Models are improving, but can they catch up?

All models are wrong, but some are useful, as the saying goes. However, when looking at how Arctic sea ice decline is modeled, one might be tempted to say that all sayings are useful, but some are wrong. To be fair, I should be the last person taking a piss at climate models. Hundreds of brilliant scientists, engineers and IT specialists are giving their best every day to make supercomputers come up with scenarios that project future changes. Unfortunately, there is no Planet B to experiment on.

But we have come to a point where fake skeptics show up in television programmes (such as last week's BBC Newsnight) and use modeled predictions for Arctic sea ice in the 2007 IPCC Fourth Assessment Report as an argument not to be worried about the disappearance of Arctic sea ice, because "none of them shows it melting before the year 2070 on a regular basis in the summer" (quote from UK Conservative MP Peter Lilley).

As always, they're not telling the whole story:

This image (taken from the Climate Crocks blog) comes from a GRL research paper by Stroeve et al. that was published in 2007, detailing how models that participated in the World Climate Research Programme Coupled Model Intercomparison Project Phase 3 (CMIP3) were doing compared to observations (red line). The 2011 dot was drawn in, based on NSIDC data on September 7th of last year. Commenter Tim took the liberty of drawing in the new 2012 record. This picture saves us the 1000 words needed to explain how off models are when it comes to matching observations, which essentially makes their projections worthless.

But as the Arctic sea ice cover has changed radically in just 6 years, so have new and improved models started a new round of simulations and projections for the Phase 5 project (CMIP5) for the next IPCC assessment report. And again, Dr. Julienne Stroeve and her colleagues from the NSIDC, NCAR and the Voeikov Main Geophysical Observatory in Russia, have taken a look at how these models are faring in a new GRL paper that was published three weeks ago in Geophysical research Letters: Trends in Arctic sea ice extent from CMIP5, CMIP3 and observations.

From the introduction:

The rapid retreat and thinning of the Arctic sea ice cover over the past several decades is one of the most striking manifestations of global climate change. Previous research revealed that the observed downward trend in September ice extent exceeded simulated trends from most models participating in the World Climate Research Programme Coupled Model Intercomparison Project Phase 3 (CMIP3). We show here that as a group, simulated trends from the models contributing to CMIP5 are more consistent with observations over the satellite era (1979–2011). Trends from most ensemble members and models nevertheless remain smaller than the observed value. Pointing to strong impacts of internal climate variability, 16% of the ensemble member trends over the satellite era are statistically indistinguishable from zero. Results from the CMIP5 models do not appear to have appreciably reduced uncertainty as to when a seasonally ice-free Arctic Ocean will be realized.

This is a very interesting paper that is easy to follow. Two metrics are used to evaluate the performance of CMIP5 climate models: 1) The distribution of simulated extents over the period of observations (1953-2011) is used to assess how well the models capture the observed state of the ice cover, and then 2) Trends in simulated ice extent are used as a measure of the ability of the models to capture the response of the ice cover to global climate change. Quote:

It is possible that a model can capture the historical state but not the trend. We compare results of these evaluations to those based on the CMIP3 simulations. The CMIP5 models will become the main source of climate projections assessed by the International Panel on Climate Change (IPCC) in its 5th Assessment Report.

Two scenarios are used for the 56 ensemble members from 20 climate models in the CMIP5 archive: The representative concentration pathway (RCP) 4.5 future emission scenario, that stabilizes radiative forcing at 4.5 W m-2 in the year 2100, resulting in approximately 550 ppm of CO2 by 2100. The other scenario is the same CMIP3 20th century and future “business as usual” (SRES A1B emission scenario) model output. A1B attains CO2 levels of 750 ppm by 2100 and is hence a more aggressive scenario than RCP4.5. Models with more than 75% of their distribution falling outside the observed range of 6.13 to 8.43 million km2 were rejected. Of the 20 CMIP5 models, 17 models were retained, resulting in a total of 38 ensemble members.

Here's how things look for modeled, observed and projected September mean sea ice extent in the 1900-2100 period:

Figure 2. Time-series of modeled (colored lines) and observed (solid red line) September sea ice extent from 1900 to 2100. All 56 individual ensemble members from 20 CMIP5 models are included as dotted colored lines, with their individual model ensemble means in solid color lines. The multi-model ensemble mean is based on 38 ensemble members from 17 CMIP5 models (shown in black), with +/- 1 standard deviation shown as dotted black lines. Figure inset is based on the multi-model ensemble mean from CMIP5 and CMIP3, +/- 1 standard deviation.

I haven't drawn in this melting season's result, but it will obviously fall outside the 1 standard deviation of the CMIP5 multi-model ensemble. Some ensemble members are even lower, but that's because they started out much lower than the actual observations.

Results are described as follows in the paper:

Based on multi-model ensemble mean extents at the beginning of the 20th century, there is a 1.1 million km2 difference in the mean September extent between CMIP3 and CMIP5 (Figure inset, N.). During the period of satellite observations, the September CMIP5 multi-model ensemble mean tends to be slightly lower than the observed extent until 2007, after which it is higher. By contrast, the CMIP3 multi-model ensemble has a positive bias throughout the period of observations and especially during the most recent decade. Turning to the end of the 21st century, the CMIP5 multi-model ensemble mean never reaches ice-free conditions (defined here as less than 1.0 million km2), but the minus 1 standard deviation drops below the ice-free threshold around year 2045. Several CMIP5 models (CanESM2, GISS E2-R, GFDL-CM3, NCAR CESM, MIROC-ESM and ESM-CHEM) show essentially ice-free conditions by 2050, with the CanESM2 model having an ensemble member reaching nearly ice-free conditions as early as 2016 (0.54 million km2). By contrast, despite the more aggressive emission scenario (SRESA1B) driving the CMIP3 models, an overall more extensive sea ice cover is retained, with the minus 1 standard deviation reaching nearly ice-free conditions in 2075.

The same thing was done for March mean sea ice extent, with the following result:

The lower CMIP5 March extent compared to CMIP3 results in good overall agreement with the observations, though the observed values fall below the CMIP5 multi-model ensemble means in recent years.

Stroeve et al. also test whether the observed trend falls within the distribution of simulated trends at a specified level of statistical significance:

Turning to the modern satellite era, 1979-2011, more CMIP5 ensembles have a smaller rate of decline than observed, which at -0.84 million km2 per decade is nearly twice as large as the trend for 1953-2011. Forty-six of 56 ensemble members have trends outside of the 2 bound for the observations and 9 ensemble members have trends that are not statistically different from zero at the 90% confidence level. Although most model trends remain slower than observed, six ensemble members have rates of decline larger than observed. Overall, 64% of the ensemble member trends are statistically different from the observed trend at the 90% confidence level. In contrast, 85% of the CMIP3 ensemble members have trends that are statistically different from observed. The multi-model ensemble mean trend over the satellite period is -0.50 million km2 decade, which is 70% larger than the CMIP3 multi-model mean value of -0.35 million km2 decade.

It's clear that the CMIP5 models do a better job than the CMIP3 models used for the 2007 IPCC Fourth Assessment Report. But better is not the same as good. In this case 'less bad' would be a more accurate description. If Arctic sea ice continues melting at this rate, the question arises whether there is any sense in trying to optimize models. By the time they capture all the processes that are involved in melting, transporting and compacting the Arctic sea ice cover, it might already be gone. Maybe some of the money and human intelligence that go into models could be better spent on observational purposes (satellites, buoys, moorings) and the consequences that disappearing Arctic sea ice is already producing: changing weather patterns, methane release, permafrost melt and erosion.

As for the new IPCC report coming out next year: This time, a crazy melting season that shatters all previous records occurs just before the deadline and not after it. Will the seriousness and potential danger of an ice-free Arctic be reflected in the relevant chapters? Or will the IPCC again be too conservative (see this piece by Bryan Walker on the Hot Topic blog), hiding behind models that still haven't caught up with reality? The (lead) authors have their work cut out for them, but I'm sure they'll do a good job. We'll see what happens then.

Thanks goes out to Julienne Stroeve for allowing me to cover her important paper. Dr. Stroeve is currently in the middle of the ice pack to survey ice conditions and collect validation data (more on that later). To share her experiences she has started a blog: Ice Edge 2012

Comments

[johnm33]

Thanks Neven i've copied the pdf/w-page for later reading, i'm thinking this heat is placed to create enough snowfall further south to get the attention of the whole east coast of the usa.
Espen are they likely to get closer to mackenzie bay? where the anomoly seems highest.
It would be interesting to see an animation of the http://polar.ncep.noaa.gov/sst/ophi/color_anomaly_NPS_ophi0.png
page over the last 9 months.

[Espen]

John,

Without knowing it, Healy is probably on route to Dutch Harbor as a intermediate stop over, true Bering Strait.

[Kevin O'Neill]

Enno - the "Magical Ice Removal" paper you mention can be found by clicking on the 'Papers' tab in the top menu then selecting 'Sea Ice Cover.' The first paper listed is: Recovery mechanisms of Arctic summer sea ice S. Tietsche, D. Notz, J. H. Jungclaus, and J. Marotzke.

As far as the thread topic is concerned, since most of us are interested in models specifically as they relate to a seasonally ice-free arctic, the answer is that there is enough variation in model outputs that one of them is bound to be correct. I include Maslowski's Regional">http://www.oc.nps.edu/NAME/name.html">Regional Arctic System Model (RASM) at the Naval Postgraduate School as well as the CMIP5 models.

The real question then becomes which one are we to believe - since there is no real consensus? I'd put my money on Maslowski's regional model.

[Twemoran]

Neven

If the Alaskan Coastal Current were responsible, wouldn't this require that the upper 50m (depth of Bering Strait)on the Alaskan side be warmer than temperatures surfacing north of the Yukon Coast?

