## An Analysis of the TOPEX Sea Level Record

Willis writes: I wanted to see if there was acceleration in the TOPEX sea level record. I have looked all over the web to find either the data used to create the following image of the sea level rise as measured by the TOPEX satellite, available here, or some estimate of any acceleration that might be present in the trend. I could find neither. Here’s the record cited above:

Fig. 1 Original graph of the change in sea level rise. Note that the trend is estimated to the nearest hundredth of a mm per year.

Being unable to find the data, I resorted to my usual technique “¢’¬? digitize it myself. This was difficult, because they used large colored circles for the data points, so it was hard to decipher the graph. As this procedure may be of interest to readers, here’s what I did.

I found the exact dates of the starting and ending of each TOPEX cycle. I used my CAD software (Vectorworks, but you can do it in other programs as well) to convert a text file of these dates to vertical lines, spaced by date. I overlaid this grid on the image to give me the exact horizontal coordinates. I then was able to figure out where all the data points were located. Here’s a closeup of the procedure in process:

Figure 2. Closeup of the digitization process. Blue circles are added by hand, and adjusted to the exact location of each data point.

Note that I left out the Poseidon satellite data, as I wanted to have a clean set of TOPEX data. This seems to be the modern preference when analyzing the data as well. Also, note that the addition of the lines for the dates allowed me to determine exactly which blob represented which data point.

To verify my digitizations, I always make up a graph in Excel, and then overlay it on the data. I found they matched exactly. Here is my reconstruction:

Figure 3. Digitized reconstruction of Figure 1.

Now, this all looks very reasonable. There is a clear annual signal, plus an overall trend. So I decided to remove the annual signal, so I could see what the underlying trends actually look like. The result was quite surprising.

Figure 4. TOPEX data with monthly anomalies removed. Note the apparent misalignment of the records, which is not visible in Fig. 1. The lines at the bottom are the Gaussian residuals, i.e., the remainder after the 7 month Gaussian average is subtracted from the data. Note the decrease in error in 1997. Red dot marks the start of the degradation of the Altimeter “A” signal.

As you can see, we are back to the old “spliced records” problem. Of course, this is known to the scientists who did the splice. A good description of the splicing procedure is shown here. They say that the changeover between altimeters A and B was because of gradually increasing inaccuracy in altimeter A from cycle 130 onwards. They also show the ~1 cm difference between the two altimeters at the time of the changeover. However, they have not removed the bad signal from the graph.

Under the reasonable assumption of a quasi-lineal change during the gradual increase in inaccuracy, it is possible to linearly remove the increasing error following cycle 130. This gives us the following graph:

Figure 5. TOPEX data showing the adjustment after Cycle 130

And now that we have a coherent record, although it is still spliced, we can look for changes in the trend. Here is the full record, with the monthly anomalies removed:

Figure 6. TOPEX sea level record with monthly anomaly removed, and trends in the TOPEX sea level record. One year and two year trailing trends of the sea level record are shown at the bottom of the record.

Note the one year and two year trailing trends. There is no significant change in these over the period of the record. The trend increased in the middle of the record, and then decreased again.

Overall, then, to date there is no sign of any acceleration in the TOPEX record of the sea level rise.

w.

1. George

Nice work, Willis, as always.

Your results square almost perfectly with those of Cazenave and Nerem (2004), who say “the geocentric rate of global mean sea level rise over the last decade (1993-2003) is now known to be very accurate, +2.8 ± 0.4 mm/yr, as determined from TOPEX/Poseidon and Jason altimeter measurements,” although they suggest that regional variations may be significant, and that decadal-scale variability may occur.

Similar results are reported by Church et al. (2004), who estimate the rate of globally-averaged sea level rise over the last half of the 20th century at 1.8 ± 0.3 mm yr-1. They also state that “decadal variability in sea level is observed, but to date there is no detectable secular increase in the rate of sea level rise over the period 1950-2000.”

Refs:
Cazenave, A. and Nerem, R.S. 2004. Present-day sea level change: observations and causes. Reviews of Geophysics 42: 10.1029/2003RG000139.

