Study: sea level rise acceleration still uncertain, we won't have statistical certainty until 2020-2030

This is a bit of a bombshell to those that claim sea level rise is accelerating and certain. From the University of Southampton:

Back to the future to determine if sea level rise is accelerating

IMAGE: This is a tide gauge at National Oceanography Centre in Liverpool, UK.

Scientists have developed a new method for revealing how sea levels might rise around the world throughout the 21st century to address the controversial topic of whether the rate of sea level rise is currently increasing.

The international team of researchers, led by the University of Southampton and including scientists from the National Oceanography Centre, the University of Western Australia, the University of South Florida, the Australian National University and the University of Seigen in Germany, analysed data from 10 long-term sea level monitoring stations located around the world. They looked into the future to identify the timing at which sea level accelerations might first be recognised in a significant manner.

Lead author Dr Ivan Haigh, Lecturer in Coastal Oceanography at the University of Southampton, says:

“Our results show that by 2020 to 2030, we could have some statistical certainty of what the sea level rise situation will look like for the end of the century. That means we’ll know what to expect and have 70 years to plan. In a subject that has so much uncertainty, this gives us the gift of long-term planning.

“As cities, including London, continue to plan for long-term solutions to sea level rise, we will be in a position to better predict the long-term situation for the UK capital and other coastal areas across the planet. Scientists should continue to update the analysis every 5 to 10 years, creating more certainty in long-term planning — and helping develop solutions for a changing planet.”

The study found that the most important approach to the earliest possible detection of a significant sea level acceleration lies in improved understanding (and subsequent removal) of interannual (occurring between years, or from one year to the next) to multidecadal (involving multiple decades) variability in sea level records.

“The measured sea levels reflect a variety of processes operating at different time scales,” says co-author Dr Francisco Calafat, from the National Oceanography Centre. He adds, “One of the main difficulties in detecting sea level accelerations is the presence of decadal and multi-decadal variations. For example, processes associated with the North Atlantic Oscillation have a strong influence on the sea levels around the UK over multi-decadal periods. Such processes introduce a large amount of ‘noise’ into the record, masking any underlying acceleration in the rate of rise. Our study shows, that by adequately understanding these processes and removing their influence, we can detect accelerations much earlier.”

Co-author Professor Eelco Rohling, from the Australian National University and formerly of the University of Southampton, adds:

“By developing a novel method that realistically approximates future sea level rise, we have been able to add new insight to the debate and show that there is substantial evidence for a significant recent acceleration in the sea level rise on a global and regional level. However, due to the large ‘noise’ signals at some local coastal sites, it won’t be until later this decade or early next decade before the accelerations in sea level are detection at these individual tide gauge sites.”

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The findings of the study, funded by the Natural Environmental Research Council (iGlass consortium), are published in this months issue of the journal Nature Communications.

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Bill_W

Impossible! I heard the science was settled.

JohnC

I presume, then, that they will train their model on data from before 1890 or 1830 exclusively, then run it forward to present to validate? Using the actual data, not the adjusted?
Thought not.

mark in toledo

I would love some really good data on Sea Level Rise and Ocean Heat Content. I notice these are two areas where the alarmists love to camp since nothing else is going their way.

Last time I checked all the satellites that read sea level say “all is normal” of course it all depends to the real experts at the Whitehouse.

Claude Harvey

” Such processes introduce a large amount of ‘noise’ into the record, masking any underlying acceleration in the rate of rise. Our study shows, that by adequately understanding these processes and removing their influence, we can detect accelerations much earlier.”
Translation: “The raw data does not show what we expected and wished to see. Therefore, we must statistically massage the data until the revised data cooperates.”
Where have I heard that one before.

Ok…waidaminnut.
One author says that it’ll take another 15-20yrs to be able to figure out what’s going on, and then another author basically says there’s so much noise it’s MASKING the accelerated sea level rise.
““By developing a novel method that realistically approximates future sea level rise, we have been able to add new insight to the debate and show that there is substantial evidence for a significant recent acceleration in the sea level rise on a global and regional level.”
How is it that when something is being masked, it’s always in their favor?
I sure wish I was as smart as these folks…then I wouldn’t have to work anywhere near as hard as I am now.
Downright clevah.
Jim

Jimbo

I always had my doubts about the ability to measure sea level rise to within a couple of millimeters in one year. I thought 10 years at least to be able to see something worth interpreting.