I'd expect the very high temperatures to occur wherever upwelling was present on the Alaskan side of the Strait if this were true.

Not saying that this couldn't contribute to what we're seeing, just that there has to be an additional source for the heat.

I believe there are moorings in Bering Strait that would give us the temperature of subsurface incoming waters, but haven't been able to find the data.

Terry

[Neven]

Terry, I agree. I just thought I'd throw out something that came to my mind. I don't how what sea bottom looks like from Bering Strait to the McKenzie estuary area, but probably just as shallow everywhere.

I believe there are moorings in Bering Strait that would give us the temperature of subsurface incoming waters, but haven't been able to find the data.

I've asked Dr. Rebecca Woodgate from the University of Washington twice, but she never answered. Maybe I should try again.

BTW, that NCEP/NOAA SST anomaly map from the
daily graphs page is created and updated by Dr Robert Grumbine. He has a great blog here. Maybe I'll ask him what he thinks of the dark red spot in the Beaufort Sea.

[LRC]

It probably is too simplistic, but I think part of the reason PIOMAS seems to be on track the best is that it has followed the path the ice seems to be going on. Where the other models seem to get hung up on is the local heat influences. As Neven pointed out in http://neven1.typepad.com/blog/2012/06/ocean-heat-flux.html a great deal of heat is coming from else where. There is also the debate as to whether one should look at area, extent OR volume. IMHO all 3 need to be looked at, because if you take an ice cube and put it in water it will melt at a very given rate. If you on the other hand grind that ice up and scatter it over the water it will melt much faster depending upon how thinly scattered that slush is. Therefore you need to know how much ground it covers (extent), how spaced out it is (from area), and how thin it is (from volume).
The argument that melt would flatten out after a time I can not see how that hold up. If you presume that melting would decrease the temperature of the water then yes a flattened out melt would be the case, but since the Arctic waters would seem to be only increasing both from local heat and the heat flux from the currents (which I do not see shutting down) you are only left with the PIOMAS model that will only be out by a very few years only if the best case non melt years occur one after another. This year proves that the ice is so slushy even a mediocre melt season makes a big dent in the ice. You get a '07 happening next summer and I do not see it holding out to the end no matter what the winter is like.
That is where another part of most models fail I believe. When the ice was a solid sheet, you could determine what it would be like just by temp alone. Storms did no mater very much because the sheet would hold together. Now you have a pile of slush and even if you have no storms that ice will still be slush with a thin layer of solid ice starting next melt season. You bring storms into the mix and it is anyones guess as to what it will look like at the beginning of melt. My hunch is that the numbers will look good at the start and then nose dive. You have too much heat around NH. Combine that with the weakening for the Jet and ocean currents allowing more incursions into there, which means more heat entering into the Arctic. The models generally seem to have missed that part.
The scary part then comes back to me is that the seem to be doing the same thing with the GIS.
I would make a guess that how cold Europe is, is directly related to how much heat gets trapped in the Arctic and GIS. The SST and air temps might not show it, but the ice shows it. If that area again has a very bad winter, watch out that cold is coming from somewhere which means you have a massive heat exchange going on. You are running out of cold in the Arctic only one place left.

[Fairfax Climate Watch]

Hi Werther, 40 years was serious. P-makers numbers don't include accelerating forcing or rapid and simultaneous onset of feedbacks - a combination of events likely never seen on this planet, ever (excluding the last 150 years).

So no irony.

[Fairfax Climate Watch]

I like P-makers thinking though, it is a nice way to introduce oneself with the quantities of energy involved in the thermodynamics of the biosphere.

[Lennartvdl]

M. Owen: "Until GIS is gone in something like 40 years from today".

How could that possibly happen in the real world? I follow Jim Hansen in his concern that GIS and WAIS could disintegrate faster than mainstream glaciology thinks likely, but even Hansen does not seem to think GIS could collapse in something like 40 years.

If I understand Hansen correctly he thinks that BAU could lead to maybe 40 meters of SLR in the coming 800 years, so about 5 meters/century, with maybe 2-3 meters until 2100.

This risk seems also included in this recent estimate by Meehl et al, by extrapolating past 2300:
http://www.nature.com/nclimate/journal/v2/n8/fig_tab/nclimate1529_F3.html

My impression is that the relatively slow SLR in the past and missing feedbacks in climate models have deceived glaciologists into thinking it cannot go faster than that. Hansen argues that the current and future forcings are likely much stronger than those in the past, so SLR will probably also be much larger than before.

There will be constraints, but these are probably wider than the mainstream thinks. How they could be wide enough to make complete collapse of GIS possible in 40 years, I can't imagine.

[Rob Dekker]

After this jaw-dropping mega-melt of Arctic sea ice, which again drops way below the projections of even the latest CMIP5 models (see Stroeve et al 2012), the much-less-talked-about, but even more important decline in spring snow cover over the Northern Hemisphere finally seems to get some well-deserved attention.

On NPR today :
http://www.npr.org/2012/09/24/161701420/as-arctic-ice-melts-so-does-the-snow-and-quickly

Which puts some scientific evidence behind Neven / MA Rodger post in early July :
http://neven1.typepad.com/blog/2012/08/the-untold-drama-of-northern-snow-cover.html#tp

Here is the scientific publication in GRL :
http://www.agu.org/pubs/crossref/pip/2012GL053387.shtml

With the interesting quote :

The rate of loss of June snow cover extent since 1979 (-21.5% decade-1) is greater than the loss of September sea ice extent (-10.8% decade-1) over the same period.

In other words, snow cover reduces at twice the rate that ice cover reduces.
Since snow cover anomaly occurs early in the melting season, when the sun is still high in the sky, it warms the Northern Hemisphere much more than ice cover changes. A back-of-the-envelope calculation shows that the June 2012 snow anomaly has added some 1000 TW to the early melting season, causing extensive wild-fires in the Boreal forests in Siberia (see Siberia on fire), as well as contributed (possibly very significantly) to the 2012 mega-melt of Arctic sea ice.

Interesting is also that, just like for the Arctic sea ice anomaly, this snow melt anomaly is twice as large as the CMIP5 models project.

It looks like models indeed have a hard time keeping up with the rapid changes of the Northern Hemisphere cryosphere that are unfolding as we speak.

I start to wonder if maybe the changes we cause to our environment may unfold more rapidly than the improvement in the models that we need to project these changes.

[Jim Williams]

Lennartvdl, what if the Labrador current collapses and changes direction, and the Gulf Stream no longer detaches from North America?

[Lennartvdl]

Jim, you have to help me here: what do you expect to happen then? How will it make the ice of GIS melt or flow into the ocean fast enough to make sea level rise 5-6 meters in 40 years?

[Jim Williams]

Lennartvdl, if the Gulf Stream starts flowing west of Greenland then instead of palm trees on the southern tip of England you have palm trees in Greenland. (Not sure about what happens to England.)

They still don't know why the Western Boundary Current (the Gulf Stream) detaches from North America at Cape Hatteras, but it may have something to do with the cold Labrador current flowing south. The Labrador current seems to be faltering, and again they don't know why.

If you look at a world map of current SST anomalies you'll see that there is currently major heating to the south and west of Greenland; which I don't think fits into any known teleconnection pattern. Someone just noted in another thread that there is cold water piling up north of Iceland.

Right now all these current changes are just random fluctuations. (As in they don't know why they are happening.) But if they happen to be part of a modal change then all Hell will break loose.

[Lennartvdl]

Jim, I don't know if that could happen, but even if it did, how could it make GIS collapse in 40 years? That would mean at least 5 meters of SLR by GIS alone, so let's say about a meter per decade. How could the ice from GIS melt of flow fast enough into the ocean?

Even Hansen seems to think that's physically impossible, since it would mean about all the extra energy in the earth system would be used for melting ice from GIS and there would be a negative feedback thru an 'iceberg cooling effect'.

I agree that faster collapse than the mainstream thinks seems possible, or even likely, but even then there must be some constraints, kinematic, energetic or otherwise. Is Hansen missing something here? Or do I misread him?

[Seke Rob]

Re some perceived Gulf Stream panic, map off the wiki commons: http://en.wikipedia.org/wiki/File:Thermohaline_Circulation_2.png showing a GS split off going past the Greenland tip. And this is an interesting read http://www.nature.com/scitable/knowledge/library/abrupt-climate-change-during-the-last-ice-24288097 to include a "Salt Water Oscillation Hypothesis". That one I'd not stumbled on before.

[r w Langford]

I found this article on model accuracy. Hope it is not old news.
http://www.springerlink.com/content/40326p42218482u4/?MUD=MP

[Jim Williams]

Seke Rob, it is the way the speculation about the AMOC seems to be the exact opposite of what seems to be happening that I find so interesting -- though it is a bit frustrating that all the noise of that speculation makes it hard to find the signal of what is really going on up there (try any sort of search on the topic and you'll find it filled with speculation and bereft of data).

Obviously, I don't trust the current models as far as I can throw them, so it wouldn't surprise me at all if they got the fact of AMOC right but the sense of how it will play out completely reversed.

What we have seen so far with warming is a poleward shift in the Western Boundary Currents. Since we don't even know why the Gulf Stream separates from North America it isn't unreasonable to speculate that it will decide to stop separating from North America.

[Jim Williams]

r w Langford, in Computer Science we call it GIGO -- Garbage in Garbage out. The paper basically said we don't know what the current state is very well and we don't have a clue what it does.

(I think "natural variability" is a cop out really. It's just another way of saying we don't know how it works.)

[Jim Williams]

There are very good reasons why Medicine is considered an Art, and not a Science. The same reasons apply to predictive climate modelling. In both cases we might understand a little here and there, but we simply don't have the understanding of the whole which allows making confident projection of the response to stimulus. The doctor knows that drug x helps some patients some of the time. The climatologist knows that forcing x changes quantity y some of the time.

