The rocky road to accurate sea-level predictions

Dirt and water under Greenland control future sea


Research News


The type of material present under glaciers has a big impact on how fast they slide towards the ocean. Scientists face a challenging task to acquire data of this under-ice landscape, let alone how to represent it accurately in models of future sea-level rise.

“Choosing the wrong equations for the under-ice landscape can have the same effect on the predicted contribution to sea-level rise as a warming of several degrees”, says Henning Åkesson, who led a new published study on Petermann Glacier in Greenland.

Glaciers and ice sheets around the world currently lose more than 700,000 Olympic swimming pools of water every day. Glaciers form by the transformation of snow into ice, which is later melted by the atmosphere in summer, or slides all the way into the sea. With climate change, glaciers are breaking up and drop icebergs into the ocean at an accelerating pace. Exactly how fast depends to a large extent on the bed below all the ice. Glaciers conceal a landscape under the ice covered by rocks, sediments and water. A new study shows that the way we represent this under-ice landscape in computer models means a great deal for our predictions of future sea-level rise. More specifically, how we incorporate the friction between the ground and the ice sliding over it in glacier models is what affects our predictions. This was found by a team of Swedish and American scientists, when they simulated the future of Petermann Glacier, the largest and fastest glacier in northern Greenland.

Petermann is one of the few glaciers in the northern hemisphere with a remaining ice tongue, a type of floating glacier extension otherwise mainly found in Antarctica, where they are called ice shelves. These floating extensions have been found to be exposed to warm subsurface water flowing from the open ocean towards the glaciers. This happens both in Antarctica and in many fjords around Greenland, including the Petermann Fjord.

“Peterman lost 40% of its floating ice tongue over the last decade. It still has a 45 km tongue, but we found that a slightly warmer ocean than today would lead to its break up, and trigger a retreat of the glacier”, says Henning Åkesson, a postdoctoral researcher at Stockholm University who led the study.

Many glaciers in Greenland and Antarctica flow towards the ocean much faster than they did a few decades ago, and therefore contribute more to global sea-level rise. Scientists have therefore mobilized great efforts into learning what is going on in these environments. This has spurred new insights into the landscape under glaciers and the shape of the seafloor where they drain. We now also know much more about what happens to the ice when glaciers meet the sea.

Still, the remote polar regions are notoriously difficult to study because of sea ice, icebergs, and often harsh weather. The under-ice landscape is a particular challenge because, frankly, it is hard to measure something covered by a kilometer of ice on top. Even in areas of known under-ice topography, describing its physical properties using mathematical equations is difficult. Computer models are therefore still somewhat in the dark when it comes to how to represent things like sediments, rocks, ponds and rivers under glaciers in the equations that describe ice flow. These equations are ultimately the foundation of the models used by the IPCC to estimate how fast glaciers flow and how much sea levels will rise under future climate warming.

“As we said, choosing the wrong equations for the under-ice landscape can have the same effect on the contribution to sea-level rise as a warming of several degrees”, Åkesson says.

“In fact, predicted sea-level rise for this Greenland glacier can quadruple depending on how we represent friction under the ice. We still don’t know which way is the best, but our study illustrates that ice-sheet models still need to progress in this respect, in order to improve our estimates of mass loss from Earth’s polar ice sheets.”


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Lance Wallace
June 10, 2021 10:21 pm

a floating tongue will not contribute to sea level rise.

Joel O'Bryan
Reply to  Lance Wallace
June 10, 2021 10:40 pm

Careful reading reveals that it is the on-shore under-ice frictional dynamics of the glacier that controls glacial flow rates that these researchers find has much uncertainty. It is those rates of flow from land which allows replenishment or retreat of the floating ice tongues in Greenland under warming or cooling sea water scenarios. Retreat of an ice tongue observed length (Petermann is the example they use) can either be due to increased ocean water warming or decreased glacial flow replenishment, or both. That uncertainty in flow dynamics can completely obscure warmer (or colder) water effects on tongue length making any such projections not only worthless but likely misleading (false infomation is worse than no information).

