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Sam

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How quickly could Greenland melt?
« on: November 08, 2018, 07:57:07 PM »
Some folks didn't care for my guesstimate of how rapidly Greenland could melt.

I suggested 100-200 years after the loss of the last Arctic ice.

Consider: Greenland's ice sheet is estimated to contain about 2,850,000 km3 of ice. That is melting today at a rate of about 195-239 km3 per year. With an area of 1,700,000 km2, the ice is on average  1.67 km thick. That's a lot of ice.   {apologies: I had an atrocious blunder in my original post, now corrected. Thank you to SteveMDFP for pointing that out!}

At the current rate, Greenland would take 12,000-14,500 years to melt.

During the Eemian interglacial ~130,000 years ago the ice sheet lost 150-650 meters of thickness. That resulted from the local warming of 8 C. Today, we are at a global warming of ~1 C with at least 1 C more already baked in, and a total potential global warming of 3-4 C as the best case and 13 C as the worst case. Recent US Government estimates are now 4-5 C.

These all result in local warming to Greenland vastly higher than the relatively brief Eemian warming.

"In a 2013 study published in Nature, 133 researchers analyzed a Greenland ice core from the Eemian interglacial. They concluded that GIS (Greenland Ice Sheet) had been 8 degrees C warmer than today. Resulting in a thickness decrease of the northwest Greenland ice sheet by 400 ± 250 metres, reaching surface elevations 122,000 years ago of 130 ± 300 metres lower than at present.[13]"

https://en.m.wikipedia.org/wiki/Greenland_ice_sheet

 "Eemian interglacial reconstructed from a Greenland folded ice core". Nature. 493: 489–494. January 24, 2013. Bibcode:2013Natur.493..489N. doi:10.1038/nature11789. PMID 23344358.

Over the last many decades, the Arctic ice sheet has annually melted ~15,200 (circa 1980) -17,900 (now) km3/year averaged over many years. Individual years have lost more or less than this. The annual melt volume rate is increasing. This change may be due to the loss of ice on the continents, or the warming of the continents. It seems likely that the heat transfer will reach sufficient levels to melt 20,000 km3/year.

Once the Arctic ice is gone, that heat shifts from melting the Arctic ice to warming the Arctic Ocean, warming and melting the permafrost, and melting Greenland.

If only half of that total energy goes to melting Greenland's ice, the ice will be gone in 285 years. If all of it goes into melting Greenland, the ice will be gone in ~142 years.

However, even these simple estimates make some horribly wrong presumptions. They presume that despite the loss of the cold pole that the heat engine driving atmospheric circulation will continue to operate as it currently does. That is of course absurd. It will collapse.

We do not understand yet what happens when that collapse occurs. We particularly do not understand what happens when the remaining cold (Greenland) is asymmetric to the rotational pole.

It seems highly likely that the standard three band atmospheric circulation will collapse. The beginning of that will be, as we have already seen, a slowing and deepening of the Rossby waves. This will drag cold south and heat north in waves. Eventually, as the driving force falls (the cold pole melts), this will destabilize further. In the extreme, once all of the ice is gone, it collapses entirely.

Heat then builds to the south expanding the atmosphere and elevating the tropopause. The dynamics then shift. Air circulation extends further north as the jet streams are compressed toward the pole, though with huge variation as already seen. Eventually, these collapse into chaos and a state change inevitably occurs in the system.

A two band circulation is unstable. That requires rising air over the North Pole. And so, most likely, we step change to a one band system with a persistent cyclonic storm over the pole.  My guess is that the higher Arctic heat leads to persistent cloud cover through most, or all, of the year further insulating and warming the pole. This further accelerates the rate of transition.

Temperatures then rise dramatically over the whole Arctic. For a time Greenland resists. Now pounding with rain and heat, the melt rate over Greenland rises dramatically, eventually exceeding ~12 meters of ice loss per year at its peak. And in 140-<285 years after the Arctic goes ice free, the Greenland ice is gone. So, by about 2170-2335, with the highest likelihood on the low end of that.

And if we continue with business as usual, which seems to be a foregone conclusion based on the recent US, Brazilian, European, and other elections (and the public sentiment that drive those), then the driving heat rise is likely to reach 8-13 C ultimately. That hugely increases the melt rates and the dramatic shift in the Earth's atmospheric, oceanic, and ecosystems.