In fact, the Medicinal Arts and Weather Forecasting are both very good examples of Useful Arts slowly working towards becoming Sciences. Climatology isn't anywhere near leaving the stage of being an Art -- and hasn't even reached the stage of being a Useful Art yet.

So far, we know that adding CO2 gives the patient a fever, and that's about all we know.

[Yazzur]

Over at Tamino's there is an interesting analysis of sea levels - since we discussed it at some length here it is worth a visit to read.

http://tamino.wordpress.com/2012/09/26/unnatural-hazards/#more-5663

[Seke Rob]

Saw this also in the Tamino thread [Burton and daveburton probably same], linking to SkS on The Minimum predictions... Toninô et al did far out worst: http://www.skepticalscience.com/lessons-from-past-climate-predictions-arctic-sea-ice-extent-2012.html

[Jim Williams]

So far, trends are doing better than models? Have I read that right Seke?

(We can ignore the socially affected projections.)

[Seke Rob]

Zhang and Folkert did not do too bad compared to the real statistic wizards, but then the statistics are not describing the physics, the models are trying to emulate.

[Jim Williams]

The models are very good for their intended purposes, but I don't see prediction as one of the purposes -- and I do see the whole IPCC project as sadly misguided. Maybe after we can properly predict 'now' we can consider predicting the future.

For now, on the whole the trend is probably going to be the best predictor. That prediction looks like "soon".

[Fairfax Climate Watch]

GIS melt when there is surface melt at sufficient rate to penetrate deeper and deeper into the ice (i.e. this decade and further back?):

1. surface melt: heat, sun, rain. Albedo change feedback, surface dirt layer formation feedback, snow loss albedo feedback.
2. meltwater/rainwater flows into the cracks and existing tunnels of the ice, melting deeper down; liquid water freezes, expands, cracks ice further. more downflowing water flows, melts deeper, freezes, cracks and tunnels expand deeper still.
3. downflowing water reaches base of ice, melts horizontally. Freezes, pops the ice upwards. More water reaches the base. The water stops refreezing, but stays liquid. the base is near zero C anyways. horizontal pockets of icy water form. More downflowing water reaches these pockets.

4. Eventually they melt out enough ice in this basal layer that the remaining support columns of ice are crushed under the weight of up to 3km of ice above. The liquid ice slurry in the base layer is forced back up the tunnels and cracks, and out horizontally along ice-rock interface, as well as down, breaking up some of the rock bed and sediment layers.

5. because much of GIS base is up to 500 meters below SL, as this process of slurry basal layer formation and destruction occurs, the liquid water tends to pool towards the lower elevation sections of the ice, and the slurry layer grows in size and depth.

6. Finally, the slurry layer grows large enough that the overlaying ice exerts enough pressure to etch out a pathway of least resistance out the side of the ice. There are three locations of primary likelihood, where only brief sections of topography rise above SL. In a blast, the slurry layer breaches the side of the ice sheet, spewing churned up sediment, rock, and ice out. Over months, the pressure equalizes, and the interior basal slurry layer (and connected tunnels above this layer) drain down to sea level.

7. Now, the sea mixes into the interior, flowing through the breach area. Warmer, salty sea surface water flows in and circulates inside, pushing the lighter fresh water out. A circulation pattern establishes itself and begins to rapidly erode/melt the ice. Now, there are air spaces, not mostly liquid water-filled spaces above sea level in the interior fractured zone of the ice sheet.

8. The ice continues to melt, and the cold fresh water that flows out of the breach area lead to localized cooling and rainfall and mist, further accelerating local ice loss in the breach area.

9. The sea water continues to circulate in the interior, rapidly melting the ice which falls into the slurry layer. Now, giant blocks collapse from above, and soon, the surface of the GIS crumbles and falls in on itself, turning into a pile of blocks ranging in sizes from a few centimeters to kilometers long. The ice sheet is now a crushed-ice pile, sitting in a pool of circulating salt water.

10. Air can now flow out form the interior because it has been shattered and is a jumbled pile of blocks. super-cold air from the center (where the ice is coldest) sinks and spills out the edges of the GIS, and especially in the summer, warm humid air from the ice-free Arctic Ocean and lower seas zip into the top and sides of the ice rubble pile. The humid air quickly cools and releases its water, thus causing a rain and mist to fall inside the rubble pile.

11. by this time, the whole thing is melting rapidly, and local weather has centered around the temperature differences, with intensely severe weather occurring frequently. Soon the whole thing is gone, and there is just a bare island with a big saltwater lake in the middle, Greenland.

12. Meanwhile similar processes have likely been happening in Antarctica, and it too by this point in time, is ready to breach its edges and start a rapid decline.

13. It should be mentioned, that the average ocean temperatures would by changed only slightly by all this ice melt. Although the term slight is loaded, because it would be enough temperature change to alter weather, circulation, and possibly lead to the extinction of some/many marine species (and possibly some/many terrestrial ones too). It is conceivable, that a rapid outflowing of ice water could get quickly transported to deeper layers of the ocean, and that in the colder polar seas, warmer deep water would get shifted upwards, thus perpetuating the rapid melting. Also, Antarctica also has a large portion of its land below sea level.

This is how I see it could happen; constructive feedback welcome.

[Fairfax Climate Watch]

On Hansen, I havn't run across statements by him that says SLR has a maximum upper limit. In fact, I just don't see anyone saying that there is a max, or when they do, their evidence is weak in my eyes. I'm waiting to find something that says the oceans can not physically transport enough energy via the atmosphere to melt the ~30 million cubic km of ice at the poles in a few decades or less. We already see strong evidence of an accelerating hydrological cycle at the North Pole. And of course, the circulation of the oceans and atmosphere is changing, so using current circulation patterns to justify a limit to energy transport wouldn't convince me either. Although, I would be interested to read such an analysis, and it might prove useful if well done.

[Werther]

Morning M. Owens,

What you describe here is a ‘Jökelhlaup’ on an almost continental scale.

Our member bloggers with knowledge of maths in physics might be able to figure out how much energy would have to be transferred into the GIS to make it pass. For my feeble imagination it seems impossible to project that on a 40 year timescale. The only part

I hold anything like that possible is on the southern tip of Greenland. The remaining Cold Pole and the position of the weakened Polar jet are, to me, capable to create a lingering gradient in the melt process somewhere between the South Dome and Summit. I think, although the time frame is geologically short, the retreat would still be a somewhat orderly process likewise to the retreating glaciers we see in the high mountain ranges. The base of these Greenland glaciers would still be the mountainous spine from Cape Farevell to Mount Forel. The ‘split’ or gradient zone would then be north of Ilulissat to the Kangerdlugssuaq Fjord.

For the sheet parts between the orderly retreating glaciers in the south we could individually see the fate you describe for the whole GIS.
In my view, the large northern sheet part would desintegrate during the period 2060-2300. The last glaciers on Mount Forel and its surroundings would also last into the 2300’s.

[Lennartvdl]

Hansen & Sato write about the 'iceberg cooling effect' (p.24):
http://arxiv.org/ftp/arxiv/papers/1105/1105.0968.pdf

"Exponential change cannot continue indefinitely. The negative feedback terminating exponential growth of ice loss is probably regional cooling due to the thermal and fresh-water effects of melting icebergs. Temporary cooling occurs as icebergs and cold fresh glacial melt-water are added to the Southern Ocean and the North Atlantic Ocean."

They then show results from some model experiments (p.25):
"By 2065, when the sea level rise (from ice melt) is 60 cm relative to 2010, the cold fresh-water reduces global mean warming (relative to 1880) from 1.86°C to 1.47°C. By 2080, when sea level rise is 1.4 m, global warming is reduced from 2.19°C to 0.89°C."

So this may suggest Hansen & Sato think about 80 cm of SLR in about 15 years is the maximum rate of SLR, or about 5-6 meters per century, if this rate could be sustained for so long. It would mean about 2.5 meters of SLR around 2100.

That would be from GIS and AIS together, so maybe about 1 meter from GIS at the most during this century. The next two centuries GIS could then maybe contribute 2-3 meters/century, which would mean (almost)complete disintegration by about 2300.

This seems in line with Werther's idea about the possible collapse of GIS. The process might very well be along the line of M. Owens' scenario, for all I know, but then a bit slower than he suspects possible.

It would be interesting to know what scientists like Hansen and Pfeffer think of these speculations.

[Artful Dodger]

Hi Mike, Werther,

This paper might be of interest:

Larsen et.al (6 Aug 2012) "A satellite perspective on jökulhlaups in Greenland", Hydrology Research, in press

The fulltext pdf is behind a paywall, but this Powerpoint is not, and makes the case nicely ;^)

Cheers,
Lodger

[Jim Williams]

M. Owens, the main problem I see with this scenario is ice strength. I don't think any sort of hollow could be maintained under Summit. This would change the shape of events in your points 6 and 7.

If you want to close off any proposal that there won't be enough energy locally available simply have the Gulf Stream reattach to North America and flow west of Greenland into the Arctic. (Note the warm water off New England last winter and current records in the same location.)

[Russell McKane]

Owen
A few points from my reading over the years that as far as I have read backwards the discussion appears to have missed.

1. Gravitational spring back from the centre of the GIS and WAIS are factors that have an influence on end sea level rise. This was one factor that was part of revising the WAIS contribution from 6 meters down to 3.5 meters in recent research. (sorry I can't access articles as my hard drives have suffered majoy meltdown and I am waiting on achieving some bounce back of my own)
2. Loss of Ice mass in GIS and WAIS will affect gravitational distribution as water redistributes around globe. This will cause a change in Poles and earths spin (Net outcome aside from massive techtonic / earthquake affects and as for any modeling predicting I think we have stuff all ability to model this one with any accuracy close to what we have managed with Arctic ice melt)
3. a rise of 0.6 meters has the potential to breakoff and float the WAIS from purely hydrolic pressure of floating Ice shelves and the geological features of the Pine Island Glacier (PIG)
So the GIS may well precipitated rapid sea level rise well before the 1 meter mark is reached.