Church, J.A., White, N.J., Coleman, R., Lambeck, K. and Mitrovica, J.X. 2004. Estimates of the regional distribution of sea level rise over the 1950-2000 period. Journal of Climate 17: 2609-2625.

2. Andre

Nice work, Willis.

Personally I digitize printed graphs simply with Windows paint. it gives the coordinates of the cursor even if the window is not active. So you don’t need to leave excel.

3. jae

Great chapter, Willis. It doesn’t look like there’s much to argue about with this analysis. But if we don’t get this global temperature under control, we are going to have another 300 mm sea rise in the next hundred years. That’s almost a foot. Let’s panic!

Is there nothing pure in so called “climate science?”

In a past age, troops of traveling gypsies and vagabonds would set up their tents in small towns. Their hope would be to lure in unsuspecting and naive country folk, hoping to sell them simple herbal broths (or worse) as miracle cures. That is the origin of a term of American slang – “snake oil salesmen.”

5. TCO

It’s very nice analysis, Willis. I don’t think that acceleration should be expected (to be shown) in a period this short.

6. John Hekman

Willis
Shouldn’t your vertical axis be labeled “mm”, not “cm”?

RE: #3 – And that assumes we don’t incur a reversal, ala the LIA, or worse. 100 years from now, the dredging business might be booming and folks wringing their hands about sea level fall. Just like warming versus cooling, which would be truly worse, sea level rise, or sea level fall? Even economic issues aside, imagine the real impacts of a sea level fall on marine life and wetlands. Utterly disasterous!

8. Jeff Weffer

What does 3.03 mm/year translate into in terms of global warming.

Sea level will rise as the sea warms and as land-locked water (ice and fresh water) is added to the sea.

Does 3.03 mm/year signal 0.1C in average ocean temperature and 10 cubic kms of ice melting? What are the metrics?

9. Jim Edwards

#8:

10 km^3 of melting ice insignificant compared to the observed rise.

Back of envelope calculation to convert observed rise into land-based ice, ignoring thermal expansion of H2O in liquid state –>

~70% of earth’s surface area x 0.00303 m / yr x ~ 1.25 [for increased volume upon freezing]

Earth Surf Area = Diameter squared divided by pi = ~ (4 x 10^7 m)^2 / pi = 5.09 x 10^14 m^2

0.70 x [5.09 x 10^14 m^2] x 0.00303 m / yr x 1.25

= 1.35 x 10^12 m^3 = 1.35 x 10^3 km^3 of ice [about 100 x 10 km^3]

10. Jim Edwards

#9 should be 1.35 x 10^3 km^3 of ice per year

11. Jim Edwards

#9

Sorry, [Diameter squared divided by pi] should be [Circumference squared divided by pi], which is what I did.

4 pi R^2 = (2 pi R)^2 / pi.

12. Steve Bloom

Melting seems to be breaking out all over. Adding this to the recent GRACE/altimeter results for Antarctica and Greenland gives a total of about 2 mm/yr from melting ice during 2004-5. Add to this increased Arctic river flow (not sure if there’s any kind of current estimate available for this). If these trends continue, we should be seeing an increase in net sea level rise within the next year or two. By that time there will also be enough GRACE data to allow for an accurate mass balance.

13. Proxy

The precision of TOPEX is remarkable. From the TOPEX technology page:

After correction for atmospheric and instrumental effects, the TOPEX/Poseidon range measurements are accurate to 3-4 centimeters. The range measurements are subtracted from POD-derived estimates of the satellite orbital height, resulting in ocean height measurements that are good to 4-5 centimeters (better than 2 inches) relative to the center of the Earth.

This accuracy figure pertains to a few-kilometer spot on the ocean surface directly beneath the TOPEX/Poseidon satellite. By averaging the few-hundred thousand measurements collected by the satellite in the time it takes to cover the global oceans (10 days), global mean sea level can be determined with a precision of several millimeters.