Neville

The Church et al 2005 study found no increase in the rate of SLR (1.8mm year) over the 20th century and the Leclercq et al 2014 glacier study found a higher retreat in the first half of the 20th century compared to the post 1950s period.
Exactly the opposite of increased co2 causing dangerous SLR nonsense. I have counted many recent studies that have found a deceleration in SLR, not an acceleration.
BTW why can’t I paste a link in the comments window, I can on other sites?

Gary in Erko

Sea level rise is real. The waterline of my kayak is a few mm higher than a couple of years ago. Of course it could be due to the extra bit of protruding roundness that’s somehow been added to my belly. But that’s just anecdotal. It’s not real science like people who we trust because they’ve got letters after their name.

Latitude

analysed data from 10 long-term sea level monitoring stations located around the world..
===
Does anyone know which 10 those are?
====
and show that there is substantial evidence for a significant recent acceleration
=====
yep, I would have guessed you would do that
=====
However, due to the large ‘noise’ signals at some local coastal sites
=====
That’s called subsidence…and what “some” local sites…you’re only dealing with 10
So they are setting out to “show” evidence for a significant acceleration………….

TobiasN

It kinda, sorta sounds like they are saying ‘nothing scary is happening, wait ten more years, we have no evidence, but we will ‘.
Maybe I have all this wrong. Are these the details? … the Dalton minimum was the coldest period in the entire Holocene. After which -totally normal for an inter-glacial – the seas began to rise/glaciers melt (delayed by Tambora 1815). Glaciers melted throughout the 19th century … very minor upticks 1900-1910 and 1990-2000, and now a minor downtick 2004-2014
and in the last 20 years, despite a billion tons of CO2(?), no acceleration. rate still at 3.5 inches a century
oh and it turned out recently the IPCC exaggerated Himalayan melt by a factor of 7.
them: “pretty please wait ten more years, give us money for at least 10 more years”

TomE

I hope these folks have something more constructive to do than wait for 15 years to determine if the sea level is rising by 1mm/year or 1.1mm/year. However based upon their paper which basically said nothing, I suspect my hopes are in vain.

mem

Sigh, including the University of Western Australia. Why is it that one automatically cringes if you are an Australian when you see that institution’s name attached to anything involving climate change research?

“… show that there is substantial evidence for a significant recent acceleration in the sea level rise on a global and regional level …”
I am sure their models and adjusted data (tortured??) will show what the people handing out grants want to see. It is worse than we thought!
This post just shows once again that most everyone involved in climate “science” have no idea what the scientific method is. It is just Fracking sad.

michael hart

OK, so if it won’t be detectable at any individual site for 10 years, then this is the opportunity for them to give us the list of their predictions. Or does that cost extra?

DaveW

Interestingly, the lead author Haigh is associated with a number of studies on sea level that don’t sound too alarmist (upper bound of 1.8 mm per year), but Rohling (unfortunately the one now in Australia) is an alarmist and associated with such objective and non-political screeds as Hanson et al.’s PLoS (2013) “Assessing “Dangerous Climate Change”: Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature”
The article appears to be open access is anyone wants to follow this up:
http://www.nature.com/ncomms/2014/140414/ncomms4635/full/ncomms4635.html

Mike Maguire

We can’t wait that long. The Arctic will be ice free by then, with no more polar bears. Bees will be gone. Crop yields down 30%. Our children will no longer have snow to go sledding on. We must take drastic measures to severely cut the use of all fossil fuels and CO2 emissions now!!!
But wait, it looks like there is hope after all. In this story of the government that cried catastrophic climate change wolf, it looks like the wolf will become extinct before any of these things happen.
Hurray!! The humans will be able to live in peace, harmony and prosperity as the plants and creatures celebrate the death of the wolf and dine on massive benefits from increasing CO2.

Peter Miller

Incredible, so just what part of this ‘climate science’ is actual science?
Anyhow, at least the clowns who wrote this nonsense are blatantly honest about wanting another 6+ years grants.

Robert of Ottawa

Er, like, we don’t know because of all the other stuff. Fund us for another 15 years or so and we’ll let you know.

amoorhouse

Surely if at 2030 you will be able to predict sea level rise acceleration for 2100, surely in 2014 you will be able to predict sea level acceleration for 2084, no?
What is that result? Or does it only work for years to two significant figures.

