Sounds about right Peter. My issue is that we have seen no acceleration whatsoever of sea level rises over the past 30-40 years. The average as you pointed out over that time is 3mm per year which matches the rate seen over the century and a half leading into the 70's.

Therefore risng global temps have not accelerated the rate of sea level rise during the period for which AGW is purported to be a factor. For me this is about what I expect given temperatures have been rising for the past 200 years or so and the rate of increase in the past 30 years has not outstripped increases seen in the first part of the twentieth century.

I know you've previously suggested that the real boogeyman in the closet is the Greenland ice sheet but the science regarding the impact of rising temps on the ice sheet is far from settled and even the worst case scenarios indicate it will be hundreds of years before it becomes a major factor. Whilst the rate of melt has been accelerating in recent years this is not entirely related to rising temps. Soot from diesel engines has been identified as a significant factor also (it can be seen aggregating at the bottom of the melt ponds). Certainly at the current rate it will be thousands of years before the sheet becomes an important factor in sea level rise. Most of the doomsday scenarios for it's "collapse" are still just theories and a long way from being scientifically proven.

Locke, quite right it is a slow and gradual process with the sea level rise. Although with the Greenland ice sheet I think it may be a matter of hundreds rather than 1000's of years before a significant part of it may melt. By significant I mean maybe 20-30%.

Cannot wait to see what happens to sea level in the next El Nino. Will be interesting to see if an acceleration in sea level rise will occur in that period, if it happens it will certainly prove that the sea level observations are being made accurately. If not then that would really raise some questions about what is going on with the climate if no observation error was made.

Where do you see 20cm , or 3mm a year rise at the gauge ?
What I see , sea level is lower now than in 1991 .

Could someone please enlighten me as to how a melting ice sheet could possibly have any effect on sea levels. Doesn't an ice sheet float on the ocean? If that is the case then shouldn't it displace roughly the same amount of water that it contains? If that is the case then when it melts it will have no bloody effect whatsoever. If the ice sheet is not floating then I am wrong and please ignore this entire post!

Re Sea Level measurement - I think my memory tells me that the Port Arthur Site (Tassie) has measured sea levels on the "Isle of the Dead" since it was first colonized. Pretty sure they said it was the oldest continuous sea level measurement site in Australia. Might be worth a look.

Brett, as the Greenland ice sheet sits on top of solid ground. It is not floating on the ocean. It is up to 2.5km thick in places and contains absolutely massive quantities of fresh water.

The rate of loss of the sheet is in the order of cm per year. I understand the theory that water undercutting the sheet will accelerate the rate of loss but I'd like to see a little more evidence of this occurring to support the theory than what is currently being observed. Whilst a big chunk of ice calved off the Petermann glacier last year this was by no mean unprecedented with a larger chunk having broken off back in 1962.

At the moment the collapse of the Greenland ice sheet remains a theory, hugely dependent upon a number of unknown factors some of which are outside of the realms of AGW theory.

Brett, much of the discussion in the science about ice relates to ice that sits on land masses, including glaciers and of course the ice on top of Antarctica. If it all melted suddenly the world would be flooded.

Sea ice behaves as you say; it displaces 8/9ths of its volume of water so if it should melt, things would pretty well even themselves out as far as the sealevels go.

Vlasta, all the gauges are here with raw monthly data since about 1991. Its 6cm over 20 years which is 3mm/year.
http://www.bom.gov.au/oceanography/projects/abslmp/data/monthly.shtml

DaveM, I had a look at Spring Bay in Tassie and its also 6cm quite surprisingly although there the rise is much more consistent than Port Kembla with a much weaker ESNO signal. Tassie surprises me since I thought there was still some uplift there. But I guess the sea level change is faster than the tectonics.

I ran a mean over the readings of 4 or 5 years to see the trend more easily. Just a matter of opening the text data in Excel and plotting. You can get an exact linear regression value if you wanted.

Haven't I seen old maps where Tasmania and Papua New Guinea where a part of the Australian land mass or am I mistaken? Because if this is the case, sea levels have been rising for a hell of a long time!!!!!

For your info Simmo. From Wikipedia ; Prehistory of Australia



There is also a pic of the vast areas through what is now Indonesia, around PNG and across the present Torres Strait that were land bridges during a time when the sea levels were 150 metres below the present levels.

The following satellite based sea level graphs is from the official AVISO site.
The very rapid downturn from a monotonic sea level rise of 3.2 mm / year going back to 1993 to a overall substantial and rapid mean global rapid sea level fall over the last year is striking.
These short term rises and falls are believed to be linked to the upper ocean heat content. Rising heat content; ie warming ocean temperatures lead to expansion of the ocean waters and therefore possibly account for most of the sea level rise.
Now with the 3000 unit global ocean wide ARGO float system data showing no warming; ie no increase in the ocean heat content in the oceans since about 2002 / 3 and then the 1998 La Nina and now the 2010/ 11 La Nina, ocean heat content is being lost ; ie cooling of the upper levels of the global oceans and therefore a contraction of the ocean waters and a falling sea level, both rapid and substantial in the last 12 months.

