How much will sea level rise?
… is the question people have been putting a lot of thought into since the IPCC AR4 report came out. We analysed what was in the report quite carefully at the time and pointed out that the allowance for dynamic ice sheet processes was very uncertain, and actually precluded setting a upper limit on what might be expected. The numbers that appeared in some headlines (up to 59 cm by 2100) did not take that uncertainty into account.
In a more recent paper, our own Stefan Rahmstorf used a simple regression model to suggest that sea level rise (SLR) could reach 0.5 to 1.4 meters above 1990 levels by 2100, but this did not consider individual processes like dynamic ice sheet changes, being only based on how global sea level has been linked to global warming over the past 120 years. As Stefan discussed, any non-linear or threshold behavior of ice sheets could lead to sea level rising faster than this estimate. Thus, otherwise quite conservative voices have been stressing the 'unknown unknown' nature of this problem and suggesting that, based on paleo-data (for instance), it was really hard to rule out sea level rises measured in feet, and not in inches. (Note too, the SLR is very much a lagging indicator, and will continue for centuries past the time that atmospheric temperatures have stabilised).
The first paper to really try and assess the future limits on dynamic ice sheet loss appeared in Science this week. Pfeffer et al looked at the exit glaciers for Greenland and West Antarctica and made some back of the envelope calculations of how quickly the ice sheets could dynamically drain.
Good news: they rule out more than 2 meters of sea level coming from Greenland alone in the next century. This is however more than anyone has ever suggested and would be comparable to the amount that disappeared at the Eemian (125,000 years ago) (see this post for more on that).
Bad news: they can't rule out up to 2 meters in total.
In summary, they estimate that including dynamic ice sheet processes gives projected SLR at 2100 somewhere in the 80 cm to 2 meter range, and suggest that 80 cm should be the 'default' value. This is remarkable in a number of ways - first, these are the highest estimates of sea level rise by 2100 that has been published in the literature to date, and secondly, while they don't take into account the full uncertainty in other aspects of sea level rise considered by IPCC, their numbers are significantly higher in any case. And this week the Dutch 'Delta Commission' published its estimate of sea level rise that the Dutch need to plan for (p111): 55 to 110 cm globally and a bit more for Holland, based on a large number of scientists' input. [Clarifying update: this is meant to be a "high end estimate".]
Lest readers think this is no big deal, the estimates for the number of people who would be affected by 1 meter of sea level rise is more than 100 million - mainly in Asia. Of some recent relevance is the fact that the storm surge caused by Gustav in New Orleans was within 1 foot of the top of the levees. Another 3 ft caused by global sea level rise would have put a lot more water into the 'bowl'.
Thus better estimates of sea level rise from ice sheets remain a high priority for the climate community. More sophisticated models and deeper understanding are coming along and hopefully those results will be out soon.
We were going to leave it at that, but we've just seen the initial media coverage where this result is being spun as a downgrading of predictions! (exemplified by this Reuters piece, drawing mainly from the U. Colorado press release). This is completely backwards. We stress that no-one (and we mean no-one) has published an informed estimate of more than 2 meters of sea level rise by 2100. Tellingly, the statement in the paper that suggests otherwise has no reference.
There have certainly been incorrect assertions and headlines implying that 20 ft of sea level by 2100 was expected, but they are mostly based on a confusion of a transient rise with the eventual sea level rise which might take hundreds to thousands of years. And before someone gets up to say Al Gore, we'll point out preemptively that he made no prediction for 2100 or any other timescale. The nearest thing I can find is Jim Hansen who states that "it [is] almost inconceivable that BAU climate change would not yield a sea level change of the order of meters on the century timescale". But that is neither a specific prediction for 2100, nor necessarily one that is out of line with the Pfeffer et al's bounds.
Thus, this media reporting stands as a classic example of how scientists get caught up trying to counter supposed myths but end up perpetuating others, and miss an opportunity to actually educate the public. The problem is not that people think that we will get 6 meters of sea level rise this century, it's that they don't think there'll be anything to speak of. Headlines like that in the Reuters piece (or National Geographic) are therefore doing a fundamental disservice to the public understanding of the problem.
Update: Marc Roberts sends along this cartoon illustrating the problem… (click for full size).
(US).jpg)
4 September 2008 at 8:49 PM
Thanx for the pointer to an excellent paper. I have heard about Niagra Falls eroding many feet in a single day, long ago. Is it possible that glaciers can enlarge their exits to the ocean through erosion ?
4 September 2008 at 9:53 PM
Good (scary) post.
I am wondering where I might find best estimates for how much a shifting pole-to-equator precipitation gradient would offset sea level rise from thermal expansion and glacier loss over the 21st century? Obviously we’re already including net growth in the interior of ice sheets, but I can’t imagine that the ratio of melt to growth remains constant with time.
4 September 2008 at 10:17 PM
We lay-folk cannot access the full text, but firstly how do the predictions take into account BAU and more importantly sensible recognition of BAL - Business as LIKELY?
We are not going to get the inertia of combined Asia, India, Europe, UK, USA, Arabia, Africa and Australia to stop commissioning a 500MW coal fired power plant every three days for the foreseeable future. Unless a realistic BAL is recognised in the expected forcing then a modest 0.8m doesn’t tell us much.
Secondly; Does the paper unambiguously declare the longer term outcome? Many people assume when scientists say that the sea is going to rise 0.8m by 2100 that that is the end of the matter, but of course its not. Unless we get CO2 back below 275ppm the ice is going to continue to melt and we are going to get +80 metres of rise, and most of the good infrastructure works in coastal cities around the world are merely serving to enhance the dive experience for future tour-boat operators.
[Response: 80 meters is all ice gone, including East Antarctica - which would take us back to the Eocene. I think we can rule that out for the time being! - gavin]
4 September 2008 at 10:25 PM
That doesn’t mean I’m going to buy property only 1 meter above sea level. Illinois is close enough to sea level.
4 September 2008 at 10:33 PM
How much will sea levels rise? From my reading and guesstimates,
I would say 70 feet by the year 2500 A.D….but that is still a long way away,
so no need to panic. Then again, it could happen much quicker if things go haywire in a way that we cannot predict now. I would be worried, very worried. Most people in the world just
want to keep driving their cars to work, though, and go on living as if there
is no tomorrow. You know what? Maybe there will be no tomorrow, if we keep this up. But give it another 500 years. No need to panic now. Ask Jimmy Lovelock.
4 September 2008 at 10:39 PM
.. well nothing to panic about until you start thinking about what is involved shifting half the worlds population, food production and industrial base up above the 80 metre line, at the same time as our primary energy source (oil) needed to accomplish this is past peak and never to be seen again. No worries! Yeah rite!
[Response: 80 centimeters (not 80 meters), though that is already large enough! - gavin]
4 September 2008 at 11:06 PM
For those of you who do not read Dutch: The Deltacommissie gives indeed 55-110 cm SLR for 2100 global, and the bit more for Holland (executive summary, p. 10, 2nd paragraph) is 0.65-1.30 m relative sea level rise (expected in Holland) by 2100, 2-4m by 2200.
4 September 2008 at 11:07 PM
Does the 80 cm include the volume expansion of sea water at higher T?
[Response: Yes. 30 cm worth which is roughly what the models suggest for A1B. - gavin]
4 September 2008 at 11:17 PM
From the draft of an article: ” Saying “Americans will never give up keeping their houses too cold in the summertime” sounds silly next to “Lots of children and older people will get sick and some will die if we don’t stop Global Warming.” ”
Thanks to RealClimate for helping the rest of us understand climate, but doesn’t it make sense to be “alarmist” when alarming things keep happening “ahead of schedule?” Things icy are a good example, from arctic icecap extent to Greenland and Antarctic glacier dynamics.
I think it is time to say that you have to be a bit alarmist to be a real conservative… as in, preserve the good that we’ve got, before it is too late.
Or maybe I’m just cranky because I can’t go home to New Orleans for a few more days.
4 September 2008 at 11:35 PM
One meter of sea level rise by 2100 would be catastrophic from my perspective on the upper Texas and Louisiana coasts. These areas provide the world with an “experiment” in sea level rise and what it means in terms of real world impacts. Subsidence from ground water withdrawal and oil and gas extraction have caused regional subsidence along these coasts ranging from 1′ to 15′. The USGS has a great publication discussing ground water extraction and subsidence. Robert Morton and others have documented the oil and gas induced subsidence and its affect on coastal wetlands and beaches in the Journal of Coastal Research and other publications. The Conrad Blucher Institute (on line) has developed apparent sea level rise rates for the Texas and SW Louisiana coasts (this accounts for both subsidence and eustatic sea level changes). Much of the area is already experiencing rise rates on the order of a meter or more per century due to the ongoing production of oil, gas and associated water causing collapse and consolidation of the producing rock strata.
The bottom line from this experiment is that simply drawing a new coastline along a topographic contour is overly simplistic and greatly underestimates the damage to human infrastructure and the loss of coastal environments. Just look at the issue of wetland loss and increased storm damage or fishery losses in SW Louisiana. Thousands of acres of rice fields have been abandoned because they no longer have the needed elevation and slope to drain. Beaches and dunes are lost entirely. Wildlife refuges and Parks and being eroded away and converted to open water. Cities once protected by tens of miles of wetlands are now near open water and are subject to hurricane storm surge damage. The NW Gulf of Mexico coast is in crisis and this is before eustatic rise really kicks in.
