2010-08-17 13:11:35Basic Rebuttal 23: Sea level rise is exaggerated REVISION 5 herein at top.
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Sea level rises as ice on land melts and as warming ocean waters expand. Sea level rise mutually corroborates other evidence of global warming as well as being a threat to coastal habitation and environments.

The blue line in the graph below clearly shows sea level as rising, while the upward curve suggests sea level is rising faster as time goes on. The upward curve agrees with global temperature trends and with the accelerating melting of ice in Greenland and other places.

Because the behavior of sea level is such an important diagnostic aid for tracking climate change, skeptics seize on the sea level record in an effort to cast doubt on this evidence. Sea level bounces up and down slightly from year to year so it's possible to cherry-pick data falsely suggesting the overall trend is flat, falling or linear. You can try this yourself. Starting with two closely spaced data points on the graph below, lay a straight-edge between them and notice how for a short period of time you may create almost any slope you prefer, simply by being selective about what data points you use. Now choose data points farther apart. Notice that as your selected data points cover more time, the more your mini-graph reflects the big picture. The lesson? Always look at all the data, don't be fooled by selective presentations.

( graph from Church 2008 )

Other skeptic arguments about sea level concern the validity of observations, obtained via tide gauges and more recently satellite altimeter observations.

Tide gauges must take into account changes in the height of land itself caused by local geologic processes, a favorite distraction for skeptics to highlight. Not surprisingly, scientists measuring sea level with tide gauges are aware of and compensate for these factors. Confounding influences are accounted for in measurements and while they leave some noise in the record they cannot account for the observed upward trend.

Various technical criticisms are mounted against satellite altimeter measurements by skeptics. Indeed, deriving millimeter-level accuracy from orbit is a stunning technical feat so it's not hard to understand why some people find such an accomplishment unbelievable. In point of fact, researchers demonstrate this height measurement technique's accuracy to be within 1mm/year. Most importantly there is no form of residual error that could falsely produce the upward trend in observations. 

As can be seen in an inset of the graph above, tide gauge and satellite altimeter measurements track each other with remarkable similarity. These two independent systems mutually support the observed trend in sea level. If an argument depends on skipping certain observations or emphasizes uncertainty while ignoring an obvious trend, that's a clue you're being steered as opposed to informed. Don't be mislead by only a carefully-selected portion of the available evidence being disclosed.

Current sea level rise is after all not exaggerated, in fact the opposite case is more plausible. Observational data and changing conditions in such places as Greenland suggest if there's a real problem here it's underestimation of future sea level rise. The IPCC synthesis reports offer conservative projections of sea level increase based on assumptions about future behavior of ice sheets and glaciers, leading to estimates of sea level roughly following a linear upward trend mimicking that of recent decades. In point of fact, observed sea level rise is already above IPCC projections and strongly hints at acceleration while at the same time it appears the mass balance of continental ice envisioned by the IPCC is overly optimistic ( Rahmstorf 2010 ).


2010-08-17 14:33:01I think its important to say
Robert Way

robert_way19@hotmail...
142.162.181.139
Doug,
I think it is important to say that it is the belief among many prominent Glaciologists that sea level rise has been underestimated significantly because of the lack of inclusion of dynamical ice loss processes associated with Greenland and Antarctic mass losses. This is an important point I think because there is quite a lot of friction over this issue. Perhaps seeing Vermeer and Rahmstorf 2009 you might find something of interest on the topic too .


2010-08-17 15:41:24Underestimation
doug_bostrom

dbostrom@clearwire...
184.77.83.151
Robert, thanks for the suggestion. Anybody else have input on that? My thinking is that nuance may be overshoot for a basic argument but I'm nothing if not all pliable and soft...
2010-08-17 17:07:08Repetition
gpwayne
Graham Wayne
graham@gpwayne...
86.156.59.156
Hi Doug - I think you nail it perfectly, but overdo it slightly. May I suggest you have another look at the paragraph starting "As an example..." because I believe if you removed that, the impact would be improved slightly. I also feel the last line could be misconstrued (Again, don't be misled...). Could you live without it, perhaps?
2010-08-17 20:58:05
Anne-Marie Blackburn
Anne-Marie Blackburn
bioluminescence@hotmail.co...
80.42.219.219

Hello Doug. Good article which only requires a little tweaking in my opinion. I think Robert's point needs to be included as it's one of the main criticism of the IPCC estimates. You could perhaps also add a little text to explain that sea levels vary according to a number of factors (give a couple of examples), which means you don't expect the rise to be linear. Which I think would tie in nicely with the ability of contrarians to carefully select periods of 'interest'.

