Guest essay by Kip Hansen, St Thomas, USVI
The Claim:
Even if research shows that Hurricane Sandy was not “caused” by Global Warming, it is certain that sea level rise caused by anthropogenic global warming increased the resultant destruction from Sandy’s storm surge.
Example:
“ … sea levels continue to rise due to global warming. The picture here is very clear. And that means that every single hurricane that hits land will push seawater farther inland when it does so. Or as one scientist told me in the wake of Sandy, “There is 100 percent certainty that sea level rise made this worse. Period.” “ (footnote 1)
“Climate Change Made Sandy Worse. Period.” (footnote 7)
Background:
From the New York State Sea Level Rise Task Force Report to the Legislature (2010) — “Sea Level Rise–Causes and Projections : Local sea levels are affected by ocean currents, gravitational forces, prevailing winds, and rise and fall of the land mass. Within the coastal regions of New York State, the land mass is slowly sinking, with the exception of the Hudson estuary north of Kingston. This movement is a result of geological forces and impacts of human activity and development. It affects local, or relative, rates of sea level rise. “
“These projections are supported by empirical data documenting recent sea level rise in New York State. For example, gauges at the New York City Battery indicate that sea level in the 2000s is 4 to 6 inches higher than in the early 1960s” (footnote 8)
“Storm surge in the NYC–LI area can result from tropical storms and extratropical cycles. Hurricanes have directly hit NYC (Scileppi and Donnelly 2007), such as on 3 September 1821 (Ludlum 1963) and 25 August 1893 (National Hurricane Center 2008). The category-3 ( ; 110 kt; 1 kt ’ 0.5 m s 2 1 ) winds during the 1821 event flooded a large portion of southern Manhattan (Ludlum 1963), but at that time the NYC population was only ; 150 000. There have been no other direct hits by major hurricanes (greater than category 2) across NYC–LI since the 1938 ‘‘Long Island Express’’ (National Hurricane Center 2008). Hurricane Gloria (1985) was originally labeled as category 3 at landfall for Long Island but has since been reanalyzed as category 1 (C. Landsea 2008, personal communication). However, it is only a matter of time before another major hurricane will impact the NYC–LI area. “ (This statement proved to be prophetic – Hurricane Sandy hit NJ/NY on 29 October 2012)
“Sea level along New York’s coast has been rising at the rate of almost one foot per century for at least 100 years” (footnote 3)
(footnote 2 – the above four quotes are all from NYS Sea Level Risk Task Force Report to the Legislature 2010)
“The mean sea level trend [at the Battery, Manhattan Island, NY] is 2.77 millimeters/year with a 95% confidence interval of +/- 0.09 mm/yr based on monthly mean sea level data from 1856 to 2006 which is equivalent to a change of 0.91 feet in 100 years.” (footnote 6)
The following NOAA graphic shows the current trend of sea level rise for the Battery at 0-3 mm/yr, based on this same tide gauge.
This is in agreement with the Battery’s tide gauge long-term trend of 2.77 mm/yr both by data from NOAA and from Leatherman 1995.
Overall Global Sea Level Rise (Douglas 1991) gives 1.8 mm/yr for the 100 year trend, 1880 – 1980, based on Tide Gauges. This figure is generally accepted throughout the field, for example, Church and White found 1.7 mm/yr for 1870 – 2004 (footnote 5) [one sees figures ranging from 1.45 mm/yr to 1.8 mm/yr (1870-2004) based on tide gauges, and 2.9 to 3.4 mm/yr, based on the still short satellite data series (1993-2003)]. (footnote 11)
We can now look back now to the causes section of the NYS Sea Level Rise Task Force Report which told us that one factor in sea level change is “rise and fall of the land mass” – which refers both to normal subsidence (in which land sinks for some immediate cause – such as settling of coastal areas created by fill as has been reported recently in Norfolk, VA) and to Glacial Isostatic Adjustment (GIA), which is “Post-glacial rebound (sometimes called continental rebound, glacial isostasy, glacial isostatic adjustment) … the rise of land masses that were depressed by the huge weight of ice sheets during the last glacial period” (footnote 9).