The overall effect from the ancillary coastal changes is to take the damage estimates and number of people affected by a future sea level rise scenario and multiply it by ten.
5 September 2008 at 12:07 AM
I was led through a reference from the paper by Pfeffer et al. to Rignot et al., Nat. Geosci.,v1, p106, specifically Fig.1, which shows mass imbalances across Antarctica. I note that the large imbalances in Pine Island and Thwaites glacier lead directly to the Byrd subpolar basin, and the small mass loss in Tottenham points to a similar, but shallower basin, as may be seen from
http://upload.wikimedia.org/wikipedia/commons/b/b7/AntarcticBedrock.jpg
A point of interest in Pfeffer et al., p1342
“The aggregate cross sectional gate area of PIG and Thwaites is ca. 120Km^2″
and refers to a private communication by Rignot. However I note that Rignot, in Phil. Trans. Roy. Soc. A, 2006, v364, pp1637-1655, notes that Thwaites is widenning and may double in width. As these (PIG,THW,TOT) glaciers retreat toward deeper basins inland, is it not the case that they would all widen?
If so, would not the gate area increase ?
5 September 2008 at 12:45 AM
Odd — the words “… Previous projections of 20 feet or more of sea level rise by the end of the century …” appear twice — attributed both to a phone call with the author by the science news writer, and in direct quotes in the official press release. Is there anything like that claim in the published paper? Else this is odd spin.
[Response: Yes. but unreferenced. - gavin]
5 September 2008 at 1:00 AM
In my opinion it is clearly the press release from the University of Colorado that is either immensely stupid or deliberately misleading, aimed at defusing the study’s results. It starts like this:
Global Sea-Rise Levels By 2100 May Be Lower Than Some Predict, Says New CU-Boulder Study
September 4, 2008
While the disintegrating Columbia Glacier in Alaska is adding to ocean levels this century, the total global sea rise by 2100 may be lower than some are anticipating, according to a new University of Colorado at Boulder study. Photo by Tad Pfeffer/University of Colorado
Despite projections by some scientists of global seas rising by 20 feet or more by the end of this century as a result of warming, a new University of Colorado at Boulder study concludes that global sea rise of much more than 6 feet is a near physical impossibility.
5 September 2008 at 2:03 AM
Tipping Points considered? The initial rises would flood and melt permafrost areas releasing Co2 and Methane. Icky, icky, mess.
5 September 2008 at 2:25 AM
Is this what you were looking for Gavin?
Hansen, J. (2007) Scientific reticence and sea level rise Environmental Research Letters 2 p.4
[Response: That’s just a thought experiment for contrast to a linear response, not an informed projection. The quote from later on in that paper is cited above where he gives his expectation. - gavin]
5 September 2008 at 2:28 AM
In addition to the comment by Ellen Thomas #7:
In Holland (at least the western part of it), most of the terrain is a mix of sand and peat bog. Since those lands have been transformed into polders, they have slowly been going down. The reason is that the peat bog dries and shrinks. This worsens our situation, and I fear Holland will finally lose to the battle with sea somewhere in the coming centuries. Long before that, silt creeping into the land and the growing risk of floods are going to be huge problems.
However, the situation in Bangladesh is much worse, the poor people there cannot afford a multi-billion delta plan like Holland.
5 September 2008 at 2:35 AM
Just now, it is raining in Greenland. Rain advects heat into the ice, even into the lower layers of ice that support huge weights of ice. As ice warms, it weakens. Warmed foundation ice is not strong enough to support the ice above it. At some point the foundation begins to collapse and the result is a ice/water debris flow with very high initial acceleration. The proper model is the Missoula floods. Such floods are only constrained by the volumes of water and ice in the system. Such water and ice floods can carve any outlets that they need. Look at the potholes in Washington State. Big holes carved into basalt by water flowing over it. The basalt was not even blocking the flow, and the water still carved big holes into it.
There is a lot of ice in the Greenland system that only needs a lot of water to flush it into the ocean. With a warm North Atlantic and a seasonably open Arctic Ocean, the amount of rain on Greenland could be considerable even by British Columbian standards. Greenland could collect more water than the old Clark River watershed, and thereby move more ice to the ocean.
Then, this article only addresses sea level rise from Greenland. If it is warm enough for Greenland to melt a bit, it is likely also warm enough for Antarctica to melt a similar amount. And, it is likely that permafrost will melt. That give us another meter of sea level rise, for a total of 5 meters of sea level rise. What would 5 meters of sea level rise do to the stability of the WAIS? Would that unpin any of it and set it sliding into the water?
My best guess based on guesses about heat transfer by rain in Greenland is that we will see 3 meters of sea level rise in the next 30 years, and another 3 meters in the following decade, for a total of 6 meters in 40 years. Of course that is outrageous. However, 30 years ago, I would have said that there was not even a 1 in a million chance that it would be raining in Greenland on 9/4/2008. In the context of an ice-only system in Greenland, my estimate is silly. However, with open water on both sides resulting in large transfers of latent heat, I think the possibility of water/ice slurries must be considered.
Before you jump up and tell me I am crazy, get out your science stuff; and go defrost a few freezers, making careful observations of the ice and melt water. Does it melt or does it fall out in chunks? What happens when a glacier gets to the ocean? It calves. The point is, ice near its melting point tends to fracture - suddenly - leaving two chunks of ice separated by a film of water. Such ice/water slurries tend to move downhill easily. For example, pieces of ice from the freezer tend to bounce out of the freezer onto the floor. How far does it fall, and how far from the freezer does it end up? And, In the case of Greenland, after it has been rained on for 20 years, we are talking about a lot of ice near its melting point.
Who would like to step forth and tell me why it is likely to stop raining in Greenland?
[Response: Rain on the flanks is not that uncommon, but enough rain on the bulk of the ice sheet to affect the surface mass balance as much as you suggest is not on. The ice sheet is 3km high, which given the lapse rate is ~30 C below the temperature at sea level - it simply can’t support large amounts of liquid water. As I mistakenly said to Mike below, going beyond the science is not helpful. - gavin]
5 September 2008 at 4:22 AM
As far as human adaptation is concerned, it seems to me that a steady sea level rise of say one metre per century for five centuries would be more difficult to cope with than a one off rise of five metres in one century.
At least in the latter case humanity would have some line in the sand above which to start trying to rebuild coastal cities and ports. A constantly shifting sea level, in whichever direction would be very difficult to cope with.
5 September 2008 at 4:33 AM
H. von Storch does not fully agree with Rahmstorf. Is there any reply yet to that?
5 September 2008 at 4:34 AM
I think it’s fair to say that in the paper you quote Hansen has gone a bit further than you suggest:
‘Under BAU forcing in the 21st century, the sea level rise surely will be dominated by a third term: (3) ice sheet disintegration. This third term was small until the past few years, but it is has at least doubled in the past decade and is now close to 1 mm/year, based on the gravity satellite measurements discussed above. As a quantitative example, let us say that the ice sheet contribution is 1 cm for the decade 2005–15 and that it doubles each decade until the West Antarctic ice sheet is largely depleted. That time constant yields a sea level rise of the order of 5 m this century. Of course I cannot prove that my choice of a ten-year doubling time for nonlinear response is accurate, but I am confident that it provides a far better estimate than a linear response for the ice sheet component of sea level rise under BAU forcing.’
I say only a bit further because his estimate is obviously tentative, but the upper estimate of Pffer et al is less than half Hansen’s ballpark figure.
5 September 2008 at 4:59 AM
What about the Nature report that it is not a practical situation to have more than 2m rise by 2100. Can you please read the paper and give us a report (us layfolk cannot access it anyway).
In any case, I agree with Andrew at 10. The impacts will be huge. For example, large areas of many of the highest producing regions are within a couple of metres of sea level. Ganges delta, Nile delta, Southern Vietnam, areas around the China Sea, Florida, Netherlands, etc. look at
http://flood.firetree.net/ and you can see what I mean.
Our grandchildren may not know what it is like to walk on a sandy beach.
5 September 2008 at 5:01 AM
Gavin no, I do mean 80 metres. 80 metres is when its all gone, isn’t it. What magik event can occur in a post oil post BAL post 400ppm CO2 world to stop continuous melt from today thru 30cm thru 80cm thru 2m to all-gone-80 metres? Anything you can think of?
5 September 2008 at 7:08 AM
If none of the Realclimate guru’s want to correct Aaron Lewis’s errors (#17) maybe they had better start thinking greater sea level rise. My unscientific freezer melting sure sounds like his experience. Don’t get me wrong, a 1 meter (default plus a little more) rise by 2100 is bad enough but 3-5 meters by 2050 is catastrophic by anyone’s judgement.
Where does Slioch (#18) think the human race will get the energy and material resources to rebuild the world’s ports? After a five meter SLR in one century mankind will be struggling to feed itself until the population adjusts significantly. Can we even consider what that stuggle will be like? It’s not likely to be pretty, that much we do know.
Finally, will someone answer Nigel Williams (#22). What will stop the melting? That there may be few if any human observers by that time (80 meters) does not render it an uninteresting question.
All of these questions stem from only one. When will the human race recognize it is rendering the planet uninhabitable with its addiction to fossil fuel? When will people stop turning the key and flipping the switch?