14. KevinUK

#12 Steve B

Knowing how much you like to request us skeptics to provide ‘linkies’, how about a link for

“Dr Kaser said that “99.99% of all glaciers” were now shrinking.” and his statement that “The glaciers are going to melt and melt until they are all gone. There are not any glaciers getting bigger any more.”, so that we can assess the precision of Dr Kaser’s claim (particular given that it is based on an extrapolation)? I’m particularly interested in knowing how he’s managed to get round all the world’s glacier to confirm this highly precise measurement. Perhaps like Father Christmas he has a sled and some reindeers.

KevinUK

RE: #12 – That article is about tropical glaciers. Please, let’s not rehash that litany today.

16. Steve Bloom

Re #14: The articles says it was published in GRL, which I would think you could easily locate without help from me. As a one-time favor, here’s the abstract:

“Working with comprehensive collections of directly-measured data on the annual mass balance of glaciers other than the two ice sheets, we combine independent analyses to show that there is broad agreement on the evolution of global mass balance since 1960. Mass balance was slightly below zero around 1970 and has been growing more negative since then. Excluding peripheral ice bodies in Greenland and Antarctica, global average specific balance for 1961–1990 was à⣃ ’ ’219 ± 112 kg mà⣃ ’ ’2 aà⣃ ’ ’1, representing 0.33 ± 0.17 mm SLE (sea-level equivalent) aà⣃ ’ ’1. For 2001–2004, the figures are à⣃ ’ ’510 ± 101 kg mà⣃ ’ ’2 aà⣃ ’ ’1 and 0.77±0.15 mm SLE aà⣃ ’ ’1. Including the smaller Greenland and Antarctic glaciers, global total balance becomes 0.38 ± 0.19 mm SLE aà⣃ ’ ’1 for 1961–1990 and 0.98 ± 0.19 mm SLE aà⣃ ’ ’1 for 2001–2004. For 1991–2004 the glacier contribution, 0.77 ± 0.26 mm SLE aà⣃ ’ ’1, is 20–30% of a recent estimate of 3.2 ± 0.4 mm aà⣃ ’ ’1 of total sea-level rise for 1993–2005. While our error estimates are not rigorous, we believe them to be liberal as far as they go, but we also discuss several unquantified biases of which any may prove to be significant.”

For a mere \$9 U.S. the text can be yours.

Re #15: Just tropical? Where did that idea come from? Read the article first, try to understand its contents despite interference from your a priori beliefs, then check to see if your instinctive reply based on the those beliefs is correct. In this case no: “The results revealed that the world’s glaciers and ice caps – defined as *all land-based ice except the mighty Greenland and West Antarctic ice sheets* – began to shrink far more quickly in 2001.” (Emphasis added.)

17. Willis Eschenbach

Thanks to everyone for their comments.

Re #2, Andre, you say:

Personally I digitize printed graphs simply with Windows paint. it gives the coordinates of the cursor even if the window is not active. So you don’t need to leave excel.

While this is an excellent solution, I generally want very good accuracy, especially when I am looking for a very small signal in a lot of noise. In this case, the problem was particulary difficult because of the overlap of the large circles used for each data point.

Re #5, TCO, you say:

I don’t think that acceleration should be expected (to be shown) in a period this short.

This, as I’m sure you know but will repeat anyways for others who might not, depends on the amount of the acceleration. There is, for example, a clear change in the trend around the year 2000, accelerating and deccelerating in a fairly short period. One of the problems with this record, as with most climate records, is the high degree of autocorrelation present. With autocorrelation present, trends need to be more pronounced in order to be statistically significant.

As you implicitly point out, however, the acceleration, if any, is likely to be quite small. Researching further, historical acceleration (including thermal and ice melt) is hindcast by the climate models to have been on the order of a trend change of +0.001 mm/year from 1900-1990. This is far too small to be seen in a record of this length.

Re #9, two questions in one, the change from ice and temperature.

Grounded and land-covered ice areas, and the ocean area, are as follows:

Location_____________ Area
Glaciers and ice caps___0.68 million km^2
Greenland ice sheet_____1.71 million km^2
Antarctic ice sheet____12.37 million km^2
TOTAL__________________14.76 million km^2

Total Ocean Area_________362 million km^2

Thus, a 1 meter change in global ice levels (neglecting isostatic rebound and sea water replacing grounded ice) would result in a ~15,000 km^3 ice loss, which would give us a ~40mm change in ocean levels. 3.03 mm/year, if comprised solely of ice loss, would be about a 75 mm global ice level change.

