Guest Post by Willis Eschenbach
Much has been made in AGW circles of the sea level forecast of Vermeer and Rahmstorf, in “Global sea level linked to global temperature” (V&R2009). Their estimate of forecast sea level rise was much larger than that of the IPCC Fourth Assessment Report (FAR). Their results have been hyped at places like RealClimate as being much more realistic than the IPCC estimates.
So I figured I’d see how Vermeer and Rahmstorf are faring to date. Their results for each of the IPCC “scenarios” are archived here, and the first thirty years of their estimates are presented along with nearly twenty years of actual observations in Figure 1.
Figure 1. Satellite-based sea level observations (blue line), along with the V&R2009 sea level estimates corresponding to the various IPCC future scenarios. Sea level observations from the University of Colorado. PHOTO SOURCE
So … how are the V&R2009 predictions holding up?
Well, … or to be accurate, not well. As you can see, the observations showed an actual sea level rise that is below the lowest of the V&R2009 estimates from the lowest of the IPCC scenarios.
At present, assuming that the distance between their “best” estimate and their “lower” estimate is two standard deviations, the data is now more than four standard deviations below the “best” V&R2009 estimate.
So in answer to how their forecasts are faring, the answer is … very poorly. Abysmally, in fact. Actual observations are lower by four standard deviations than the V&R2000 “best” estimate, and are two standard deviations lower than their “lower” estimate.
w.
Technote 1 – The Colorado folks have recently included a 0.3mm/year increase in sea levels in their results. They say (possibly correctly) that this is necessary to adjust for the sinking of the ocean floor with the increasing weight of sea water from the melting at the end of the last ice age. However, since neither the IPCC nor the V&R2009 figures include that adjustment, I have not included it in this analysis so that we can compare apples to apples.
Technote 2 – I have aligned the Colorado observational results so that their trend line is zero in 1990, in order that they can be compared directly with the V&R2009 results, which have 1990=0 as their starting point. This also aligns the starting observations with the V&R2009 “best” estimate.
Technote 3 – some folks felt that my last post, “Yes, Virginia, there is an FOIA” was short on science content and long on passion … hey, what can I say, I’m a passionate guy. I trust this post will redress the balance in their estimation.
[UPDATE] Steven Mosher has graciously pointed me to a stunning disassembly of V&R2009, at the blog Climate Sanity. Makes my effort above look simplistic by comparison. He shows, among other things, that the V&R formula for sea level leads to ridiculous results when it is fed with actual data rather than IPCC scenarios … quite lethal to their claims. Well done, that man. – w.
Steven Mosher: model looks pretty simple. wonder why they just dont supply code
They did. In the SI to the paper. Cunningly hidden away in an archived mischieviously entitled ‘Sea Level Code’
http://www.pnas.org/content/early/2009/12/04/0907765106/suppl/DCSupplemental
Anyone actually reading the paper also discovers a model/obs data comparison covering the satellite era. I’m curious: do you agree that V&R went to press with a model that was 3cm out at the time of publication, and it got into the literature solely due to sloppy peer review?
u.k.(us) says:
July 3, 2011 at 6:24 pm
LazyTeenager says:
July 3, 2011 at 4:45 pm
…”you do understand don’t you that if the sea floor falls the continents rise and vice versa .”…..
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Assuming your theory is true, what causes the rise and fall?
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when we entered the current interglacial the ice on land melted. Less weight on land and more weight on the ocean floor.
The continents and oceans together behave like a seesaw or even better a water bed. You shift weight from one side to the other so one side goes down the other side goes up
It is a bit hard to visualize if you are not accustomed to thinking of solid rock as a very viscous fluid.
Compensation for increased water column seems to me to include an unnecessary correction. Compared to the weight of the lithosphere the water column is negligible and extra water from ice melt smaller still. Oceans deepen from the ridge system, where new ocean bed is being produced, due to lithospheric thermal contraction ie. cooling as it moves away from the ridge.
“The sea floor moves down, the continents move up”. That is correct. Look up isostacy, essentially equilibirium. The mechanism is loading of one area of crust will cause subsidence, and displace the equivalent mass of mantle causing uplift elsewhere.
On a longer time scale, the area of the oceans remains relatively constant through time, but the volume does not. The mechanism here is the rate of sea floor spreading. As newly formed oceanic crust moves away from spreading centres it cools and shrinks, the oceans essentially get deeper away from the ridges. When spreading rates are high, a greater proportion of hot crust is preserved and sea levels are high. Vice versa for periods of low spreading rate.
