Antarctic Ice Melting from Warm Water Below

Prove its dramatically different.
Theres only a tiny proportion of ice left,how is that going to cause a dramatic rise?
Especially when we know it didnt melt during previous interglacials WHEN IT WAS WARMER THAN TODAY?
And meanwhile the continents are rising 2mm per year.

 

We think sea levels may have risen as much as 10 meters higher than today in the last interglacial, they definitely rose 6 meters higher. Plenty of ice to do either of these without greenland or antartica completely melting.

I am with you it is extemely unlikely seas rise more than 2 meters by 2100 with what we think we know about ice, and they will likely rise much less. Currently they are only rising about 3.2mm per year, and this is uneven because of changes with land masses.

 

Current best estimate is for 75 - 190 cm rise by 2100.
Global sea level linked to global temperature

600 million people flooded by a 100 cm rise, as of present day population and distribution.

 

@61 "And meanwhile the continents are rising 2mm per year."

Isostatic rebound is global? Is there a youtube video on that or sumpin'?

@63 this publication would certainly qualify for my list of 'not so bad' news from climate science research.

Storm surge effects and salt-water intrusion into coastal aquifers are two of the issues being considered for even relatively minor sea-level rises. Whether one's house or farmland is below mean sea level is not the whole story.

Antarctica has 61 meters and Greenland 7 meters of ice in terms of total sea level. The bulk of both is certainly stable on the century time scale. Seriously, haven't we been all through this already?

 

Do you have an argument with that?

 

the volumetric expansion rate for water is 207 (10**-6/C), so we are taking about 0.0207% per 2.2F. This is alot but there are other things to consider:
- when ice is melting the water temp stays more or less constant. This is true for small volumes, will be to lesser degree with larger ones.
- due to thermohaline circulation surface and deep water does not mix, so oceans are warming on surface in shallow parts not all the way through.
- if all of the arctic ice to melt the volume of water would rise sea level by 60m (200').

I am not saying it isn't bad; actually it is worse when you look at other side affects like thermohaline shutdown when ice melts with imminent methane belch and possible PTE magnitude extinction but the "rising ocean levels" are probably not of near term concern. At least in your/mine lifetime, whatever left of it.

 

Not to quibble over what "bulk" means, but I'll repeat a few points that Hansen gets (mis)quoted about repeatedly, and toss in a third.

One is that the IPCC numbers are all caveated with "absent any large-scale dynamical changes in ice sheets". So all of those projections are, more or less, for ice that sits still and melts, or moves at about the current pace, and melts. The point is that the risk from violating that caveat is one-sided, and could be large. Nobody can model chaotic disintegration of the edges of the ice sheets. But nobody thinks that warming is going to help keep them in place and stick together better.

Two is that the paleo data show evident meltwater surges. So, melting of the big ice sheets from the last ice age was not a smooth process, and clearly saw some eras of rapid sea level rise, embedded within a lower overall mean rate of rise.

Three is that the projected rate of increase of temperatures is faster than, say the average rate coming out of the last ice age. Globally, the end of the ice age was maybe 4.5 or so C rise over 10,000 years. Some reasonable projections would have us doing that increase in the next 100 years. Or roughly 100x as fast. Nobody really knows what the dynamics of ice melt are going to be at that rate of increase. If the ice sits still, you can estimate the melt. If you get "collapse", whatever that might mean, you can't even guess.

This is why Hansen says, in effect, sure, the projected average is (fill-in-the-blank, 2 feet, 5 feet, whatever) in the next century, but there's nontrivial risk of tens of feet. And, based on the paleo data, it's likely that sometime in the next few centuries, you're going to get that tens-of-feet rise. Even if we dodge the bullet, somebody down the road likely will not.

That said, I'd say sea level rise is a lagging indicator, and really, just about the least of my worries. I pity the people in Bangladesh, I get why Gore got the peace prize, I understand why the Pope came out on the issue, but I'm not the one who's going to have to fight to find a new place to live. So it's not high on my list.