Under those conditions, conceptually at least we could see Greenland ice free and a global sea level rise of over 7 meters before 2150. My suspicion is that the dynamics of it will result in greater heating of the Arctic Ocean and slower melting of Greenland with the net result being an ice free Greenland closer to the year 2200-2250. But that is guess-work. A lot of the heat will also no doubt go to melting the Himalaya, creating yet another set of catastrophes.

But this is by no means the worst case, or even the most likely case, scenario. If, as expected, the Arctic Ocean releases 50 GT of carbon as methane from clathrates, and the tundra releases 1,650 GT of carbon as methane and CO2, these estimates all shift to higher global mean temperatures vastly higher Arctic temperatures, rising ocean temperatures and far faster melt rates.

These are each and all by any measure geologically instantaneous changes in Earth's conditions.

Needless to say, most creatures cannot survive such a rapid transition. Concomitant with this we must expect large swaths of land area to exceed the ultimate wet bulb conditions that disallow human survival in those areas. This has already begun in a swath from Iran through Pakistan and India. Combined with widespread drought and deluge as the warming soaks in, and the climate bands breakdown, we will see acceleration in the mass migration of people, starvation, pestilence, and war to name but a few of the horrid impacts.

My only consolation is that I am old enough that I likely will not live to see a fully ice free Arctic Ocean, and hence not see the beginning of the calamities to follow. But that is cold comfort, as the global changes with population migration and other disasters has already begun. These will accelerate in scope and impact until the Earth stabilizes into a new 'normal' for the northern hemisphere a few centuries from now. That new 'normal' seems likely to look a lot like the Eocene.

The focus then shifts to the melting Antarctic ice and the ultimate question of whether mankind was so foolish as to push the Earth's systems so hard that over a few millennia the Antarctic goes ice free. I doubt that. But 30 years ago, I would not have believed mankind would be as foolish as we already have been.

Sam



« Last Edit: November 08, 2018, 08:27:01 PM by Sam »

SteveMDFP

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Re: How quickly could Greenland melt?
« Reply #1 on: November 08, 2018, 08:12:33 PM »

Consider: Greenland's ice sheet is estimated to contain about 2,850,000 km3 of ice. That is melting today at a rate of about 195-239 km3 per year. With an area of 76,000-100,000 km2, the ice is on average 28-38 km thick. That's a lot of ice.   

No, per the wikipedia entry, it's much more area and much less height.  Area of the ice sheet is 1.7 million km2.  "The mean altitude of the ice is 2,135 metres."

Not sure how that affects your calculations.  But absorbing sunlight, atmospheric heat, and atmospheric humidity would depend strongly on area.

Sam

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Re: How quickly could Greenland melt?
« Reply #2 on: November 08, 2018, 08:35:39 PM »

Consider: Greenland's ice sheet is estimated to contain about 2,850,000 km3 of ice. That is melting today at a rate of about 195-239 km3 per year. With an area of 76,000-100,000 km2, the ice is on average 28-38 km thick. That's a lot of ice.   

No, per the wikipedia entry, it's much more area and much less height.  Area of the ice sheet is 1.7 million km2.  "The mean altitude of the ice is 2,135 metres."

Not sure how that affects your calculations.  But absorbing sunlight, atmospheric heat, and atmospheric humidity would depend strongly on area.

Thank you Steve!  The original is fixed.

And yes, you are correct, the area exposed to heating is vitally important, especially if the heating is largely solar. If, as I suspect, the heating is largely from rain and air temperature, this too changes the dynamics.

A slower melt rate on Greenland means that all of that extra heat goes into warming the Arctic Ocean, the land and the permafrost. That increases the risk from and rate of release of methane and CO2, which in turn increase the heating driving force and speed everything up.

A lengthened period of melting on Greenland with increased Arctic heat potentially sets up conditions for wicked storms.