Reply to  Joel O'Bryan
June 11, 2021 12:10 am

” Retreat of an ice tongue observed length (Petermann is the example they use) can either be due to increased ocean water warming or decreased glacial flow replenishment, or both”

Good point. And decreased glacial flow replenishment could be caused by less ice/snow accumulation up stream OR colder temperatures leading to less melt water erosion around and beneath the glacier OR less rainfall??
I’m just guessing….

Reply to  Lance Wallace
June 10, 2021 11:17 pm

The Petermann glacier is nearly totally floating just as Lance Wallace says. It has been recorded as losing 80& of its mass annually since at least a decade ago, when it was known to be stable — gaining nearly as much or more mass seasonally every year. It grows from the top, and melts from the bottom, and mostly the latter during the North hemispher summer — like now.

Today’s surface air temp ranged from -2 to -10C.

2011 Study
Ocean circulation and properties in Petermann Fjord, Greenland;Journal of Geophysical Research:Oceans/Volume 116, Issue C1; H. L. Johnson, A. Münchow, K. K. Falkner, H. Melling;06 January 2011

The floating ice shelf of Petermann glacier interacts directly with the ocean and is thought to lose at least 80% of its mass through basal melting. Based on three opportunistic ocean surveys in Petermann Fjord we describe the basic oceanography: the circulation at the fjord mouth, the hydrographic structure beneath the ice shelf, the oceanic heat delivered to the under-ice cavity, and the fate of the resulting melt water. The 1100 m deep fjord is separated from neighboring Hall Basin by a sill between 350 and 450 m deep. Fjord bottom waters are renewed by episodic spillover at the sill of Atlantic water from the Arctic. Glacial melt water appears on the northeast side of the fjord at depths between 200 m and that of the glacier’s grounding line (about 500 m). The fjord circulation is fundamentally three-dimensional; satellite imagery and geostrophic calculations suggest a cyclonic gyre within the fjord mouth, with outflow on the northeast side. Tidal flows are similar in magnitude to the geostrophic flow. The oceanic heat flux into the fjord appears more than sufficient to account for the observed rate of basal melting. Cold, low-salinity water originating in the surface layer of Nares Strait in winter intrudes far under the ice. This may limit basal melting to the inland half of the shelf. The melt rate and long-term stability of Petermann ice shelf may depend on regional sea ice cover and fjord geometry, in addition to the supply of oceanic heat entering the fjord.

Petermann dramatically calves huge ice sheets almost every year.
It just needs a little snow.

Åkesson, article above:

In fact, predicted sea-level rise for this Greenland glacier can quadruple depending on how we represent friction under the ice.

The claim of 4x increase in sea-level rise from this glacier is not consistent with it’s documented normal yearly summer loss of 80%..

You don’t get sea level rise from floating ice.
Perennial EurekAlert disclaimer:

   AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.

The “news release” is entirely the responsibility of its hero and writer, Henning Åkesson, who even took the selfie.

Got funding?

Reply to  dk_
June 12, 2021 1:07 pm

“In fact, predicted sea-level rise for this Greenland glacier can quadruple depending on how we represent friction under the ice”

It says predictions can quadruple, not that iceloss can. Which is absent, reference to DMI’s report of gains for 10 months and loss for 2 months per year where net variance is increasing total ice mass.


Reply to  Lance Wallace
June 10, 2021 11:42 pm


Future Projections of Petermann Glacier Under Ocean Warming Depend Strongly on Friction Law; Journal of Geophysical Research: Earth Surface; 126, issue6; Henning Åkesson, Mathieu Morlighem, Matt O’Regan, Martin Jakobsson; 04 May 2021

Henning, et al. work on modeling the surface of the small bit of shelf on which Petermann hinge. I find no mention of any of the authors actually visiting and measuring the glacier. Instead, the work appears to be modeling a theoretical law for friction between ground surface and the ice on the land hinge shelf, based on many other crews actual measurements and soundings (including the Johnson, et al. 2011 paper). The model “experiements” were run based on projected rises in temps from 2.5º to 5ºC.

Forgot to link the edit of the previous post — the 2011 Johnson et al paper is at

Which lists the actual temperatures measured beneath the glacier (coldest -1.5ºC and establishes a gradient depth curve for actual measured temps.
Johnson doesn’t mention shelf friction as being significant, only water temp at depth and salinity mentioned as factors that cause the glacier mass to be balanced.