[Response: But where are you getting the idea that sea level will rise 3 to 5 m by 2050? No-one serious has ever predicted that. The problems that exist with the projections grounded in some physics are serious enough without having to male up even scarier monsters. You might think it helps ‘up the ante’, but it doesn’t - it just allows people who don’t want to think that there is any problem the opportunity to paint all statements as alarmist nonsense. If you decry the abuse of science by the disinformation campaigns, you should try harder to follow the science (uncertainties and all) on these issues as well. - gavin]
[Updated response: Sorry! I missed the comment above (#17) that you were referring to. So transfer all of the above response to #17. - gavin]
5 September 2008 at 7:18 AM
Re #7 Ellen Thomas,
The Deltacommissie based its estimates on the work of… Stefan Rahmstorf, thus no wonder that they see a higher rise than the estimates of the IPCC AR4.
Btw. satellites show a declining ocean level since the end of 2006, partly by La Niña conditions, but still going on now (switch of PDO to negative?). How will that affect future projections?
[Response: It’s worth pointing out that the list of authors also included Hans von Storch as well as many others. - gavin]
5 September 2008 at 7:24 AM
Re #17 Aaron Lewis:
When I visited Greenland in 2000, we had several days of rain, including in Ilulisat/Jacobshavn, the endpoint of the largest ice fjord of Greenland, be it in August, not early September.
According to the temperature trends around Greenland, current temperatures are just reaching the temperatures in the period 1930-1945. Summer temperatures are even slightly below that period. See:
http://www.ferdinand-engelbeen.be/klimaat/greenland_temp.html
[Response: But glacier retreat is much further along than in the 1930s (see here for instance) - and that’s the key for sea level rise. - gavin]
5 September 2008 at 7:39 AM
Ricki, above, no. 51 post, re: “Our grandchildren may not know what it is like to walk
on a sandy beach.”
Powerful thought, Ricki. But I think it will most likely be our grandchildren’s descendants in far distance future who will have that experience, maybe 30 generations hence. We are okay for the next 200 years, I think. But the problems that will come later are arising (no pun intended) now, and we need to tackle them now, if indeed they can be tackled. I think your projection is too, soon, but it is poetic one. And this discussion sometimes need poetry, too. Science and poetry combined. Thanks for that.
Our greatgreat X 30 grandchildren might also know what it is to live in a Lovelock Retreat. A what, you asked? Google it and see.
5 September 2008 at 8:05 AM
SLR of 80 cm by 2100 above what level? (1990? pre-industrial? 2008?)
[Response: Present-day. But I’ll check whether it’s specifically 2000 or 2008 - though I doubt the exact year is of much relevance given the uncertainty. - gavin]
5 September 2008 at 8:07 AM
In a minor but related question not really suited for the moderators of this blog, has anyone considered the economic affect of the growing belief of significant sea level rise among real estate buyers worldwide?
Because of my belief in global warming and its effects, you could not sell me a piece of property within 3 meters of sea level. When this becomes a popular view, many trillions of dollars in real estate value are going to disappear. Poof! What are going to be the ramifications of this staggering loss of wealth to a significant percentage of the populace?
5 September 2008 at 8:54 AM
Gavin,
I only asked in #23 that you refute #17. I have no interest in “upping the ante”. (The losses we are facing in economic wellbeing and probably personal safety and liberty with the “default SLR” are already way more than I want to bet.) I’m originally from Louisiana and very well may live long enough to see the town I was conceived in be abandoned to the Gulf of Mexico.
By the way I considered your “Don’t abuse the science” comment a cheap shot. Employ the science and tell me why post #17 is wrong. Please just don’t say “No one else has said that.” Someone is always the first person to say something whether that something is correct or not. Aaron Lewis’ statements are so out of the mainstream discovering “incorrectness” should be easy. Take your time, the floor is yours.
Thanks for your time and devotion to this educational website.
[Response: My bad - I missed the earlier comment. Apologies. - gavin]
5 September 2008 at 9:05 AM
A Jim Hansen quote from the text of his recent testimony to congress:
“In my opinion, if emissions follow a business-as-usual scenario, sea level rise of at least two meters is likely this century. Hundreds of millions of people would become refugees. No stable shoreline would be reestablished in any time frame that humanity can conceive.”
Page 2 of this document:
http://www.columbia.edu/~jeh1/2008/TwentyYearsLater_20080623.pdf
Clearly the issue is not how much sea level will rise but how fast. Another Hansen paper, which I’m having trouble finding the link to at the moment is, “Target Atmospheric CO2: Where Should Humanity Aim?”. While it has been some time since I read it, the paper makes a good case based on paleoclimatinc evidence that a large proportion of the world’s ice is unstable in the long term even at current CO2 levels. Hence Hansen argues for a 350 ppm long term target.
It is probably the case that most of the GIS and WAIS are unstable at current and projected CO2 levels. If CO2 reaches 450 ppm and remains there for decades, parts of the EAIS will become unstable too. Long term sea level rises of 12 to 25 metres are reasonable under those circumstances. But how fast? If the sea is rising at 0.2 metres or more a decade, coastal urban areas, ports and other infrastructure - not to mention the heavily populated agricultural delta regions of the planet - will have to contantly respond. The challenge for human society will be unprecedented.
5 September 2008 at 9:46 AM
It will be interesting to discuss the assumptions underlying the Dutch projections of >1 m. SLR by 2100. I have seen the draft report, it will be published eventually as an annex to the Deltacommission report. Some info in Dutch on my blog.
5 September 2008 at 10:05 AM
RE #10
Andrew, I looked into the coastal infrastructure in the Houston-Galveston ship channel and inland conditions where subsidence continues despite expensive efforts to reduce mining aquifers.
Bottom line for me is steady loss of 42 percent of America’s petrochemcial industry.
And, assuming much of the world’s petrochemical and oil refining capacity is also at or close to seaports, Houston will not suffer alone.
Maybe, in the not too distant future, Algeria will supply the chemicals Houston cannot. That is not good news.
John McCormick
5 September 2008 at 10:06 AM
Hansen’s paper last summer looked at 3 time scales — 10s, 100s, and 1000s of years — for the scary sea level rises and decided that millennial was out: the geological record showed that if the seas were to rise, they’d rise pretty fast. The most likely was a time scale of centuries, but that they couldn’t rule out decadal. Which isn’t alarmist, but is pretty scary.
5 September 2008 at 10:36 AM
5 meters = 16.4 feet, approximately. So he’s not talking about Hansen. The 20 foot number shows up two places: the famous Associated Press typographical error that was widely spread in the news and so hard to correct, and the “total melt of Antarctica” projections. (It took me multiple emails to our local SF Chronicle paper to get that mistake fixed on their website — with help from the science writer!. Editors had it repeated in the text and took out only one error each time we complained to them.)
I think the university must be trying to lessen the impact of this paper, which would be expected to draw scary-new-large-estimate headlines, coming out right during the political conventions.
Shorter press release:
“Yes, we’ve found alligators, but no ichthyosaurs, while trying to drain the swamp — good news!”
It’s an election year in the US. This makes everything weirder than usual.
5 September 2008 at 10:40 AM
I think this whole discussion (and posts #21 and #26) raises a real problem. Things will be bad in this generation, and worse in the next. The issue is the really unliveable and cataclysmic stuff - onwards and upwards to the 80m “eventually” level - is still probably hundreds of years off. And people don’t respond on an emotional level to problems that are so distant - although our actions right now (and specifically, I’d contend, our decisions at Copenhagen in 2009) may or may not make that future almost inevitable.
If our decisions right now kill billions in a few hundred years, are we any less culpable than if it were our own generation? Logically no, but I fear it won’t be seen this way…
5 September 2008 at 11:11 AM
Just to nail this down, the original error, based on error in Associated Press wire report, began thus as it appeared locally:
________excerpt follows________
OCEANS RISING FAST, NEW STUDIES FIND
Melting ice could raise levels up to 20 feet by 2100, scientists say
David Perlman, Chronicle Science Editor
Friday, March 24, 2006
Glaciers and ice sheets on opposite ends of the Earth are melting faster than previously thought and could cause sea levels around the world to rise as much as 13 to 20 feet by the end of the century, scientists are reporting today….
…. The teams then compared that era to what might happen in this century …
They concluded that … would lead to an average global temperature increase of at least 4 degrees Fahrenheit and a rise from today’s global sea level of 13 to 20 feet…..
————–end excerpt from original story as printed—————–
Oops. (AP failed to state over what span of time, leaving the earlier “this century” mistakenly attached to the longer term number). Then they listed a long range of scientists as supporting the research, after grossly misstating the research papers.
Belatedly as corrected:
Current page:
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2006/03/24/MNG22HTITV1.DTL&hw=global+warming&sn=005&sc=526
noted at the bottom says
“This story has been corrected since it appeared in print editions.”
OCEANS RISING FAST, NEW STUDIES FIND
Melting ice could raise levels up to 3 feet by 2100, scientists say
David Perlman, Chronicle Science Editor
Friday, March 24, 2006
Glaciers and ice sheets on opposite ends of the Earth are melting faster than previously thought and could cause sea levels around the world to rise as much as three feet by the end of this century and 13 to 20 feet in coming centuries, scientists are reporting today. …
———-
My thanks to David Perlman who persisted until the Chron’s editors fixed the error not just in the headline but also, eventually, in the text of the article. Pity they only say corrections were made but not how and why it was corrected, eh?
5 September 2008 at 11:12 AM
Pfeffer et al. consider the Ross and Filchner-Ronne shelves to be stable for this century (p1342). Woul this assumption hold after, say, a 1M SLR ? ie
would rising seas destabilize the shelves ?