This from my undergraduate days at UEA, in a time long, long ago, when they taught science.
Ditto with temperature. At which point are we going to scrap the IPCC? It is as useful to policy makers as used toilet paper.
We must act now!
Chris from Norfolk va reckons
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Sea level is a very very VERY complicated thing…and it has much much MUCH more to do with ocean floor sinking (or rising) and continent action of the same.
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This is rather ambiguous Chris.
I did reread my post Chris and as far as I can tell there is no indication that I am claiming that sea floor movement is the only factor affecting sea level. I did offer an explanation of just one contributing factor out of many.
I hope you are no longer confused.
In the opening graph the worst case scenario was 10cm rise in 20 years and the actual observed rise was 5cm. That ain’t all that bad of a guess IMO even though an octopus would have likely guessed as well. The problem is that these model predictions are couched with far more certainty than they deserve. At the end of the day they are no more or no less than the proverbial “educated guess”. The problem with educated guesses nowdays is education in some instances has become more like indoctrination whereby the guesses are steered more by
ideology than objectivity.
How does this square with Greenland’s ‘record’ meltdown, WAIS ‘Armageddon’ crack ice, the dissolving glaciers around the world in the hottest decade on the record? Am I using my common sense correctly or is increased rate of sea level rise in the pipeline? ;o)
I’m still trying to get my head round this new theory that the real sea level rises are being masked by the falling sea bed that results from the weight of all this melting ice. As this melting ice has been occurring since the end of the ice age, why is the falling sea bed only now begun to mask the rising sea levels?
To be even more specific, the sea levels were measured to be rising at a rate of about 3mm per year – until about 6 years ago, then stopped rising. Does it mean that the rate of fall of sea bed has increased by 3mm per year since then, and if so, why would that be?
Yes, the floor may be sinking, but it is also rising. Else why do we take core samples to help us proxy changing conditions by studying all the stuff that falls onto that sinking floor?
Isotasy is not a new theory. Fred Vine (Professor of Geophysics at UEA, Vine and Matthews 1964, the man who interpreted magnetic stripes as sea floor spreading) ran through isostasy (Airey model vs McKenzie model) very nicely. This was in about 1982. Sea level change is not simple. It is very very complex.
Jared says:
July 3, 2011 at 5:54 pm
I’m not understanding the point of the .3mm/year adjustment. We live on LAND and if .3mm of water is added each year and the sea floor sinks .3mm a year then all of us on LAND could care less.
What follows is quite a banal analogy but it’s all I could think of, so here goes:
Imagine you’re pulling some cable out of a hole in a wall and want to know how much you’ve pulled out. You could find out by measuring from the wall to the end of the cable you’ve pulled through.
Imagine now that someone comes in every few minutes and snips a couple of centimetres off the end of the cable. Your measurement methodology is now inadequate because the length of the cable on your side of the wall has been affected by something other than the amount you’ve pulled through. You will need to find out how much has been snipped to calculate the correct figure.
Hopefully you can see how this fits measurement of sea level. When people talk about sea level change what is measured is essentially the height of the sea. If, say, the sea floor drops our measurements will show the sea reducing in height but that’s not what actually happened. To get the true height of the sea you need to account for the sea floor drop.
Whether you apply the adjustment or not depends on what you want to measure. Obviously it’s not relevant if you just want to find out the sea level relative to your local city at any one point in time, for reasons of flood risk assessment etc. Likewise if you only want to find out how much continuous cable is extruding from the hole in the wall the basic measurement is fine. It’s only when you want to find the total amount pulled through that you have to make further adjustments.
If you want to construct a time series of changing sea height you need to account for any factors that will bias the measurements.
Willis, none of these sea level data are corrected for water held in storage as they should be. Chao, Yu, and Li (Science April 11th 2009) did that for more than 70,000 impoundments built since 1900 and discovered that when these corrections were applied to published sea level curves the sea level rise became linear for the last 80 years or more. Something that has been linear for more than 80 years is not likely to change anytime soon. The slope of that curve was 2.46 millimeters per year which is 24.6 cm or just under ten inches per century. I think all these newly published data should have the impoundment correction applied to them and then compared to Chao, Yu, and Li. Theirs is the most believable long term sea level record we have. Things like melting glaciers or the effect of sea bottom responding to glacial loads are already subsumed into their long term curve and should not be used to confuse the issue. Any observations that deviate from linearity should be viewed with suspicion. And any predictions of accelerating sea level rise should be labeled for what they are – alarmist attempts to falsify our climate future.