The “thermosteric” sea level change (from changing temperature) is a much trickier question. It depends on such things as how deeply the ocean is heated, the spatial distribution of the heating, the increase in evaporation due to temperature change, and the “halosteric” sea level change (from changing salinity). As Lyman describes it in his recent paper on global sea temperature cooling,

The recent cooling of the upper ocean implies a decrease in the thermosteric component of sea level. Estimates of total sea level [Leuliette et al., 2004; http://sealevel.colorado.edu%5D, however, show continued sea-level rise during the past 3 years. This suggests that other contributions to sea-level rise, such as melting of land-bound ice, have accelerated. This inference is consistent with recent estimates of ice mass loss in Antarctica [Velicogna and Wahr, 2006] and accelerating ice mass loss on Greenland [Rignot et al., 2006] but closure of the global sea level budget cannot yet be achieved.

New satellite observations from the Gravity Recovery and Climate Experiment (GRACE; launched in March, 2002 and administered by NASA and Deutsches Zentrum für Luft-und Raumfahrt, GRACE will map Earth’s gravity field approximately once every 30 days during its lifetime) should soon provide sufficient observations of the redistribution of water mass to more fully describe the causes of recent sea-level change.

We can give some estimates for the thermosteric expansion, however. The thermal expansion of water at ~15°C is .00014/°C. The ocean surface warmed about 0.15° over the period of record. If this warming were evenly spread over say the top 1000 meters of water, and other things being equal, it would create a sea level rise of about 1.7 mm/year.

Or alternately, if the warming goes evenly to 1000 meters, the thermal expansion is about 140 mm/°C.

Climate models show a slightly smaller change, estimated by an 11 model ensemble at about 112 mm rise/°C.

So there’s no clear answer to your question, but we can make some order-of-magnitude estimates.

w.

RE: #16 – Look at the title of the article for starters, to paraphrase “they’ll go thirsty in China and India” etc. Most of the mentions in it were of tropical glaciers. Alarmists overemphasize the well known diminishment of tropical glaciers and either downplay or fail to mention higher latitude ones that are in various states, some declining, some neutral and some growing. The favorite midlatitude poster child is the case of the Alps, where the glaciers really got bulked up during the LIA. So are the Alps’ glaciers disappearing or adjusting to the rebound from the LIA? My point stands however about that article, overemphasis on tropical glaciers.

I see they also mentioned the tropical Andes in addition to the Himalayas. Also, the other midlatitude poster child, Glacier NP, near the edge of a very arid climate zone. They try to brush off Norway and New Zealand, which are great examples of glaciers that are neither in the tropics and influenced by land use changes, nor at the edge of inland arid zones. Hmmmmmm …..

20. Jeff Weffer

Wikipedia has what seems to be a pretty good page on this.

http://en.wikipedia.org/wiki/Sea_level_rise

Looks like sea level has been rising at more than 3 mm per year since about 8,000 years ago (after all of the ice from ice age melted.) It appears to have been rising faster in the past than today. There is also quite a bit of variation in estimates of sea level rise with those estimates.

http://en.wikipedia.org/wiki/Image:Holocene_Sea_Level.png

And between 8,000 to 14,000 years ago, sea levels were rising as fast as 40 mm per year at the height of ice age melting.

Overall, I think sea level rise is the only concrete evidence we have for global warming. Ocean heating and land-locked glacier melt have to be reflected in sea levels.

It seems historical records indicate nothing special is happening today.

21. Willis Eschenbach

Dr Kaser said that “99.99% of all glaciers” were now shrinking. Increased winter snowfall meant that a few, most notably in New Zealand and Norway, got bigger during the 1990s, he said, but a succession of very warm summers since then had reversed the trend. His team combined different sets of measurements which used stakes and holes drilled into the ice to record the change in mass of more than 300 glaciers since the 1940s. They extrapolated these results to cover thousands of smaller and remote glaciers not directly surveyed.