5 September 2008 at 11:18 AM
For anyone who would like to explore what sea level rise would mean for the US coastline, check out this interactive map I made using the EPA’s data. It’s not the .8 meter-2meter estimate, but it’s close:
http://blogs.edf.org/climateatlas/2008/06/02/us-sea-level-rise-maps-general-maps-for-the-entire-lower-48/
5 September 2008 at 12:01 PM
Sea level has potential to be a big problem; no doubt about that. But there are a couple of others that scare me more.
Ocean acidification has the potential to cause a breakdown of large segments of that ecosystem. How many people depend on the ocean for food?
Speaking of food, farmers will really struggle in a climate in flux. Rice, corn, wheat, etc., they all need specific and different amounts of rain and temperatures to grow well. Whatever changes are coming, there will be changes. It is not easy to switch from one thing to growing something else. Worldwide, there is not much of a food surplus now. Let us hope the changes don’t accelerate too much. How many people depend on farmers for food?
Add in the decrease in cheap energy and food production becomes even more of a problem. People crib about $4 gas; $4 (or more) bread will cause a real ruckus.
5 September 2008 at 12:14 PM
FWIW, there’s a fairly interesting interview with Tad Pfeffer in middle of the 5 September 2008 Science podcast. It starts on page 5 of the transcript.
5 September 2008 at 12:25 PM
Complete layman here, with a history background, not science.
Here’s my uneducated question - while I respect Gavin’s comments about not abusing the science, it seems to me that many measurable indicators of climate change are (to the extent I can tell) occurring/progressing/worsening faster than predicted by most models, whether we’re talking about atmospheric CO2 levels, arctic ice melting, glacial retreat, etc.
Is it too much of a stretch to assume that sea levels will rise faster than currently predicted, largely because many of the factors that contribute to sea levels rising are occurring at faster-than-predicted, and possibly accelerating, rate?
5 September 2008 at 12:25 PM
Jason/Topex measurements indicate sea level is increasing at 3.2 mms per year.
In the last 15 years, sea level has increased by:
- 1 inch
If the trend continues for 100 years, sea level will increase by:
- 1 foot
Where do people get all these exagerated figures from?
[Response: Current trends in sea level rise are larger (> 3mm/year), and estimates of future changes rely on more that the excel linear regression routine. Read the papers linked to above to get an idea. - gavin]
5 September 2008 at 12:27 PM
How is the “ozone-hole-repairing-itself-in-’50-years’-so-that-the-antarctic-warming-catches-up with-the-arctic-warming” figured into this? Is this still not figured in or is it?
5 September 2008 at 12:31 PM
An informative piece and an interesting discussion. Sea level rise gets more attention than other aspects of climate change.
Is that because it is the worst?
5 September 2008 at 2:21 PM
A quicky Sandbox101 clarification: Stefan’s paper says 3.4mm/yr/degree. I do not understand the \per year\ part. If global surface temp goes up 1 degree, does the sea level rise 3.4mm per year for ever? Seems odd, but I don’t know.
[Response: My paper is here, if you want to read it. The simple approach is only valid for the initial sea level response to large and rapid rise in global temperature, as sketched in Fig. 1 of my paper. Some people have misunderstood this. Obviously this rise will not continue forever but asymptotically approach a new equilibrium. And obviously this approach will not work for the small natural sea level fluctuations found in the preindustrial centuries, since these are ruled by different physics. You have to have a big rapid global warming that sticks out well from the natural variability for this approach to make any sense at all. stefan]
5 September 2008 at 2:35 PM
Geoff Beacon wrote: “Sea level rise gets more attention than other aspects of climate change. Is that because it is the worst?”
I am more worried about drought. Even the worst-case scenarios of sea level rise suggest that it will take many years, perhaps decades, to have truly catastrophic effects (e.g. to displace tens of millions of people in coastal areas).
On the other hand, another effect of global warming, namely massive, continent-wide, intense, persistent drought, could begin at any time and have catastrophic effects on agriculture, leading to widespread famine within a few years. Indeed there is evidence that such intense, chronic drought may already be kicking in with a vengeance in Africa and Australia, as well as parts of North America.
Surely this is a more urgent and imminent danger than sea level rise, yet it doesn’t seem to get as much attention.
5 September 2008 at 2:38 PM
#44: Yes, because [1] one of the big problems with sea level rise is that there is very little one can do to stop it. How big of a wall are we going to build to hold off the water? How strong can we really make it? Just the eastern seaboard of the US has a daunting enough length, what about the rest of the world? And [2] as they mention in the post, sea level continues to rise for a significant period of time even after temperature rise is stopped or reduced.
5 September 2008 at 3:11 PM
#49–”People crib about $4 gas; $4 (or more) bread will cause a real ruckus.” I want to validate everything about your post except the timeline: the good bread I used to buy regularly hit $4 last year. I still miss it. . .
5 September 2008 at 3:22 PM
It’s always advisable to read the paper first, but the authors public comments are informative, too:
ScienceNOW Daily News 4 September 2008
“They calculated how fast glaciers would have to flow in order to raise sea level by a given number of meters and then considered whether those flow rates were plausible or even physically possible. In Greenland, they calculated ice loss through specific rock-bounded “gates,” which are carved in the edges of the island. In West Antarctica, the gates are not well defined, so the team used approximations of how flow might respond to rising temperatures….estimates of several meters of sea level rise made by some other researchers are “physically untenable” because not enough ice could be pushed through the glacial gates, according to the paper’s authors. ”
PhysOrg Sept 4, 2008
“…global sea rise of much more than 6 feet is a near physical impossibility…
Most of the marine-based ice in West Antarctica is held behind the Ross and Filcher-Ronne ice shelves, which Pfeffer’s team believes are unlikely to be removed by climate or oceanographic processes during the next century….
Policymakers need to be able to predict sea level accurately if communities, cities and countries around the world are going to be able to plan effectively, Pfeffer said. “If we plan for 6 feet and only get 2 feet, for example, or visa versa, we could spend billions of dollars of resources solving the wrong problems.”
Daily Telegraph 04/09/2008
“…estimates of future rises remain hazy, mostly because there are many uncertainties, from the lack of data on what ice sheets did in the past to predict how they will react to warming, insufficient long-term satellite data to unpick the effects of natural climate change from that caused by man and a spottiness in the degree to which places such as Antarctica have warmed….
“We simply don’t understand the physics of ice dynamics well enough to make accurate model predictions,” says Dr Harper. “There are just too many uncertainties…”
Climatologists usually present possibilities and probabilities, here I’m pleased to see “a near physical impossibility.”
5 September 2008 at 3:36 PM
Rod B #45 yes, a very good question. Note that Stefan calls this a “semi-empirical” approach, meaning that there isn’t much physics behind it.
But there is this much physics behind it: both the melting of glaciers and the warming of ocean water is driven by the imbalance between incoming and outgoing heat energy. As a proxy for this you could take the difference between current mean temperature and the equilibrium mean temperature for current forcing. But as we well know, the latter is not very well known.
So, instead, StefaSo, instead, Stefan takes current (realized, transient) mean temperature excess. In the simplified situation where the excess forcing grows exponentially, this quantity is proportional to the excess forcing, as well as to the above described heat imbalance. For the 20th century the assumption of exponentiality is roughly OK.
Note that this is the same kind of idea that was behind Pat Frank’s writing, only there it was a fallacy
5 September 2008 at 3:36 PM
SecularAnimist,
You are right, drought is right up there as one of the worst problems associated with AGW. I don’t know. Some RC regulars may know that I am very sensitive about drought around the Med, but sea level rise is a pretty nasty problem too. Maybe our moderators can provide some perspective?
5 September 2008 at 3:39 PM
Figen Mekik wrote on 5 September 2008 at 2:38 PM:
“And [2] as they mention in the post, sea level continues to rise for a significant period of time even after temperature rise is stopped or reduced.”
This cannot be overemphasized. There will be no stable coastline for centuries. We will have to either a)keep building higher levees or b)keep retreating from the coastline for centuries
5 September 2008 at 3:46 PM
Some people appear to think that we are balming (sic) the media for the misleading headlines on this story. That is certainly not the case since most of the spin originated from the press release (as we stated clearly above). It is unfortunate that these headlines arose because they will mislead, but it is not because of the ‘bad media’ (though many stories did see past that press release). Pielke makes another error in equating thought experiments (as performed by Hansen in his ERL paper) with an informed prediction. Postulating a non-linear doubling process in order to get an order of magnitude estimate is not the same as making a prediction as he makes very clear, and later in that article, he states what he fears may happen (quoted above). Pielke might think that the Pfeffer et al constraints are reduction in the projections, but as we have stressed numerous times, the projections that matter are the ones that come out of the assessment processes, not from the musings of individuals (however their sometime ambiguous pronouncements are interpreted). With many people (linked above), still incorrectly insisting that sea level won’t rise above 10cm in a century, these latest constraints should be sobering. We’ll see.
5 September 2008 at 3:48 PM
North and south ice sheets are breaking up. Greenland is a hollow bowl. Has anybody calculated how much sea rise is required to turn Greenland’s interior into a grounded ice sheet?
5 September 2008 at 4:08 PM
Hi Gavin-
Now it’s the press release?