And I agree with Graham - I think the 'As an example...' paragraph can be removed.

How does that sound to you?

2010-08-18 02:05:10Example no or yes?
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Oh, golly I'm going to sound oppositional here but...

JC's intermediate article does not address future sea level rise but is a rebuttal to the notion of instrumentation faults concerning -present- assessments of sea level. So if I do Rahmstorf et al John's article would need to be updated. Speculations about future sea level rise are really a different topic

What I don't tackle here but which is included in John's article is the acceleration issue which is a matter of nuance I think is beyond the basic issues of "is sea level rising" and "do we we  trust the instruments."

Carrying on with being stubborn, I'm dithering about the "example" paragraph. I really tempted by the idea of helping people to think about how easy it is to be misled; a hands-on "laboratory demonstration" is quick to do and highly illustrative of how this and so many other bogus arguments are constructed.

In fact, if we consider that many of these rebuttals are "atomic" in the sense they'll be viewed alone and not as part of a linear narrative, such educational examples of how skeptic arguments are thrown together could be duplicated in various rebuttals having to do w/longitudinal data, such as the "It's cooling since 1998" wheeze. It's easy to think that readers grasp the problem but the reason we're here doing these rebuttals is precisely because we're not typical readers and as well clearly this simple graphical trick has been effective.

So are basic rebuttals an appropriate place to insert some (brief) fundamental lessons on critical thinking w/general applicability for readers?

Or could basic rebuttals include a link to a little  generic "lab session" where readers could demonstrate for themselves how easy it is to distort conclusions?

2010-08-18 05:28:56
Andy S

skucea@telus...
66.183.162.8

Doug

 

I think the words "as ice above sea level melts" are misleading. Perhaps a clearer wording would be "glaciers and icecaps".  Floating ice is partly above sea level and when it melts it does not add (much) to sea level; conversely, some parts of outlet glaciers are below sea level (but not yet floating) but when those glaciers melt or calve they do raise sea levels.

 

I agree that a brief discussion of cherry-picking is on-topic and instructive. But rather than say "Choose appropriately spaced data points...." (the choice is actually statistically inappropriate), I would rather say something like: " Because the sea-level curve bounces up and down  it's possible to cherry-pick short term trends that falsely suggest that the overall trend is falling."

 

Changes in ground elevation are not just due to isostatic uplift  but also due to subsidence (sediment compaction and isostatic loading effects) and tectonic/volcanic activity. So it might be safer--and simpler--to refer to "localized land elevation changes due to geologic processes" rather than just isostasy.

2010-08-18 05:46:48Thanks Andy
doug_bostrom

dbostrom@clearwire...
184.77.83.151
All good points. I'm trying to keep my verbosity under control, may be over doing it. The "ice above sea level" thing was intended to convey what you said, but see what happened? I managed to speak more while saying less, heh!
2010-08-18 06:25:49Revisions
doug_bostrom

dbostrom@clearwire...
184.77.83.151
Removed some redundancy while integrating notion of cherry-picking directly w/demo, broke apart tide gauge and satellite observations because the old para was too much of a roll-up, too dense.
2010-08-19 16:39:19
Ari Jokimäki

arijmaki@yahoo...
192.100.112.211

Overall this is a good article. I have only one objection on this sentence:

"Various technical quibbles are mounted against satellite altimeter measurements, ignoring the expertise of scientists employing satellite altimetry and who taking such matters into account demonstrate satellite sea level measurement accuracy to be within 1mm/year."

Here the part about ignoring the expertise is quite close to a logical fallacy called appeal to authority. I would leave that part out and just say that they have taken such matters into account.

2010-08-20 04:40:32Experts claim...
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Thanks, Ari. Yeah, I get your point, the sentence necessarily compresses a vast amount of effort into a simple error number.

I'd sure like to find a Holy Grail sentence crisply describing how deniers are oblivious to their own ignorance.

2010-08-20 06:34:00Typo - (possibly) one "as" too much
BaerbelW

baerbel-for-350@email...
93.231.178.172

Hi Doug,

not sure which is the most recent version of your text - the one here in the thread or the one I can see via the rebuttal-preview -  but, in the previewed text there seems to be an "as" too much in the last paragraph:

"As as can be seen in the latter part of the graph above, tide gauge and satellite altimeter measurements agree with each other quite adequately to mutually corroborate their respective records, as is visible in the inset portion of the graph above."

As an aside: it might help if the previews contain a date/timestamp for when they were last updated. The same goes for any updated posts within a thread. I'll add this to the forum-suggestion thread also.