Gary Pearse

“whether the rate of sea level rise is currently increasing”
Yeah the committee checked to be sure they had everything rising at least. How in heck can you find if rate of sea level rise is CURRENTLY increasing by looking at 15 to 20yrs more data? I hope they don’t receive a cheque each year for this study. How are they sure sea level will even be rising at all by 2030? What prevents it from falling. Now that you have found it is accelerating in 2030, how do you decide what it will be 70 yrs later. We’ve let the mice play for too long when we see the preconceived nonsense that they spout with no shame.

Ack

Only 10 stations? Seems like a small sample size.

Rud Istvan

Many commenters here have missed the subtlety of this paper’s purpose. I just finished an essay for the next book on this subject, so here is a synopsis.
It has been a CAGW article of faith that SLR is accelerating. (Hansen, 5 meters by 2100, etc.) Alas, NOAA in the satellite era says it is not, rather constant at 2.8mm/ yr. Worse, the satellite data can be interpreted as saying it has been decelerating since 2003-2006 (pick your own cherries) to 2.4mm/ yr. Still worse, the closure problem (SLR must equal GIA plus melt plus thermosteric volume expansion) says probably less than 2.4. It was supposed to be about 3.1 and accelerating. This has occasioned two ridiculous peer reviewed explanations. First, that the heavy rains over Australia and elsewhere in 2011 caised that years indisputable dip. The water had not returned to the sea. Trenberth, of course. The only problem is, the recorded rainfall (whether or not it returned to the sea) equals less than half of the dipwater volume. The other explanation is that an El Nina biased period dumped extra rain on Australia, the Amazon, and the Congo since 2006 that has not yet returned to the sea. (Climate Etc discussed this recently). Also falsifiable easily. Australia has been in net drought, and the Amazon and Congo basins cannot retain extra rainfall by their fundamental hydrology.
So the only option left other than to admit the pause has slowed meltin and thermostatic rise is to say, well, we just cannot be sure until 2030. Move the goalposts. A climb down of sorts. Does paint AR4 into a falsified corner. Does make the previous papers look even more stupid than they already were.

Political Junkie

Current sea level – half way up a duck.
My prediction is that in year 2100 it will still be half way up a duck.

Mike McMillan

Gary in Erko says: May 9, 2014 at 3:43 pm
Sea level rise is real. The waterline of my kayak is a few mm higher than a couple of years ago. Of course it could be due to the extra bit of protruding roundness that’s somehow been added to my belly.

Relax, it ain’t all that bad. You just forgot to apply the Glacial Isostatic Adjustment.

Katherine

“By developing a novel method that realistically approximates future sea level rise, we have been able to add new insight to the debate and show that there is substantial evidence for a significant recent acceleration in the sea level rise on a global and regional level. However, due to the large ‘noise’ signals at some local coastal sites, it won’t be until later this decade or early next decade before the accelerations in sea level are detection at these individual tide gauge sites.”
In other words, yes, we’re sure sea level rise is accelerating, but you’ll have to wait 10 years or so for confirmation. So just take our word for it for now.
Le Sigh.

James Strom

A somewhat oddball question: back in 1986 Louis Frank proposed that Earth was acquiring water from a continuous snowstorm of icy comets. I haven’t read that this theory was disconfirmed; has this input been quantified, and how would it affect sea level?

Latitude

mem says:
May 9, 2014 at 3:54 pm
Sigh, including the University of Western Australia. Why is it that one automatically cringes if you are an Australian when you see that institution’s name attached to anything involving climate change research?
================
For the same reason, the sales of Pepto Bismol goes up when we see this……..
the University of South Florida,

Latitude

Rud Istvan says:
May 9, 2014 at 4:27 pm
(SLR must equal GIA plus melt plus thermosteric volume expansion)
====
Rud, forgetting the obvious things they’ve hit on….subsidence, ground water extraction…..
They are completely ignoring sedimentation and erosion…..adding mud/silt…takes up space too
And shorelines, rivers, etc are constantly pumping mud and silt, gravel and rocks, 24/7
————
“”First, that the heavy rains over Australia and elsewhere in 2011 caised that years indisputable dip. The water had not returned to the sea. Trenberth, of course. The only problem is, the recorded rainfall (whether or not it returned to the sea) equals less than half of the dipwater volume.””‘
===
Thanks for that, I’ve been looking for it…..

RoHa

I’m 68 now, and yet when I look at the sea it looks just the same as it did when I was a small boy. If it has moved at all, I can’t see it. It’s still wet. It’s still salty. So I’m not worried.