You would be better served by simply correcting your silly claim that “no-one (and we mean no-one) has published an informed estimate of more than 2 meters of sea level rise by 2100″. Anyone can read Hansen and see that he thinks that his estimate was “informed” and likely to be more “better estimate” than Rahmstorf’s approach for 2100.
I have little confidence in the ability of the scientific community to accurately predict sea level rise — though the constraint approach by Pfeffer et al. helps move beyond the prediction problem. After all the 1990 IPCC grossly overestimated sea level rise to date:
http://sciencepolicy.colorado.edu/prometheus/verification-of-ipcc-sea-level-rise-forecasts-1990-1995-2001-4315
And in 2007 didn’t really offer any predictions.
If there is anything to take issue with in the Colorado press release it is the idea that decision makers can optimize a response to sea level rise, they cannot.
[Response: Roger, my interactions with you are always singularly unproductive and so my patience in pointing things out to you is limited. Having said that, please read the line in the above post (third paragraph from the bottom) that starts “(exemplified by…”. Perhaps you missed that earlier, but in case it still isn’t clear, we were pointing out how the spin in the Reuters piece took a very clear lead from the press release. So it’s not “now” that the press release is an issue it was “then”. Are you even disputing this? And as for IPCC AR4 not making statements about sea level projections, I have no idea where you get that notion (see section 10.6 in WG1). We might be able to agree that they were inadequate or poorly communicated, but not nonexistent. - gavin]
5 September 2008 at 4:34 PM
re no 25. I was in Thule AFB in Greenland for 2 weeks around the end of August. In 14 days, we had perhaps 4 days where it did not rain.
I was speaking with a few local workers at the base, who indicated that the tongue of the glacier visible about 30K west used to be almost at the end of the runway 10 years ago.
Interestingly enough, we were not able to resupply one arctic location as the runway was too soft for landings (2nd year ever it happened) and had to stop a couple of days at our main location as the top of that runway softened due to the landings and the constant wet snow and drizzle (Alert).
5 September 2008 at 4:34 PM
Here is another example:
“Sea-level rise from melting of polar ice sheets is one of the largest potential threats of future climate change. Polar warming by the year 2100 may reach levels similar to those of 130,000 to 127,000 years ago that were associated with sea levels several meters above modern levels; both the Greenland Ice Sheet and portions of the Antarctic Ice Sheet may be vulnerable. . . Corals on tectonically stable coasts from the last interglaciation period (LIG) provided strong evidence that sea level was 4 to >6 m above present levels during a sea-level high stand that likely lasted from 129,000 ± 1000 years ago to at least 118,000 years ago.”
http://www.sciencemag.org/cgi/content/full/311/5768/1747
From the NCAR press release:
“Ice sheets across both the Arctic and Antarctic could melt more quickly than expected this century, according to two studies that blend computer modeling with paleoclimate records. The studies, led by scientists at the National Center for Atmospheric Research (NCAR) and the University of Arizona, show that Arctic summers by 2100 may be as warm as they were nearly 130,000 years ago, when sea levels eventually rose up to 20 feet (6 meters) higher than today.”
http://www.ucar.edu/news/releases/2006/melting.shtml
[Response: You aren’t reading carefully (though both cases could have been much better worded). The polar warming at 2100 was projected to be comparable to Eemian warmth, but the sea level rise was a long term response with an unknown timescale. However, I’m sure it’s comforting to know that you aren’t the only person to get that wrong. - gavin]
5 September 2008 at 4:41 PM
Richard C. asked at 3:48 pm on 5th Sept 2008:
“how much sea rise is required to turn Greenland’s interior into a grounded ice sheet?”
Parts of Greenland’s interior are currently below sea level. There are some pretty deep spots under Petermann , Humboldt, in the NW and Nioghalvfjerdsbrae (how does one pronounce that ?) and Zachariae Istrom in the NE just south of Independence Fjord (where the NEGIS emerges)
might want to look at http://membrane.com/sidd/greenland.html and an animation
http://membrane.com/sidd/greenrockturn.html
5 September 2008 at 5:02 PM
One meter sea level rise in a century will do no good, and potentially some harm, to the near-shore marine life community; shellfish such as clams and limpets are particularly at risk. During the transition for LGM to the Holocene the sea level rose about 120 meters over, say, 12,000 years; an average of a meter per century. During this the near-shore marine community of eastern South America, with a gentle grade to what is now the continental slope, was compeletely (or nearly so) disrupted; it only recovered during the Holocene. In contrast, the Pacific shore of South America, very steep, suffered no ill effects.
Sandy beaches: sandy beaches are the result of along-shore currents and also wave action bringing sand from production areas to dewposition ares. For example, Maine and further north are production areas for the east coast of North America; the sand is transported further south and eventually to the deposition areas of the Carolina Outer Banks and off-shore thre. (I don’t know what happens further south.)
This action won’t stop due to a 1–2 meter rise; winter storms will continue to pile up sand onto the current beach. Wherever there is sand now there will continue (mostly) to be sand. Wherever there are rocky shores that state also will (mostly) continue.
So your grandchildren will be able to go to the beach, but there will be no need to bring a spade and a bucket for clamming.
5 September 2008 at 5:05 PM
Gavin-
Indeed, you suggest that Hansen made an “ambiguous pronouncement” . . . Overpeck could have been “much better worded” . . .
But perhaps you could point me to the Real Climate admonishments of these scientists for their imprecision/bad writing when their work was widely misinterpreted? Or perhaps to where these scientists sought to correct the egregious public misinterpretations?
[Response: So now it’s my fault? Well, we spelled out what it meant at the time. As for corrections, it’s definitely happened - the original headline after the 2006 Science papers in the San Francisco Chronicle had “20 feet by 2100″ or similar, the authors immediately contacted the paper and they changed the headline to something better (but not perfect) “OCEANS RISING FAST, NEW STUDIES FIND” and corrected the text from what appeared in the print edition. And RC has often criticised press releases for leading the press astray. I’m very much of the opinion that most of the press does a pretty good job overall given the constraints they work with, but there are fault lines that occasionally get tripped - through a combination of bad framing, or uncontextualised press releases, or naive scientists - that end up (predictably) producing vastly misleading headlines. Maybe you’d like to come to my class at the J-school where I go over these examples and more… - gavin]
5 September 2008 at 5:05 PM
Richard C. asked at 3:48 pm on 5th Sept 2008:
“how much sea rise is required to turn Greenland’s interior into a grounded ice sheet?”
In my last comment I should have mentioned the Pfeffer paper, in Fig 1, shows the marine based outlets as including almost all the usual suspects, not just in the NE and NW.
5 September 2008 at 5:16 PM
#23 Mike Tabony asked, “Where does Slioch (#18) think the human race will get the energy and material resources to rebuild the world’s ports?”
I don’t. I was suggesting that coping with a one metre per century change in sea level continued for several centuries might be even worse than a one-off catastrophic change, since at no point would we be in a position to even begin to rebuild coastal communities and would be in a state of constant flux.
In other words, it is not just how much sea level rises, but how long it takes which is important. The latter is usually not emphasised.
5 September 2008 at 5:20 PM
Gavin, what value for “total sea level rise in the next 100 years” would you give to an engineer or policy maker that needs to be 99.9999% (1 in a million) certain that his design or policy will protect the public safety for 100 years? Not just for today, but a number we can be certain of for 100 years. If you make a mistake and people die, how many deaths can you live with? I am not being dramatic. You are a climate expert, and we need to set public policy. We need a number.
As you suggest, it rains on the flanks of the GIS. Where does that water go, how much heat does it carry, and where does it release that heat? It is a foundation engineering problem of the first water. The top of the ice sheet can stay cold, strong , and rigid, but, if the foundation fails, the whole structure fails. The flanks act as compressive buttresses to the ice foundation that supports the central massive. (Think of a concrete building tipping over as its permafrost foundation weakens.) Weaken the flanks of the ice sheet, and the ice under the massive is subject to compressive failure. Worse, it is a basin with its outlets plugged with ice, allowing the formation of subglacial and intraglacial lakes large enough to produce significant hydrostatic pressures. The problem today, is that we have both known unknowns and unknown unknowns in this system.
Pfeffer, et al’s number is not total, and it has no certainty. To be useful in planning, we need a value for total sea level rise. Without good estimates of uncertainty and defining both ‘known unknowns” and unknown unknowns,” Pfeffer et al’s is useless for engineering or public planning. If our best estimate of sea level rise contains substantial “unknown unknowns” then we might want to adopt a procedure similar to the one used by the US EPA for Human Health Risk Assessments a while back, and apply safety factors.
They would say:
“The estimated number is 2 meters, the safety factor is 10, so the maximum plausible sea level rise from Greenland is 20 meters by 2100, take precautions accordingly”.
They might go on to say:
“The estimated SLR from permafrost melt is 1 meter with no unknowns, and the estimated sea level rise from Antarctica is 2 meters with very large unknowns so the safety factor is 100. Thus, the total maximum sea level rise for public safety purposes is 221 meters. If you do not like that number, go do the research to eliminate the unknowns and uncertainties so we can remove the safety factors.”
Ahh! Those were the days when federal agencies had more . . . . funding.
If our federal agencies, said firmly, “The SLR number is 221 m. DOW, Exxon, BP, US DOE, US DOD, and so forth ; What are your plans for dealing with a 221 m rise in sea levels?” We would have the data to resolve the unknowns real fast, and we would be in a low carbon economy, real fast! True, nobody would be happy. Nobody liked CERCLA either, but it saved a lot of lives.