The other interesting thing is that the Eemian melting at 400 meters was about one quarter of the thickness of the ice sheet in some areas, and ~8% thickness loss overall. With an 8 C local temperature rise, this perhaps gives a better handle on the limiting rate for ice melting from Greenland under a 20+ C local rise in temperature.


sidd

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Re: How quickly could Greenland melt?
« Reply #3 on: November 08, 2018, 08:51:53 PM »
Mr. AbruptSLR posted reference once which argued that the GIS could melt in 500 years, but i do not immediately recall the paper. There was some followup discussion in one of the Greenland threads. That is probably the lowest estimate around.

sidd

Sam

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Re: How quickly could Greenland melt?
« Reply #4 on: November 08, 2018, 09:50:02 PM »
Mr. AbruptSLR posted reference once which argued that the GIS could melt in 500 years, but i do not immediately recall the paper. There was some followup discussion in one of the Greenland threads. That is probably the lowest estimate around.

sidd

Sidd,

If the GIS does persist for 500 years, and with all of the excess heat pouring into the Arctic heating the land and ocean; it would seem that that should set up conditions for a dramatic temperature gradient between the GIS and surrounding areas. With downflow over Greenland and rising air around it, that sounds like the potential for a strong persistent extratropical low.

If that did develop, it would probably drive counterclockwise circulation around Greenland. And that in turn would have large influences on global circulation and weather. The most dramatic impacts would seem likely to be on Iceland and Nunavut, though Ireland, Britain and Scotland would also be strongly impacted with lesser impacts on the continent.

I wonder how much this might push heat into Europe offsetting the loss of heat from the collapse of the oceanic current, or whether the intense Greenland melting might serve as a temporary replacement for the Arctic Ice melt in driving the oceanic conveyor. The location of the cold surface water input would differ from the Arctic Ice melt and be much lower in volume.

All of this just serves to reinforce the point that this is all becoming a rapidly changing system. Models that depend on the previous stable conditions may not serve us at all well in predicting future conditions or events. Great caution is warranted in applying any of the models, or extrapolating them to conditions outside the range in which they have been shown to operate well.

Sam

oren

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Re: How quickly could Greenland melt?
« Reply #5 on: November 08, 2018, 10:15:31 PM »
Sea ice melting energy will be required each year even after "the ice is gone" (=BOE in September). And the melting energy is spread around 15 million km2. So assuming all this energy goes into melting Greenland is wrong. At worst it will be 10-20%.
In addition, there is a negative feedback of all that meltwater cooling the ocean surface around Greenland. Hansen has explored this in his important paper outlining the possibility of 3m SLR by 2100.
There is another negative feedback of the water around Greenland receding once a significant part of the GIS is gone, due to gravitational effects. As a lot of the melting is marine-based, this could slow down total meltout.
My gut feeling, 500-1000 years is more reasonable.

AbruptSLR

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Re: How quickly could Greenland melt?
« Reply #6 on: November 08, 2018, 10:27:23 PM »
Mr. AbruptSLR posted reference once which argued that the GIS could melt in 500 years, but i do not immediately recall the paper. There was some followup discussion in one of the Greenland threads. That is probably the lowest estimate around.

sidd

Applegate et al. 2015 is a peer-reviewed reference that with a local Greenland surface temperature increase of 9C indicates a 7m contribution to SLR, or a with a local Greenland surface temperature increase of 12C indicates an 8m contribution to SLR by 2500 from the GIS (see the first attached image).  sidd provided the second attached image relating the Greenland amplification factor of 1.52 after 100 years and 1.41 after 300 years, so a local Greenland temperature increase of 12C would correspond to a GMSTA of 6C by about the year 2200 (for RCP 8.5).

Applegate, P.J., Parizek, B.R., Nicholas, R.E. et al. (2015), "Increasing temperature forcing reduces the Greenland Ice Sheet’s response time scale", Clim Dyn 45: 2001. https://doi.org/10.1007/s00382-014-2451-7

https://link.springer.com/article/10.1007/s00382-014-2451-7#citeas
&
https://static-content.springer.com/esm/art%3A10.1007%2Fs00382-014-2451-7/MediaObjects/382_2014_2451_MOESM1_ESM.pdf