[Jim Williams]

Hi Russell, that 0.6 in your point 3 is the first time I've seen an actual number attached. Would you happen to have a reference? (I'm not doubting it, but I want more information.)

A number that small could have important implications, especially if smaller numbers would have smaller similar results. In fact, 0.6 meters as measured from what year?

[Russell McKane]

Jim
As I said my main computer where I have most stuff is not available, I will see if I have it on my old backup drive tomorrow and post as soon as I can.

[Twemoran]

M Owens

Your #4

Do we know with any certainty what the GIS is presently grounded on. Is it bedrock thruout, some bedrock & some sediment/gravel, or mainly sediment/gravel.

If anything but mostly bedrock I'd guess the process you've described could proceed fairly rapidly.

Are there land forms in areas once covered by ice sheets that indicate a similar process has occurred in the past?

Terry

[Fairfax Climate Watch]

I have a figure of 19.8 deg. C lowering of temperature in the top 360 meters of worlds oceans to supply the energy needed to melt the ice caps (to zero).

spread that over 20 years, and its 0.1 deg. C. temperature drop per year for the top 360 meters of ocean to do the same thing.

That checked the work for that result, and it looks right at first glance, I'll check in more detail when I get a chance Friday.

[Lennartvdl]

Russell,

Would that 0.6 meters for WAIS break-off imply this has happened before during interglacials like the Eemian and Holsteinian? Sea levels seem to have been about 8-10 meters higher then at maximum, with a maximum rate of SLR of maybe 2.5 meters/century (during the Eemian).

Lennart

[skywatcher]

M Owens, I don't think your first four points are very physical - you're neglecting that moulins close up as well as open, that ice flows (thus destroying moulins and englacial conduits), that the interior of an ice sheet is very cold, and that most water that reaches the bed drains from under the ice, driven by the very large lateral pressures. Most moulins are nearer to the edge of the ice sheet in the ablation and slush zones, locations from which it is hard to pool water under the middle of the ice sheet.

At the risk of suggesting teaching a grannie how to suck eggs, I'd recommend reading up on glacier processes (Benn and Evans "Glaciers and Glaciation" or Paterson "Physics of Glaciers" might be a good start), and perhaps having a good read of research publications concerning englacial and subglacial hydrology. If this is all old news to you, please forgive me, but IMHO your hypothesis as it stands is not viable.

I'd be quite concerned enough with accelerated glacier flow and surface melt. But with Greenland's topography not conducive to a rapid collapse (peripheral mountains to hold back the ice sheet and restrict access of seawater under calving ice streams) we can reasonably hope that these processes, while operating fast on a geological scale, will be slow enough to give us good time to adjust to the large SLR implications. But there's plenty else to be concerned about in the meantime (weather pattern changes not least)!

[Lennartvdl]

skywatcher,

Based on your knowledge of glacier processes, what would you consider reasonable maximum rates of SLR in the coming centuries, and why?

Hansen seems to think 5-6 meters/century would be possible under BAU. Rohling suggests 2.5 meters/century was the maximum rate during the Eemian. What is your estimate?

To me this question seems quite urgent for proposing and deciding on mitigation policies in the coming years/decade.

[skywatcher]

Lennartvdl, my knowledge is a lot more limited than the likes of Hansen! You'd get a better and fuller answer from a professional glaciologist or ice sheet modeller. If I were to stick some flags in the sand, so to speak, I'd go for 1-2m SLR by the end of the century, based on gradually accelerating contribution from the ice sheets. I suspect Hansen may be on the high side, but a lot depends on processes that we are not completely on top of, such as encroachment of warm water under ice shelves or dynamic acceleration of ice streams. There is an outside chance that ice sheets have the potential to deliver a much larger burst of SLR (along the lines of a Meltwater Pulse 1A, up to 10m/century), but I don't think Greenlnad has a suitable configuration for such an event. West Antarctica on the other hand might have more potential for that - much would depend on the consequences of the loss of the Ross and Ronne-Filchner Ice Shelves, whenever that happens. But such an event could be many centuries into the future, or even not at all.

To me, the most likely actual outcome is of a gradual acceleration of sea level rise over the coming centuries, until the ice sheets return to being in mass balance with atmospheric temperature. That may result in total loss of ice sheets and large sea level rises (dependant on whether we find a way of sequestering CO2 and how warm the planet gets), but that ice sheet loss will be (so far as people are concerned) a "slow" process. It's quite enough SLR for low-lying cities and countries to worry about, but I'm more concerned in the short term about ocean acidification and of the impacts of temperature rises/albedo changes/weather pattern changes on agriculture. Not that we should take our eyes off any one issue to solely focus on another!

[Lennartvdl]

skywatcher,

I agree that in the short term in most places other problems than SLR will be more urgent for adaptation. My concern is that the risk of SLR is being grossly underestimated, even in Holland where I live.

Meltwater Pulse 1A had a rate of SLR of 4-5 meters/century, as far as I know, maybe as a consequence of circumstances that do not apply in the future. But who knows?

The main argument Hansen offers for his higher projections is that the current climate forcing is much stronger than the initial forcing during earlier interglacials. I'm still not clear on the accuracy and implications of that argument, so would love to hear others on that.

Lennart

[Jim Williams]

skywatcher, what about the fact that the hard paleological evidence is for sudden change? When they talk about changes "in under 100 years" this is with data which cannot measure changes in timespans under 100 years. All the "point in time" data is for extremely rapid change, such as massive flooding in southern Washington State which happened "in less than a day", or the Lewis and Clark overthrust where 26 miles of rock moved over the existing surface "in less than a day."

We have little geological evidence for gradual changes over time. We a lot of have evidence for sudden changes.

[Chris Reynolds]

Bangs head on desk...

[Chuck Yokota]

Hello; thanks to Neven for this site and to everyone for their informative contributions.

Since the GIS is being discussed, I would like to ask if the spreading microbial staining of the ice is known and discussed.

http://ajw.asahi.com/article/behind_news/social_affairs/AJ201209280006

[Lennartvdl]

Jim,

Do you have evidence of more than 2.5 meters of SLR per century during an interglacial? Do you think it could be more than 5-6 meters/century in the coming centuries? What do you think of the potentially limiting negative feedback that Hansen calls the 'iceberg cooling effect'? Could that be overcome by a change in ocean currents, as you seem to propose?

Lennart

[Lennartvdl]

Chuck,

Interesting, hadn't seen that mentioned before. Another positive feedback by lowering albedo? Or otherwise?

Lennart

[skywatcher]

Lennart - don't get me wrong, I'm not advocating ignoring SLR! My thoughts are that I do not expect the GIS to suddenly collapse, given its configuration. The current forcing is very large, but as far as I know, it's not (yet) big enough to waste the ice sheet entirely and quickly, and there is an awful lot of ice to melt there. But if you're in the Netherlands, I can certainly sympathise that SLR would be the first concern.

Jim - "palaelogical"? (palaeoecological, palaeoenvironmental?) There's copious evidence for gradual changes over time, as well as some rapid, dramatic events. You cannot compare a glacial lake drainage flood (which is always going to be rapid) with other ice processes like melting or glacier retreat (or any number of other geomorphic processes), which can perfectly well be gradual. Even with the large forcings involved, you need to find a way to allow 3 million cubic kilometres of ice to melt or discharge quickly into the sea. With mountains round the edge of Greenland, this is not as easy as it first appears. The best estimates are that deglaciation will take many hundreds, perhaps thousands of years. The estimates could, of course, be wrong, but there is no a priori reason to think so... yet.

Knowing a little about thrust faulting from the Moine Thrust in Scotland, I'd be interested if you could point me to a reference suggesting that the Lewis Thrust occurred and moved 26 miles "in less than a day"? Aside from the obvious issues in dating such an event so precisely, the only reference I found suggested it occurred between about 72 and 58 million years ago. A day seems a wee bit fast for 26 miles of fault movement? Catastrophism has its uses (K-T springs to mind) but is not the only answer to every question. Gradual processes have played a big role in shaping many landscapes.

[Jim Williams]

What I don't have, Lennart, is evidence that that 2.5 is per century rather than per one year somewhere in that century. The numbers are averaged over a period of time, but there is no reason to believe that the rises happened as an average -- and a fair amount of evidence that the rises happened as events.

I'm saying that the slow change theory has nothing to back it up. The norm is the earthquake, the volcanic eruption, the collapsed ice shelf.

A claim that the collapse of the WAIS will wait until next century is worth reading to see why they think it would be that timeframe. A claim that the WAIS will melt out over millenia stinks and I'll not read it without a lot of external evidence that the claim might have merit because slow changes are the exception, not the rule. I don't have time for the speculation.

[Jim Williams]

skywatcher: "The estimates could, of course, be wrong, but there is no a priori reason to think so... yet."

Given recent history, there is no a priori reason to accept them either.

When watching the discussions of current global climate modelling I think about all the time I've spent reading the National Hurricane Center's Forecast Discussions over the years -- and they have models that have been actually tested.

It will be a long time before our climate models are any better than sticking one's fingering in their mouth and holding it up in the air.

[skywatcher]

Catastrophism also depends upon your frame of reference. Sea level rise over the past century has been apparently gradual, with acceleration up to the present 3mm/a. But on the scale of the Holocene, it's extremely fast! A palaeoclimatologist 100,000 years in the future might have trouble determining if it was a single "catastrophic" event or not, rather than a progressive gradual rise. [which is very fast for geological timescales]

For glaciers, it depends on topography - which is of course why the WAIS is more susceptible to rapid deglaciation than the GIS. The question is most probably a matter of when the WAIS will go fairly quickly, and surely more quickly than the GIS (Jim I think we're in agreement there), but the tipping point for the WAIS is unknown - it may be soon, may be some distance away. When it goes, it's worth bearing in mind that what the Earth thinks is catastrophically quick, and what shows up in the palaeoenvironmental record as quick, on human timescales may be "slow" (ie notably longer than a human lifetime).

