Sea Level Rise by 2100 (POLL)

[OldLeatherneck]

There are various estimates and models of how much sea levels will rise during the 21st century.  If and when policy makers and planners begin to take AGW/CC seriously they need to have some basis for determining what to be prepared for in terms of sea level rise.  If you were to advise them of what they need to be prepared for in terms of anticipated sea levels, how would you advise them, and why?

[Laurent]

I already posted that when I am arrived on the forum but without answer ! if you can say me with facts that i am a fool, I will appreciate.
The scientists say the rise will be 1 meter at the end of the century !? I think they take the last two centuries and calculate the sea level rise in 2100, to me, that's really a fool's game !!!
Once the arctic melt we will have an excess of energy every year of 1000 km3 of ice (which is around 10y20 joules or 1.587.301 Hiroshima bombs (http://en.wikipedia.org/wiki/Little_Boy) and this quantity does seem to increase exponentially (double every 10 years (for the moment)). We have to expect the halocline to break, then it is not anymore 10y20 Joules but much, much more...
What we know is that :
20.000 years ago the sea level was 120 meters below present with 180 ppm of CO2.
Today sea level is balanced with the CO2 level before industrial era  (-20 cm)! around CO2 = 283 ppm
125.000 years ago sea level was 8 meters above with C02 = 290 ppm
The link between C02-temperatures-sea level is linear as shown in all the drillings in Antarctic !
It does seem that for 1 ppm we have around 1 meter of sea level rise (slightly more indeed).
We are not far from 120 ppm above the industrial era which could mean 120 meters above is expected !?
There is only 70 meters of ice volume available, yes but the dilatation is 50 % of the rise (yes-no?) and there is certainly an other effect with the moving of the crust that does follow (?).
When, I don't now but as we see an exponential grow in the melting we have to expect the same exponential with the sea level rise as the ice melt completely.

[ChrisReynolds]

1m to stand for 1 to 1.5m as a maximum. Reason:

Pfeffer 2008, Kinematic Constraints on Glacier Contributions to 21st-Century Sea-Level Rise.

On the basis of climate modeling and analogies with past conditions, the potential for multimeter increases in sea level by the end of the 21st century has been proposed. We consider glaciological conditions required for large sea-level rise to occur by 2100 and conclude that increases in excess of 2 meters are physically untenable. We find that a total sea-level rise of about 2 meters by 2100 could occur under physically possible glaciological conditions but only if all variables are quickly accelerated to extremely high limits. More plausible but still accelerated conditions lead to total sea-level rise by 2100 of about 0.8 meter.

A probability distribution function centred on 0.8m will have an upper tail above 1m, hence my vote. I'll probably forget I posted here, so this can be considered a drive-by.

[gfwellman]

Rahmstorf got more like 1.3, so I'm choosing 1.5 as a maximum.  It could happen that dynamic ice sheet losses are more limited and the actual SLR will turn out a bit lower than 1.0, but we certainly don't know that yet.

[Artful Dodger]

Hi, OLN

Appreciate the thought and well-deserving of a polling thread, but I don't like the question much

There is no maximum SLR. NOT even 80 meters. This is level is EXCEEEDINGLY unlikely, but it isn't a non-zero probablility, it's just like 0.0000001%. But it is still NOT the max!

So a better question, and the one I choose to answer, is what is the median SLR you expect by 2100?

Therefore, I voted 2 meters.

[Glenn Tamblyn]

I have gone for 1.5

Mainly because the likely source of faster rise is the WAIS. There are warning signs of the possibility there with things like changes in the grounding line of the PIG. Also, later this century as CFC concentrations start to really decline, the cooling effect they seem to have had in Antarctica by increasing the speed of the circumpolar winds is likely to drop away, allowing Antarctica to warm faster. Weighted against that is that for the ice in the WAIS to really start declining, it needs an exit path to the Southern ocean and the patheways through to there in places like the PIG aren't that wide. If warming and incursion started to bite in the Ross Sea however, all bets are off.

[Wipneus]

Since you are asking for a maximum, I picked 2.5 m somewhere on earth.