Abstract: "Damages from sea level rise, as well as strategies to manage the associated risk, hinge critically on the time scale and eventual magnitude of sea level rise. Satellite observations and paleo-data suggest that the Greenland Ice Sheet (GIS) loses mass in response to increased temperatures, and may thus contribute substantially to sea level rise as anthropogenic climate change progresses. The time scale of GIS mass loss and sea level rise are deeply uncertain, and are often assumed to be constant. However, previous ice sheet modeling studies have shown that the time scale of GIS response likely decreases strongly with increasing temperature anomaly. Here, we map the relationship between temperature anomaly and the time scale of GIS response, by perturbing a calibrated, three-dimensional model of GIS behavior. Additional simulations with a profile, higher-order, ice sheet model yield time scales that are broadly consistent with those obtained using the three-dimensional model, and shed light on the feedbacks in the ice sheet system that cause the time scale shortening. Semi-empirical modeling studies that assume a constant time scale of sea level adjustment, and are calibrated to small preanthropogenic temperature and sea level changes, may underestimate future sea level rise. Our analysis suggests that the benefits of reducing greenhouse gas emissions, in terms of avoided sea level rise from the GIS, may be greatest if emissions reductions begin before large temperature increases have been realized. Reducing anthropogenic climate change may also allow more time for design and deployment of risk management strategies by slowing sea level contributions from the GIS."
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gerontocrat

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Re: How quickly could Greenland melt?
« Reply #7 on: November 08, 2018, 11:17:03 PM »
Off-topic, except the start date of accelerated Greenland melt may be being brought forward.

Quote from Sam a few posts ago...

Quote
If, as expected, the Arctic Ocean releases 50 GT of carbon as methane from clathrates,

Maybe a vast underestimate and looks like something may be happening now.
Research suggests that the clathrates in shallow seas suchas the ESAS are just the lid on free methane under pressure formed from immense thicknesses of highly organic deposits laid down a long time ago over a long period. Below are extracts of a post by A-Team some time ago.

But first....
Quote
MOSCOW, October 29. /TASS/. Russian scientists during an expedition on board the Akademik Keldysh research vessel found new sources of methane emissions in the Arctic, the Ministry of Education and Science’s press service said on Friday.

Experts say thawing of the Arctic Ocean’s underwater and coastal permafrost causes massive emissions of greenhouse gases - methane and carbon dioxide. The growing emissions may affect the planet’s climate system.

"Russian scientists have found a new big area in the East Arctic’s seas with big emissions of greenhouse gases," the press service said. "They also saw that emissions in earlier found areas had become more active."

Quote
Permafrost / Re: Arctic Methane Release
« Message by A-Team on November 13, 2017, 06:01:31 AM »
Quote
My reading of S&S is that they see the over-pressurized free methane gas, never mind the hydrates, as by far the greater problem that faces us.
That's correct, Terry. Semiletov estimates the methane hydrates as less than 5% of total ESAS methane; because of this, Shakhova can say the decay timeline of the hydrate stability zone is completely irrelevant because there's already enough free methane gas to catastrophically affect global climate, should even a fraction of it reach the atmosphere.

According to S&S, there do not exist any published studies to date showing ESAS methane hydrates even occurs, whereas we're real sure that methane is currently being released in volume. That methane, from triple isotope studies, is a waste product of archaeal decomposition of buried organic matter. It is not geothermal methane nor destabilized clathrate.

It would be more interesting to chase down the observational basis for S&S's estimate of pressurized free methane volume reserves. Is there really as much down there as they say? How is it distributed relative to the coastline, riverine sediment inputs, and shelf break? Would it really matter if the estimate were 50% too high (or too low)?

And how much pressure has built up under the (deteriorating) permafrost lid and what is its connectivity? That greatly affects the fraction of escaping methane that can reach the atmosphere because slow occasional bubbles have a very different fate -- dissolving into seawater -- from vigorously fountaining methane.

The ESAS, especially the near-coastal regions rich in methanogenic sediment, is exceedingly shallow, much of it less than 10 m deep. Again, it's baffling why people keep referring to deep sea methane studies or inconsequential shelf areas like the Beaufort with very different histories. Sure, those bubbles will get swept aside by currents and dissolve in sea water, eventually getting metabolized before Henry's Law kicks in.

That isn't the case for over-pressurized methane in shallow water because high volume hotspot vents physically entrain seawater, bringing the methane rapidly near and to the surface where it can equilibrate with (ie raise) the currently low partial pressure of atmospheric methane.

In the interview, Shakhova says "a fraction" will inevitably reach the atmosphere, not specifying that fraction other than to say given the immense estimated methane reserves, its pressure, the erosion of permafrost lid, and beyond-linear rate of hotspot development, that this fraction is all that it would take to seriously disrupt global climate.