 

This is much is true.

Its not a caveat, it is an assumption. The assumption was that other mechanisms of ice melt would be small compared to thermal expansion and normal melt rates. We can test that assumption though, and have much more information since the last report. Even before the report came out some were making wild assumptions about possible huge melt rates of the glaciers based on sea ice melts. Always a good to question these assumptions with scholarly peer reviewed research. We should not just assume the IPCC is always right.

Well people called glaciologists can try. They model how these are melting now and look at the record. It is a fairly new science but we should not throw up our hands and say it can not be done. We can also look at satelites and sea levels and see if the models are working. If say we were getting a 5 meter rise in 100 years we would need the sea at some point to be rising faster than 50mm/year for a long time. Lately it has been rising at a rate of 3.2mm/year with variation, but no sign of a great speed up.

Excellent source of data, in fact this is probably the best. This is where the glaciologists start going wow, if we rise as fast as possible starting now we may get up to 2 meters by 2100. They say a melt this fast is highly unlikely though. Hanson on the other hand, says we have more ghg now so somehow the paleo data doesn't show the full catastrophy. As a minority of one scientist he says things can and will go much faster than we think it has ever gone before.

And my skeptical minds says, hey maybe he is right and everyone else is wrong. But don't we need some kind of data? Shouldn't we be seeing the sea levels accelerate fast now. Should not we have evidence of some mechanism cracking up the ice now? I good hypothesis needs data.

You and I can't guess well because we haven't studied the ice. I do trust that those that do study it may know better than hanson. If hanson was basing this on data that may be another mater, but he is basing it on a previous projection that was based on faulty data, taht the glaciers were melting because the sea ice is. Now this theory is trying to explain that other rejected one was correct. Greenland has indeed been warmer in the past than it is today, and we have had rapid temperature rises.

Can you show me a paper where he shows it is based on paleo data? The paper that he put it forth in, I posted here. The paleo data in that paper is not what he used as evidence. The last time a 6 meter rise seemed to take thousands of years. He talked around the issue saying it "may be" much faster this time because of ghg.

If you read the hanson paper he says those folks are already screwed, even if we abandon fossil fuels today. If you listen to the other scientists people in low lieing areas can be moved. We have a little time. Hanson has the benefit of being old. He knows he will be long dead before anyone shows his predictions are wrong.

 

Rohling et al 2008 in Nature Geoscience found an average sea-level rise of 1.6 m per century during Marine isotope stage 5e, which was apparently a rather "fast time". They cite other references, pertaining to other periods, with rates up to 5 m per century.

Next is just me talking, not the ice-ologists. I would not suppose that the highest rates could occur in the present setting, because there was much more grounded ice available for melting then, than now.

Better constraints, I am sure, would come from better knowledge of current ice dynamics. I read the last few comments as mainly agreeing with that.

@63 (and giving one of those Al Gore sighs), the point is not whether I argue the matter one way or another. The point is that geologists actually study where ice unloading allows rebound, and how rapidly. They study where plate collisions cause uplift, and how fast. They also study where subsidence occurs by way of plate separations. None of this is by any means secret. However, one has to want to find the knowledge, and put some effort into doing so.

Here's the great part: it's all free. Only personal effort is required to know all of these things (and more). All that being the case, how could anyone with an express interest not want to know?

 

Thanks for the slight correction. They did indeed say at glacial terminations sea levels have in the past risen as much as 5 cm.
Antarctic temperature and global sea level closely coupled over the past five glacial cycles : Abstract : Nature Geoscience
its a pay or sight license site, I was able to read it with a license, but didn't feel proper posting. here is a article about the research
Close Relationship Between Past Warming And Sea-level Rise

+1

Yep. That high number was just when the ice started melting. There are some high sea levels coming if you trust the paleodata, just not in our lifetimes.

 

I'll guess you mean @65, and not my post.

 

Regardling Nature's and publishers paywalls in general. I am sure we could post excerpts of text or graphics here w/o problems. I can send papers that I have to individuals by email, this is basically a standing offer.