[slow wing]

I don't like to take the end bin but, since you asked for the maximum, I have to go with >3m.

James Hansen might be wrong, but I don't think we can rule out that he is right.

For the maximum, we have to consider high end forcings. And the best candidate for providing most of that rise is the unpinning of those areas of the West Antarctic ice sheet that are below sea level. There is always going to be enough heat available in that scenario because if the ice floats then it can always float around until it finds enough heat somewhere in the Southern Ocean.

See http://en.wikipedia.org/wiki/West_Antarctic_Ice_Sheet for a non-technical overview.


If someone can provide a simple dynamical explanation for why that is not possible, whether from Pfeffer 2008 or elsewhere, then I would be willing to revise my answer.

I would be genuinely interested to hear any such explanation if it can be made, and I'm sure others here would also.

[Jim Williams]

The evidence for dynamic collapse of the WAIS is strong enough to make 4-6 meters a real possibility.  I think the biggest unknown is what will happen in Antarctica in response to the SLR which has already happened.  There's certainly some signs of acceleration.  If that persists then we have a massive positive feedback.  Whenever we get 3 meters of rise, I'd expect most of it over about a 10 year timeframe.

[Chuck Yokota]

I picked 2m, one step more than I think likely, on the precautionary principle that they should be prepared for worse outcomes.

[frankendoodle]

http://www.tidesandcurrents.noaa.gov/sltrends/
Interactive map showing sea rise and decline trends around the world.

[frankendoodle]

Assuming a 5C ocean temperature increase over the next 90 years would create an approx. increase of 1.8 m just taking thermal expansion into account. The rough estimate is this:
360 km3 of water to raise GSL by one mm. World oceans are between 1.3 and 1.37 billion km3. A 5C increase across the board would increase volume by about 0.5%. While I wouldn't bet real money on 1.8m I don't think it is that far off.
This plus my suspicion the GIS and WAIS will lose significant mass in the coming century lead me to my vote of >3m.

[frankendoodle]

A 5C increase across the board would increase volume by about 0.5%.

Sorry, I meant 0.05%.

[Vergent]

I think that an ice free arctic creates an arctic storm(think GAC12 on steroids) That dumps albedo(ice) down to 50N. There were no negative choices! You create a poll, but the restrictions on choices is like a butcher putting his thumb on the scale. This planet has a back-up air conditioner. Humanity has thrown the switch. I hope you like wind.



800,000 years of history says that the only direction for sea level is down. Why are there no negative choices?

ftp://ftp.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/gisp2/chem/iond.txt

BTW Sodium is the proxy for wind(Sea spray). About 4,998 YBP, there was a storm like we are about to experience. It lasted for six years(till -4,992) and buried the ice man in ice.  Take a dive through time. During the ice age(12k-99k YBP), the wind almost never stops!



This fall, or next, I am expecting the North Pole to look like this(Saturn's north pole). This is what happens when underlying heat can circulate to the pole.



When the arctic goes ice free, the warm tropical waters will be able to circulate to the pole. This will supply the energy for the polar storm. This is how the Earth rebuilds albedo during an inter-glacial. This is also the type of storm that deposits the ice in the ice age. But in the ice age, the circulation is enhanced by brine outflow from the Fram.

No references, these ideas are my own. I've spent the last 12 years trying to disprove this. I have failed to do so.

So, if you can, disprove that a polar storm(like Saturn's) is the result of an ice free arctic filled with warm water.

Vergent

[Dromicosuchus]

Vergent:  I'm hardly equipped to prove or disprove your hypothesis, nor do I necessarily think that the formation of such a polar storm is unlikely, given an ice-free Arctic--but are you certain that it'll have a cooling effect?  It would massively increase albedo over the Arctic, yes, but given an Arctic ocean that only becomes free of ice at the end of the melt season (the state of affairs that, one assumes, we'll hit before we hit any other more exotic states), in the polar night most of that reflectivity will go towards trapping heat within the Arctic ocean, discouraging the development of thick ice rather than encouraging it.