S&S have laid out plausible concerns based on decades of observational data. How events will actually play out in the near future depends on the numbers. For those, far more sonar surveys are needed, both of vent activity and subsurface structural changes. The ESAS is so vast and the season so short that it's time-consuming to sample its area with line surveys, much less repeat them to establish a time series.

However -- and this is the whole point of the 2017 NatComm paper -- they have been able to conduct repeat transects and repeat drill cores to a limited extent. Those don't indicate the worst case scenario (a massive one-time blowout) but support decadal-scale accelerating emissions that come close enough in effects.

It won't work to simply monitor atmospheric methane increase (though that's the final arbiter) because it's a lagging indicator for deterioration of the ESAS permafrost lid. As such, it wouldn't give enough time to 'make room' whereas better data might
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Pmt111500

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Re: How quickly could Greenland melt?
« Reply #8 on: November 09, 2018, 04:14:36 AM »
Question here of the local warming around Greenland and on Greenland during Eemian, how was this estimated? Is it a summer or winter or whole year estimate? Currently the Arctic has warmed the fastest, especially during winters. How large would the equivalent local area warming be currently? My understaning has been that it'd be parts of the West Antarctic that are speediest to go, what do you think of the relative speeds of melt between GIS and WAIS? Mechanisms are somewhat different of course one being marine-based while other has deep channels and associated choke-points, so extremely large-scale jökullhaupts are not very possible in Greenland.
« Last Edit: November 09, 2018, 05:45:12 AM by Pmt111500 »
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bbr2314

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Re: How quickly could Greenland melt?
« Reply #9 on: November 09, 2018, 04:32:35 AM »
Mr. AbruptSLR posted reference once which argued that the GIS could melt in 500 years, but i do not immediately recall the paper. There was some followup discussion in one of the Greenland threads. That is probably the lowest estimate around.

sidd

Applegate et al. 2015 is a peer-reviewed reference that with a local Greenland surface temperature increase of 9C indicates a 7m contribution to SLR, or a with a local Greenland surface temperature increase of 12C indicates an 8m contribution to SLR by 2500 from the GIS (see the first attached image).  sidd provided the second attached image relating the Greenland amplification factor of 1.52 after 100 years and 1.41 after 300 years, so a local Greenland temperature increase of 12C would correspond to a GMSTA of 6C by about the year 2200 (for RCP 8.5).

Applegate, P.J., Parizek, B.R., Nicholas, R.E. et al. (2015), "Increasing temperature forcing reduces the Greenland Ice Sheet’s response time scale", Clim Dyn 45: 2001. https://doi.org/10.1007/s00382-014-2451-7

https://link.springer.com/article/10.1007/s00382-014-2451-7#citeas
&
https://static-content.springer.com/esm/art%3A10.1007%2Fs00382-014-2451-7/MediaObjects/382_2014_2451_MOESM1_ESM.pdf

Abstract: "Damages from sea level rise, as well as strategies to manage the associated risk, hinge critically on the time scale and eventual magnitude of sea level rise. Satellite observations and paleo-data suggest that the Greenland Ice Sheet (GIS) loses mass in response to increased temperatures, and may thus contribute substantially to sea level rise as anthropogenic climate change progresses. The time scale of GIS mass loss and sea level rise are deeply uncertain, and are often assumed to be constant. However, previous ice sheet modeling studies have shown that the time scale of GIS response likely decreases strongly with increasing temperature anomaly. Here, we map the relationship between temperature anomaly and the time scale of GIS response, by perturbing a calibrated, three-dimensional model of GIS behavior. Additional simulations with a profile, higher-order, ice sheet model yield time scales that are broadly consistent with those obtained using the three-dimensional model, and shed light on the feedbacks in the ice sheet system that cause the time scale shortening. Semi-empirical modeling studies that assume a constant time scale of sea level adjustment, and are calibrated to small preanthropogenic temperature and sea level changes, may underestimate future sea level rise. Our analysis suggests that the benefits of reducing greenhouse gas emissions, in terms of avoided sea level rise from the GIS, may be greatest if emissions reductions begin before large temperature increases have been realized. Reducing anthropogenic climate change may also allow more time for design and deployment of risk management strategies by slowing sea level contributions from the GIS."

These graphs are ridiculous. 2018 proves them all wrong. They are all up up and away without any thought or inclusion of negative feedbacks. Why is SMB+ for 2018 if we are on a Greenland hockey stick?