Most direct and almost always effective: Email directly to the paper's lead author. For me the record short response time so far has been 10 minutes. Time zones being what they are, I re-replied to that author "you should be in bed now".

 

One example of rapid sea level rise as the earth warmed from the last ice age is so-called meltwater pulse 1a.

[ame=http://en.wikipedia.org/wiki/Meltwater_pulse_1A]Meltwater pulse 1A - Wikipedia, the free encyclopedia[/ame]

Taking the smallest plausible time interval, that's 30 feet per century (20 meters, 200 years). Estimates of both the size and time extent vary. Typically attributed to melting in Antarctica.

 

I'm quite sure hanson's critics understand this melt better than Hanson does. It may be good if you get the article I quoted above to see some analysis, hopefully the author will provide it without charge. Faster melts had much more continental ice.

Nor does hanson's idea of exponential melt rates make much sense. Those criticizing the idea of more than 2 meters by 2100 were looking at the fastest rates they thought the ice could melt. Hanson even in 2009 talked about large negative feedbacks if the rate got over 100mm/year yet in his model has melt rates greater than 300mm/year to get his 5 meter melt in 90 years. But why listen to other scientists critisms. Look at the past prediction and see if you can see some of the alarmism

Stormy weather - Global Warming - Salon.com

Now Hanson and Reiss in 2011, when this was critized since it did not happen, said it really was 40 years, which means 2028 for the West Side Highway to be underwater, and Reiss said a doubling of CO2 to 560ppm, which seems unlikely by 2028. But there was not thought about how fast the ice could melt.

Now with only a little more thought, and his peers saying ice can not melt that fast, Hanson is still at the predictions. He just has moved the extremely unlikely catastrophe to 2100 from 2028. I don't think this non-scientific scare mongering does hanson's reputation any good. He could have easily just admitted he was wrong in 2011, and looked at the new evidence and come up with a number that was not so far away from possible.

 

The sea rise over the past 18,000 years was not from melting in Antarctica.It was from everywhere else except Antarctica.

 

OK, let me start with the anti-Hansen diatribe first. Look into the history of that particular quote. That's from a journalist, who was promoting a book, who apparently waited 14 years before revealing what he now recalls that Hansen had said. Not quite sure of the year.

So this is not quite in the same league as, say, an article written by Hansen, where he made a firm prediction.

Seems a little peculiar, doesn't it? That Hansen would be so totally clueless about potential rates of ice melt? When he has otherwise made some fairly impressive predictions.

Note a further peculiarity. This journalist appears to be the only person Hansen ever said that to. This one particular quote, from this particular interview, is what gets recycled over and over on the denialist blogs. So, on the one hand, Hansen is supposed to be this lying alarmist, out to scare people. On the other hand, apparently he only said this once, to one guy.

Does any of that make sense to you? It doesn't to me. Why don't I Google it and see what Hansen says about all this. I'm not quite credulous enough to take that quote at face value.

As described here, he says he was asked to say, off the cuff, what could happen in 40 years, with an instantaneous doubling of C02.
http://www.skepticalscience.com/Examining-Hansens-prediction-about-the-West-Side-Highway.html

And, Hansen's description of the question matches what was written in the book. Quoting from above:

"The book The Coming Storm and the salon.com article are different. In The Coming Storm the question includes the conditions of doubled CO2 and 40 years, while the salon.com article which is quoted by skeptics does not mention doubled CO2, and involves only 20 years. "

Well, whatever.

As for the rest of it, it boils down to the large changes in ice sheet dynamics. If you rule out large changes of that type, you rule out rapid rises in sea level. You also seem to rule out things like meltwater pulse 1A. So take your pick. It's completely reasonable to dismiss highly nonlinear responses and make projections based essentially on the status quo. And it's completely reasonable to say, well, that ignores some upside risk. I think Hansen is doing a service in reminding people of the upside risk if there are large dynamical changes in the ice sheets.