A couple of points from the graphs below.
The very strong El Nino of 1998 does not appear to have much impact at all on the sea levels. Certainly no rises in sea levels due to expanding ocean waters with increased heat content is seen in 1998 on the graphs.
The 2008 La Nina had some impact ie a small and short lived 12 to 18 month fall before a full recovery in the formerly monotonic sea level rise was resumed.
But the real kicker is the very large, marked and continuing fall in sea levels since early 2010 which from the previous ENSO phase effects on the global sea levels seems to be much more severe than can be explained by just the 2010 /11 La Nina.
There may be other unknown or poorly researched processes at work here on the global sea levels and it doesn't seem likely that the monotonic rise in sea levels that is claimed by the warmistas, like so many other claims and predictions they have made over the last decade and a half, will ever be even close to what actually happens in the real world.


A composite of the different satellite sea level measuring technologies.


The graphs below are the results from the different in sea level measuring satellite technologies.

Thank you Rom... Very informative....

This article I took from S Goddard blog . Thats exactly what I thought when there was6mm drop .
On the other hand warmistas claim , glaciers loss of ice last century was 2000 cubic miles . For god sake , where is the water then ?

http://www.eoearth.org/article/Aquifer_depletion

The ENSO leaves a signal in sea level. It takes a few steps to see how this occurs.

During a La Nina, more precipitation occurs as water vapour is being drawn out of the cooling atmosphere (-1.0 mm) / falling as precipitation. Water vapour cycles through the atmosphere 40 times per year so during a La Nina, as much as 5 mms of precipitation accumulates on the Land (not making it back to Oceans) and sea level falls by the 5 mms.

During an El Nino, the opposite happens and as much as 5 mms gets evaporated off the Land to fall (with the 40 times per year cycling through) as rain on the Ocean. Sea level goes up.

Its a little counter-intutitive but this is what happens.

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Regarding the long-term sea level. Southern Greenland is too far south to have continental glaciers if an interglacial lasts for 20,000 years or so. The southern Greenland glaciers are farther south than Finland, which gets to 25C in the summer.

Southern Greenland has glaciers because northern Greenland has 3 km high glaciers and there were 4 km high glaciers there in the ice ages. Sea level will continue rising as southern Greenland continues to melt out until the next ice age starts up.

During the interglacial 400,000 years ago, which lasted about 23,000 years, the southern third of Greenland melted to the surface and small trees even grew there. During the last interglacial, the Eemian 100,000 years ago, the interglacial lasted about 15,000 years and Greenland was up to 5C warmer than today. But this was not enough time to melt out the southern glaciers. It takes a long time to overcome the thermal inertia of all that ice, next to 3 kms of more ice.

I didnt make my self clear .
That article points out , how much ground water has been extracted and not being able to be replanished .
As population rise demand for water increases . That alone I would account for half sea level rises till now .
Quick look at VIC storages , there is 6 cubic km more water locked in , than 2 years ago . Thats only Victoria .
2-3 years ago Perth Brisbane were in water crisis .
How many more cubic km of water is locked up or seeped to ground . Your guess is good as mine . But its a lot .
I think , once ground water in some countries is gone , sea levels will stop rising that fast .

We have the Tuvalu sinking meme in the news again...



http://www.abc.net.au/news/2011-12-09/tuvalu-kiribati-climate-change/3720408?WT.svl=news0

The “authorative” BoM Pacific Country Report on Tuvalu doc from 2006 has this to say with respect to Tuvalu.




From this has stemmed the meme that the islands are drowning – and we see pictures like the one linked above.

Good old John Daly, may he RIP, he still has valuable contributions to make!

This graph apparently is from the Adelaide based National Tidal Facility news release "Sea Level in Tuvalu: It's Present State". Reference to this can be found on this John Daly page . The link to this article is now no longer valid…

If you overlay the two graphs – the one from John Daly’s site and the one from the “authorative” 2006 report, you get this:

There is some mucking about with scales – but almost a perfect match across the coincident years (they are offset a bit to make this clear).

If you then have a look at what the Sea Level did recently:

http://www.bom.gov.au/ntc/IDO70056/IDO70056SLI.pdf

Then there really is bugger all increase. There is like no way that the King Tide floods are just a feature of the recent period. There has been nothing like a 6.4mm/year raise in max sea level (from 1978 to 2011 – some 33 years – at that rate the increase would have been over 20 cm).

I posted a BOM reference that claimed a greater present sea level rise at Sydney than they posted for WA at the same time - several months ago. Do not believe sea level figures progged by the (now-dimishing) Global Warmists/Alarmists.