Now, if such a storm sprawls out as far down as 50˚ N, as you propose, and dumps immense quantities of snow on the surface...well, that would increase albedo, sure.  But it would increase it during winter, when it matters least.  I'm also somewhat uncertain about your statement that a polar storm is responsible for the decline into a glacial state, and that brine outflow through the Fram is enhanced during glacials (wouldn't it be reduced, given that with less summer melt there would also be less winter refreeze, and consequently lower brine rejection?).  Do you know of any papers supporting those two hypotheses?

(Edit:)  Another possible issue occurs to me; are you sure that the [Na+] is a proxy only for the windiness around Greenland?  Sodium would also be present in dust in saltpans, deserts, etc, and of course the Earth as a whole was a drier place during the last ice age, with more extensive desertification than is the case at present.  It may be that there was simply more dust in the air in general, rather than increased transport of salt spray on to the Greenland ice.  I suppose one might be able to determine if that was the case by examining the ways in which the [Na+] and, say, [SiO2] varied relative to one another.  If the ratio between the two changes dramatically at certain times, with far more Na+ relative to SiO2 than is the case during interglacials, that might support your position.

[ChrisReynolds]

Vergent,

Did it happen during the Holocene Climatic Optimum, when the Arctic was virtually sea ice free?

I checked the Na ion concentrations after downloading that data, thanks, interesting stuff. There is no significant peak of Na around the time you state (during the Holocene Climatic Optimum), it is consistently down below  about 20ppb, except for about 8 spikes a bit above 20ppb. Then the Younger Dryas is around 50 to 80+ ppb, there's a drop before that then high levels again until 20kyrs BP, which is as far as I went.

[Vergent]

Don'want to pull this excellent poll off topic. The reason I haven't started a thread on this is we need an "Ice Age" category in "Cryosphere". I will start a topic there, if Neven responds to my request. I just wanted to explain why I was the standout vote. For now I have to go to work.

Vergent

[TerryM]

My guess was for 2.5. One for the Antarctic, one for the GIS and .5 for thermal expansion.


I'm not sure we'll have the ability to measure or report on it by 2100.


Terry

[johnm33]

The maximum I would expect is about 6m but I don't think 10m is beyond the bounds of the possible. So I voted <3
One set of reasoning is that since the cold water sinks at the poles and heads towards the equator it will always be replaced by surface waters from warmer climes, so at some point Greenland and Antarctica could be playing their version of ping pong each in turn impelling warm water S/N leading to an accelerated melt of both.
Another is that once the arctic is ice free and the freshwater lens has gone nothing will cause the Atlantic water to dive, if it doesn't dive nothing will hold back the highly saline bottom water, [ very little of which makes its way out through Fram, which mostly sees recently chilled Atlantic Waters recycled out the base] which I expect will gush out, and huge volumes of surface water will flow into the arctic [ timed badly this would make last summers Greenland melt seem trivial]  kickstarting the above process and releasing silly amounts of methane.
The only ameliorating factor would be the massive increase in evaporation in the arctic leading to the dumping of prodigious depths of snow in Europe and North America, but to begin with I think that would melt out every year dissolved by rain from the same source.  At least until the methane crisis passed.

[Vergent]

Johnm33,

We have come to the same conclusions. I call it the arctic flush.

Vergent

[johnm33]

Vergent
Hope we're wrong.

[fred]

> 3 meters is not only the maximum but also what I expect.

Very subjective reasoning based, today, on the fact that a dog bit me when I was walking my dog and then when I forgot the code for my phone, the phone company texted me the temporary password: Wild Dog.

Seems unrelated but what are the chances of those two events happening together? Given all the different changes that are happening in the arctic and the fact that NONE of them, eh.. to my knowledge, are negative, I think we are screwed.

I say "we" in the general global warming sense, however obviously those people in Miami, Baltimore, the Amazon, Sri Lanka, etc are far more so.