[Chuck Yokota]

I have a hard time imagining that a single collapse event could involve all or most of Greenland. Its 2655 north-south length is farther than the distance between Halifax and Miami.

[skywatcher]

Jim, if you're comparing GCMs or ice sheet models (two different things in themselves) with hurricane models, I think you're comapring apples with grapefruit. And as such, I think you lose a lot by allowing doubts based on weather models to colour your views on GCMs - which have a great many successful elements, even if some, like the sea ice, are clearly poorly represented.

And I don't think you've really supported your 20:18 point about sea level - just look at the past century as an example - all the sea level rise didn't happen in a single year! As such, there is very good reason to think that rises can happen at rates comparable to the averages, rather than individual catastrophic events. We should still be concerned about the rate of acceleration in SLR, and keep a close eye on the ice sheets for signs of more rapid changes of course.

[Jim Williams]

skywatcher, weather modelling has the benefit of repeated experiments; which GCM do not. The comparison is not in global modelling's favor. Also, you've missed my point entirely. My point is that the GCM as a prognostic tool are a dangerous waste of time. (They are very useful as an analytic tool.) I'm not claiming that I can make good predictions. I'm claiming that they cannot either.

Chuck, as a practical matter, neither can I. It seems unlikely that the GIS located in a bowl can be destroyed so easily -- however, I don't see and good arguments given the current state of our understanding why not.

On the other hand, a goodly chunk of the WAIS seems to be just waiting for a push.

[Twemoran]

Chuck

Very much liked your post re the microbes, I'd assumed that what we were seeing was an accumulation of soot dating back possibly to the age of steam.

Terry

[Espen]

In my "short" time on this planet, + 50, I have experienced an average sea level rise at about 25 cm, some places more and other places less.
These estimates are first hand observations or talking to locals (fishermen) in different parts of the world. (Africa, South Asia, South East Asia and Europe), what is the numbers observed by scientist and researchers, and these numbers be confirmed?

[Lennartvdl]

Jim,

Agreed that an average doesn't show variations on shorter time scales. But to follow your extreme suggestion, what process could cause 2.5 meters of SLR in one year, implying a stable sea level the other 99 years?

[Kevin O'Neill]

Jim Williams said "...the Lewis and Clark overthrust where 26 miles of rock moved over the existing surface "in less than a day."

From Geological Survey Professional Paper 294—K
The Rocks and Fossils of Glacier National Park: The Story of Their Origin and History, The Lewis Overthrust

Millions of years probably elapsed between the time when the overthrusting began and the time when it completely ceased. During this long interval, the overthrust slab must have moved very slowly and with frequent pauses. Though the total displacement eventually amounted to many miles, some of the individual movements might have gained only a few inches before cumulative resistance forced a halt.

[Fairfax Climate Watch]

“We found clear evidence that supraglacial lakes—the pools of meltwater that form on the surface in summer—can actually drive a crack through the ice sheet in a process called hydrofracture,” said Das, an assistant scientist in the WHOI Department of Geology and Geophysics. “If there is a crack or defect in the surface that is large enough, and a sufficient reservoir of water to keep that crack filled, it can create a conduit all the way down to the bed of the ice sheet.”

[Fairfax Climate Watch]

As far as the 'bowl' somehow stopping GIS slow disintegration, yes - from the perspective of slowing glacial flow (i.e. the solid ice from sliding and deforming towards the sea). But, for GIS rapid disintegration, NO. From the perspective of accelerating quantities of water reaching the base of the glacier, NO. This bowl, will fill with a slurry IF there is a sufficient rate of meltwater reaching that layer of ice. There WILL BE a sufficient rate of meltwater IF the Greenland surface keeps melting faster, and IF it keeps raining harder over the ice. (How much faster do you think the surface will melt if the rainfall increases to a foot per year? How about 3 feet?) Then, when the bowl is full, it will find a way to drain to the ocean, and soon, the breach event I mentioned above would be unstoppable. If the water reaching the bottom melts out some of the ice there, there will not be an immediate pressure problem, because there will be a matrix of melted areas and the still solid ice areas will be sufficient to support the few percent volume of the bottom that is melted out, again in a matrix-like fashion. - and keep in mind when ice melts, the resultant water takes up less volume. Yes, the ice deforms and fills back in over time, and yes the moulins fill in. But new ones also form, I don't think anyone is willing to suggest that IF water is ALREADY reaching the base, that more melting up top and more rain will reduce the amount of water reaching the base as opposed to increasing it. It’s when this slurry finally melts enough of the supporting solid ice to break that critical support layer that pressure on the slurry pockets goes from nada to hasta la vista. Think pressure washing times a billion and then a billion more.

AND we have in the lovely article posted above about microbe-driven albedo, a wonderful quote from the guy on the ice, saying to the journalist, "I didn't think it could rain this much on the Greenland ice sheet." Hmmm. Indeed.

As to the previous assumption mentioned that the 'dirty' looking ice was from soot from the last 150 and more years. You weren't far off in your first impression. Life requires essential elements and nutrients. And thus, the microbes growing on the surface of the ice now are taking full advantage of the increased CO2 (presumably some are photosynthetic, as would be expected wherever microbial communities are exposed to sunlight) AND soot, AND nitrogen, AND dust, AND a whole host of other particles humans have churned up into the air over 100's and even many thousands of years. Of course, our impact has only been growing stronger, and by a lot. And also, don't forget that naturally there are dusts and aerosols and all kinds of things in the air too, but just not as much. So, yes, that soot and other human pollution is microbe food. And once those essential elements get into that layer of microbes in the ice, they are likely going to stay there, being recycled/cycled over and over ad infinitum by the different species in the community. Carbon, oxygen, and nitrogen tend to escape back to the air, but they also get pulled back in from the air. At least, this is what happens in other microbial communities, like in water and soil. The carbon may be the crucial limiting nutrient though, allowing these microbes to really take off by fueling the photosynthetic aspect. CO2 really boosts growth rates, its amazing, especially in aquatic environments, and presumably, even though this is ice, the microbes use water, and have similar CO2 nutrient limitations that aquatic photosynthesizers face. And of course, warmer temperatures. Once that layer of microbial living material and detritus builds up, it will also increase the capacity to hold heat, thus giving it an increased time to grow at accelerated rates before the ice pulls its temperature back down. That microbe community must be quite fascinating. AND, last but not least, the oceans contain lots of nutrients, and they also contribute significantly to the nutrient content of the air. SO, when the arctic sea ice is reduced in extent, more open water means more sea-sourced nutrient content in the air available to deposit on the ice surface. Feedbacks galore!

And if you’ll bear the scattered response, the base of the Greenland ice sheet has all kinds of junk down there. From bedrock to thick sediment layers. That sediment probably smells terrible!

[skywatcher]

M Owens - how familiar are you with glaciological literature, particularly on englacial/subglacial drainage, ice sheet plumbing, formation/stability of subglacial lakes, and concepts like hydraulic potential? Also on monitoring of englacial/subglacial lakes through interferometry, altimetry and radar? How do you get significant meltwater to the base of the centre of the Greenland Ice Sheet when the centre is dominated by the "dry snow zone", and subglacial drainage flows towards the ice sheet edge, driven by pressure gradients? How do you pool large amounts of meltwater under the ice sheet when stable pooling regions are under the ice divides (under the dry snow zone)? Why do you think the subglacial hydraulics are insufficient to evacuate the meltwater reaching the base, most of which is entering near the margins and leaves at the margins due to the large hydraulic pressure gradients present on sloping parts of the ice sheet? I think there are a lot of questions remaining with your hypothesis, and there's a lot of research out there with which you can improve your ideas.

[LRC]

@ skywatcher: I claim total ignorance on topic of glaciers, but I have found out that the dry-snow you are referring to only occurs in the high altitude regions of the GIS. Also buy definition of dry snow one has to revisit which sections are true ice snow as a good deal saw melting this year.
If you read M Owens argument, he was not talking about the high altitude regions, he has talking about the depressed bowl regions. The argument has always been that those parts would move very slowly because they have to move uphill to get away from their area. What he was saying that if those bowls got filled up with water from melt water drilling down into the depression, then the ice no longer has to move uphill, there radically increasing the speed at which it can travel.
We do have extensive knowledge of how glaciers work, The one issue that comes into play about being too set on what is or is not possible to occur with glaciers is GW. At no time in known geological history has the been such a fast increase in warming and with it all the weather related influences. It is that which could be a deal breaker as to what will happen on both Greenland and Antarctica.
We are discussing in this post about how models missed the melting of the Arctic so badly. Could not the same thing happen on the GIS, because we get too determined we understand how everything works with glaciers, when in fact that is still massive amounts to learn? Then you end up with models making similar mistakes again, because of presumptions that prove out to be wrong?
Models will only improve if you are willing to learn from what went wrong before. The will never get better if you end up making similar mistakes all over again.

[skywatcher]

Of course, LRC, I'm neither suggesting that current ice sheet models and physical understanding are perfect, nor are they immutable to change in the light of what is a pretty much unprecedented forcing. It would go without saying that I am extremely concerned about how much faster the sea ice melt has been compared to the models, and I imagine that is pretty humbling for those coding the sea ice components of existing GCMs.