Our BOM? - its well and truly playing the cash hand out game. Type in Climategate 2.0 to any search engine and filter for Aust BOM posts - I was shocked (to see my own suspicions confirmed in an instant)!

The ABC are a joke... just like the Government... Hang on!! Who owns the ABC??

From WUWT; Sea level still not cooperating with predictions




Plus the leveling off in the ocean heat content shown in Bill Illis's "Ocean Heat content" graph in Science in AGW thread.

The plateauing of the global temperature rise since 2006 and now showing signs of a very slowly developing decline in global temperatures.

The unforecast solar activity slow down plus the dramatic decline in solar UV output and the collapse of the solar magnetic field strength.

The switch in the PDO phase to a cooler negative phase plus it's accompanying increase in La Ninas and lower incidence of El Ninos.

The change in the AMO to a cooler phase.

The slow down in the rise in global CO2 increases possibly due to less em-missions from oceans that are no longer warming.

Himalayan Glaciers that are not retreating en masse but are about stationary in total ice mass.

Arctic Sea ice now showing signs of having been through it's low cycle point and starting to indicate a yearly increase from now on..

Antarctic ice fields expanding and etc and etc.

NONE of which were forecast by the IPCC's climate models.

The WUWT article, “Sea Level is not cooperating with the predictions”, Feb 14 2012, is out of sync with the latest research paper on this issue. Recent contributions of glaciers and ice caps to sea level rise by Jacob, Wahr, Pfeffer and Swenson, Nature, 8 February 2012
This paper is covered in the YouTube video: Himalaya Glaciers – “No Melt in 10 Years” The video, produced by a “warmist”, shows screen captures of the research paper in question, but should be referenced against the Jacob, et al, research paper for which the abstract reads:
'Glaciers and ice caps (GICs) are important contributors to present-day global mean sea level rise1, 2, 3, 4. Most previous global mass balance estimates for GICs rely on extrapolation of sparse mass balance measurements1, 2, 4 representing only a small fraction of the GIC area, leaving their overall contribution to sea level rise unclear. Here we show that GICs, excluding the Greenland and Antarctic peripheral GICs, lost mass at a rate of 148 ± 30 Gt/yr from January 2003 to December 2010, contributing 0.41 ± 0.08 mm/yr to sea level rise. Our results are based on a global, simultaneous inversion of monthly GRACE-derived satellite gravity fields, from which we calculate the mass change over all ice-covered regions greater in area than 100 sq. km. The GIC rate for 2003–2010 is about 30 per cent smaller than the previous mass balance estimate that most closely matches our study period2.
The high mountains of Asia, in particular, show a mass loss of only 4 ± 20 Gt/yr for 2003–2010, compared with 47–55 Gt/yr in previously published estimates. For completeness, we also estimate that the Greenland and Antarctic ice sheets, including their peripheral GICs, contributed 1.06 ± 0.19 mm/yr to sea level rise over the same time period. The total contribution to sea level rise from all ice-covered regions is thus 1.48 ± 0.26 mm/yr, which agrees well with independent estimates of sea level rise originating from land ice loss and other terrestrial sources6.' [url= http://www.nature.com/nature/journal/vaop/ncurrent/full/nature10847.html]Recent contributions of glaciers and ice caps to sea level rise[/url]
To avoid paying the $US 32.00 to read the full article, the issue of the Himalayan Glaciers not melting as fast can be put in context with a post on 25 February, 2012 at the following link:: GRACE and glaciers . It may pay to check because the SkepticalScience website is a “warmist” site although, in the same genre, WUWT is a “coldist” site.
Here is the SkepticalScience post:
'Satellites find over 500 billion tons of land ice melting worldwide every year, headlines focus on Himalayas.
The GRACE program is a triumph of our technology – a pair of satellites nicknamed ‘Tom’ and ‘Jerry’ that act like a pair of scales for the Earth below them. They have weighed Australia getting heavier as floodwaters rose, the Earth getting fatter thanks to ice cap melt, and the drying up of Texan water supplies.
Now scientists have produced the first global map of change in the mass of land ice on Earth for 2003-2010 (Jacob et al, 2012), see it in all its glory in Figure 1. Unfortunately the resolution of the GRACE satellites means they can't reliably measure ice areas smaller than 100 km2 (almost 40 square miles), so these are not included in the study.

[
Figure 1 - Map of changes in ice thickness estimated by Jacob et al. Blue means losing ice and red means gaining ice. Changes in geology and groundwater have been accounted for (supplementary information). The red spot in Africa is an artifact. The units are 'centimetres of water equivalent per year': the change in water thickness that would be needed to cause the measured mass change.