The NYSSLRTF Report quoted above stated clearly that “Within the coastal regions of New York State, the land mass is slowly sinking”. But by how much? In his seminal 2007 paper on North American Glacial Isostatic Adjustment, which was based on GPS data, Giovanni Sella states “The uplift rates generally decrease with distance from Hudson Bay and change to subsidence (1 – 2 mm/yr) south of the Great Lakes. “ (footnote 4) In plain English, the coastal areas of New York, including NY City, much of coastal New England and areas to the south are sinking at a rate ranging from 1 to 2 mm/yr due to the effects of GIA. To be clear here, while GIA normally refers to land masses rising, in the area concerned, coastal NY, GIA has caused the local land mass to subside or sink.
Assumptions for Analysis:
None of the numbers — facts and figures — contained in the quotes above are controversial — they represent the mainstream views on sea level rise and GIA subsidence, both qualitatively and quantitatively, in the area of concern, New York State, and certainly apply to New York City and surrounds as affected by Hurricane Sandy.
All quoted figures are referenced in footnotes (linked directly to source materials where possible) and come from open source (non-pay-walled) peer-reviewed journal papers and government agency web sites.
I take it as a given that, for the purposes of this discussion, we can all agree that sea level change is an entirely LOCAL issue. Hurricane Sandy’s storm surge and resulting damages therefrom depend ONLY on local sea levels relative to local land mass. NY City’s tunnels were not flooded by any putative sea level rise in Sydney, Australia or the South Sea Islands. (There is another discussion about Global Sea Levels, but this is not it.)
This is a common sense, rough-estimate hypothesis-testing exercise, not a proof of anything – so we only need reasonably accurate and readily agreed upon approximations. Therefore, for our “back of the envelope” calculations, I will use the following:
a) Time period = 50 years (1960-2010) – because this is the time period used by the NY State SLR Task Force (footnote 2)
b) For relative sea level rise in NY City, I will use NYSSLRTF 2010’s “4 to 6 inches higher than in the early 1960s”. (footnote 2) This is the same (+/-) as the tide gauge data from NOAA for the Battery, Manhattan Island, NY. It is the longest tide gauge time series in the US — beginning in 1856 and running to the present day. (footnote 6) (footnote 10)
c) For Global sea level rise, I will use Church and White’s 1.7 mm/yr as it covers 1870 – 2004 (Douglas 1991 found 1.8 mm/yr for 1880- 1980). (footnote 5)
d) For subsidence at NY City, I will use the mean of 1.5 mm/yr but give as range extremes both 1 and 2 mm/yr. (footnote 4)
The following section gives the elementary school level mathematics (addition, subtraction, multiplication, and division only – no statistical methods or analysis).
Calculations:
Start with NYSSLRTF’s “at the New York City Battery indicate that sea level in the 2000s is 4 to 6 inches higher than in the early 1960s.” As our other numerical quantities are all in millimeters, as is common in science, we will use these numbers: 4 inches = 101.6 mm (let’s use 100 for ease…it changes nothing). 6 inches = 152.4 mm (let’s use 150, same reason) , the mean is 5 inches which is 127 mm (we’ll use 125). Note that this is well within keeping with NOAAs trend of 2.77 mm/yr for the entire length of the Battery’s tide gauge record.
NYSSLRTF’s stated sea level change at the Battery, 1960-2010, is in mm:
plus 125 mm. (mean of 100 to 150). Note that this is approximately 2.5 mm/yr over the 50 year period. If we were to increase this figure to 138 mm, it would agree precisely with NOAAs 2.77 mm/yr—instead we use the figures from the NYSSLRTF Report for consistency.
For subsidence take 1.5 mm/year (halfway between 1 and 2 mm/yr) times 50 years == 75 mm or 2.95 inches of subsidence. This number has a negative sign, as it is land sinking (as opposed to the sea rising). The Battery has apparently sunk approximately 3 inches since the 1960s.
As the New York State Sea Level Rise Task Force has estimated that “sea level in the 2000s is 4 to 6 inches higher than in the early 1960s” and we find that approximately 75 mm or 2.95 inches of that was due to the land sinking (GIA effects only — nothing included here for subsidence caused by the settling of land created by fill), that leaves us with:
Or, in pictures: (footnote 12)
To cover all the bases, let’s include a grid of both variables, Relative SLR and GIA:
This grid shows that the mean value (highlighted) at about 2” of absolute sea surface rise over our 50 year time period at the Battery.