Are such safety factors good climate science? No! However, they are good risk management science. They are good engineering and very good public policy. Such policies protected the public health and safety from hazardous waste in the environment with unknown characteristics. Are such numbers alarmist? No, they are the basis of good,conservative engineering.
[Response: I’ve not consulted directly with planners on this issue, but people I know do this on a regular basis. The most questions come up when some new infrastructure is being planned - a recent example was storm drains in New York City - the planners wanted to know how high above max high tide levels they should build the drains. The factors were that the infrastructure was going to last for 50 or so years, and they didn’t need a guarantee or perfect prediction but just an range that would likely keep them out of hot (cold?) water. I think that the advice was that an allowance for 1 meter additional rise over an above what their storm surge estimates gave. That’s pretty conservative advice (as in erring on the safe side), but it will be much clearer in 2050 (when they are planning for the following 50 years) what the trajectory really is. Advice that no allowance for SLR was needed would have been irresponsible, advice in the mid-range of projections would not have been useful either. The point is that you can give useful advice even in the midst of great uncertainty without having to exaggerate the likely effects. - gavin]
5 September 2008 at 6:10 PM
Aaron Lewis wrote at 5:20 pm on the 5th of September, 2008:
“[Greenland] is a basin with its outlets plugged with ice, allowing the formation of subglacial and intraglacial lakes”
I suspect that some of the outlets might melt open. Is there any evidence yet of substantial subglacial lakes in Greenland? I have heard of several in Antarctica, some of them interconnected, changing sometimes on a daily basis.
5 September 2008 at 6:41 PM
sidd, click here for your question, as Googled:
http://www.google.com/search?q=subglacial+lakes+in+Greenland
5 September 2008 at 6:45 PM
“… Eventually all of Greenland’s floating ice could disintegrate. At that point the ice streams may stop accelerating. Then again, they may not, Steffen says. The weight of Greenland’s ice sheet has forced its bedrock down into a vast basin, much of it below sea level. As the glaciers retreat inland, the ocean may follow, prying them off their bed in a runaway process of collapse….”
http://ngm.nationalgeographic.com/print/2007/06/big-thaw/big-thaw-text
5 September 2008 at 7:52 PM
There is a nifty interactive sea level inundation mapper at the flood.firetree.net website. Just zoom into your part of the world, select a sea level rise amount (up to 7m) and then strap on a snorkel.
5 September 2008 at 8:25 PM
Gavin,
For about a year i’ve been looking at the material on SLR and 3 months ago I began to summarize SLR for a friend who happens to have a house over the water (S. California). So from a real world perspective he is very interested in potentials. I spoke with a friend at Scripps and he said a cm is a cm regarding wave height, but related the problem of potentially stronger storms in our region as ocean temps rise.
To my friend, I basically started by saying his question is one of the most difficult to answer scientifically. And I did resort to what you referred to as “male up even scarier monsters” with a high concentration on the uncertainty in that realm (I was careful when discussing the dragons). My objective was to show him the scientific analysis IPCC and Stefans paper and then compare that to Hansen, current SLR observed and paleo record as currently understood re. past SLR and estimated temps, GHG levels, length of time at those levels and hypothesized negative feedbacks such as cloud albedo, even though it seems the climate system managed to get past such effects in the past and of course feedbacks and non linear potential.
Along the lines of the Arron Lewis question in comment #63, if you feel it is plausible, can you characterize the risk potentials based on the following considerations:
The PDO is supposedly entering a cool phase, or finishing its warm phase, for eastern pacific, and still we had an unusually strong El Nino event with significant coastal erosion.
Is there a scientific way to discuss the potential or likely effects such as storm damage rather than SLR, since that is the greater immediate danger as far as I can tell pertaining to ocean temp rise increasing storm strength a as opposed to SLR for the eastern pacific, i.e. specifically the west coast. It’s obvious the gulf and Atlantic regions will get stronger storms but the Pacific has a different tempo and being a larger body, slower thermal inertia.
So then, just as models indicate stronger hurricanes generated in the Atlantic, Is it then reasonable to expect higher potential for a similar El Nino event to the 98 event, especially considering the likelihood of increased solar forcing when the Schwabe cycle gets back into gear? Was the 98 event just an El Nino riding on top of the global warming wave, or an even more significant event? I’m not sure how to talk about this? Because if that event was more signal than noise, so to speak, then the next one could be even stronger. Or is this too much weather talk and not enough climate?
5 September 2008 at 8:42 PM
> where these scientists sought to correct the
> egregious public misinterpretations?
I recall the original error was in the Associated Press wire story. By the time I contacted the SF Chronicle science writer Perlman, if I recall correctly, he had already heard about the problem (as Gavin points out, someone was trying to catch the error). He’d told his editors — but they hadn’t done anything. He told them again; they changed the headline. They didn’t change the text. We exchanged more email. He told them again. They finally changed the text. Way too late.
Wasn’t this AP wire story and error correction talked about on Pielke’s blog at the time? Oddly it’s impossible to find mention of it with Google, for me.
Anyone know where the Associated Press keeps their errata and corrections list, presuming they have such a thing? Andy Revkin might know.
5 September 2008 at 9:00 PM
Gavin’s inline at #63:
Good response. Seems you have learnt a little engineering. Lots more similar understanding may be needed. Hint: Setting levee crest levels is tougher. Overtopping is (literally?) a “tipping point”. It tends to kill people.
G.
5 September 2008 at 9:06 PM
The effects of a 1 or 2 metre SLR over a century is not a big deal compared to the changes we’ve made to coastlines over the last century, much of New Orleans was below sea level when it was built, and Man’s engineering abilities are far greater now than they’ve ever been.
As for 100 million displaced, how many people have been displaced as a result of human factors over the last century, I’ll bet more than 100 million.
Not disputing than AGW’s happening, or that the effects of some of the changes may be dire, but can we please be realistic about what the numbers actually mean?
5 September 2008 at 9:58 PM
I took Mr. Roberts most excellent advice, and discovered these references to subglacial lakes in Greenland:
this one is rather good i thought:
http://topex.ucsd.edu/rs/fricker.pdf
and this one is good too
http://rsl.geology.buffalo.edu/documents/csatho_icelandigs2006.pdf
and some nice models by Schoof, Evatt and many others. For some reason i feel compelled to add this last link
http://arhiv.rgo-speleo.ru/rgo/books/glacier_karst7/mavlyudov_1_68_73.pdf
lastly: are the proceedings of this:
http://www.macsi.ie/igs/Programme.html
to be published soon ? in the Journal of Glaciology, perhaps ?
5 September 2008 at 10:54 PM
Gavin inline comment on #63
For storm drains in NYC, a SLR of 1 meter is a cost effective design criteria.
Do not get me wrong, I love good storm drains, but there is no law saying NYC storm drains must be designed to withstand 200-year return event storms. Thus, PE liability and bonding issues are minor, and the value of enhanced storm drains is limited by the vulnerability of legacy infrastructure.
The question stands. What is the value for SLR that you are 99.9999% sure will not be exceeded in the next 100 years?
5 September 2008 at 10:59 PM
“We stress that no-one (and we mean no-one) has published an informed estimate of more than 2 meters of sea level rise by 2100.”
[edit]
Here’s James Hansen’s presentation on the 20th anniversary of his 1988 testimony to Congress:
http://www.columbia.edu/~jeh1/2008/TwentyYearsLater_20080623.pdf
“Debate among scientists is only about how much sea level would rise by a given date. In my opinion, if emissions follow a business-as-usual scenario, sea level rise of at least two meters is likely this century.”
Or is James Hansen’s estimate not “informed?”
6 September 2008 at 12:10 AM
Maybe RC needs a media contacts address book, so corrections can be e-mailed to science reporters. Maybe they’ll eventually start viewing press releases with a more critical eye, or even wait a day for some third-party analysis.
6 September 2008 at 12:25 AM
This discussion seems to drift between Artic ice conditions and sea level rise.
Well global ice is maimly concentrated in the SH not the NH! Not that you would realise that from most of the posts here.
As far as sea level rise is concerned there is absolutely no evidence of an accelerating trend, which would be necessary, for some of the dire predictions, stated here, to come to pass. Indeed sea levels have been stable for 2 or three years now. how come?
Alan
6 September 2008 at 1:14 AM
I just noticed something about the press release. It notes that “Some scientists have theorized that continuing warming trends in Greenland and Antarctica could warm the Earth by 4 degrees F over the present by 2100. The last time that happened, roughly 125,000 years ago during the last interglacial period, glacier changes raised sea level by 12 to 20 feet or more. But the time scale is poorly constrained and may have required millennia, Pfeffer said.”
I thought 4 degrees wasn’t exactly at the extreme end of the IPCC projection range, and that the IPCC would constitute more than just “some scientists”. Am I mistaken? And do we have a reliable estimate of the rate of temperature change during the LIG, and how it compares to projections for this century?
6 September 2008 at 2:13 AM
Roger Pielke, Jr in #55 states that the IPCC’s first assessment report “grossly over-estimated” sea level rise to date. I see a link to his own blog, but I cannot check the original report as it is not online (and the Wikipedia summary a rather hopeless stub, which I hope can be improved upon). As a layman, I’d expect to see a range presented, but on Roger’s blog it is a single trajectory for each report (with the first report over-estimating, and the following two underestimating).