2010-08-20 08:28:30A few suggestions
John Russell

jr@johnrussell...
84.92.176.215

My suggestions...

1) " ...as ice not floating melts..." change to "...as ice on land melts..." .

2)  Don't use 'isostatic' -- it's a meaningless word to a lay person.  Perhaps say 'geological movement'?

3) Rather than, "Not surprisingly, these details have not escaped scientists measuring sea level with tide gauges; confounding factors are accounted for in measurements", use, " "Not surprisingly, scientists measuring sea level with tide gauges are aware of, and compensate for, these factors."

4) 'Satellite altimetry' is mentioned three times in three lines. I think the second could be changed to read, " ...ignoring the expertise of scientists employing this height measuring technique." Doing this also gives the reader a second chance to understand the phrase.

5) The phrase, "...tide gauge and satellite altimeter measurements agree with each other quite adequately to mutually corroborate their respective records..." would perhaps be better as "...tide gauge and satellite altimeter measurements track [or 'follow'?] each other with suprising similarity [or 'accuracy'?]. Thus each corroborates the other record...". 'Quite adequately' strikes me as typical scientists' understatement! Compared with some other graphs the similarity is remarkable! I've broken the sentence into two, as I think it was longer than it needs to be. And I think 'mutually' is perhaps redundant?

6) The sentence, "Again, don't be misled by selective disclosure.", on this occasion, I think, is too succinct. I suggest, "Again, don't be mislead by only a carefully-selected portion of the available evidence being disclosed." I know it's longer but on this occasion I think it helps ensure the point sinks in to a less able brain than your's, Doug. 

Best wishes,

JR  

 

2010-08-20 08:54:05
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Baerbel, thanks and indeed I did not update the preview version, have been doing edits over here. 

An explosion of coding exceptions would be required but wouldn't it be cool if the initial posts in these rebuttal review threads were sourced from the -same- db field as the preview? Forget it, JC, your kitchen is crowded with bubbling pots...

Good points all, JR. Will weave 'em in. I think I'll go hog-wild w/word count, take a cue from Andy and go with "local geologic processes."

Looking for suggestions on "ice not floating," "ice on land." Here we're speaking of glaciers, ice sheets and grounded ice. That last is the one making this so difficult to convey, leading to the awkward "ice not floating" which is probably most correct but also quite ugly. "Ice on land" doesn't quite get it. Help!

2010-08-20 19:45:42Ice sitting on land
John Russell

jr@johnrussell...
84.92.176.215

I wouldn't worry too much about the small amount of 'grounded ice', Doug. I understand your desire to be accurate as a professional scientist but a doubt anyone can pick you up on that and not be thought of as being anal. If you prefer, say "ice that is sitting on land".

Best wishes,

JR

2010-08-20 20:18:30Ice
gpwayne
Graham Wayne
graham@gpwayne...
217.44.86.17

Doug: how about "ice sheets and glaciers (sea ice will not contribute to sea-level rise because it has already displaced its volume in the water)"? More words, but an implicit explanation.

Sorry to come up with a substantial point this late, but I'm bothered by two omissions: you do not state how much fresh water is locked up in the cryrosphere. It's an amazing amount of water, as I recall. The other thing you don't mention is history - how high have oceans been in the past? Surely these two points are valid, basic and compelling?

It does strike me that the first and last paragraphs are much more about methods of argument than the rebuttal itself. I agree this is a worthy topic, but is this in the right place?

2010-08-20 20:23:59Twitter title suggestion
gpwayne
Graham Wayne
graham@gpwayne...
217.44.86.17
Mountain Dwellers: Sea level rise "nothing to worry about"
2010-08-20 21:21:57ice sheets
John Russell

jr@johnrussell...
84.92.176.215

I don't think most of our 'basic' audience understands the difference between 'ice sheet' and 'sea ice', Graham. Thats why "ice that is sitting on land" is clearest.

Best wishes,

JR 

2010-08-21 02:56:10
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Thanks for the help, folks. I agree that trying to wrap my words around the relatively small amount of grounded ice is a bit neurotic. I'll go w/"glaciers and ice sheets" or "ice on land."

Graham you make good points about future perils and what history can tell us. However I'm a bit constrained here because I'm using JC's article as a point of departure. John's article does not  deal with future sea level rise but is instead a look at instrumentation and data issues w/tracking current sea level rise. I'm reluctant to introduce information in a "basic" treatment that is not amplified or at least mentioned in the next step up. What I do omit from this article is his reference to acceleration and I make make a brief reference to the curvature of the graph to acknowledge that.

