gains-2400-manhattans-worth-ice-overn...
28 Sep 2012 – Southern hemisphere sea ice has been steadily expanding since 1979, but nary a ... Antarctica gains 2,400 Manhattans worth of ice overnight ...

Oct 22, 2012 at 1:59 PM | Registered Commenterpeterwalsh

Thon Brocket says-

"The change mechanism is an imbalance between ablation via glacier outflow and accumulation due to precipitation."

Also, direct sublimation to vapor is a significant contributor to glacial ice loss.

I thought death spiral Zwally just published a paper indicating Antarctic glacier ice was seeing a net accumulation of 49 GT/yr or 134 MILLLLLION tons per day! *If trends continue*, we'll be in another iceball EAarth before too long!!!

wattsupwiththat.com/2012/09/10/icesat-data-shows-mass-gains-of-the-antarctic-ice-sheet-exceed-losses

Once again the result is buried in the measurement error, +/- several parts per million per year.

Oct 22, 2012 at 2:34 PM | Unregistered Commenterchris y

My head is going to explode! After six or seven years of following the global warming/climate change debate I think I have reached my saturation point. But I believe I have come to one conclusion...Mankind simply does not have the data nor the understanding to reliably say what the climate is doing, is going to do, or what is causing it to change or will cause it to change. I am no scientist but if we built and repaired airplanes with the same level of robustness and arrogance that I have seen in climate science nobody would fly.

Oct 22, 2012 at 2:52 PM | Unregistered CommenterEric H.

'Ice not melting in Antarctica" probably isn't as arresting a headline, though.

I enjoyed the following remark on a post I read recently:

"Asking scientists to deny climate change is like asking Cadbury's to deny Easter" :-)

Oct 22, 2012 at 3:24 PM | Unregistered CommenterJames P

GRACE is rubbish.

It measures gravity pretty well but it it has no idea what causes the local change in gravity. Hence the models. Technique:

1. Decide what you want the answer to be
2. Use model to separate the various causes of change in local gravity
3. Fudge Tune model to produce desired answer

Any questions?

Oct 22, 2012 at 4:08 PM | Unregistered CommenterBilly Liar

Eric H: 'I am no scientist but if we built and repaired airplanes with the same level of robustness and arrogance that I have seen in climate science nobody would fly.'

Yup, but this is post-normal science. Use a 170 year old hypothesis and build it into a computer model so it's a perpetual motion machine then claim your right and prevent anyone publishing a contrary explanation. Add a side-salad of outright scientific lies plus accuse the true scientists who protest as 'denialerists' and it's easy. 6 mistakes, 3 cringe-making, 3 more subtle plus lie about past temperatures.

Oct 22, 2012 at 4:37 PM | Unregistered CommenterAlecM

If the Antarctic is losing ice it it is not caused by temperature changes but by lack of precipitiation ( I realise that sublimation and ablation remove ice, but if it snows it gets replaced doesn't it?). So we have a bunch of scientists telling us the earth is warming and that the warming will produce water vapour that will cause more warming. Even the great George Monbiot told us that bollock freezing winters with lots of snow where a sign of global warming, and he's right, but where has the precipitiation on the Antarctic gone to?

Oct 22, 2012 at 5:03 PM | Unregistered Commentergeronimo

Eric H @ 2:52: A climate science vehicle was built with 'robustness' and arrogance and now it has flown too high.
============

Oct 22, 2012 at 5:37 PM | Unregistered Commenterkim

For those of us too tired to look at the facts, the Arctic Circle's temperatures this summer were at, or below, average (DMI). Therefore, given that other seasons which were at, or above, average temperatures failed to produce a loss in ice cover consistent with this year's it would, to anyone with half a brain, be obvious that there was something else in play. Geddit!

Oct 22, 2012 at 8:45 PM | Unregistered Commentergeronimo

nothing lasts forever....except CAGW:

22 Oct: Toronto Star: Raveena Aulakh: Antarctic sea ice is increasing — is global warming over?
Not at all, say climatologists.
The Antarctic is land covered with ice and surrounded by water; the Arctic is water surrounded by land. “That makes them hugely different and how climate change affects them is also different,” said Gordon McBean, director of research at the University of Western Ontario’s Centre for Environment and Sustainability.
“In the Antarctic, there is ice in the centre and as it meets with ocean, currents lift it a bit,” said McBean. “It can result in more sea ice.”…
Scientists say there is also the issue of depletion of ozone in the stratosphere in the Antarctic, which makes the stratosphere even colder, preventing ice from melting.
But McBean says while the Antarctic is still cooler than the rest of the world, it is also warming up. “Just not as quickly,” he said.
The phenomenon in the Antarctic is not inconsistent with global warming, said McBean. “It was expected . . . it’s a complex situation.”…
But the growing sea ice in the Antarctic will have not have an impact on sea level, said Jing Chen, professor with the department of geography at the University of Toronto…
“We should not be too complacent about the recent ice increase,” he said. “If (global) warming keeps increasing, it pushes average temperatures above freezing points and the Antarctic area ice will decrease and the trend will quickly reverse.”
Growing sea ice in the Antarctic is good news “but (we) have to take it in the right perspective: it will not increase forever.”
http://www.thestar.com/news/world/article/1275441–antarctic-sea-ice-is-increasing-is-global-warming-over

Oct 22, 2012 at 9:06 PM | Unregistered Commenterpat

pat -
From that article, while I agree that Antarctic effects will not parallel those in the Arctic, I have to take issue with Gordon McBean's statement that the growth in Antarctic sea ice "was expected."

AR4 WG1 Figure 10.13(d) shows the projected Antarctic sea ice extent for the austral winter. A rapid decrease was forecast, with an even stronger downward trend than that of Arctic sea ice extent for the boreal winter [panel(a)].

The recent positive change in Antarctic sea ice is likely not statistically significant, but ice extent is definitely *not* trending downward at -5 million km^2/century as projected in AR4.

Oct 22, 2012 at 9:41 PM | Registered CommenterHaroldW

The bottom line is Climate Change is Natural and CO2 is Life.Have a great day and enjoy our beautiful ever changing World.

Oct 22, 2012 at 9:42 PM | Unregistered Commenteragwnonsense

But when it snows with the "wrong kind" of snow this is not counted. Antarctic "scientists" now use the same methodology as old Charlie Monnett of polar bears fame. In other words they estimated total losses from looking at just a tiny percentage of examples, and then extrapolate to get an overall result which is not based on any real world evidence or realistic scenario.

Utter Piffle and Fiddle-Faddle !

Oct 23, 2012 at 6:19 AM | Unregistered CommenterJist Wan Cornetto

Oh such beautiful irony

http://www.abc.net.au/news/2012-10-23/antarctic-supply-ship-icebound/4329708

Or maybe not

Oct 23, 2012 at 6:48 AM | Unregistered CommenterAlan

Antarctica isn't adding much to sea level rise.

OK, what IS causing the fabeled 3mm/yr rise in sea level????

Oct 24, 2012 at 2:13 AM | Unregistered Commenterkuhnkat

Has anyone told Al??

Oh yeah, he bought a seal level condo in San Francisco a year or so back.

Oct 24, 2012 at 2:15 AM | Unregistered Commenterkuhnkat

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