Could someone expand on what was actually in the original 1990 report? Is Roger’s summary fair? Specifically - what is each line on his chart - the average forecast? The maximum? And was there a projection for the century? Obviously the first report was based on much less research than followed even four years later (let alone right now), but just interested in getting a better historical conext for this latest paper following Gavin’s thoughts - thanks.
[Response: We’ve had this discussion before with Pielke, about the temperature projections of the first IPCC report. Gavin can probably quickly find the link. The key point is that the first report included only the warming effect of greenhouse gases, but not the cooling effects of anthropogenic aerosol pollution. You have to remember that scenarios are not predictions, but “what…if” type calculations. What would happen if greenhouse gases rise by that much? Thus, as a calculation of the warming and sea level rise that these greenhouse gas emissions would produce (by themselves), this may well have been correct. But there was an additional effect that IPCC did not include in the scenarios at the time, namely the aerosol pollution. Hence these scenarios were not realistic, even if technically the estimates were correct. -stefan]
6 September 2008 at 2:21 AM
As the glaciers retreat inland, the ocean may follow, prying them off their bed in a runaway process of collapse
I must confess I’ve never understood this particular prediction of doom. If the ocean is able to “pry them off their beds”, it follows that they must already be sufficiently far below sea level that they would float. And if they’re floating, then the sea level rise from melting them is zero. Surely it’s exactly the other way round - the deeper below sea level the Greenland bedrock is, the better?
6 September 2008 at 4:46 AM
Gavin,
To quote from above, “…no-one has published an informed estimate of more than 2 meters of sea level rise by 2100.”
Firstly, Hansen is on record as expecting a SLR of more than 2 metres under BAU - see my post #30. I accept this does not appear in a peer reviewed publication.
Secondly and more importantly, when it comes to the cryosphere, informed estimates have so far proved to be gross underestimates. Prior to 2007 the informed consensus was for artic sea ice to be gone in mid summer between 2050 and 2100. Now some scientists have “informed” expectations that this will happen within 5-10 years and 30 years is a reasonable consensus.
As you well know, projections of global temperature rise are underpinned by sound physical models that have proven reasonably accurate since Hansen’s 1988 paper (if not earlier). But projections of SLR is not underpinned by sound understanding of the physics of ice sheet collapse.
Until models can reproduce the gyrations in SL over the last 100,000 years or so - including the 5 metre per century rise over 4-5 centuries during “Meltwater Pulse 1A”, one wonders what value peer-reviewed “informed” estimates have. (Peak rates were probably greater than 0.05m/yr.)
Until then surely we can really only attempt to “constrain” the range of expected SLR. (Pfeffer’s paper appears to be an attempt to do this - I can’t access it to check.) Using the IPCC lower bound would be a reasonable, although highly unlikely, lower bound SLR. The maximum might best be determined by paleoclimatic-geologic estimates - at least they *really* happened.
Meltwater Pulse 1A occurred under substantially less forcing than we currently have, but it almost certainly was preceded by millennia of “build-up”. So, on balance, 5 metres by 2100 is a reasonable, perhaps equally-unlikely, upper bound.
This gives a range of SLR from 0.2 to 5 metres by 2100.
6 September 2008 at 4:47 AM
David B. Benson posts:
Note, also, that one meter of sea level rise is enough to make many, many coastal cities uninhabitable. All the seawater has to do is back up sewers and seep into aquifers, and bingo — you’ve got a city nobody can live in, unless they take special equipment with them.
6 September 2008 at 4:51 AM
Andrew W. posts:
It’s enough to make Miami, Jacksonville, and many other coastal communities around the world uninhabitable, along with much of Florida and Bangladesh. See my earlier post here.
6 September 2008 at 4:59 AM
Re 45 Rod B:
I suspect 3.4mm/yr/degree should be interpreted as follows: for every degree C global mean temperature rise we predict a sea level rise of 3.4 mm per year or 0.34 metres per century.
6 September 2008 at 5:55 AM
For those who are interested, the ongoing Thames Estuary 2100 project has involved intensive research into how London’s resilience against flooding can be maintained/improved over the next century (and somewhat beyond). The Consortium have indicated confidence that, through the implementation of a portfolio of measures, it is possible that the greater part of London could be protected against 5.25m of sea level rise; contingent on the development of effective decision-making, financial and construction plans (e.g. Thames Barrier 2.0) and processes within an adequate timescale.
Paper is not online but full citation is:
REEDER, T., WICKS, J., LOVELL, L. & TARRANT, O. (2008) Protecting London from Tidal Flooding: Limits to Engineering Adaptation Paper presented at the Tyndall Centre for Climate Change Research Conference “Living with climate change: are there limits to adaptation?” 7th & 8th February 2008. RGS, London.
6 September 2008 at 6:21 AM
I recall reading somewhere that it would take decades for sea level
rise occasioned by ice-sheet melt to reach distant coastlines like
those of South Asia. Is this true? It seems implausible, but if true,
it gives valuable time.
[Response: No. Most of the sea level rise travels as a gravity wave (like a tsunami) which would go around the world in a day or two. There certainly are longer term adjustment processes that work slower (and a paper recently by Stammer discussed this). - gavin]
6 September 2008 at 6:49 AM
Don’t wait too long to see Venice.
6 September 2008 at 7:27 AM
Ref 63, 73 on probabilities and risk factors for use in design.
Thanks for raising this point. It is critical to the response of policy makers.
Factors of 10 or 100 appear to be a bit extreme, particularly when dealing with a 50 or 100 year life (as would be the case for infrastructure. Normally, in the world we knew a couple of decades ago where the environmant was basically stable, we would take the bell curve of data such as wind speeds (extreme values of these above some cut-off) and say that for safety we will assume the 95th percentile value is suitable for design. Then a design event would be chosen that would typify this level of probability of the wind (or other event) being exceeded within the life of the structure.
In practice due to the conservatisms used in the design and construction process the true safety factor for structures has been of the order of 5 or more above this event. In fact the real safety factor is often not known as we don’t have enough data on building collapses to determine it. Buildings often fail not due to the design being too low, but the details of construction being lacking in some way.
A method has been derived that sets a ‘reliability’ level for the structure and this is used to determine the probability values used for design. There is a lot of mathematics in this method and not relevant here in this blog. However, for the simplest approach, structures are designed for an ‘event’. Drainage might be designed for a 1 in 20 or 1 in 50 year event (based of course on the “stable” climate we all know). Buildings are dsigned for winds of the order of 1 in 500 year event and earthquake is similar (with an additional look over the sholder at the 1 in 2000 year earthquake in high risk areas such as California).
If we start to look at SLR, we might say that we should take the 95th percentile of the upper extremes of the peer reviewed ranges provided in the last say 2 year period (rounded to a logical value). It would seem appropriate to then make some assessment of the rate of change in such predictions over the last 5 years to see if there was some adjustment to be made. On the basis of this there may be an additional factor put on the 95th percenbtile value as a sort of “uncertainty” factor for safety reasons.
A review process would be necessary to adjust the “design value” given emerging new data and better predictions. Such adjustment may allow for a reduction in the uncertainty factor while raising the 95th percentile number, thus leading to a best approximation of the likely value as understood at the time it was set.
From a very limited understanding of the current range of predictions (please correct me if you know of further info), I would say the value should be of the order of 0.5m for 2050 and 1.0 for 2100 with an additional factor of 2 for 2050 and say, 3 for 2100; giving
1m for the 50 year design
3m for the 100 year design
These design values would have to be revised on a 6 mth or yearly basis at the moment, as the information available is changing so rapidly. Personally, the IPCC should be giving us a report every 1 or 2 years, not every 4. Knowledge is changing to quickly in this area.
6 September 2008 at 9:49 AM
There are a few places on Earth that are below sea level where inland seas have evaporated away, like e.g. Death Valley. If we flood these areas again and recreate the inland seas, we can lower sea levels.
[Response: Yes. but do the math - to get rid of 1 m of sea level from 70% of the globe is a lot of water. You would have to flood a lot more than Death Valley and the Dead Sea. Something more like Montana/Ontario and Quebec to recreate the paleo-Lake Agassiz for instance. - gavin]
6 September 2008 at 10:17 AM
#78 inline response - thanks Stefan, that helps enormously. Am I right in thinking, then, that really the IPCC have only made two sets of outright all-encompasing predictions, then - in 1995 and 2001? 1990 was a scenario, and 2007 left out dynamic ice sheet processes completely because they were so uncertain.
From my reading of Roger’s blog, I guess he’d interpret the “scenairo” 1990 explanation as spin. I’ve no reason to doubt that the 1990 and 1996 processes were quite different, and exactly as you say, although I don’t have access to the reports. I’d hope that those writing reports - especially IPCC ones - would flag up very clearly important distinctions such as this one (I didn’t realise that the critical significance of the different methodology in 2007 until Real Climate pointed it out). And I’d hope that all climate scientists would help get these sorts of messages across to clarify to the public, rather than point score based on comparisions which should not legitimately be made.
6 September 2008 at 10:22 AM
Aaron, your question
> What is the value for SLR that you are 99.9999% sure will not be exceeded in the next 100 years?
indicates you haven’t taken a statistics course. Look up ‘long tail’ for pop science articles that may be helpful.
Peter Ellis,
William Connolley would have fixed “pry them up off their beds” if that had been from Wikipedia (where someone had the glaciers dragging themselves out of their beds).
What the National Geographic writer was waxing (or waning) poetic about is this: the Greenland ice, like the Antarctic ice, has piled up quite high above ground and above sea level —- look at the elevation of the top of the ice in both cases.