Biggest ice sheets: melting faster than 2007 UN figures, no surprise there!
The first things that jump out at you are probably the big blue areas around Greenland and Antarctica. The new results are similar to those already covered at skepticalscience, such as Garder et al, 2011's work on Baffin & Ellesmere islands, plus other measurements of Greenland and Antarctica. It's no longer news that the 2007 UN Intergovernmental Panel on Climate Change (IPCC) computer simulations were far below what has happened.
Greenland and Antarctica have lost almost 400 billion tons of ice every year according to these measurements, twice the loss expected from all the world's other glaciers. This helps to explain why sea levels are rising at the high end of IPCC expectations.


Figure 2 - tide gauges (red), satellite measurements of sea level (blue) and IPCC computer model expectations (grey area) from Allison et al, 2009.
Worldwide glaciers mostly in retreat - down 1.2 trillion tons in 8 years
For the first time, entire mountain ranges of glaciers have been weighed. There are at least 160,000 glaciers worldwide and in the World Glacier Monitoring Service's last update only 136 were weighed. Thousands have been pictured by satellites (e.g. Le Bris et al, 2011, Paul & Svoboda, 2011, Narozhney & Zemtsov, 2011) and found to be mostly shrinking in area, but photos can't measure thickness and therefore total weight.
GRACE shows about 150 billion tons a year of glacier melt which is actually less than some expected. It seems that glaciers in the high mountains of Central Asia (around the Himalayas) only lost about 4±20 billion tons of ice a year. Previous work expected closer to 50 billion tons of loss.

The big picture
We now have the first global map of glacier weight change. The ice sheets are doing much worse than 2007 predictions and glaciers in most of the world are doing just as badly as thought. However, glaciers in the high mountains of Central Asia appear to have been stable for 8 years when old measurements would have expected 400 billion tons of ice loss. Meanwhile, over 4.2 trillion tons of ice have melted worldwide over 8 years.
2003-2010 is a short time though, so it's too soon to say anything about what will happen next here.
Seas are rising faster than computer simulations had expected, and these simulations are also lower and slower than has happened in the past (Vermeer & Rahmstorf, 2009). It's possible that the simulations didn't properly include the processes that shrink ice sheets so these results are consistent with faster future sea level rise. Figure 4 shows that the rate of melt in the big ice sheets is much larger than the swings caused by seasonal weather and the long term trend is obvious.


Figure 4 - Change in the ice mass of Greenland (blue) and Antarctica (orange). Notice how the trend is much larger than seasonal changes, and how each vertical dash is now 200 billion tons.

The good news is that the highest mountains in Asia seem to be almost 50 billion tons a year better off than expected. But this is small change next to the 500 billion tons a year being lost elsewhere.'

Coincidently, the WUWT article, “Sea Level is not cooperating with the predictions”, Feb 14 2012, is out of sync with NASA Satellites Detect Pothole on Road to Higher Seas Aug 23 2011 which concludes “While most years have recorded a rise in global sea level, the recent drop of nearly a quarter of an inch, or half a centimeter, is attributable to the switch from El Niño to La Niña conditions in the Pacific. WUWT did a full report on this NASA update but dismissed it because it had no numbers attached.



An Update from NASA's Sea Level Sentinels:
'Like mercury in a thermometer, ocean waters expand as they warm. This, along with melting glaciers and ice sheets in Greenland and Antarctica, drives sea levels higher over the long term. For the past 18 years, the U.S./French Jason-1, Jason-2 and Topex/Poseidon spacecraft have been monitoring the gradual rise of the world's ocean in response to global warming.
While the rise of the global ocean has been remarkably steady for most of this time, every once in a while, sea level rise hits a speed bump. This past year, it's been more like a pothole: between last summer and this one, global sea level actually fell by about a quarter of an inch, or half a centimeter.
Climate scientist Josh Willis of NASA's Jet Propulsion Laboratory, Pasadena, Calif., says that while 2010 began with a sizable El Niño, by year's end, it was replaced by one of the strongest La Niñas in recent memory. This sudden shift in the Pacific changed rainfall patterns all across the globe, bringing massive floods to places like Australia and the Amazon basin, and drought to the southern United States.
So where does all that extra water in Brazil and Australia come from? You guessed it--the ocean. Each year, huge amounts of water are evaporated from the ocean. While most of it falls right back into the ocean as rain, some of it falls over land. "This year, the continents got an extra dose of rain, so much so that global sea levels actually fell over most of the last year," says Carmen Boening, a JPL oceanographer and climate scientist. Boening and colleagues presented these results recently at the annual Grace Science Team Meeting in Austin, Texas.
But for those who might argue that these data show us entering a long-term period of decline in global sea level, Willis cautions that sea level drops such as this one cannot last, and over the long-run, the trend remains solidly up. Water flows downhill, and the extra rain will eventually find its way back to the sea. When it does, global sea level will rise again.'