Definitely I do take this basic rebuttal as an opportunity to inoculate readers against future infection.  However the first main paragraph ("Because the...") is jarring because I don't introduce it properly. I'll go over the whole thing so as to make sure the meta-pedantry is smoother.

2010-08-21 17:29:36Moving on then...
gpwayne
Graham Wayne
graham@gpwayne...
217.44.86.17

Hi Doug - I know what you mean about the consistency issue, but complementary arguments are not contradictory. But I don't think this is a deal-breaker in any way, and it's about time you got some thumbs, so here's one...

(Can't get to admire "quibbles" - isn't "criticisms" more appropriate and less dismissive?)

2010-08-21 17:41:36...and a thumb from me
John Russell

jr@johnrussell...
84.92.176.215

I have no more quibbles.

2010-08-21 18:02:03
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Taking onboard suggestion about "quibbles" and thanks Graham, that escaped me but you're quite right.

Also gently introduced the notion of future problems via pointing out curved trend.

2010-08-21 19:40:50Acceleration
gpwayne
Graham Wayne
graham@gpwayne...
217.44.86.17

Yes, the curve is vital and I'm pleased to see it because I need better data for my own arguments about the acceleration. I agree it's enough 'future' to be getting on with. I am now quibble-free :)

2010-08-25 11:24:04Comment
Robert Way

robert_way19@hotmail...
142.162.177.145
I think its good. But I do think its important to note that glaciologists and sea level rise think that it is underestimated. Kinda a "skeptics say exaggerated but real experts say the IPCC underestimated sea level rise" sort of thing. I commented this before and I know you might not have space but I do think that the common attack comes at the IPCC SLR predictions as being over-generous. I can picture sorta a sentence like "So are the IPCC predictions off the mark? In Short, Yes. According Glaciologists and sea level rise experts the IPCC vastly underestimated SLR contributions from polar ice sheets which are not clearly and unequivocally contributing about a third of sea level rise.


Just a thought. I do agree it could be hard to fit in.
2010-08-25 17:51:02Bump
gpwayne
Graham Wayne
graham@gpwayne...
217.44.86.17
More thumbs required here too...
2010-08-26 04:17:27
Anne-Marie Blackburn
Anne-Marie Blackburn
bioluminescence@hotmail.co...
212.139.81.253
One more thumbs up
2010-08-28 08:39:12
doug_bostrom

dbostrom@clearwire...
184.77.83.151
Robert's suggestion on "are IPCC predictions off the mark" produced a nice way to add a concluding paragraph incorporating his suggestion. Revised herewith.
2010-08-28 08:54:58Good to go
Robert Way

robert_way19@hotmail...
142.162.188.138
Nice final paragraph. I thought i gave my thumbs up last time anyways. whoops. I didn't know about the rahmstorf article... looking it up as I speak lol
2010-08-30 03:20:27Wordsmithing...
Jim Meador

jimm58@gmail...
68.164.185.100
Here are some wording suggestions, which you can accept or ignore as you see fit... "Sea level rises as ice on land melts and as the ocean itself expands due to warming." I suggest: "Sea levels rise as ice on land melts and as the warming ocean waters expand." "Sea level rise is a helpful corroboration of other effects of global warming as well as a threat to coastal habitation and environments." I suggest: "Rising sea levels confirm global warming even as they threaten coastal settlements and environments." "As the blue line in the graph below indicates, the rise of sea level is not following a straight line but is instead gently curving upward." I suggest: "The blue line in the graph below clearly shows that sea levels are rising, and the upward curve shows that they are rising faster as time goes on." "This tells us that sea level rise is accelerating, in keeping with what we know of increasing global temperature trends as well as accelerating loss of ice in such places as Greenland." I suggest: This upward curve agrees with global temperature trends and with the accelerating melting of ice in Greenland and other places. Overall my tendency would be to shorten this rebuttal, but I am willing to support it either as it is, or with the suggestions above.
2010-08-30 05:53:23
doug_bostrom

dbostrom@clearwire...
184.77.83.151

Thanks for the suggestions KIR and I've woven 'em in.

The length bugs me a little bit too but in the end a compelling case was made to project the story forward w/the final para. Meanwhile I'm hell-bent on exploiting opportunities to stiffen plastic minds with some resistance against common cherry-picking techniques, so there's a little extra payload there as well.

2010-08-30 10:35:57Published
John Cook

john@skepticalscience...
124.187.125.135
I think it's a good idea to include future sea level rise in this. Am open to suggestions on how to integrate that content into the intermediate version. I'm a little concerned that this basic rebuttal is a little long but hey, there are much greater things in life to worry about :-)