Then using the long term, pre-AWG 100-year trend for Global Sea Level Rise of 1.7 mm/yr, we would expect, for 50 years (1960-2010): 50 times 1.7 mm = 85 mm (or 3.35 inches) of sea level rise due to this inexorable rise of the sea as the world works its way out of the last ice age
Subtracting the expected geologically-caused sea level rise from the actual sea level rise experienced should result in a remainder that would be the portion of the absolute sea level rise that could be attributed to recent Anthropogenic Global Warming.
Thus we now can calculate:
plus 50 mm attributable to rising sea level minus 85 mm expected from long-term general worldwide sea level trends equals minus 35 mm or 1.37 inches less than expected from the geologically-caused sea level rise trend, leaving less than nothing to be attributed to AGW-induced sea level rise.
All of this in pictures:
Using our grid of two variables:
Note that only under the Highest Relative SLR/Lowest Subsidence Rate scenario does this result even become positive – and then only by 15 mm/0.6 inches.
This brings us the somewhat surprising conclusion that the relative sea level change at the Battery in NYC which can be attributed to Anthropogenic Global Warming (by any of its commonly used names) is probably less than zero and certainly not significant. Rather, sea level change at the Battery, when calculating with the means of the variable ranges, is approximately 35 mm less than would be normally expected if the sea level change at the Battery was simply following the long-term slow and gradual rise seen to have begun worldwide at least 150 years ago (long before AGW is posited to have begun). It is not suspected that AGW caused this deficit.
Summary:
At the Battery, Manhattan, NYC over the period 1960-2010, we found less than zero mm/inches of sea level rise to be attributed to post-1960 AGW. With admittedly rough calculations, it appears that NY City has seen “4 to 6 inches” – 100 to 150 mm — of sea level change over the last 50 years, which is approximately equivalent to “8 inches in 100 years”, but over 3 inches — 85 mm of the relative change — was due to subsidence (land sinking) as a result of GIA. Subtracting the subsidence from the relative rise leaves only 2 inches — 50 mm –of rise attributable to the sea actually getting higher – which is less than the 3.3 inches — 85 mm — which would be expected from long-term pre-AGW (150 year) worldwide positive sea level rise trends, the trend agreed by all not caused by AGW, but attributed to geological causes, usually to the ocean water warming and expanding after the end of the last Ice Age.
Bottom Line:
The claim is a “Scientific Urban Legend” – made up of the TRUE and obvious fact that any positive change in local average relative sea level will make any storm surge “worse” – by the simple effect of the relative water level being higher by whatever amount — blended with the FALSE assumption/assertion that some or all of the oft cited 8 inches of Global Sea Level rise over the last 100 years had actually taken place in or around NY City and that this sea level rise had been caused by Anthropogenic Global Warming.
At the Battery, Manhattan, NYC, there has been, so far, no significant sea level rise attributable to AGW. Period. Therefore, it is extremely unlikely that AGW-induced sea level rise contributed in any real world sense to the destruction caused by Hurricane Sandy’s storm surge.
EPILOGUE:
None of the above means that NY City and surrounding areas should quit worrying about sea level rise. The sea is rising, has been rising, and will continue to rise. The coastal areas of NY and NJ are sinking and will continue to sink. Both of these conditions will continue until geological conditions change to stop them—perhaps in millennia. The recent warming of the atmosphere may yet cause discernible additional sea level rise at the Battery. NY/NJ should plan for a continued sea level rise range of 1.7-2.8 mm/yr for the foreseeable future and take positive steps to mitigate the known dangers. So far, it simply has had nothing to do with AGW.