 

Which is why I put 40 years out there, which your pro Hansen sight confirms. Bad prediction. He didn't think about maximum ice melt rates. If you look at his latest paper, there isn't a chance in the world he has this prediction coming true in 2028. Those skeptics that disagree with the prediction all changed it to what hansen said the question was after he replied. It doesn't really mater, facts are the important thing. Weather caused sea levels to actually fall in 2010. The current long term rate of rise is 3.1mm/year. If its going to happen by 2028, there needs to be a massive acceleration of ice sheet melt starting now. But the satelites only show yearly variability.

I am saying I trust the scientists that study the melting ice. I pointed you to a recent paper about the paleo data. The meltwater pulse did not come from the small amount of ice that we have now, it was from large continental melting glaciers at the beginning of the interglacial. I guess if we are doing this raw speculaion then sea levels could fall 10 meters this century as this has occurred in previous ice ages. If you read Alley's paper on sea levels that includes Hanson's 5 meter by 2100 prediction it is mentioned as an outlier that requires huge melts to start now.

Hansen is doing harm to his reputation, by going against the paleo record to keep up his alarmist prediction of huge sea level rise in the near future. Please read his paper, if you do you will note he does not find supporting evidence, only says it is possible. Much of the paper is about why he thinks other scientists are wrong. When it comes to Alley versus Hansen on ice, I've got to go with Alley. The ice is melting and humans are accelerating this melt, but when predictions are so outrageously wrong, it hurts the public trust in the climate scientist doing good work.

 

Well, clearly I'm not going to change your mind on much of anything. Nor you mine.

Maybe it's worth quoting Richard Alley. In his 2010 testimony in front of the US Congress (http://science.house.gov/sites/repu....gov/files/documents/hearings/111710Alley.pdf), he had this to say:


“Much scientific and popular discussion has focused on the possibility that human-caused climate change may force the Earth to cross one of its tipping points. Paleoclimatic history shows clearly that very large, rapid and widespread changes occurred repeatedly in the past (e.g., National Research Council, 2002; CCSP, 2008). An ice-sheet collapse, a large change in the circulation of the North Atlantic Ocean, a rapid outburst of methane stored in sea-floor sediments, a sudden shift in rainfall patterns, or others are possible based on available scientific understanding (CCSP, 2008).”

…

“Synopsis. With high scientific confidence, human CO2 and other greenhouse gases are having a warming influence on the climate, and the resulting rise in temperature is contributing to changes in much of the world’s ice. Shrinkage of the large ice sheets was unexpected to many observers but appears to be occurring, and the poor understanding of these changes prevents reliable projections of future sea-level rise over long times. Large, rapid changes in the ice sheets, or in other parts of the Earth system, may be unlikely but cannot be excluded entirely, and such an event could have very large effects.”

So, Alley is, quite reasonably, making projections based on a standard model without large changes. But he by no means rules out rapid change. By contrast, Hansen's reasoning has led him to have a much higher (subjective) probability of a non-linear rate of melting.

It would clearly be a waste of effort on my part to try to explain to Hansen’s reasoning to you in detail. But, briefly, other than the paleo evidence cited by Alley, Hansen focuses on extent of disequilibrium in ice volume, rather than temperature per. I believe that is uniquely his insight. That, coupled with a lack of data sufficient to distinguish between a standard model and his simple doubling time, is, I think, the core rationale for his continuing to make this point.

I guess this wouldn’t be so funny except that scientists have already identified the first one that's going to blow. I mean, a potential candidate for non-linear melting of the sort that is the focus of Hansen's concern. The Pine Island Glacier, on the west antarctic ice sheet. Fifteen years ago, that glacier was predicted to last 600 years, based on then-current flow rate. Two years ago, it was predicted to last 100, based on its then-current flow rate. Since the recent British expedition there a few months back, as I read it, all bets are off. Nobody’s even willing to guess, because now they now know how deeply its ice shelf is being undermined by warm currents in the Arctic Ocean.