Hmmm … he has measured 300 glaciers, and “extrapolated” this to cover the world’s glaciers … which, according to the World Glacier Inventory, currently number some 67,000

If he really said that “99.99% of all glaciers” were now shrinking, that means all but .0001*67000 = 7 glaciers are shrinking … and it also means he’s making it up.

Before you get too passionate about the effect of glaciers on sea level, however, consider:

1) glaciers comprise about 0.3% of the total ice volume of the planet, and

2) glaciers contain about 190,000 km^3 of ice, and

3) current loss rates are around 300 km^3/year.

This means that, ceteris paribus, regarding glaciers we stand to possibly lose 0.3% of the planetary ice in 600 years …

A few more notes from the abstract of the paper. They say the current rate of loss is “‘Ë†’219 ± 112 kg m-2 a’Ë†’1″. That means the 95% confidence interval is from -443 to +5 kg m-2 a-1. They also put the current (2001-2004) 95% confidence interval at -308 to -712 kg m-2 a-1.

This means:

1. We cannot say that the earlier (61-90) loss rate is significantly different from zero.

2. We cannot say that the current (01-04) loss rate is significantly different from the earlier rate.

They also note that:

While our error estimates are not rigorous, we believe them to be liberal as far as they go, but we also discuss several unquantified biases of which any may prove to be significant.

w.

22. Posted Oct 13, 2006 at 8:06 PM | Permalink | Reply

Re #20, I am pasting a piece I had on RP Sr’s blog here that is relevant to the matters you raise:

There seems to be an assumption implicit in many discussions of sea level rise (and ice sheet “collapse”) that geological catastrophes such as the disappearance of the Greenland or the West Antarctic Ice Sheets also necessarily equate to socio-economic catastrophes. At the risk of being politically incorrect, let me note that while that may prove to be the case, it has never been proven satisfactorily, as far as I am aware. There is no doubt such events could/would potentially impose substantial and serious socio-economic costs but if: (1) the total amount of SLR and, perhaps more importantly, the rate of SLR can be forecasted, (2) the rate of SLR is slow relative to how fast populations can strengthen coastal defenses and/or relocate, and (3) there are no insurmountable barriers to migration, it need not be dangerous to life and limb.

Consider, for example, that Lowe et al. [in Avoiding Dangerous Climate Change, H.J. Schellnhuber et al. (eds), Cambridge University Press, Cambridge, 2006, p. 32-33], based on a “pessimistic, but plausible, scenario in which atmospheric carbon dioxide concentrations were stabilised at four times pre-industrial levels”, estimated that a collapse of the Greenland IS would over the next 1,000 years could raise sea level by 2.3 meters (with a peak rate of 0.5 mm/yr). If one were to arbitrarily double that to account for potential melting of the WAIS, that would mean a SLR of ~5 meters in a 1,000 years (with a peak rate “¢’¬? assuming the peaks coincide “¢’¬? of 1 meter per century).

It seems that human beings can definitely get out of the way of such a sea level rise, especially if they have 1,000 years to do so and there are no insurmountable barriers to migration. In fact, if they can get “early” warning of such an event they could probably get out of the way in a matter of decades if not years.

Can a relocation of such a magnitude be accomplished?

Consider that the global population increased from 2.5 billion in 1950 to 6.5 billion this year. Among other things, this meant creating the infrastructure for an extra 4 billion people in the intervening 56 years (as well as improving the infrastructure for the 2.5 billion “non-extra” people). These improvements occurred at a time when every one was significantly poorer. Therefore, while it will be costly, in theory, today’s — and, more to the point, tomorrow’s “¢’¬? wealthier world ought to be able to relocate billions of people to higher ground over the next few centuries, if need be. In fact, once a decision is made to relocate, the cost differential of relocating, say, 10 meters higher rather than a meter higher is probably marginal.

What about the rest of nature?

While I can’t pretend to know what the consequences might be, I note that supposedly today’s sea level is 120 meters higher than what it was 18,000 years ago. This means an average SLR of 6.7 meters per 1,000 years. The peak rate of SLR was undoubtedly much greater. So one must ask: what were the consequences of such a rapid rate of rise, and what do they tell us about the resilience of the rest of nature?