1 – Here Comes the Story of No Hurricanes by Chris Mooney | Fri Sep. 6, 2013 6:55 AM PDT
http://www.motherjones.com/environment/2013/09/hurricane-season-ipcc-sandy
2 – New York State Sea Level Rise Task Force Report to the Legislature — Dec 31, 2010 http://www.dec.ny.gov/docs/administration_pdf/slrtffinalrep.pdf
3 – NYS Sea Level Rise Task Force Report 2010 cited this to:
Leatherman, S.P., R Chalfont, E. Pendleton, S. Funderbunk and T. McCandless. 1995. Vanishing Lands , Sea Level, Society, and Chesapeake Bay. Univ. of Maryland Laboratory for Coastal Research & US Fish and Wildlife Service Chesapeake Bay Field Office
http://www.fws.gov/slamm/vanishinglandssealevelsocietyandchesapeakebay2.pdf
4 – Observation of glacial isostatic adjustment in ‘‘stable’’ North America with GPS — Sella et al GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L02306, doi:10.1029/2006GL027081, 2007
http://www.ngs.noaa.gov/CORS/Articles/2006GL027081.pdf
5 – http://users.coastal.ufl.edu/~arnoldo/ocp6050/homeworks/douglas91.pdf also “A 20th century acceleration in global sea-level rise” Church and White 2006 http://naturescapebroward.com/NaturalResources/ClimateChange/Documents/GRL_Church_White_2006_024826.pdf
6 – data from NOAA http://tidesandcurrents.noaa.gov/sltrends/msltrendstable.htm
text from http://reason.com/blog/2012/11/01/hurricane-sandy-and-sea-level-rise-in-ne
7 – “Climate Change Made Sandy Worse. Period.” —By Chris Mooney | Thu Nov. 8, 2012 http://www.motherjones.com/environment/2012/11/climate-change-made-sandy-worse-period The scientist that makes most of the sea level claims is Dr. Ben Strauss who “holds a Ph.D. in Ecology and Evolutionary Biology from Princeton University, an M.S. in Zoology from the University of Washington, and a B.A. in Biology from Yale University” and is a paid employee of Climate Central, a AGW advocacy organization.
8 – NYSSRLTF Report cited this as:
Colle, B.A., K. Rojowsky, and F. Buonaiuto. 2010. New York City storm surges: Climatology and an analysis of the wind and cyclone evolution. Journal of Applied Meteorology and Climatology 49 : 85 – 100. Pub ID# 3772
http://journals.ametsoc.org/doi/pdf/10.1175/2009JAMC2189.1
9 – Definition from the Wiki:
https://en.wikipedia.org/wiki/Post-glacial_rebound
10 – The NOAA reported sea level trends at http://tidesandcurrents.noaa.gov/sltrends/msltrendstable.htm and in the graph at
http://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8518750
are relative sea levels – where the sea surface is in relation to a certain point on the land mass. There are no adjustments made, as they would be irrelevant. So, in plain English, the relative sea level change is the sea surface movement (up or down) plus the land mass movement (up or down). This is the sea level change you would see with your eyes if you were there.
11 – Although Church and White arrived at a figure of 1.77 mm/yr, CSIRO cites Church 2011 for uncertainty bars but states that the graph shown indicates “an average rate of rise of about 1.6 mm/yr over the 20th Century” rather than Church’s finding of 1.77 mm/yr. http://www.cmar.csiro.au/sealevel/sl_hist_few_hundred.html
12 – For our cartoon pictures, we assume that the US Geological Survey Team installed a brass reference marker at the 1960 Mean Sea Level position on our imaginary sea wall at the Battery and placed a reference tide gauge marked in inches alongside, all for our convenience.
13 – h/t for the format of this article to snopes.com
# # # # #
Two links with analysis showing very low changes in sea level.
First is a NOAA assessment using best data available from 2005.
http://hockeyschtick.blogspot.com/2012/12/noaa-2012-report-finds-sea-levels.html
Second is an analysis of the Tasmanian tidal benchmark made in 1841 with documentation.
http://bruderheim-rea.ca/warming10.htm
Also, I’ve seen a Will Soon video where he comments to the effect that satellite altimetry raw data shows zero sea level rise, but is “corrected” to match tidal gages.
Thanks for your reply Kip and I will read the link in detail when I get a moment. But my point was something a little different. I was just observing that regardless of some absolute effect of SLR, a storm surge can’t have an effect outside of an expected range if the local tide height was within the historical range. Was the predicted high tide at the time Sandy struck within historic norms – say last 50 years? If so then the flooding could not be worse than planning would indicate.
That of course ignores questions of intensity but I think again Sandy was within norms there.
From gary turner on September 19, 2013 at 2:41 pm (with slight correction):
Didn’t this all come from telegraphs and telegrams?
I AM LEAVING YOU PATCHY COMMA FOUND MODEL I CAN TRUST PERIOD
URGENT STOP WEE BAIRN FELL IN WELL STOP SEND REPLACEMENT WATER TO WHISKEY MAKER NOW STOP FULL STOP
Things would be so much easier if Morse had known enough computer science to make EOL and EOF codes.