If .1% mass loss since 2002 produces a result like the attached, I shudder to imagine what 1% would do. We already have an explanation for 8.2Kyr and Younger Dryas staring us in the face, stop listening to the media's ridiculously optimistic (yes, saying we are experiencing +AGW while ignoring local cooling and corresponding negative feedbacks is OPTIMISTIC) narrative and it becomes obvious.

oren

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Re: How quickly could Greenland melt?
« Reply #10 on: November 09, 2018, 04:52:00 AM »
These graphs are ridiculous. 2018 proves them all wrong. They are all up up and away without any thought or inclusion of negative feedbacks. Why is SMB+ for 2018 if we are on a Greenland hockey stick?

If .1% mass loss since 2002 produces a result like the attached, I shudder to imagine what 1% would do. We already have an explanation for 8.2Kyr and Younger Dryas staring us in the face, stop listening to the media's ridiculously optimistic (yes, saying we are experiencing +AGW while ignoring local cooling and corresponding negative feedbacks is OPTIMISTIC) narrative and it becomes obvious.
Enough. One year's weather simply cannot prove something when discussing a centuries-long process.
SMB is only one part of the equation that also includes calving. SMB has been positive for most years except 2012, and yet Greenland continued to lose mass.
The explanation for the 8.2 Kyr event was a sudden catastrophic release of accumulated melt-water stored in a lake in the middle of a continent, not a .1% reduction in an ice-sheet's mass. Greenland's size and topography do not lend themselves well to such a lake being formed and then released.
However, strong Greenland melt (much higher than today's) IS expected to cool the ocean surface around it. This does not mean another 8.2Kyr event, but it does throw complexities into a seemingly simple process. Hansen has explored this complexity in his important SLR paper, as I have mentioned above.
And when talking about the "media's ridiculous narrative of AGW" do you mean published science's narrative? I have yet to see published science supporting theories of reglaciation or claiming more 8.2Kyr events are expected because of Greenland melt.

bbr2314

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Re: How quickly could Greenland melt?
« Reply #11 on: November 09, 2018, 07:02:52 AM »
These graphs are ridiculous. 2018 proves them all wrong. They are all up up and away without any thought or inclusion of negative feedbacks. Why is SMB+ for 2018 if we are on a Greenland hockey stick?

If .1% mass loss since 2002 produces a result like the attached, I shudder to imagine what 1% would do. We already have an explanation for 8.2Kyr and Younger Dryas staring us in the face, stop listening to the media's ridiculously optimistic (yes, saying we are experiencing +AGW while ignoring local cooling and corresponding negative feedbacks is OPTIMISTIC) narrative and it becomes obvious.
Enough. One year's weather simply cannot prove something when discussing a centuries-long process.
SMB is only one part of the equation that also includes calving. SMB has been positive for most years except 2012, and yet Greenland continued to lose mass.
The explanation for the 8.2 Kyr event was a sudden catastrophic release of accumulated melt-water stored in a lake in the middle of a continent, not a .1% reduction in an ice-sheet's mass. Greenland's size and topography do not lend themselves well to such a lake being formed and then released.
However, strong Greenland melt (much higher than today's) IS expected to cool the ocean surface around it. This does not mean another 8.2Kyr event, but it does throw complexities into a seemingly simple process. Hansen has explored this complexity in his important SLR paper, as I have mentioned above.
And when talking about the "media's ridiculous narrative of AGW" do you mean published science's narrative? I have yet to see published science supporting theories of reglaciation or claiming more 8.2Kyr events are expected because of Greenland melt.
OK well 450 years ago "published science" still believed the sun revolved around the Earth so I don't exactly give prevailing narrative credence when the work of James Hansen and others shows it to be profoundly stupid in the exact same way. Look at Hansen's work, look at what is HAPPENING, and tell me the hockey stick nonsense re: Greenland is plausible. It isn't. We live on a planet of senseless apes and unfortunately that includes most scientists.

Sleepy

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Re: How quickly could Greenland melt?
« Reply #12 on: November 09, 2018, 07:43:20 AM »
Question here of the local warming around Greenland and on Greenland during Eemian, how was this estimated? Is it a summer or winter or whole year estimate? Currently the Arctic has warmed the fastest, especially during winters. How large would the equivalent local area warming be currently? My understaning has been that it'd be parts of the West Antarctic that are speediest to go, what do you think of the relative speeds of melt between GIS and WAIS? Mechanisms are somewhat different of course one being marine-based while other has deep channels and associated choke-points, so extremely large-scale jökullhaupts are not very possible in Greenland.
This was up in the ice apocalypse thread recently and here's was what I wrote there, don't have the time right now to dig up the references.