23. Bob K

I can understand why sea level rise would be an easy crude way to explain to the general public what is happening with the oceans. But sea level rise doesn’t seem to cut it when trying to determine the natural rate of change in the past.

120m rise defines little if the container shape is variable. How do you define the natural trend over time, if the container shape changes with elevation?

I’m sure the topographic structure of the oceans must be well known by this time. Are there studies that reflect the ocean volume change from the last ice age until now?

24. Francois Ouellette

Question: I’ve read somewhere (maybe here…) that there was a time lag of about 70 years between atmospheric warming and glacier melting. If that were correct, the melting seen today would reflect the warming of the first half of the 20th century, which, in the opinion of many (including “mainstream” scientists) could be largely due to natural forcings. Any comment?

Comment on water expansion coefficient: it varies a lot with temperature (max density is at 4 C, so expansion coeff. changes sign at that temp). Any attempt to estimate ocean volume change will require a knowledge of vertical temperature distribution AND vertical warming distribution. Are there data sets available that would allow such an estimate to be made? Or simplifying assumptions such as a warming occuring only in the first 100 m’s or so?

Finally another question: is there any sort of good correlation between, say, SST trend and SLR ? It seems to me that if the SLR has been constant for thousands of years, it can’t be correlated with SST, which must have had all kinds of different trends over the pas centuries (even today, e.g. Lyman paper).

25. Allan MacRae

Can anyone explain the annual sawtooth pattern in the ocean levels?

Also the annual sawtooth pattern in the atmospheric CO2 data?

Are they related in cause or effect?

Best regards, Allan

26. Jeff Weffer

Can anyone explain the annual sawtooth pattern in the ocean levels?

This is a seasonal artifact that relates to the fact there is more landmass in the Northern Hemisphere than in the South. In the North’s winter, more water gets land-locked in ice and snow which then returns to the ocean in summer.

RE: #20 – “It appears to have been rising faster in the past than today. ”

Indeed, the expectation from the great melt of the large continental ice masses would be a decaying exponential rise in MSL, relative to the zero potential spheroid absolute datum, world wide.

28. Willis Eschenbach

Question: I’ve read somewhere (maybe here…) that there was a time lag of about 70 years between atmospheric warming and glacier melting.

Without a citation, I’d tend to doubt that. What would be the reason for the lag?

w.

29. Eduardo Zorita

#17

Some discrepancy between observed sea-level rise and sea-level rise estimated from the steric effect (temperature and salinity) and from land-ice meltic seems to persist. The steric effect in the last decades is too small (about 0.5 mm/year) , against observed 1.5-2 mm/year. Estimations from melting yield also lower values than the steric sea-level rise.
Perhaps one should not forget the other anthropogenic contribution: water storage and aquifer use. There still large uncertainties in this contribution.

Miller and Douglas, Nature 428, 406 (2004)
Antonov et al. GRL 32, L12602 (2005).

30. Steve Bloom

Re #24/8: I recall seeing several mentions to “since the 1970′s,” so possibly that’s what Francois is remembering. The thermal lag makes obvious sense (since much of the ice is well below freezing and so must be warmed up before it can melt), but I’ve never seen a paper that justifies the 1970′s reference.

Re: #12

Melting seems to be breaking out all over. Adding this to the recent GRACE/altimeter results for Antarctica and Greenland gives a total of about 2 mm/yr from melting ice during 2004-5. Add to this increased Arctic river flow (not sure if there’s any kind of current estimate available for this). If these trends continue, we should be seeing an increase in net sea level rise within the next year or two.

Woohhh, Steve B, I’m frightened now!…Well, I would be…if I didn’t know that global sea levels have risen over 120 metres since the last (big) ice age.

RE: #31 – decaying exponential, completely in accordance with what one would have expected from the great melt. When this thing completely flat lines (we’re nearly there!), does that mean we are ready for ice world again? Just a thought ….

33. Michael Jankowski

Francois

24: Question: I’ve read somewhere (maybe here…) that there was a time lag of about 70 years between atmospheric warming and glacier melting.