[Anne]

The Finnish Meteorological Institute has updated its estimates concerning the impact of rising sea levels on the Finnish coast, taking into account post-glacial rebound, changes in Earth's gravity field, and regional variation. They say the regional rise in Finland will remain below the global average, but

If the highest projections come to pass, the sea level will rise everywhere on the Finnish coast: by as much as 90 centimetres in the Gulf of Finland by the end of the century, by 65 cm in the Bothnian Sea and by about 30 cm in the Bay of Bothnia.

http://www.sciencedaily.com/releases/2013/04/130429094933.htm

[fred]

I read over on the "why does the sea level rise unevenly" (under the consequences category) that in some cases there could be even 100s of meters of difference in rise based one location.

Based on what i understood from skimming that article that shallow oceans near mountains and continents would gain the most rise. In other words, based on the geoid, the mediteranean and Asia would be hit the hardest.

All the sealevel rise projections I have seen to my knowledge just show flooding based on topography, i.e. if every one walked out to the high water mark of their nearest ocean and stood there for 100 years, eventually they would be waist deep.

However, is it true that the sea level rise is this different from place to place based on gravity, et al?

[Jim Williams]

I'm not sure we'll have the ability to measure or report on it by 2100.
Terry

Either we won't have the ability or we won't care.  We're in a race between future technology and past technology.

[wili]

I put over 3m, mostly for reasons similar to those A4R states above.

The most likely  (rather than max) rise I would put at 2 m (global average, much higher in some places.) It turns out CO2 actually weakens ice structures, so it is not just the warming we have to worry about, and studies based just on warming or on past warming events are going to be conservative.

But I do think that Vergent and John are right about increased precipitation of snow from an increasingly ice-free Arctic. It is already happening, imho. In Minnesota, we have had the longest and snowiest winter in a long time, and more snow is predicted for Thursday--that will be record matching or breaking late snow in many places. This after years of earlier and earlier melt off, culminating in last year's "Summer in March."

I have to assume that this is because the vast new areas of melt in the Arctic set up a pattern of increasing snow, that worked its way down to our latitude. I can't help but assume that the expected even-greater Arctic sea ice loss this September will lead to an even longer and snowier winter next year. That may push snow falls into June. Would a totally ice free Arctic push snow fall all the way into July and August? I don't know. I tend to assume that the very high sun would quickly melt everything away by the time we got that late. But the sun is as high now as it is in mid-August, and yet there are still piles of snow here and there.

This is a climate tug of war, and I expect that over-all gw will eventually win, and we will return to summers in March and winterless winters. But, as always, predicting the timing is difficult.

And, as they say, winter is coming.

[Richard Rathbone]

The energy imbalance is around 0.5-0.75 W/m2 averaged over the earth. This goes into heating water or melting ice (air and earth don't take much to heat up).

I don't see the energy imbalance getting much larger because the surface temperature follows the forcing up.

In round numbers this gives enough heat to expand the oceans to raise sea level by 1mm/yr or melt land ice enough to raise sea level by 100 mm/yr.

Since we are talking maximums thats 10m/century. Assuming that the proportion going into ice doubles every 10 years gets to that rate in around 60 years time, and sea level is 4m higher at the end of the century.

[ccgwebmaster]

The energy imbalance is around 0.5-0.75 W/m2 averaged over the earth. This goes into heating water or melting ice (air and earth don't take much to heat up).

I don't see the energy imbalance getting much larger because the surface temperature follows the forcing up.

Not much larger? Really?

Carbon dioxide is around 1.6 W/m^2 currently. The only reason you can quote around half that is because of the offsetting effect of short lived industrial pollution (especially sulphate aerosols). There are other contributors (methane for example) to add in. Within only years of switching off industry, the energy imbalance is significantly altered therefore.

The Arctic albedo flip loosely is likely good for another 1-1.5W/m^2, including land based snowpack retreat. That's viewing it as a global average - and not considering that all the extra input is focused in space and time within the earth system.

Then there are numerous other processes that can add substantial amounts of extra greenhouse gas into the system rapidly - far more rapidly than the temperature can equalise - causing both greater rate of warming and a bigger radiative imbalance.

And then you can toss in the methane wildcard. Over 100 years it is around 23x as effective as a greenhouse gas as carbon dioxide. But anyone quoting that figure is in fantasy land as far as the earth system goes because the half life (under normal atmospheric conditions where the breakdown mechanism is not overloaded) is nearer a decade. Over a 20 year timescale it is 105x as potent as carbon dioxide - I don't even know the figure for a decadal timescale (any takers?).