Using the Eemian as an analogy, with Greenland as the new "cold pole" doesn't really work. First, we now know that the year-to-year variability in SMB can be high and is highly dependent on the weather. Second, the ice on Greenland covers "only" ~1,700,000 km², the Arctic Ocean ~14,000,000 km². Third, during the Eemian it was warmer summers that melted the ice thanks to different orbital parameters. Fourth, CO2 levels during the Eemian peaked around 280ppm.







Edit; removed an image doublet, sorry.
« Last Edit: November 09, 2018, 07:57:56 AM by Sleepy »
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AbruptSLR

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Re: How quickly could Greenland melt?
« Reply #13 on: November 09, 2018, 03:50:34 PM »
I note that the Applegate et al. (2015) work assumed that mean value for ECS is currently around 3C; however, per the following Andrew Dessler believes that consensus climate science will soon (maybe by AR6) accept that the mean value for ECS is currently close to 4C, and that ECS increases with continued warming.

Title: "Climate sensitivity uncertainties leading to more concern"

https://www.skepticalscience.com/climate-sensitivity-uncertainties-concern.html

Extract: "Dessler said his “best guess” currently, based on the evidence he’s seen, calls for an increase of 3 to 4 degrees C from a doubling of CO2 concentrations over pre-industrial levels.

“The idea that climate sensitivity from observations is a lot lower than the models, that the models are ‘running hot'” and showing more warming and not less … “that idea is headed for the junkyard,” Dessler concludes."

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AbruptSLR

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Re: How quickly could Greenland melt?
« Reply #14 on: November 09, 2018, 04:08:32 PM »
...
My understaning has been that it'd be parts of the West Antarctic that are speediest to go, what do you think of the relative speeds of melt between GIS and WAIS?
...

While there is 'deep uncertainty' associated with the relative rates of ice mass loss from the GIS and the WAIS, the attached image shows that only the WAIS is likely to be a major contributor to SLR this century.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Sleepy

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Re: How quickly could Greenland melt?
« Reply #15 on: November 10, 2018, 07:56:02 AM »
Thanks for that summary post by Peter Sinclair above, ASLR. Haven't followed him for a while and since I visited a very old blog post of mine this morning, found myself posting this back then, Mars Attacks from 2009:



He was more fun back then wasn't he? Ah well, can't blame him.
Omnia mirari, etiam tritissima.

Martin Gisser

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Re: How quickly could Greenland melt?
« Reply #16 on: November 10, 2018, 09:18:36 AM »
He was more fun back then wasn't he? Ah well, can't blame him.
Thanks a lot for this reminiscence! Good ol times. Where is Lord Monckton now? I miss this clown... Maybe it's time for a best-of collection. For fun and to remind the deniers of their old shit.
"The universe is irrelevant for all practical purposes, so better forget about being thrown into it." --Florifulgurator

Klondike Kat

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Re: How quickly could Greenland melt?
« Reply #17 on: November 11, 2018, 12:04:56 AM »
Sea ice melting energy will be required each year even after "the ice is gone" (=BOE in September). And the melting energy is spread around 15 million km2. So assuming all this energy goes into melting Greenland is wrong. At worst it will be 10-20%.
In addition, there is a negative feedback of all that meltwater cooling the ocean surface around Greenland. Hansen has explored this in his important paper outlining the possibility of 3m SLR by 2100.
There is another negative feedback of the water around Greenland receding once a significant part of the GIS is gone, due to gravitational effects. As a lot of the melting is marine-based, this could slow down total meltout.
My gut feeling, 500-1000 years is more reasonable.

IMO, your gut feeling is still too soon.  However, this is all speculation as to what might possibly happen over the next millennium.