Re #24/8: I recall seeing several mentions to “since the 1970′s,” so possibly that’s what Francois is remembering. The thermal lag makes obvious sense (since much of the ice is well below freezing and so must be warmed up before it can melt), but I’ve never seen a paper that justifies the 1970′s reference.

What Francois is referring to is right out of the IPCC TAR and has come-up several times on this board with regard to MBH98.

“…Glaciers are generally not in equilibrium with the prevailing climatic conditions and a more refined analysis should deal with the different response times of glaciers which involves modelling (Oerlemans et al., 1998). It will take some time before a large number of glaciers are modelled. Nevertheless, work done so far indicates that the response times of glacier lengths shown in Figure 2.18 are in the 10 to 70 year range. Therefore the timing of the onset of glacier retreat implies that a significant global warming is likely to have started not later than the mid-19th century. This conflicts with the Jones et al. (2001) global land instrumental temperature data (Figure 2.1), and the combined hemispheric and global land and marine data (Figure 2.7), where clear warming is not seen until the beginning of the 20th century. This conclusion also conflicts with some (but not all) of the palaeo-temperature reconstructions in Figure 2.21, Section 2.3 , where clear warming, e.g., in the Mann et al. (1999) Northern Hemisphere series, starts at about the same time as in the Jones et al. (2001) data. These discrepancies are currently unexplained…”

RE: #33 – and that is given that equilibrium is even driven primarily by temperature. It is interesting to me that the places where glaciers are currently expanding tend to be high precipitation areas that are in marine west coast alpine margins, or subarctic climate zones, whereas, the most acclaimed retreat areas are:
1) The Alps – on the edge of the Old World’s Mediterrannean and Humid Subtropical climate zones
2) The Rockies – on the edge of the interior Steppes of North America
3) Misc tropical glaciers – which depend on Monsoonal orographic precip during Summer, and by definition, only suffer loss during the dry season, during the cold winter, due to sublimation and melting from direct insolation.
All three look to be largely controlled by the amount of excess precip. During excess years they grow or hold their own, during normal to dry years they go into lossy disequilibrium.

35. Willis Eschenbach

There’s a new study of sea level variations out:

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 111, C09012, doi:10.1029/2005JC003229, 2006

Nonlinear trends and multiyear cycles in sea level records

S. Jevrejeva
Proudman Oceanographic Laboratory, Liverpool, UK

A. Grinsted
Arctic Centre, University of Lapland, Rovaniemi, Finland

J. C. Moore
Arctic Centre, University of Lapland, Rovaniemi, Finland

S. Holgate
Proudman Oceanographic Laboratory, Liverpool, UK

Abstract

We analyze the Permanent Service for Mean Sea Level (PSMSL) database of sea level time series using a method based on Monte Carlo Singular Spectrum Analysis (MC-SSA). We remove 2–30 year quasi-periodic oscillations and determine the nonlinear long-term trends for 12 large ocean regions. Our global sea level trend estimate of 2.4 ± 1.0 mm/yr for the period from 1993 to 2000 is comparable with the 2.6 ± 0.7 mm/yr sea level rise calculated from TOPEX/Poseidon altimeter measurements. However, we show that over the last 100 years the rate of 2.5 ± 1.0 mm/yr occurred between 1920 and 1945, is likely to be as large as the 1990s, and resulted in a mean sea level rise of 48 mm. …

They show the following estimate of sea levels and sea level rise:

Note that the rate of sea level rise 1920-1945 was about the same as today’s rate. Also, sea levels have risen about a foot since 1850, and there have been no floods of environmental refugees … humans seem able to deal with these rises without problems.

w.

36. Allan MacRae

RE #25 and 26 – thanks Jeff for your answer to Question A:

Can anyone explain the annual sawtooth pattern in the ocean levels?
Answer: This is a seasonal artifact that relates to the fact there is more landmass in the Northern Hemisphere than in the South. In the North’s winter, more water gets land-locked in ice and snow which then returns to the ocean in summer.

Question B remains:

Also the annual sawtooth pattern in the atmospheric CO2 data?

Are they related in cause or effect?