Of course, Åkesson and team will verify their model with physical experiments, right?
Wonder where he took that selfie?

Martin C
Reply to  Lance Wallace
June 11, 2021 8:45 am

From the article: Many glaciers in Greenland and Antarctica flow towards the ocean much faster than they did a few decades ago, and therefore contribute more to global sea-level rise.”

What an alarmist statement. What, they didn’t think that maybe MORE SNOW being add on he glacier might ALSO contribute to how fast it flows ? And if more snow and ice is being added is, that means water FROM the sea was evaporated, which is working to REDUCE sea level.

Obviously the speed of the glacier is a combinations of these things – increasing snow/ice, nature of the glacier ‘bed’, etc. But to make just that statement is pure alarmism.

David A
Reply to  Martin C
June 11, 2021 11:28 pm

Indeed. As there is zero acceleration in SL rise, there us zero reason to accept the statement as factual, or indicative of anything to be concerned about.

Joel O'Bryan
June 10, 2021 10:25 pm

They just admitted that the glacier modeling researcher can employ personal bias to generate any glacial melt outcome they want and have it still look plausible and believable to the non-expert.

There is no reason to trust anything published from glacial melt models related to climate change by the rent-seekers’ pursuit of career enabling research grants.

Bob Johnston
June 10, 2021 10:49 pm

Since there is not 1 single Tidal Gauge on Earth set in bedrock that is showing an upwards trenď in sea level rise, it can not possibly be true that the melt accelerate as the narrative always is telling us

Chris Nisbet
June 10, 2021 11:04 pm

“We still don’t know which way is the best”.
Quite a crucial bit of information to toss out right at the end, I reckon.

June 10, 2021 11:04 pm


June 10, 2021 11:09 pm

If “predicted sea-level rise for this Greenland glacier can quadruple depending on how we represent friction under the ice.”, it follows that the rate could also be one fourth as much as currently modeled. There is also something unsettling about choosing “the largest and fastest glacier in northern Greenland” for study to understand glaciers in general. If it is the largest and fastest, you would expect a lot of flow regardless what parameters you use. Looks like an opportunity to produce scary numbers.

Philip Mulholland
Reply to  KentN
June 11, 2021 1:31 am

700,000 Olympic swimming pools of water every day.

“Looks like an opportunity to produce scary numbers.”

Quite so. Why stop at Olympic size swimming pools? Domestic bath tubs would be better and if they went for teacups/day the number would be off the scale /sarc.

Reply to  Philip Mulholland
June 11, 2021 2:10 am

Bah, think Big…. or Small!

Petagrams, petagrams. To the devil with metric tons, and surely do away with gigatons. Imagine measuring the worlds oceans in terms of grams or ml. The mind boggles. Of course, if you used gigatons, you reduce the number by 6 orders of magnitude, but whats a few orders of magnitude between friends.

And petagrams is used for worldwide carbon flux and amounts in the oceans and atmosphere. The carbon people know about big scary numbers.

Steve Z
Reply to  TonyL
June 11, 2021 9:13 am

Actually, a petagram and a gigatonne are the same thing. A petagram is 10^15 grams. A gigatonne is a billion (10^9) metric tonnes, and a metric tonne is 1,000 kg = 10^6 grams, so that a gigatonne is 10^9 * 10^6 = 10^15 grams.

Of course, using Olympic swimming pools as a unit of volume is deceptive when comparing to glaciers and oceans. If an Olympic swimming pool is 50 m long by 20 m wide by about 3 meters deep, that’s a volume of 3,000 cubic meters, which seems like a lot when watching the Olympics, but is ridiculously small compared to the oceans.

The estimated area of the oceans is 510 million square kilometers, or 510 trillion = 5.1(10^14) square meters. If an ice cap lost 700,000 Olympic swimming pools a day, or about 2.1(10^9) m3/day, that would raise the level of the oceans by 4.1(10^-6) m/day, or 1.5 millimeters per year, enough to raise sea level by a whopping 5.9 inches over the next century.