So, from 600 years, to 100 years, to who can even guess, in under two decades’ time. Driven by a process (Arctic ocean warming) that could plausibly affect a lot of those ice shelves. When I see that, I find it hard to dismiss Hansen as being obviously wrong. It’s not clear that he’s right, but, as Alley puts it, “Large, rapid changes in the ice sheets, … , may be unlikely but cannot be excluded entirely.” And I think Hansen does us a favor to continue to remind us of that.

 

To alley and the other scientists mentioned here 2 meter rise by 2100 is very fast melting of the ice. It is the ice melting at 20mm rise/ per year versus the 1mm rise Hansen says is going on now from glaciers.

The difference is the others presume to get to the limiting rate faster. They all get there in a non-linear fashon and then the melt continues at the high rate. What hansen has done is attempt to explain why we won't see his high rate for decades, by using a slower acceleration. The big difference is Hansen's exponential growth gets to over 300mm/year, a point where we see no evidence in history. The question is really can ice melt at 100mm/year and continue its accelerated melt.

I guess I would like to see more than hand waving from him to demonstrate others are wrong with limiting melt rates. I guess I can not rule out the possibility that you will win the lottery and then get hit by a car, but the odds make the scenario extremely unlikely. What hansen has done is move his rapid rate out over 50 years, so we can still have the possibility in some minds. We know his rapid melt predictions came before the ice cores were examined. We know the idea of the fast melt was the melting sea ice. But for high limiting rates the glaciers must march to the sea rapidly and cause massive amounts of sea ice. This will limit how fast they can continue to melt.

It seems that instead of doing us a favor, he is acting like chicken little, except instead of the sky falling he is saying the sea is rising and we will soon all drown. Why is he acting like chicken little, he wants us to act. He wants to kill the tar sands, at least that is what he got arrested for last. But his paper says we are already past the tipping point. Questionable scientific practices hurt scientists that play by the rules. It does not do the scientific comunity a favor to greatly exaggerate.

I'll leave you with some Alley slides circa 2009. Things have changed slightly but good summary of where we are
http://www.pages-igbp.org/products/osmysm09/OSM_talks_PDF/HotTopicSessions/OSM09_HT_Alley.pdf

 

I'm not yet ready to weigh in on Alley vs Hansen.. but I do feel compelled to comment on the above. The story was that he was asked if CO2 doubled overnight, what would happen in 40 years. Its not enough to give him 40 years as the CO2 increase has nothing like doubling (about 10% increase since 1980). I would presume, having worked under Hansen from 81-83, in the exact building mentioned in the quote, that he was answering a reporters off the wall question to help them understand the implications, not making a real predictions. CO2 does not double overnight, though that is easy to program into the types of simulations his group was doing and see what the effects would be.

There are a lot of people out to discredit Hansen, because he is vocal and farther out on edge of the prediction window, but ignoring the facts about the incident, apparently properly reported by the journalist and then taken out of context, is simply wrong. If you want to talk about science, then don't use mis-use it.




I'm not ready to comment on Alley vs Hansen because I don't know enough. But I do know enough to known I don't, and probably won't, know enough to draw a conclusion. The underlying equations for the climate are extremely complex, interconnected and extremely sensitive/brittle (in a numeric analysis sense) and so very small changes, compounded over time, are critical. Change cloud cover by 0.1% and compounded over years its a huge impact. Change cloud grow rate as a function of temperature by .001% and it a different answer after 100 years. (I know as the part of the project on which I worked, estimation of cloud and ice cover from satellite images, and even issues like minor transmission glitches from satellites (think JPEG blocks when on TV), had to be very accurately addressed. ) The other climate feedback cycles from the solubility pump, ice melt impact on thermohaline circulation and the circulations impact on oceanographic flows are just too much for me to take the time to dig through to draw a good conclusion. Arm chair science is even worse than arm-chair football -- the systems are way more complex and way more sensitive. I'll leave it to the climate scientists and just do my part to reduce my own carbon impact in a reasonable way.