10 stations would be enough to find a solar cycle.
Hehe.
Reducing uncertainty is a good thing.
But folks here have no appreciation for that kind of hard work

ferdberple

Our results show that by 2020 to 2030, we could have some statistical certainty of what the sea level rise situation
=========
“could have”? Sea level cannot be rising very much if you are not certain you will even have a trend by then!!!!!!!!!!!!!
Holy cow batman. How can sea levels be rising if you can’t even be sure you can detect it?

Lattitude:
“accelerating” My first thought also and my BS meter went off. But then I remembered my high school physics and that we live on a spheroid so off course it must be accelerating at approximately 9.8m/s^2 just to stay level. ;-D

North of 43 and south of 44

Mike McMillan says:
May 9, 2014 at 4:47 pm
Gary in Erko says: May 9, 2014 at 3:43 pm
Sea level rise is real. The waterline of my kayak is a few mm higher than a couple of years ago. Of course it could be due to the extra bit of protruding roundness that’s somehow been added to my belly.
Relax, it ain’t all that bad. You just forgot to apply the Glacial Isostatic Adjustment.
———————————————————————————————————-
Don’t forget the inverse barometric pressure adjustment. Can’t just use one.

Latitude

DaveW says:
May 9, 2014 at 3:59 pm
The article appears to be open access is anyone wants to follow this up:
http://www.nature.com/ncomms/2014/140414/ncomms4635/full/ncomms4635.html
====
you bet, and thank you
here’s their 10 tide gauges…
Sydney
Fermantle
Trieste
Den Heider
Newlyn
Brest
New York
Key West
San Diego
Honolulu
..and without exception….every one of them are showing a faster subsidence rate than sea level rise
That’s what I wanted to see…and exactly what I thought I’d find
http://www.sonel.org/IMG/png/ulr5_vvf-2.png

AJ

I find the rate of SLR interesting. Some, like Tamino, and then Church and White will assert acceleration. Others will assert steady state since 1930.

RobertInAz

Rud Istvan says: May 9, 2014 at 4:27 pm
+1.
IMHO, the key point is: “The error bars are so large we cannot establish an acceleration trend. ”
The second point is: “If there is an acceleration trend, it will take 10 years to overwhelm the error bars.”
The final point is – “We think there is an acceleration trend in there somewhere.” which, of course, is required to get published in this environment.
I see this as a very pro-skeptic paper.
1. We cannot detect accelerating sea level rise.
2. If sea level rise is accelerating, it will take another ten year for it to be detectable.
I am very grateful for a paper that apparently has an honest assessment of the measurement error.

KenB

I welcome that study, in the vast bulk of the report there is a scientific approach and an acknowledgement that on present indications there is plenty of time for planners to adapt to whatever nature serves up. It also shows up the difference between strict scientific observation of the quality of data and the snide injection of alarmist spiel that wants to claim certainty on something that is plainly not certain in scientific terms.
I am also quite sad that the unscientific claim was associated with the University of Western Australia, but it does show the political ambitions of some alarmists who cling to old memes in the face of diminished credibility, who still try try to impose their belief and bias to “hold the line” against political change away from carbon taxing and in opposition to the present Australian governments business as usual but work responsibly with environmental issues.

This post reminds me of another Is Sea Level Rise Accelerating? May 16, 2012, WUWT, by Paul Homewood.
This was a study of 12 long record tidal gauges from a set of 24 collected by Bruce Douglas. I objected to the clustering of the 12 records. 4 from California (3 with in 180 km and 150 km of the San Andreas Fault, 2 in NW Europe 200 km apart. 2 in the Med, 3 in Florida, 1 in Hawaii, all North of the Equator. The criteria was to avoid areas of glacial rebound and collisional plate boundaries. But by my count at least 7 of the 12 failed the stability test.
The Permanent Service for Mean Sea Level says
http://www.psmsl.org/train_and_info/faqs/

[1]…These currents lead to differences between the MSS and the geoid of 1-2 m, [1000 – 2000 mm] even after averaging out time dependent motions such as tides. The differences in the MSS generated by the currents means that the Atlantic is 1m lower on the north side of the Gulf Stream than further south.

Slow changes in currents, whether it be from AMO, SOI, PDO, could have long period effects could induce tidal readings that could be mistaken for changes and accelerations in sea level. A couple of decades of readings might not be long enough. In the Homewood paper, the three stations around Florida, 800 km from each other, had a difference in sea level rates for the 2000-2011 span in the range is -3.36 to +2.82. mm/yr (a diff of 6.18 mm/yr). How anyone could reject the hypothesis of a zero acceleration is beyond me.