Those 700,000 Olympic swimming pools a day don’t sound nearly as scary when expressed as sea level rise!

The strategy of the warm-mongers is clear–try to scare people with large numbers of units of volume to which people can relate, and hope that nobody who knows how to use a calculator can figure out that the real effect is tiny on a global scale.

Patrick B
Reply to  Philip Mulholland
June 11, 2021 7:04 am

My first thought was is that “net” or simply “gross”?

June 11, 2021 2:11 am

So once again the science isn’t settled.

Peta of Newark
June 11, 2021 2:14 am

Isn’t it nice that we can afford people like Henning?
That we still have time and space to accommodate children and their games, that some folks appear still to have the time and inclination to make any.

Let the children play, be proud of what they do but don’t attach too much seriousness to it.

Now then, what are your kids up to.
Miles high on sugar, caffiene, nicotine and sexting and when thats not enough, reducing an 8 year autistic girl, half their age, to a sobbing wreck.
Video coming soon, watch this space.

In a public playground, under a CCTV that no-one monitors, watches or records – by any chance?
While you slob out on the sofa, full of pasta, chocolate and alcohol in front of perfectly dysfunctional TV and Media (social and otherwise) – worrying about the weather in 100 years time.
While, just yesterday, your bloated alcoholic buffoon Prime Minister spent every penny, and more, of what they will ever earn in their future lives

Is that what you call “Thinking of the Children”

Henning did good didn’t he….

Ben Vorlich
June 11, 2021 3:45 am

I find it difficult to get alarmed by the claims of unprecedented, which really means not seen in our limited data for a few decades. My usual houghts are is it unprecendented since the Younger Dryas? Answer probably not, shrug shoulders and get on with life.

Arte Johnson as Wolfgang?

June 11, 2021 3:59 am

“currently lose more than 700,000 Olympic swimming pools of water every day”

Stopped reading right there. First, that’s a really small amount in comparison to the whole. Second, anyone who writes so patronizingly and illiterately isn’t worth reading.

Steve Keohane
June 11, 2021 4:42 am

With climate change, glaciers are breaking up and drop icebergs into the ocean at an accelerating pace.
An accelerating pace means accelerating growth.

June 11, 2021 6:18 am

Glaciers sliding faster toward the ocean do not add to sea level rise if the mass of glaciers remains constant.

The continuity equation must be accounted for.

Glaciers are merely frozen rivers. Rivers that flow faster to the ocean do not contribute to SLR either if the flow is faster due to higher precipitation rates and volumes, which precipitation of course is sourced from the oceans.

It is true that the bottom surface profile of any river – whether it be liquid or semi-solid like ice – affects the flow velocity and volumetric flow rate, but what controls is always the continuity equation. The change in volume must always equal the volume input minus the volume output.

The warmists do not understand the continuity equation which is the bedrock of all hydraulic modeling. It is beyond their ken.

Bruce Cobb
June 11, 2021 8:53 am

EurekAlert? More like, WeStinkAlert.

June 11, 2021 9:04 am

More “Climate Crisis Me Too” research. Åkesson’s research is essentially irrelevant to glacier melting and sea level rise but he stuffs the press release with the usual doomsday scenarios so he can get some media exposure and ensure his next research grant.

June 11, 2021 9:50 am

Wait so modeling and equations contribute to sea level rise? And here I thought it was real tangible systems that did that. Well, problem solved: Do away with the models!

Citizen Smith
June 11, 2021 10:15 am

Seems a more direct source would be a tide gage record. You know, the one down there at the shore on the rock.

Reply to  Citizen Smith
June 11, 2021 9:42 pm

So they’re the ones causing all the SLR?
Sea Level Trends – Sydney, Fort Denison 1 & 2, Australia – NOAA Tides & Currents

But “we have the power to slow that rate by slowing the rate of warming.”
Fears Antarctic glacier could melt faster as it speeds up and ice shelf ‘rips apart’ (
Won’t San Fransicans please think of seaside Sydneysiders’ home values here?

June 11, 2021 10:17 am

Want to measure sea level? Use know positions with extensive and long running human occupation, and a ruler. Quit pissing away my tax money on stupid crap that doesn’t matter.

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