Reply to Graeme M (September 19, 2013 at 3:52 pm): Read this NOAA web page along with my earlier link to clarify the differences and similarities of storm surge, storm tide, etc. Enjoy! http://www.nhc.noaa.gov/surge/
NOAA, in the report The Budget of Recent Global Sea Level Rise 2005–2012
http://ibis.grdl.noaa.gov/SAT/SeaLevelRise/documents/NOAA_NESDIS_Sea_Level_Rise_Budget_Report_2012.pdf ,
finds the more recent trend of overall Global SLR for 2005-2011 to be 1.6 ± 0.8 mm/yr.
Pretty close to the 1.7 mm used in my calculations above.
h/t to commenter bw (September 19, 2013 at 3:31 pm)
CNC says:
September 19, 2013 at 6:57 am
I covered the 1962 storm in http://wattsupwiththat.com/2012/03/06/50-years-ago-the-great-atlantic-storm-of-1962/ I think it’s much better than the Wikipedia article, especially if you want an LBI focus. Heck, I even included on of my Dad’s photos of Old Barney.
From Googling |sandy 1962 site:wattsupwiththat.com| I see several articles that, including comments, mention both. Three from me, one from you, one from someone else:
http://wattsupwiththat.com/2012/11/02/next-time-somebody-tries-to-tell-you-hurricane-sandy-was-an-unprecedented-east-coast-hurricane-show-them-this/
http://wattsupwiththat.com/2012/11/18/discovery-channel-fail-sandy-was-not-a-megastorm/
http://wattsupwiththat.com/2012/10/26/noaa-and-fema-gearing-up-for-sandy/
http://wattsupwiththat.com/2012/10/28/stunning-super-high-res-image-of-hurricane-sandy-plus-forecast-of-a-large-storm-surge/
http://wattsupwiththat.com/2013/08/29/the-great-labor-day-hurricane-of-1935/
Aside – I’m trying to write an article about the Hurricane of 1938. Well, other weather events that should be mentioned will be the focus. Too many distractions these days, so I may not make it in time.
Ric Werme says:
September 19, 2013 at 5:40 pm
“I covered the 1962 storm in….”
Sorry I missed those comments. Good stuff. Looking forward the the article on the Hurricane of 1938.
Please use, or add, synonyms for the word “significant” whenever it is employed in the scientific sense in articles like this. In lay speech, it means large, or important not merely statistically different from zero.
Izen says:
“But the reality is that the local sea level rise is always a combination of the global rise and the much smaller local effects.”
Actually the local effects are probably more often than not larger than the global rise.
Kip
I don’t know if you’re still reading comments on this article, but a couple of more, then I’ll leave you in peace:
———————-
Remember, it takes a long time (months at least) and specialized GPS equipment and analysis to get results to this accuracy
That’s my impression, but I haven’t researched the issue in detail. A factoid to file away if you don’t already know it is that there is a geometric issue with GPS or any other “astronomical” position measurement in that most observations will be at low locally measured elevation because much more of the visible hemisphere is at low elevation angle than at high. Low elevation angle means lots more (local) horizontal information than (local) vertical information. i.e. for a given set of observations — especially a large set — the horizontal (lat-lon) estimate will probably be considerably more accurate than the vertical (altitude) component.
———————–
It’s probably impossible to determine with current information to precisely estimate sea level rise. Much less partition it into natural and human causes. If it were easy, tidal gauge and satellite estimates would agree closely. But one thing everyone should be able to agree on is that humans have been building far too much vulnerable infrastructure at/near “sea level”. Shorelines are a great place for parks, parking lots, airport runways (If you don’t mind their being out of service from time to time). They are a poor place for permanent structures unless the “buildings” are either hardened against occasional flooding or can be moved out of harms way when necessary.
Reply to Brian H (September 20, 2013 at 12:57 am): You are right, of course, in prose about science, “significant” is a loaded word, with too many contradictory meanings. I try to write in plain everyday English (and wish everyone would do so). In my “Bottom Line” sentence “At the Battery, Manhattan, NYC, there has been, so far, no significant sea level rise attributable to AGW” I meant this:
sig·nif·i·cant (adjective)
1. sufficiently great or important to be worthy of attention; noteworthy.
Reply to Don K (September 20, 2013 at 2:15 am): If the time stamp is valid for your time zone, you’re staying up way too late on the ‘Net. You are right about GPS vertical accuracy being less and harder, right about measuring ‘global’ sea level (at all, in my opinion), and right again about building cities on mud flats, barrier islands and sand bars. You’re batting 1000.