Bill Illis

You cannot determine anything from 10 tide gauges. After working with the datasets a lot, it appears to me you need about 400 widely-distributed tide gauges to get a good enough signal.
Someone needs to use the long-term records of about 400 tide gauges (with 400 co-located GPS stations operating for at least 4 years) in order to answer this question properly.
Forget the satellite measurements, it is physically impossible for the satellites at 1400 km orbits to resolve sea level down to 1 mm. The data is just algorithm-driven by the scientists working with the data (and if they admitted it was physically impossible to resolve sea level down to 1 mm or if they said the sea level was only increasing at the same steady 1.5 mms/year rate it had always increased it, what would happen the next time they asked for $200 million and $10 million in operating costs for 5 years to launch the next satellite – yeah, they would have to find another job).

Latitude

Stephen Rasey says:
May 9, 2014 at 6:20 pm
How anyone could reject the hypothesis of a zero acceleration is beyond me.
=============================
the raw satellite data showed zero………all the sea level rise can only come from adjustments
http://globalwarmingsolved.com/wp-content/uploads/2013/11/Raw-TOPEX-Poseidon-according-to-Morner-2004.jpg
they no longer release the raw data…….if anyone knows where, post a link

Steve Case

Latitude says at 5:35 pm posted ten tide gauges. They all run at least from 1916 to 2012, here they all are with that overall rate in mm/yr and for the last 30 years and the difference:
Station ……. All Time .. Last 30 .. Change
Sydney ………. 1.0 ….. 1.3 …… 0.3
Fremantle ……. 1.2 ….. 1.4 …… 0.2
Trieste ………… 0.3 ….. 0.3 …… 0.0
Den Heider ….. 0.6 ….. 0.1 ….. -0.6
Newlyn ……….. 0.7 ….. 0.3 ….. -0.5
Brest ………….. 0.8 ….. 0.7 ….. -0.2
New York ……. 1.4 ….. 1.0 ….. -0.5
Key West ……. 0.7 ….. 0.3 ….. -0.4
San Diego …… 0.8 ….. 0.3 ….. -0.5
Honolulu ……… 0.5 ….. 0.1 ….. -0.4
Looks like a 6 to 4 split minus to plus. In other words, no acceleration
None of them are any where near the 3.2 mm/yr commonly quoted.

Bill Illis

GPS uses 4 individual satellites operating in tandem which are carefully controlled by the US military and they use the speed of light calculations including Einstein’s special relativity effects in order to reach a resolution of about 500 mms.
Do you think a single satellite operating at the same altitude using just radar bouncing off the variable sea surface is going to get down to the less than 1 mm resolution. I mean it is a joke that they are still in operation and anybody is taking it seriously.
.

Re Bill Illis
For you and others – what is the actual sea level, what is the shape of the earth, does gravity change, does that change sea level, what is going on inside the earth and outside the earth that impacts sea level and the shape of the geoid on which we live.
Interesting quote:
“Although for practical purposes, at the coastline the geoid and MSL surfaces are assumed to be essentially the same, at some spots the geoid can actually differ from MSL by several meters.”
I don’t know if this is a good link but it makes an interesting read (I have used their software and had an interest in a company that did work for them) :
http://www.esri.com/news/arcuser/0703/geoid1of3.html
“A brief examination of elevation readings for Esri headquarters in Redlands, California, demonstrates these differences. The campus elevation is shown on topographic quadrangle maps and high-resolution digital elevation models (DEMs) for the area as approximately 400 meters above MSL. However, a precise, nonadjusted GPS reading for the same location typically shows the elevation as 368 meters.”

Leo Geiger

This is a bit of a bombshell to those that claim sea level rise is accelerating and certain.
That’s an interesting spin. When the Houston and Dean sea level paper was published in 2011, this was the lead off to that WUWT post:
Bombshell conclusion – new peer reviewed analysis: “worldwide-temperature increase has not produced acceleration of global sea level over the past 100 years”
http://wattsupwiththat.com/2011/03/28/bombshell-conclusion-new-peer-reviewed-analysis-worldwide-temperature-increase-has-not-produced-acceleration-of-global-sea-level-over-the-past-100-years/
And what does this paper say about that Houston and Dean “bombshell”:

Thus, our analysis implies that the argument presented by Houston and Dean is invalid….it is intriguing that arguments persist that because only small accelerations are presently evident, the IPCC sea level projections must be wrong, when in fact the observations over the last 20 years agree closely with the Third Assessment Report and AR4 projections and are statistically consistently with AR5 RCP8.5 projections.