But for the GIS there is a lot that glaciologists already do know about glacial hydrology and ice sheet monitoring, and I am unconvinced that M Owens is sufficiently aware of that body of literature - hence I was unconvinced by the original hypothesis. I'm reading M Owens as speaking about the whole ice sheet, not small parts of it, which may be susceptible to stagnation. M Owens' original comment certainly appears to refer to the whole ice sheet. Maybe (s)he's right, but I don't think the drainage hypotheses are feasible, as I have explained, as some hopefully "constructive feedback".

You shouldn't confuse brief summit melt events with the kind of melting that goes on in the slush and ablation zones, which takes a very great deal longer and more persistent melting. When we see the kind of melting at the ice sheet summit that we see lower on the flanks of the ice sheet, which takes a lot more energy and time, then there will be a great deal more to be concerned about! When we see ice sheet stagnation (such that the surface profile of the ice sheet is no longer convex, driving ice flow and hydraulic pressure gradients outwards), caused by dynamic thinning and surface melt, then equally there will be a lot to worry about. But IMHO there's a fair way to go before either of these things happen.

[Artful Dodger]

Jumping forward from the 1960's to the 1970's, academic research continued into the effectiveness of various schemes to remove the Arctic sea ice cover. Here is the abstract from Aagaard & Coachman (1975)

"The strong salinity stratification of the Arctic Ocean prevents substantial ice-free conditions in winter by suppressing convection and reducing upward heat flux from the Atlantic Water. These conditions would be significantly altered in the sensitive southern Eurasian basin if suggested diversions of western Siberian rivers were accomplished."

Aagaard, K. and L.K. Coachman (1975), Toward an ice-free Arctic ocean, Eos Trans. AGU, 56(7), 484, doi:10.1029/EO056i007p00484.

It's Geo-engineering, the Love Boat edition. I won't be surprised if extended drought conditions end up being the justification for extensive water diversion projects such as discussed in the paper above. Of course, diverting North flowing rivers (including the Mackenzie) would bury any chance of retaining Winter Arctic sea ice.

[Jim Williams]

In other words, skywatcher is making an appeal to authority.

[Account Deleted]

an appeal to authority how so? he is arguing that at moment some people on this site seem to be trying to predict the rapid demise of the GIS, without providing any evidence to support their case.

[Apocalypse4Real]

In regard to the earlier conversations of ocean currents and also atmospheric jet stream changes impacting the GIS and Arctic Ocean, this recent research in phys.org might be of interest - demonstrating the modeling of stratospheric jet stream change and its impact on ocean currents:

North Atlantic 'Achilles heel' lets upper atmosphere affect the abyss

September 23, 2012

http://phys.org/news/2012-09-north-atlantic-achilles-heel-upper.html#ajTabs

More information: DOI: 10.1038/ngeo1586

Journal reference:Nature Geoscience

[skywatcher]

Oh dear Jim, as opposed to claiming that thrust faults can progress 26 miles in a day?! I'll take an appeal to authority over that any day of the week. The point is that there is a very great deal of detailed understanding about glaciology and glacial hydraulics out there, and it is really unwise to toss that out in favour of hitherto unsupported conjectures, unless you have a very good evidentiary basis for doing so.

Diving into hypotheses without the understanding of existing literature is just the kind of thinking that has tied many climate skeptics in knots: it would be a shame to see any good people round here fall into the same traps. If people think they can do better on their ice sheet mechanics than Tad Pfeffer, Doug Benn, Bob Bindschadler, Pete Nienow, Martin Sharp and all the rest of the glaciological community, then that's great, and good luck! ... but do so in the light of the published literature, not in spite of it! I apologise if that sounds hard, but the quickest way to make serious mistakes in science is to ignore what has gone before.

[Lennartvdl]

skywatcher,

I agree with you that we should start from current science, so let's pick up again at the discussion between Pfeffer and Hansen.

Pfeffer et al assume it's very unlikely, but maybe not impossible, that all GIS glaciers can speed up quickly to on average the speed of Jakobshavn Glacier in 2004-2005 (12.6 km/yr):
http://courses.washington.edu/ess203/RESOURCES/READING/pfeffer_sealevel_science_2008_with_suppl_info.pdf

They assume the same for the most important marine glaciers on AIS. For surface melting they assume continued acceleration at present day rates of change. Total SLR by 2100 could then be about 2 meters.

Hansen & Sato think this may be too cautious an estimate (pp.22-23):
http://arxiv.org/ftp/arxiv/papers/1105/1105.0968.pdf

"The kinematic constraint may have relevance to the Greenland ice sheet, although the assumptions of Pfeffer at al. (2008) are questionable even for Greenland. They assume that ice streams this century will disgorge ice no faster than the fastest rate observed in recent decades. That assumption is dubious, given the huge climate change that will occur under BAU scenarios, which have a positive (warming) climate forcing that is increasing at a rate dwarfing any known natural forcing. BAU scenarios lead to CO2 levels higher than any since 32 My ago, when Antarctica glaciated. By mid-century most of Greenland would be experiencing summer melting in a longer melt season. Also some Greenland ice stream outlets are in valleys with bedrock below sea level. As the terminus of an ice stream retreats inland, glacier sidewalls can collapse, creating a wider pathway for disgorging ice.

The main flaw with the kinematic constraint concept is the geology of Antarctica, where large portions of the ice sheet are buttressed by ice shelves that are unlikely to survive BAU climate scenarios. West Antarctica's Pine Island Glacier (PIG) illustrates nonlinear processes already coming into play. The floating ice shelf at PIG's terminus has been thinning in the past two decades as the ocean around Antarctica warms (Shepherd et al., 2004; Jenkins et al., 2010). Thus the grounding line of the glacier has moved inland by 30 km into deeper water, allowing potentially unstable ice sheet retreat. PIG's rate of mass loss has accelerated almost continuously for the past decade (Wingham et al., 2009) and may account for about half of the mass loss of the West Antarctic ice sheet, which is of the order of 100 km3 per year (Sasgen et al., 2010).

PIG and neighboring glaciers in the Amundsen Sea sector of West Antarctica, which are also accelerating, contain enough ice to contribute 1-2 m to sea level. Most of the West Antarctic ice sheet, with at least 5 m of sea level, and about a third of the East Antarctic ice sheet, with another 15-20 m of sea level, are grounded below sea level. This more vulnerable ice may have been the source of the 25 ± 10 m sea level rise of the Pliocene (Dowsett et al., 1990, 1994). If human-made global warming reaches Pliocene levels this century, as expected under BAU scenarios, these greater volumes of ice will surely begin to contribute to sea level change. Indeed, satellite gravity and radar interferometry data reveal that the Totten Glacier of East Antarctica, which fronts a large ice mass grounded below sea level, is already beginning to lose mass (Rignot et al., 2008)."

To me the key part seems to be that Hansen & Sato say the current "climate forcing is increasing at a rate dwarfing any known natural forcing", and this will continue under BAU.

During interglacials the fastest SLR seems to have been about 2.5 meters/century, according to Rohling et al (2008):
http://www.nature.com/ngeo/journal/v1/n1/pdf/ngeo.2007.28.pdf

So if Hansen & Sato are right that the climate forcing this century is, or will be, much stronger than during previous interglacials, then it would seem to be reasonable that SLR could be much faster than 2.5 meters as well, if not already this century, then at least in the next ones.

So what do we know about the climate forcings, now and during previous interglacials? The initial forcing now is mainly CO2. Back then it seems to have been stronger orbital summer insolation on the Northern Hemisphere. Both apparently cause strong albedo feedbacks.

Hansen & Sato seem to argue the current CO2 forcing is an order of magnitude higher than the orbital forcing during the Eemian. If that's correct, wouldn't they have a strong argument for expecting more SLR than Pfeffer et al think likely? So does anyone know if the current forcing really is so much stronger than the one during the Eemian?

[Jim Williams]

Colin Maycock, it seems to me that they are speculating, not attempting to predict. Given the failure of authoritative predictions it seems to me that speculation is the best current approach.

The statement "I have measured x" is worth paying attention to, as is "they have measured x," though less so. Before paying attention to "They have computed x" I think we are totally justified in asking how well the previous predictions have fared.

The experts are currently best seen as unknown drips under pressure. Before telling me what one thinks first tell me what their predictive skill has been. I don't give a damn what their peers think.

Without a statement of what the authority predicted and how that prediction has fared I'd rather not have their opinion/computation.

[Neven]

North Atlantic 'Achilles heel' lets upper atmosphere affect the abyss

A4R, I saw this press release as well and thought it was really, really interesting. If I have the time I'll do a piece on it, but first the quakes and the microbes.

[bluesky]

Does anybody have access to this Science news and analysis article, where there seems to be some discussion about how far the models are from the current melting trend:
http://www.sciencemag.org/content/337/6102/1591.summary

[bluesky]

Lennartdvl, there is also a recent article inferring 40 mm of sea level rise per year 14600 years ago:
http://211.144.68.84:9998/91keshi/Public/File/34/483-7391/pdf/nature10902.pdf

apparently related to "saddled" ice sheet (much bigger than the ones in AIS?):
http://xa.yimg.com/kq/groups/18383638/1133003027/name/nature11257.pdf

[me.yahoo.com/a/nSjChi4X3vr8X3DRw93GkY1.cerja.8nvWk-]

bluesky they quote Serreze, Stroeve, Maslowski and Steele, estimates range from 2016 to 2030. Here's the last para:
"Serreze and others think Maslowski’s volume extrapolation exaggerates the problem. “It could happen [by 2016],” Serreze says. “I just don’t think so. I think he’s being too aggressive.” There is, however, a hint that enhanced pessimism may be appropriate. Stroeve is just back from a cruise to 83°N, beyond northern Greenland. She saw only 30% to 40% ice cover there. “We never expected that,” she says, because satellite data had not suggested it."

[opensheart]

Can Sea Level Rise be Regional instead of evenly spread over the globe?

Could Sea Levels rise in the Arctic and North Atlantic Oceans as compared to the Pacific?