Accordingly the warming from a large methane release can be seriously front loaded and disconcertingly rapid for potentially some decades at least (much bigger initial thermal budget imbalance).

In any case even if average surface temperature was capable of following the forcing change as rapidly as you suggest (to keep radiative imbalance fixed at the current figure) - that's little better - it just means we cook even faster.

With respect to the implied rate of sea level rise and setting aside the original point - are you taking into account that ice doesn't have to melt to directly contribute rapidly to sea level rise? (it isn't clear to me how you go from energy imbalance to the amount of ice being melted - even if the energy imbalance did remain constant or maxed - there's still a lot more energy from original baseline to affect the ice).

[Richard Rathbone]

The forcing isn't the same as the imbalance. Surface temperature has gone up, which increases outgoing radiation, so the imbalance is smaller than the forcing. Its a measure of how much warming remains in the pipeline and its also a measure of the energy available for melting ice.

All those extra forcings will push the surface temperature up more, but I don't think they will expand the imbalance much.

See this paper for the details on the energy imbalance.

http://www.atmos-chem-phys.net/11/13421/2011/acp-11-13421-2011.html

Going from energy imbalance to sea level rise is done by dividing by the latent heat.

[AbruptSLR]

For reasons elaborated here:

https://forum.arctic-sea-ice.net/index.php/board,13.0.html

I have voted for over 3m; but I think that 5 to 6m is a better answer.

Best,
ASLR

[Bruce Steele]

I think all that heat going into the ocean will transfer into the Antarctic circumpolar current and exacerbate the changes ASLR has highlighted. I vote for 3 meters. If the formation process for Antarctic bottom water slowdown continues ( Katie )bar the door.

[OldLeatherneck]

............Appreciate the thought and well-deserving of a polling thread, but I don't like the question much

So a better question, and the one I choose to answer, is what is the median SLR you expect by 2100?

I am also a bit disappointed in my choice of words for the question.  What most chagrins me is that, during my career, I have had opportunities write survey questions and also have had the task of analyzing survey results when the questions and potential answers were very poorly written.

If I were to do this again, I would make several significant changes to this poll.

1.  Since I am also aware that SLR will not be felt evenly across the globe,  I would reword the question to read thusly:

     What do you anticipate the median global SLR during the 21st century will be?

2.  Secondly, while I knew that there were concerns about the SLR contribution from the WAIS, I did not anticipate that there would be that may votes reflecting those concerns.  Had I added additional bins up to 6 meters we probably have seen a truer bimodal distribution.  I would have loved to see the distribution between 3-6 meters.

Of concern to me now, looking at the results of the first 72 hours of polling, is that none of the predictions from official sources are as dire as what we see from this poll.  Therefore, those few policy makers that want to be prepared have no idea that the situation may well be worse than they think.

I have a great deal of faith in the collective knowledge of the members of Neven's blog and forum.  Outside of glaciologists, climatologists and other scientists actively researching these issues, this forum has assembled a very robust knowledge base of "All Things Cryospheric."

[Anne]

I can't view the results without voting. I'd love to know what they look like. I haven't voted because I honestly can't claim to have better access to, or ability to process, relevant information than the Finnish Meteorological Institute mentioned above - who place their end of century local maximum at 90 cm. Having just revised it upward! I wish I had confidence that it could be anything like as low. Like others on here, I am alarmed at the prospects of Antarctica and Greenland shedding vast quantities of ice, but in my case without being able to assign any probability within that time scale. As for the clathrate gun, hopefully that comes into the territory of NEO strike: devastating but unlikely. I don't think any of us on this forum will still be around if and when it ever goes off.

[ChrisReynolds]

Anne,

Here are the results as of the time and date of this post.