That part didn’t get mentioned here.
So yes, you can ignore all of that and focus on the very particular part that says if interannual to multidecadal variability is not taken into account it could take several decades to detect an acceleration at the 95% confidence level in a local tide gauge record. The opening of the concluding paragraph puts this supposed “bombshell” in its proper context though:

Considering all this, there is substantial evidence, in both GMSL data sets and coastal averaged sea level time series (corrected for internal variability), for the existence and significance of a sustained increase in the rate of sea level rise over the 20th century and early part of the 21st century. In addition, the magnitude of the acceleration currently being observed is consistent with the latest understanding of sea level budgets and since about 1990 cannot be explained solely as part of internal variability.

You would never know the paper says any of that by reading this blog post. People should read the full paper themselves. Here’s the link again:
http://www.nature.com/ncomms/2014/140414/ncomms4635/full/ncomms4635.html

Julian Williams in Wales

If there is so much noise that they cannot measure the rate of sea level change how can they know it is accelerating. For all they know it might be decelerating. Why have they made up their minds about eh results before they have enough data in to make their measurements?

@Latitude at 5:35 pm
here’s their 10 tide gauges…
Same as the Homewood paper, May 16, 2012.
Trieste – fail – a compression zone at the foot of the Alps and Adriatic ranges and Adriatic Sea plate boundary.
Newlyn, Brest (200 km apart, both suffer some glacial rebound effects)
Key West (why keep this one and not the other 2? Pensacola and Fernandia )
San Diego (awfully close to one of the fastest moving transform faults in the world)
Honolulu (bolted to an oceanic plate that sinks as it gets older and colder. But if it is 7,000,000 mm in water depth, then subsidence is probably less than 0.1 mm/yr. Then again, what’s the GIA Correction fudge factor NOAA uses? 0.3 mm/yr for ocean basin deepening?
Not in Homewood.
Sydney, Fermantle (Oh good! some south of the equator, 3300 km apart on the Australian plate. +2)
Den Heider, Netherlands. On a barrier island of the North Sea. 800 km from Brest and Newlyn.
New York, USA. Attached to granite of the N. American Plate. But seaward of the Glacial rebound hinge point so is subsiding slightly.
http://marine.usgs.gov/news/images/H02_129SallengerHowdDoran.jpg
http://web.ics.purdue.edu/~ecalais/projects/noam/noam/ Map of North America vertical GPS movements.

Louis

They admit they won’t have “statistical certainty” for 6 to 16 years, yet they are already convinced that the rate of sea level rise is accelerating. It’s just being “masked” by all the noise. All they have to do is understand the noise and then remove it to uncover the hiding acceleration. Having already staked their claim, I have little doubt they’ll find what they’re looking for. But if they don’t, they’ve given themselves a decade to tweak their “novel method” until it produces what they want. Am I being too cynical?

braddles

Surely if writing a detailed paper on changes the rates sea level rise, you would start by stating what rates of rises were being observed, yet I can see nothing in this paper that states what the rates of rise are or were at the 10 sites. (correct me if i am wrong) All there is is a statement that rises are “broadly consistent with” the IPCC report. Now I can spot an IPCC-style weasel phrase when I see one. Another one is “corrected for internal variability”.

Sceptical lefty

There is a significant number of unquantifiable variables. Assuming (!) the gauges are dead accurate … is the local land rising or falling relative to the rest of the planet? Is the planet, itself, expanding or contracting? How do ambient temperatures, local and remote, affect the readings? How do wind and weather patterns, local and remote, affect the readings? What is the quantity, over time, of landlocked ice and snow? What is the contribution of submarine outpourings of plutonic water? Are there any anthropogenic (what a word!) activities over the relevant period that could influence the readings? Is all that heat hiding in the deep oceans (where it can’t be found — but we know it’s there) affecting the readings?
This list is hardly exhaustive, but it seriously begs the question: “How the hell do you separate the signal from the noise?” Small changes over a long time will be undetectable and/or unattributable.
Still, it must be conceded, if computer models of an unbounded chaotic system (like Earth) can predict the climate over the next century (cough, cough) we may as well recognise the validity of this project.
For my money, if the Greenland ice sheet slid into the sea tomorrow we could probably make a robust causal connection with any observed rise in sea level.