Sleepy

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Re: How quickly could Greenland melt?
« Reply #18 on: November 11, 2018, 08:18:12 AM »
 .
Omnia mirari, etiam tritissima.

nukefix

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Re: How quickly could Greenland melt?
« Reply #19 on: November 11, 2018, 02:44:55 PM »
Over the last many decades, the Arctic ice sheet has annually melted ~15,200 (circa 1980) -17,900 (now) km3/year averaged over many years. Individual years have lost more or less than this. The annual melt volume rate is increasing.
Those numbers are grossly incorrect. The Greenland Ice Sheet has lost about 3000km3 if ice from 1991-2011, so almost two orders of magnitude less ice loss than the quoted numbers.

http://imbie.org/imbie-2012/result.


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Re: How quickly could Greenland melt?
« Reply #20 on: November 11, 2018, 03:14:44 PM »
Over the last many decades, the Arctic ice sheet has annually melted ~15,200 (circa 1980) -17,900 (now) km3/year averaged over many years. Individual years have lost more or less than this. The annual melt volume rate is increasing.
Those numbers are grossly incorrect. The Greenland Ice Sheet has lost about 3000km3 if ice from 1991-2011, so almost two orders of magnitude less ice loss than the quoted numbers.

http://imbie.org/imbie-2012/result.





At this time there is roughly 1.7 M km3 of ice? If it's 3000km3 in 20 years then there is only  11,000 years left. (please check my numbers- mostly just numbers in my head)

edit: By weight and current loss according to NASA it came to 7000'ish years.

oops :) talking about two different things  :)
« Last Edit: November 11, 2018, 03:42:57 PM by mostly_lurking »

oren

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Re: How quickly could Greenland melt?
« Reply #21 on: November 11, 2018, 03:41:38 PM »
Over the last many decades, the Arctic ice sheet has annually melted ~15,200 (circa 1980) -17,900 (now) km3/year averaged over many years. Individual years have lost more or less than this. The annual melt volume rate is increasing.
Those numbers are grossly incorrect. The Greenland Ice Sheet has lost about 3000km3 if ice from 1991-2011, so almost two orders of magnitude less ice loss than the quoted numbers.
Sam was referring to the arctic ice cap - namely the sea ice. Assuming that when the sea ice is gone this melting energy will be directed towards the Greenland Ice Sheet, to which I have responded above.

nukefix

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Re: How quickly could Greenland melt?
« Reply #22 on: November 11, 2018, 04:01:55 PM »
Ok, better to keep the terminology straight. For example Austfonna is an ice cap (= glacier), and sea ice is sea ice.

kassy

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Re: How quickly could Greenland melt?
« Reply #23 on: November 11, 2018, 10:18:27 PM »
As more of Greenland melts it will become lower and thus warmer at the top?

Off course there are all kinds of horrible things that could happen to the total energy budget before that becomes important...

oren

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Re: How quickly could Greenland melt?
« Reply #24 on: November 11, 2018, 11:29:04 PM »
Yes, the lowering altitude is a positive feedback, but a very slow one. All kinds of other horrible things will happen before it matters.

FredBear

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Re: How quickly could Greenland melt?
« Reply #25 on: November 12, 2018, 12:23:36 AM »
Lapse rate (cooling with increase in altitude) is commonly about 6.5oC per km., so it would take a melt of about 80m to add 0.5oC. to the effective climate. Dry air would be worse, especially under foehn effect conditions - circa 65m melt would give 0.5oC. increase.

sidd

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Re: How quickly could Greenland melt?
« Reply #26 on: November 12, 2018, 05:27:40 AM »
Re: dry,wet air in GIS

wet (hi humidity) is worse because  the latent heat release as water condenses on GIS

Re: lapse rate

There are interesting papers by Gregoire on lapse rate induced saddle collapse. As such i watch precip, melt and elevation at the saddle on GIS at 67 N between N and S dome.

sidd

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Re: How quickly could Greenland melt?
« Reply #27 on: November 12, 2018, 02:20:34 PM »
Under high humidity, condensation can give heat to the surrounding air, precipitating the water as cloud -> rain -> snow, especially at higher altitudes/latitudes, protecting glaciers. Foehn winds probably more destructive as they are cloud-free, allowing any solar radiation through.

P.S. Foehn winds only occur over lee slopes, so the windward slopes will have benefitted from the precipitation which dried the air.

sidd

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Re: How quickly could Greenland melt?
« Reply #28 on: November 12, 2018, 11:57:46 PM »
Vox_mundi posted a link to a paper by Pattyn et al. which finds tipping point for GIS of around 1.8C

doi: 10.1038/s41558-018-0305-8

sidd