Pippen Kool says: @ur momisugly September 19, 2013 at 6:31 am
Regardless of subsistence and other geological changes, flooding has to be worse with additional sea level rise….
>>>>>>>>>>>>>>>>>
To put it into pictures what is being said: graph Sea Level Rise
Significance is in the eye of the beholder. Meaning that if you drill down to a tiny piece of graph and use a finer scale, then include only that tiny piece of data string in your overall linear trend analysis, all kinds of potentially spurious significant and scary things can be said about your findings when examining a piece of your tiny piece of graph on a scale that allows you to see a gnat wriggle his ass.
For example, if I were to measure the size of all bird beaks, I could say that the range is very wide indeed and that significance does not appear to come into play. The data is that noisy. However within the species of sparrows, I could say that there are significant differences and I would try to determine why. If I were to measure the size of beaks within a single subspecies of sparrows, I could say that there are significant differences and I would try to determine why. If I go too narrow (say a subspecies within a regional range) significance begins to disappear again, UNLESS I use a finer scale. It is here where spurious significance is most likely to raise its head. Many species of birds have been divided up into subspecies to the point of ridiculousness, which is now slowly being reversed back to reasonableness.
Most researchers understandably try to find what I call the “sweet spot”. Which is that point within the broad range of data that I could possibly find significance but not too fine a point where true significance begins to disappear again.
I think the problem with our current field of climate researchers is that they have drilled down past the true sweet spot and have changed the scale to too fine a division. So now they are finding all kinds of potentially spurious significant and scary things that can be said about their findings when they are examining a piece of their tiny piece of graph that allows them to see a climate gnat wriggle its ass.
Reply to Gail Combs (September 20, 2013 at 8:05 am): The graph you link to represents Post-Glacial Sea Level Rise, and covers a time span of 24,000 years. Please note that for practical purposes, the part of this graph that concerns mankind
is the last, nearly flat, 7,000 years. The part of this graph that applies to the subject of this essay is represented by a single dot, containing zero discernible information. The graph that does apply to this essay is at the NOAA web site here –>http://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8518750 and the graph from CSIRO in the body of the essay above.
Kip, thanks for your replies to my earlier comments, but I think you may have missed the point I was making. Or else my point is well… pointless 🙂
I was observing something about the claim that AGW driven SLR will make EVERY storm surge worse.
While in an absolute sense that might be true, ie a storm surge on top of a water level that is one foot higher will therefore be one foot higher than it would otherwise have been, that’s a somewhat meaningless statement.
The point is that (disregarding factors of storm intensity and duration) you cannot predict beforehand the time of a storm’s arrival. So the severity of any storm surge is dependent on the tide height at the time of that storm’s arrival, as you note in your article.
For any given location, the local range of tidal variation gives you the likely range of storm surge effect. That is, if your range is 1 foot to 4 feet, then a surge of 3 feet will give you a storm tide range of 4 to 7 feet.
What I am saying is that in a planning scenario, a storm surge of any height at all that arrives on top of a tide that falls within the local tidal range cannot produce a storm tide outside of historic likelihood.
This means that while you might be able to suggest that a storm surge will cause a storm tide of greater proportion in an area where local SLR has changed the MSL, that’s a meaningless fact UNLESS it occurred at a time when the local tide was outside of the historic range. For the simple reason that it is not until the local tide is higher than the historic range that you will have a storm tide outside the historic range.
In the case of Sandy, we’d need to know if the predicted high tide for the time that Sandy struck is outside the expected range. Of course it was if we use say 100-150 years ago as our period, but in fact we know that the current National Tidal Datum Epoch was set in the period 1983-2001. That’s a bit recent, so we could go to the next earlier one, 1960-1978. That’s a good period as it’s closer to the time after which AGW really is supposed to have kicked in.
So, was the predicted high tide for Sandy’s time of arrival higher than the highest high tide measured in the period 1960-1978? My rough figures from the data tell me that the high tide was predicted to be 1444mm. Adjusted, that is 2446mm above the local Benchmark.
The Mean Higher High Water for the period 1960-78 was 2496mm, so we can see that the high tide was about 50 mm below the max likely range for the period in question.
Now, thats a rough calc and I am making no guarantees of accuracy and maybe I’ve missed something, buit it APPEARS as though Sandy’s storm tide was not outside the range that could be expected to occur. My point is simply a conceptual one.
What do you think?