I believe the Pacific Ocean is currently 'higher' than the Arctic and Atlantic Oceans.

Would it be possible for the Arctic Ocean to rise to be 'higher' than the Pacific?

Would it be possible for the Atlantic to rise higher than the Arctic while the Arctic is still higher than the Pacific?

Pacific < Arctic < North Atlantic

And if so, would that not be a tipping point in terms of global ocean currents and everything that goes with it?

[Account Deleted]

Come on Jim - which predictions about the GIS have failed?
Some of the speculations about how glaciers/ice sheets are going to respond aren't supported by field observations e.g. the increase in atmospheric water vapour due to loss of sea ice turning the GIS into a giant slushy which will disintegrate in the blink of an eye idea (to paraphrase). If this is a valid idea why hasn't this happened to tropical glaciers which, unlike the GIS which has a temp of -20+C, exist at temperature close to melting point.

[bluesky]

me.yahoo.com/a/nSjChi4X3vr8X3DRw93GkY1.cerja.8nvWk-
Many thanks for the summary, well if the sattelites underestimate the melting, maybe it explains the pessimism of Wadhams, and Maslowski...although there might still be a range of years of uncertainty...

opensheart, the following gives some answer to your questions following a collapse of WAIS, in fact the divide is more North hemisphere/ South hemisphere, with some variance for the NH, impact from partial east antarctic collapse would be different:
ftp://dossier.ogp.noaa.gov/NCASLR/Publications/GomezetalGeophyJInt2010FutureSeaLevelEarthResponseMitrovicaStory.pdf

[Account Deleted]

bluesky - there isn't anything in the Kerr article that Neven hasn't discussed/analysed here (only difference is they get a few comments from various researchers)

[P-maker]

Owen, Lennart, Skywatcher, LRC et al.

Please have a look at this image: http://ocean.dmi.dk/arctic/images/MODIS/Qaanaaq/201209280000.MERR.png

Along the NW coast of Greenland (aka Melville Bay), we have a large pool of warm water at the moment. It is roughly 1000 km long (from Ilulissat to Pituffik), 100 km wide and maybe 0.5 km deep. These 50,000 cubic km of 5 degree water is moving N close to the Greenland Ice Sheet. According to the Canadian Ice Service at a speed of 7 knots at the surface. Do we know why?. Is it due to salinity differences in the Baffin Bay? Is it due to deep water formation? Is it due to katabatic winds coming off the GIS? Maybe some of the best oceanographic models could provide some insight. However, if it is the katabatic winds, we have a problem, since then we would have to deal with another type of model. Katabatic winds are not normally part of a weather models. You could say it is just a simple combination of gravity, topography and “lack of weather”.

According to a recent paper in Science (Kurt H. Kjær et al. (2012): Aerial Photographs Reveal Late-20th-Century Dynamic Ice Loss in Northwestern Greenland Science 337, 569-73), the slope of the Inland Ice has steepened over the past three decades. The ice edge along the Melville Bay has retreated a couple of kms and the ice surface is some 20-60 meter lower now near the coast. This steepening due to melting and calving leads to stronger katabatic winds – which is yet another positive feedback in the ice-atmosphere-ocean system, which no model is able to pick up. Do we know why the glaciers are shrinking in this area?. Yes, the paper gives us a hint. It is most likely due to SSTs, which have increased 0.5 deg C in the area since the turn of the century. Remember that right know we have 50,000 cubic km of 5 degree warm seawater waiting close to the ice edge. Do we have a detailed fjord-model, which can tell us how this water will attack the tidewater glaciers?. Do we have a detailed ice-sheet model, which will tell us how the glaciers will respond to this attack?. Do we even know the bathymetry of all these fjords along the coast? Do we know the topography of the valleys under the ice streams?. Do we know the glacier hydrology in any detail?

No we don’t. All we know is that we ought to have four or five models coupled together, and we would need to get a hold on all the rapidly changing initial conditions, and we would need a lot of time to calibrate models and publish papers before we would be able to say anything with confidence about the whole system. The problem is, that this type of warm water – maybe not this year – but one year in the very near future, may find its way under the ice barrier through one of the fjords. Once we see a good solid pool of warm water behind the palisades, we should start talking about “Greenbay” instead of Greenland.

Models are fine for analytical work, but not for projections at this stage.

[colincr]

@ opensheart | September 29, 2012 at 00:36

"Can Sea Level Rise be Regional instead of evenly spread over the globe?"

You may want to see Satellites trace sea level change.

[Fairfax Climate Watch]

Skywatcher, and others I appreciate your feedback on my post. This is an important issue, and the recent decline in the ASI makes it all the more important. This site really pulls together a lot of great info that is just scattered out there, with very few people making the connections.

As for the details, that have raised the doubts of some (or many): I am saying that liquid water which reaches the base of the glacier from the top (and other sources to an extent) can form persistent pockets of melted water, especially in the below-sea-level areas of the ice. At first these pockets will be small, perhaps just a few thousand atoms per pocket. But they will grow. The ice will rot from the bottom. When the pressure from the overlying ice exceeds the structural support capacity of the still-solid ice, THEN the water pockets/'slurry' will be displaced in a demolition-style movement down of the ice. I'm not sufficiently versed in the specifications of the penetrating radar that is being used over Greenland to say what threshold level of such described water pocket formation would be detectable. Assuming, such a signal is even being looked for. If I have the chance, I'll look into it ASAP.

An interesting addition to the concept is this recent news from Reuters:

"OSLO (Reuters) - A British plan to drill into a sunless lake deep under Antarctica's ice in December could show the risks of quicker sea level rise caused by climate change, scientists said on Friday.

Sediments on the bed of Lake Ellsworth, which is several hundred meters (yards) below sea level and buried under 3 km (1.6 miles) of ice, may include bits of ancient seashells that could be dated to reveal when the ice sheet last broke up...

... There are 360 known sub-glacial lakes in Antarctica"

Those liquid water lakes are theorized to have been down there a long time. Or so they think. Not that I'm doubting, but I haven't seen any evidence to lead me to believe they have been there since before the ice formed. I don't know how you can prove (without a water sample to test for radioactive carbon 14 ) that the lakes were there from before the ice sheets formed, especially in light of this evidence on melt mechanics:

“We found clear evidence that supraglacial lakes—the pools of meltwater that form on the surface in summer—can actually drive a crack through the ice sheet in a process called hydrofracture,” said Das, an assistant scientist in the WHOI Department of Geology and Geophysics. “If there is a crack or defect in the surface that is large enough, and a sufficient reservoir of water to keep that crack filled, it can create a conduit all the way down to the bed of the ice sheet.”

Reuters quote from http://www.huffingtonpost.com/2012/09/07/antarctica-lake-ellsworth-drilling_n_1864189.html

hydrofracture quote from http://www.whoi.edu/page.do?pid=7545&tid=3622&cid=40786

Also see Spencer Weart's site on the changing perception (and resistance thereto) of climate change through time (a great read!): http://www.aip.org/history/climate/index.htm

Reuters quote from http://www.huffingtonpost.com/2012/09/07/antarctica-lake-ellsworth-drilling_n_1864189.html
hydrofracture quote from http://www.whoi.edu/page.do?pid=7545&tid=3622&cid=40786

Also see Spencer Weart's site on the changing perception (and resistance thereto) of climate change through time (a great read!): http://www.aip.org/history/climate/index.htm

[Fairfax Climate Watch]

"GCM as a prognostic tool are a dangerous waste of time. " - posted by Jim Williams above.

Yes, this is worth repeating, because it trips a lot of people up. What's more, if you read the actual papers all the way through (which is often daunting), then you'll see that the modelers say just what Jim Williams said! Read between the lines (and all the lines) and you'll see that the scientists who've been the least-surprised by the recent accelerations in climate are the same ones who've gone out of their way to mention all the uncertainties (most of which are to the upside (more warming, kind of a downside really)) involved in their models.

And more specifically, one of the things they repeat over and over , which gets lost in the typical mainstream news mangling (getting better in a few isolated pockets lately) of their results is that local and short-term variability ARE NOT included in their models - which has big ramifications. For example: if a climate model turns out an accurate average over a given time, but the reality of that average is that it is composed of extremes both high and low, AND that the extreme highs cause feedbacks, which then push the entire system to a higher state (I mean more total energy in circulation, which typically leads to increased warming)...then what you have is a ratcheting up. Skip over that fine line just by a touch and bam! the permafrost is melted (for example).

[Jim Williams]

I was reading this: http://www.aip.org/history/climate/GCM.htm An interesting part of a general discussing of the history of climate science -- the discovery of Global Warming. Near the end I ran into the following interesting paragraph (I think the state of knowledge is still as represented, but I'm not positive.)

"Modelers were particularly worried by a persistent failure to work up a reasonable simulation of the climate of the mid-Pliocene epoch, a few million years ago, when global temperatures had reached levels as high as those predicted for the end of the 21st century. Paleontologists claimed that the Pliocene had seen only a modest difference in temperature between the poles (much hotter than now) and the equator (not much hotter). The modelers could not figure out how the oceans or atmosphere could have moved so much heat from the tropics to the poles. The same problem showed up in the Cretaceous epoch — a super-greenhouse period a hundred million years ago when the Earth had a CO2 level several times higher than the present. Paleontologists reported dinosaurs flourishing in Siberia, basking in warmth not much cooler than the tropics. No model was able to reproduce that. If our greenhouse emissions heated the Earth that far, there would apparently be conditions (super hurricanes? radical changes in cloudiness?) stranger than anything the models were designed to calculate. Modelers worried, as one of them remarked, that "the field is missing fundamental feedback processes that amplify warming." These uncertainties persisted through the first decade of the 21st century."