Yes, ice floats. But if you take a cubic foot block of ice and put it in water an inch deep, it doesn’t float. It rests firmly on the bottom of the container. You can look up “basal temperature” and “subglacial lakes” for more — at the bottom of these huge thick piles of ice there are often voids or layers of meltwater just from the pressure, but the pressure is still enormous. Maybe enough to ‘float’ the ice or maybe enough to force any fluid there to move ‘uphill’ if a route is available. It’s not just sitting there inert.
6 September 2008 at 10:42 AM
when the sea level rises and all the ice melts whats gonna happen to the water?? if global warming was to slow down and cease would their be a refreeze?? what does the moon have to do with this??
6 September 2008 at 10:54 AM
Odd is’t it.
“Sea rises may be lower than some predicted”.
But the corollary is that the sea rise WILL be higher than some predicted.
Odd is that they word it so as to push “we’re A-OK, people!”
6 September 2008 at 12:22 PM
Hansen is on record as expecting a SLR of more than 2 metres under BAU - see my post #30. I accept this does not appear in a peer reviewed publication.
Hansen has, if I remember correctly, acknowledged as much. I think his phrase was that his predictions aren’t matched by any model except the geological record.
6 September 2008 at 12:36 PM
Thanks, Martin (50) and Bruce (83), but my question remains. It sounds like Stefan is saying if global surface temperature increases one degree (and then stays there forever) oceans will then rise 3.4mm each and every year hence. Doesn’t sound right. Actually seems impossible. What does he (the units) really mean?
[Response: See my response above (#45) Stefan]
6 September 2008 at 1:24 PM
jose posts:
It will become slightly more fresh and less salt. Ocean currents which depend on temperature and salinity may change.
Not for a long time.
Nothing that I can think of. The sea level rise is far too small to affect the tides noticeably.
6 September 2008 at 2:06 PM
Paul Barton Levenson, a link for you:
http://en.wikipedia.org/wiki/Land_reclamation
“It’s enough to make Miami, Jacksonville, and many other coastal communities around the world uninhabitable, along with much of Florida and Bangladesh.”
Only if nobody does anything for a hundred years.
6 September 2008 at 2:15 PM
Stefan, thanks. Makes considerably more sense!
6 September 2008 at 2:20 PM
Rod B #94:
Yes it does, doesn’t it. But that’s precisely the misunderstanding you shouldn’t make as I tried to explain. Caveat, I cannot access the article, but am somewhat familiar with the theory.
In the general (not: 20th century exponential) situation the proportionality that should exist is not between sea level rate and anomalous temperature (your one deg), but between sea level rate and disequilibrium, say, the warming that is still “in the pipeline”.
If warming stops at +1 deg, then the warming “in the pipeline” will start decreasing at that point, going asymptotically to zero. And so will the sea level rise rate do.
This is actually compatible with the paleo observation that every forcing situation has not only its own equilibrium mean temperature, but also its own equilibrium continental ice situation and equilibrium sea level. Change the forcng, and all of these will start changing to a new equilibrium, which will not depend on the history of getting there, only on the amount of forcing. (Ideally; Snowball Earth is an exception.)
I know this is tricky. Try thinking house, furnace, thermostat, temperatures in different rooms. Sea level is but a special proxy of global mean temperature.
6 September 2008 at 2:26 PM
Barton Paul Levenson wrote: “… one meter of sea level rise is enough to make many, many coastal cities uninhabitable … enough to make Miami, Jacksonville, and many other coastal communities around the world uninhabitable, along with much of Florida and Bangladesh.”
I’d note that coastal areas may become economically uninhabitable long before they become, literally, physically uninhabitable. I am thinking for example of the American southeast — Florida and the Gulf coast region — which will be impacted not only by rising sea levels but also by more large, powerful hurricanes. Well before it becomes physically impossible for people to inhabit these places, it can become economically impossible to inhabit them, given the enormous cost of not only holding back or retreating from the gradually rising sea level, but of repeatedly and frequently rebuilding in the aftermath of huge, powerful, massively destructive storms.
6 September 2008 at 2:48 PM
Yes, ice floats. But if you take a cubic foot block of ice and put it in water an inch deep, it doesn’t float. It rests firmly on the bottom of the container.
Well yes, that’s kind of my point. And adding another inch of water doesn’t pry it off the floor either. It doesn’t actually rise off the floor until you’ve added about 9/10 of a foot of water, at which point of course it will begin to float. And at that point, if the block melts, it won’t make the water rise any further.
To turn the same situation on its head, say you have a nice flat sheet of water, and a 1 foot cube of ice sitting on a table at sea level. Melt the ice, the water level will rise. Now say you have a nice flat sheet of water, and a cuboid 1×1x10 feet of ice floating vertically in it. You have the same 1 foot cube of ice exposed above sea level, but this time when you melt it there is no sea level rise because it’s already floating.
I can’t see why the same doesn’t apply to Greenland. The more of the ice there that’s already below sea level, because of crustal depression, the better: it means less sea level if the ice does melt out. And yet the fact that the centre of Greenland is below sea level is often raised - on this blog and other sites - as a concerning factor in regard to sea level rise.
Is it simply that the [i]rate[/i] of sea level rise may be higher if the glaciers/ice sheet are grounded below sea level? I can see that in that circumstance, a rise in sea level would increase buoyant forces - and reduce friction between the ice and the bedrock, allowing for faster outflow?
Captcha fortune cookie: Rickman Valera. An odd couple that might have revolutionised the course of Irish independence. Or maybe not.
[Response: The issue is different. For glaciers that are grounded below sea level, there is generally a cavity below the glacier tongue and a point at the back of the cavity (the grounding line) where there is a transition between floating and grounded ice. As I understand it (and this could be corrected by someone who actual knows something), the ability of the ice stream to sustain shear changes radically at this point - floating ice (I think) has no shear (velocity differential in height), while grounded ice does (it moves faster at the top). Therefore, as the water warms and the grounding line retreats, the part of the ice that was grounded now starts moving much faster delivering more ice to the ocean. Grounding line stability is a big unknown and for some glaciers, once the old one is released, a new might not form until the glacier has retreated kilometers up the fjord. The issue with WAIS and for a significant chunk of Greenland is that in extremis, it might not stop at all (until all of that ice is spread out and floating). (Please someone correct me if I have this wrong!). - gavin]
6 September 2008 at 3:05 PM
Rod, I see now that Stefan Rahmstorf’s paper was put on-line. It’s even simpler than I thought it would be. Obviously the problem with the approach outlined by me is, that warming “in the pipeline” is not observable, and using model computations to construct it introduces model uncertainty… then it is a good question if the method is anymore worth applying as compared to direct model simulations. Still it might be a useful consistency check.
6 September 2008 at 3:30 PM
The issue with WAIS and for a significant chunk of Greenland is that in extremis, it might not stop at all (until all of that ice is spread out and floating).
Nope, sorry, still can’t grasp this. You can’t float a significant chunk of Greenland until you get to the point where melting that chunk doesn’t cause any sea level rise. That’s what floating is (modulo fractional changes due to differing density of saline/fresh water, but that’s not what we’re talking about).
Say we have a shallowish tray a couple of inches deep, with your 1-foot cube of ice sitting in the tray. That corresponds to the Greenland ice sheet, sitting in a depression in the bedrock. There are a couple of cracks in the tray rim where ice is oozing out. The tray is sitting in water, which is gradually rising up the sides as the sea level increases.
As the sea level rises closer to the rim of the tray, I can buy that it might make the streams of ice move faster. I think your point about shear is simply a restatement of my “less friction with the bedrock” in other words - it’s the friction with the ground that causes shear.
As sea level continues to rise, it will eventually overtop the rim of the tray - i.e. the grounding line of the glacier moves far enough back that it reaches the part of the ice sheet that is below sea level. That will not magically float the huge cube of ice in that tray. You just cannot float the Greenland ice sheet until you have already attained the 7m sea level rise you’d get from melting it down! It doesn’t make physical sense.
[Response: You are assuming that the ice sheet retains the same shape. It doesn’t. Imagine your ice cube suddenly becoming much thinner - now all of it is floating, and everything that was above sea level (minus 0.1 times the amount below sea level initially) has added to the water being displaced. (Note that we are really talking about WAIS, only a small part of Greenland is drained in such a manner). - gavin]
6 September 2008 at 3:47 PM
…and Rod, I committed a thinko above. It is true that both the temperature “in the pipeline” and the sea level rate “in the pipeline” go asymptotically to zero under constant forcing — but in completely different ways.
The temperature change “in the pipeline” is about half of the total temperature change, and most of this comes out over decades, only a small fraction over centuries.
For sea level rise, however, as for the volume warming of the ocean, the amount “in the pipeline” is almost all of it, and it will take many centuries to fully come out. Like warming up the deep ocean, and melting continental ice sheets do.
What this means is that Stefan Rahmstorf’s approximation (temperature anomaly == imbalance) isn’t really an approximation at all, but pretty realistic: any sea level rise that we start now by elevating global mean temperature will go on “forever”, many many centuries, before levelling out.
6 September 2008 at 4:12 PM
Ryan T (77) — Here is the peak of the Eemian from Petit et al. analysis of the Vostok ice core (ybp, temperature above present, i.e., 1950 CE)
128309 2.78
128357 3.23
128405 3.16
128453 3