Reply to Graeme M (September 20, 2013 at 2:12 pm): “While in an absolute sense that might be true, ie a storm surge on top of a water level that is one foot higher will therefore be one foot higher than it would otherwise have been, that’s a somewhat meaningless statement.” I do see your point. You hit it right on the nail head, Graeme. I can see that you had trouble seeing how the authors of “The Claim” could be so simplistic. Astonishing, isn’t it?
My comment on that was “…the TRUE and obvious fact that any positive change in local average relative sea level will make any storm surge ‘worse’ – by the simple effect of the relative water level being higher by whatever amount” and, of course, you are right, any relative sea level rise–from whatever cause–has the same effect. The meaninglessness of it is that we (Mankind) are not masters of the sea level, the sea does not do our bidding.
Kip, just an aside to this. I have little free time to read through all the comments and I’d need to spend a few minutes thinking through your post in more detail, but I wondered if you’d made allowance for the adjustments to datum points for The Battery?
I have to admit to not understanding this stuff so my comments may be well wide of the mark.
Mean tide heights and hence MSL are calculated from the reference point of Mean Lower Low Water which is set to zero. However I think that relative to the local benchmark. Tidal datum are set according to a 19 year cycle called the National Tidal Datum Epoch. The current value for the Mean Lower Low Water is 1.002 metres whereas for the previous Epoch (1960-78) it was .936 metres.
In effect, I think what I am saying is that although the tidal datum values (eg MSL) are directly comparable, their basis is adjusted regularly to allow for things like land movement.
So there is an adjustment of some 66mm in there which may affect your calculations? And if you are calculating since 1960, you probably need the adjustment for the Epoch prior to the 1960-78 one as well. Assuming it would be similar, that could be as much as 100mm.
Could be quite wrong cos I am no expert, just wondered if you’d allowed for that? Or if it’s even relevant.
Reply to Graeme M (September 20, 2013 at 4:45 pm): The graph at http://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8518750 (which is in the essay above) is the local sea level relative to a solidly mounted brass marker (benchmark) on bed rock. It is NOT adjusted for anything, as far as I know. There is an explanation at http://tidesandcurrents.noaa.gov/sltrends/ under the heading ‘Products’. There is further clarification/confusion at http://tidesandcurrents.noaa.gov/datum_options.html . For my simple essay, I use only the very simple statement from the New York State Sea Level Rise Task Force “4 to six inches” of rise at the Battery, 1960-2010. I am sure that there is a lot to know about how NOAA takes a dynamic system like “sea level at the Battery” and reduces it to a series of numbers. Hope this addresses your concern.
Kip check the level of the MLLW datum for both the current and previous tidal epochs.
Here is the current epoch in meters:
MLLW 1.002 Mean Lower-Low Water
Here is the previous epoch:
MLLW 0.936 Mean Lower-Low Water
Here’s tidal datums for the present epoch. Note that MLLW is shown as zero. I assume that at all times the MLLW value is zero, but its offset varies depending on epoch.
Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:
HIGHEST OBSERVED WATER LEVEL (10/30/2012) = 4.280
MEAN HIGHER HIGH WATER MHHW = 1.541
MEAN HIGH WATER MHW = 1.443
North American Vertical Datum NAVD88 = 0.846
MEAN SEA LEVEL MSL = 0.783
MEAN TIDE LEVEL MTL = 0.753
MEAN LOW WATER MLW = 0.063
MEAN LOWER LOW WATER MLLW = 0.000
Imagine if the world spent a quadrillion dollars to make itself carbon-neutral and then the post-LIA warming and SLR trends continued unabated! Then they spent a few million on sea walls around Manhattan and got on with life.
Reply to Graeme M (September 20, 2013 at 8:31 pm): Looks like you are well on your way to having enough background material to write an essay on “How Sea Level is Determined”. I look forward to reading it here.
THANK YOU!
Thanks to all the WUWT readers who read this essay, and especially to those who commented, asked questions, and clarified points for other readers.
My personal thanks to Anthony Watts for providing this important forum for Citizen Science. He is an inspiration to me, as he is to many others. And thank to all those who, in big and little ways, support Anthony and the WUWT blog.
I will be working on other projects this week and probably not responding daily to comments on this essay.
Blue skies and following seas,
Kip Hansen
PS: Those who simply must communicate with me on this or any other issue may email me using kip and the domain i4.net.