< 1 meter   1 (2.4%)
1.0 meters   2 (4.9%)
1.5 meters  11 (26.8%)
2.0 meters   8 (19.5%)
2.5 meters   4 (9.8%)
3.0 meters   1 (2.4%)
> 3 meters  14 (34.1%)

[Anne]

Thanks, Chris R. That's really interesting. And the penultimate bin, and the >3m dump bin, show the same sort of pattern as the April minimum ice poll - presumably for the same reasons.

ETA: Correction. There are more people pessimistic, it's not a simple long tail. But it's early days. I will be interested to see how this pans out.

[AbruptSLR]

OLN,

As you would like to know our estimate of the median eustatic SLR value by 2100: in my opinion that would be about 3.5m.

Best,
ASLR

[OldLeatherneck]

OLN,

As you would like to know our estimate of the median eustatic SLR value by 2100: in my opinion that would be about 3.5m.

Best,
ASLR

Thank you for your clarification as well as the major efforts you are making to educate the community about the southern half (or more) of the Cryosphere.

[Pmt111500]

I picked 2,5m since expecting Southern Greenland to move to a phase of constant melt (through winter, that is) somewhere down the line (2040-50s?) due the continued and rising accumulation of heat in the N-Atlantic. At the same time I'm hoping southern vortex won't crack, and thus opposing the speculations of increased WAIS meltdown, could easily be wrong about this. Further I'm  thinking that increased water vapor in the atmosphere will make it feel worse than 2,5m, where it does rain. Expecting also, that the Grover robot measuring changes on Greenland will fall to some crevasse hidden by a snow bridge by the end of 2014. I mean, ask again after three years :-/.

[Artful Dodger]

Hi, OLN

Thanks for the clarification. May I also ask, is there a closing date on this poll? There's lot's of interesting discussion on this thread. Perhaps when the poll closes you would consider starting another with your revised poll questions?

[OldLeatherneck]

Hi, OLN

Thanks for the clarification. May I also ask, is there a closing date on this poll? There's lot's of interesting discussion on this thread. Perhaps when the poll closes you would consider starting another with your revised poll questions?

Lodger,

I haven't decided how long to keep the poll open, probably at least for the remainder of this month.  I'm learning a great deal from the many valuable comments on this thread and would like to keep this discussion active.

What I have already learned from this poll, is that this community believes that global SLR will be much greater than any IPCC or other formal predictions.  That being the case, we have a lot of work ahead of us getting the politicians and policymakers to understand the gravity of the situation.  I am, however, startled by the large number of votes predicting an SLR in excess of 3 meters this century.

As far as when to start a revised poll, I'd like to wait until we see what this year's melt season is like on Greenland.  If this year is as bad or worse than 2012, it could be a game-changer as far as future predictions.

I'm open to suggestions.

[AbruptSLR]

OLN,

As you are startled by the large number of votes for SLR greater than 3m by the 2100, I would like to note that my vote in this category based upon (contingent upon) by belief that the global society will induce radiative forcing at least as high as RCP 8.5 (comparable to the business-as-usual case) at least until about 2050.  This radiative forcing need not only include that from anthropogentic GHG, but may include: black carbon effects; albedo flip due to the Arctic Sea Ice retreat and NH snow cover retreat; natural methane emmissions from the permafrost and marine methane hydrates; increases in the global warming potential, GWP, for methane as its future atmospheric concentration increases (due both to future natural emissions and shale gas leaks); possible future reversal (due to biological stress from climate change) of the current trend of increasing biological absorption of CO2 which could re-release temporarily sequestered CO2 and should decrease future absorption of anthropogenic CO2 emissions; not to mention CO2 emission from accelerating permafrost degradation.

[OldLeatherneck]

As promised, I've closed the voting the 2100 SLR.  Thanks to all who contributed insightful comments as well as recommendations for improved wording when I open another poll at the conclusion of this years melt season in Greenland.

What surprised me was the number of voters who predict an SLR in excess of 3 meters at the end of this century.  This is in stark contrast to the recent Ice2Sea report which predicts an SLR of <1 meter.

It will be most interesting to watch events unfold in future years as well as whether the "official" predictions get more in line with the knowledgeable and informed posters here on the Forum.

[Tom_Mazanec]

I wonder:
Have any of you have changed your minds since you voted on the Poll?