What strikes me about this paragraph is that we might have touched upon the solution to the modelling problem mentioned in our discussions here. Is it possible that it isn't heat moved from the tropics to the poles, but rather heat moved from the poles to the tropics? The physics of ice sheets is not well understood, and it is quite possible that they have broken up and dispersed in the past -- cooling the tropics to be much more like the poles.

[wayne]

Jim, we get an idea about what happened, by every summer holistic look of the entire Northern Hemisphere climate system. In addition, Greenland should have been Islands and there was no Polar atmosphere as we know it, just tropical and temperate all the way to the pole. The best way of seeing this is the disappearance of the 546 decametre level at 500 mb during winter. This means a much weaker global circulation, much slower jet streams, much warmer seas due to the lack of heat exchange etc. I wonder why they have had trouble duplicating this?

[idunno]

Hi all,

The very high anomalies in SSTs on the West Coast of Greenland are not an entirely new phenomenon.

There were some very odd high air temp readings in Greenland which were first widely commented on here around Xmas 2010, New Year 2011.

Looking back from then on one of the SST maps I began squeaking periodically that SSTs up the Greenland West Coast seemed very high back until 2009. There were problems with the refreeze in Eastern Baffin Bay in 2010/11 also, IIRC.

I also did some speculating that the main Gulf Stream may be turning in a more Northerly direction, and therefore a wisp of it was passing to the West of Greenland, and keeping a small coastal fringe of Baffin Bay almost perennially ice-free...

And now, after some thunks wot I had on my recent e-vacation, I thunk I bet it's all to do with that research by Dr Jennifer Francis, which posits that the Polar Vortex is slowing down.

So, also with a H/T to the article linked by A4R above, that might mean that the "Gulf Stream" (wotever - equatorial heat carried up to the Arctic by ocean currents) has a tendency to travel more Northerly than North Westerly.

This would also help explain the large pool of warm water referred to by P maker, and discussed by Jim Williams and skywatcher, above...

Woah, it's coming from Barbados,
in the sunny Carribean Sea.

http://uk.video.search.yahoo.com/video/play;_ylt=A2KLqIqwGmdQxgUAGKF2BQx.;_ylu=X3oDMTBrc3VyamVwBHNlYwNzcgRzbGsDdmlkBHZ0aWQD?p=we%27re+going+to+barbados&vid=E9334EC28D0544157B77E9334EC28D0544157B77&l=3%3A34&turl=http%3A%2F%2Fts3.mm.bing.net%2Fvideos%2Fthumbnail.aspx%3Fq%3D4583868992258154%26id%3D129570db76937133de556a7cc7a181d5%26bid%3Dd3sVRAWNwk4z6Q%26bn%3DLargeThumb%26url%3Dhttp%253a%252f%252fwww.youtube.com%252fwatch%253fv%253dUc-9QV9H_VU&rurl=http%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3DUc-9QV9H_VU&tit=Typically+Tropical+-+Barbados+1975+The+original+of+a+Vengaboys+hit&c=5&sigr=11a81c388&

[LRC]

@ wayne: I believe the major problem is that the whole system is similar to having a tube of say oil and water. You start spinning it and things are pretty predictable and to what is going on there comes a point though when you get it going faster that the clear boundary between the 2 liquids becomes a heaving unpredictable mess at the boundary layer. If that is not where we are it is close to it. Now when you get beyond that chaos no longer exists but neither does the boundary. Two issues I see at play right now is that 1) the spin up (rising temps) is much faster then ever before. 2) could it be possible that there comes a point that when things get hot enough what part of the earth is getting sun or not getting sun no longer matters it becomes equally warm all over. Then of course when something brings the temp down the reverse happens. Although there I see a big danger in that the slow downs tend to be fast and uncontrollable (ice ages).

[Jim Williams]

idunno, I saw something in passing while I was searching yesterday that talked about how extreme NAO conditions had briefly connected the Gulf Stream directly to the West Greenland current (I think it was in the Winter of 2010). I'll see if I can re-find it -- I don't think I bookmarked it.

There's so much noise from thermohaline collapse speculation that it is hard to find out anything real about the northwest Atlantic.

[idunno]

Hi Jim,

I just came across this:

http://thinkprogress.org/climate/2012/09/22/891751/record-ocean-temperatures-recorded-off-new-england-coast/

[Jim Williams]

Idunno:

http://www.dailykos.com/story/2010/01/06/822520/-Freak-Current-Takes-Gulf-Stream-to-Greenland

The information source here is not the most traditional....

I'm aware of the record temps. What is a bit more obscure is the record temps last Winter.

[Jim Williams]

wayne, it can be assumed that they're having trouble duplicating it because there is something about the real system they're not including. My GUESS, given how poorly understood ice sheet dynamics is, is that the something is the movement of ice from the poles towards the tropics.

(I'm assuming that their models are handling the current differences in tropic verses pole warming fairly well, or the questions being asked would be different.)

[LRC]

As we have drifted somewhat from Ice caps to glaciers, Came across 2 pieces. http://e360.yale.edu/content/feature.msp?id=2115 http://e360.yale.edu/content/feature.msp?id=2120
The 1st one is an interview and down right scary, because if you take a SLR of 1m by 2050, that will truly change many models dramatically. Add that back as a feedback loop to the ice shelves. BRRRR.

[wayne]

Jim,

"(I'm assuming that their models are handling the current differences in tropic verses pole warming fairly well, or the questions being asked would be different.)"

Current GCM's are very good for near 7 day term forecasts, but they utterly fail the ice melt by a serious factor as this post shows. I think the models should try runs without ice. And achieve 365 days without having 546 decametre or lower pressure height levels at 500 mb. My guess (as I suggest elsewhere) is that Greenland may be playing a larger role when sea ice pack is no longer expansive, so if the models still have Greenland packed with ice the weather as it is now can't warm a whole lot more because there is still a huge static cold air source. If they eliminate all the ice of Greenland they might indeed have very warm Siberian conditions.

The North Atlantic THC may be also enhanced at this time, because sea ice refreezes over a very much larger area of Arctic Ocean open water. This is very newish, and I wait for more THC reports, it should go faster because of the production of more brine salty water going to the deep ocean, not less. But this is just a statement awaiting the facts.

[Yuha]

Jim,

"(I think the state of knowledge is still as represented, but I'm not positive.)"

Found a couple of recent papers:
http://dx.doi.org/10.5194/cp-7-603-2011
http://dx.doi.org/10.5194/cpd-8-2969-2012
It seems that problems with the proxy data explain at least part of the discrepancy but the models are not in the clear either.

[Espen]

There is a DMI article on the the paradox of less sea ice in Barents and Kara Sea, and cold winters in north west Europe.
But the article is in Danish, use translators:
http://www.dmi.dk/dmi/smeltet_arktisk_havis_giver_kolde_vintre_i_europa

[Jim Williams]

Thanks Yuha! Proving to be interesting.

[Espen]

There is an article in Aftenposten ( Norwegian Newspaper) about the relation between less sea ice and extreme weather:
http://www.osloby.no/Polsmelting-kan-ha-skylden-for-den-vate-Oslo-sommeren-7004901.html

[Fairfax Climate Watch]

Some of my above statements on rapid SLR from Greenland ice sheet disintegration are now followed up at http://climatewatch.typepad.com/ .

And following up on my other statements about microbe accumulation on the ice surface: the recent Journal of Glaciology has an article by J.M. Cook et al. http://www.igsoc.org/journal/58/212/j12J001.html that says carbon fixation by photosynthetic microbes (i.e. algae which are pulling CO2 from the air and building living cells with it) is an order of magnitude greater than previously estimated for the surface of the Greenland ice. The authors go on to say that, this fixation has a significant impact on albedo, causing increased rates of ice loss. As I mentioned before, the open water over the Arctic now should do what all open oceans do: contribute minerals and nutrients from the ocean to the air, which then are deposited on surfaces as the air moves around. So, you get the picture.

Also, in reference to some of skywatcher's counter-points: in last month's issue of Glaciology, there is a piece by Gulley et al. (abstract available here: http://www.ingentaconnect.com/content/igsoc/jog/2012/00000058/00000211/art00011 ) that states "Because conduits have no direct causal relationship with gradients in effective pressure, this recharge can form conduits in areas of glacier beds that may not be predicted by hydraulic potential theory to have conduits." This indicates that meltwater may in fact be penetrate further towards the center of Greenland than is widely thought possible today.

Regarding the models: A number of papers have been misrepresented by others who claim/think they say that the Greenland sheet cannot totally melt for at least 1,000 or more years. However, you will find in the details of those papers, that the models they use do not have many feedbacks at all. The albedo feedback just newly estimated by Cook et al. is on such example. And there are others.

In addition to lacking feedbacks, the models are oversimplified (oftentimes greatly), which again, is stated within the papers’ details. In order to appreciate this, it is necessary to understand the other cycles and processes within the biosphere. Having a multifaceted view of the problem is vital to accurately place the significance of model results based upon which aspects they’ve left out and which are important for the particular area being modeled.

But I do not think holding the model results against the scientists running them is generally a great idea. After all, the point of the models is to learn about the process, not predict the future directly. At least, that is what the purpose is supposed to be! In that vein, they are very useful. Reading Hansen for instance, will show you that he goes to great lengths to use the models and their discrepancy from observation to try and unveil more feedbacks.

[BlackDragon]

Great post. Thanks, Neven.

[LRC]

OT but best place I could find to put this. http://phys.org/news/2012-11-massive-volcanic-eruption-climate-people.html
Common presumption has been that Sulfuric Acid at high altitudes cool the earth. This study seems to call that into major question. To tie that into this topic, presumptions can lead you into wrong directions. Everything around us influences everything else. Even small forgettable things can have major impacts. For this reason focusing on our presumed impacts of a few things may brig us to totally wrong conclusions just because things are far more complicated then we will ever know.