Phil
Thanks for the link,
Talk to people in Emsworth (Amoung others), Hampshire, England. Hundreds of years of…errrmmm…nothing in terms of sea level rises. Unless of course, the LAND rose at EXACTLY the SAME rate of sea level rise (Or near too it)! Huh?
Just a little background on sea floor changes, from sinking to building.
http://people.hofstra.edu/j_b_bennington/135notes/sequencestrat.html
Natural plate tectonics causes of order one to a few millimeters per year change in the continental landscape. If the motion is vertical then any sea level rise, more water in the oceans, will be offset by centimeters of continental rise over ten to thirty year periods. Presumably modelers correct for this, if they are honest.
Also, a question, if the glaciers melt, then the continents will weigh less, so they should float higher on the mantle. This would tend to offset, and decrease the effective sea level rise for land use planning.
Is this mechanism related to “bounce” the U of Colorado research unit is talking about?
Thanks Willis, a good article as always.
Happy Independendence Day!
RoHa said: So …. we’re not doomed?
Oh no, we’re still doomed, we just need to find out the mechanism. But rest assured, we are doomed!
John F. Hultquist said: That might just be a sign that the coast of Washington is warping up as this is an active plate margin.
Precisely the point. We’re not stable at all, and claiming that a rising OR falling sea level is a disaster is simply ludicrous. Even in my other home, Shanghai, we see changes in land elevation from subsidence and pressures well beyond the supposed 1mm per year. The land itself is changing at a rate faster than the oceans, yet the concern is over the ocean’s average elevation (as if such a thing could be calculated).
I submit that worrying about a millimeter a year of change in average ocean level is a waste of time; better to worry about things that will affect people in the next 200-300 years like power, pollution, fresh water, and food. By the time water elevations could possibly change enough to impact huge, low-lying areas like the Shanghai/Yangtze basin (which would need a 40-50 cm rise), we’ll have many, many more problems to overcome first.
But then again, fresh water and power restrictions aren’t as fear-mongeringly-huge sounding of a problem as flooding from the rising ocean levels…
Hi Willis,
I have never posted on this site before, but I was quite interested in the Rahmstorf paper when it came out. I looked into it at that time and thought it was very weak. The update with Vermeer was little better. I had been thinking about looking at this lately because my intuition was that they had done poorly so far. But actually your graph doesn’t really show how poorly. Their formulas are attempts to predict the rate of sea level change, not sea level. So if you really want to see what is happening you would have to take the years since their paper was published and look at their predicted rate of change versus the actual. They also have little excuse for this to be a short term issue since their formula assumed that the rate of change was predicted from the temperature deviation from a baseline temperature, and that deviation has continued throughout the period (although it hasn’t increased). My original blog post on this topic is;
And now my usual disclaimer. I think the IPCC AR4 is good overall. Their paper attempted to say that that report was wrong. I am actually just going with the consensus view on this, as I tend to on this entire issue.
http://nierenbergclimate.blogspot.com/2009/04/published-comments-on-rahmstorf-2007.html
@ur momisugly Pamela Gray says:
July 4, 2011 at 9:20 am
Pamela, is there any peer reviewed study with indicates how muck sediment is replacing the subsiding sea bottom?
In climate science rule one rule states , that when the model and reality differ in value its reality which is in error . So there is no problem the sea levels have increased as predicted as the models prove . The physical level of the sea has no bearing on this.
The reason the Colorado Plateau has risen for the past 10my is that sediment has been eroded from it. This continental lift compensates for the sedimentation which of itself of course would tend to raise the sea level. So no, sedimentation will not reverse the GIA. What about impoundment? This is more than made up for by groundwater depletion in developed continents, and remains a minor contribution.
But I repeat like a broken record: LOD constrains our interpretation of sea level rise, about .1ms/cm rise, and no such LOD increase is witnessed. Lately mentioned hydrate contribution from the mantle is a very interesting subject which I knew nothing about–I’ll stay tuned to any further commentary on this.
I for one, am interested in knowing how deep is the ocean–not just how high–and I don’t feel threatened by CU’s adjustment. –AGF
Shanghai Dan says:
“Oh no, we’re still doomed, we just need to find out the mechanism. But rest assured, we are doomed!”
Phew!
Thanks. I like to get these things clear.
David says:
“Pamela, is there any peer reviewed study with indicates how muck sediment is replacing the subsiding sea bottom?”
Sequence stratigraphy is used universally in the oil industry for interpreting marine seismic data. There are masses of published papers on it. Search “Vail sequence stratigraphy”.
Start with the SEPM here: http://sepmstrata.org/history/vail.html