Best regards, Allan

P.S. – some thoughts:

Seasonal:
Note the atm. CO2 and ocean level sawtooth patterns are almost perfectly 180 degrees out of phase, with peaks in ~May and ~September. Oceans peak in September and then fall ~20mm through NH winter as more ice forms, reversing trend in May. CO2 peaks in May and then falls ~5.6 ppm through NH summer, reversing trend in September.

Annual/Long term:
Oceans rise avg ~3 mm /year, CO2 increases avg. ~1.4ppm/y.

Doesn’t this look like a simple physical relationship?
Is it not more likely that CO2 is the result, not the driver in this equation?

Sorry if this all seems a bit naive, but I’ve never looked at this sawtooth data before – I always assumed (though not necessarily accepted) that the CO2 growth was humanmade, and challenged the exaggerated amount of (resultant) warming.

37. Allan MacRae

PPS to # 36:

Note also the peak years for atm. CO2 growth were typically El Nino (warm) years.

The maximum recorded grwoth in atm. CO2 was 2.91 ppm/y in 1998, second highest was 2.71 in 1987, both El Nino years. I think we will find that the atart of the El Nino’s preceeded the increased CO2, not the reverse.

So is increased atm. CO2 the driver or the result of warming? I guess it is the result. This is consistent with Veizer (2005), etc.

I am aware of the isotope studies that challenge this hypo, but have never studied or critiqued them.

Best regards, Allan

38. bender

Re #36
Sawtooth CO2 is due to the seasonal sinking of carbon during summer and subsequent release during autumn leaf-fall in the temperature deciduous forests of the NH. That’s the story I’m told, at any rate.

39. bender

Re #36 A fuller explanation of annual CO2 cycles can be found here.

40. Allan MacRae

RE #38 & 39:

Repeating without typos:

Note also the peak years for atm. CO2 growth were typically El Nino (warm) years.

The maximum recorded growth in atm. CO2 was 2.91 ppm/y in 1998, second highest was 2.71 in 1987, both El Nino years. I think we will find that the start of the El Nino’s preceeded the increased CO2, not the reverse.

Does the above observation fit the theory? Has anyone tried to quantify or otherwise “prove/disprove” this theory? Are there alternative theories to explain the CO2 sawtooth?

RE: #40 – I’m having a beer brewer moment … so, when sparging with CO2 temperature is certainly important. In order to saturate the liquid we’d put the carboy in the fridge to get it cold prior. We’d then take the cold liquid and put in into precooled cylander and only then would we sparge. We’d then carefully raise the temperature to our storage temperature periodically depressurizing the cylander for safety reasons as the CO2 came out of solution.

42. Allan MacRae

Exactly Steve.

Seems this whole question might be solved by pondering it slowly over a case of good home brew. Got to keep it nice and cold though – not only does the beer taste better, but we don’t want to contribute to AGW by releasing all that CO2.

Best, Allan

43. Reference

NASA Scientist Finds a New Way to the Center of the Earth

Argus says this new reference frame could make important contributions to understanding global climate change. The inference that Earth is warming comes partly from observations of global sea level rise, believed to be due to ice sheets melting in Greenland, Antarctica and elsewhere. In recent years, global sea level has been rising faster, with the current rate at about 3 millimeters (.12 inches) a year. Uncertainties in the accuracy of the motion of Earth’s center of mass result in significant uncertainties in measuring this rate of change.

FYI – an oldie but a goodie:

http://neptune.gsfc.nasa.gov/publications/pdf/pubs2002/4_Direct_estimation_sea.pdf

45. Mike

A linear increase in heat applied to a block of ice, will find no melting for quite a long time, followed by a sudden conversion of ice to liquid. Apart from the obvious fact that ice is solid until zero degrees is reached, there is furthermore a period of heat absorption as the ice takes up the heat, before any of this is converted into actual melting. Its called the latent heat.

The result of this is that while melting may continue at a linear rate for some time, there does exist the potential for a sudden, rapid rise in sea levels, as major masses of ice finally have absorbed enough heat to melt. Looking at the levels of melting in the arctic and the antarctic which are presently occurring, as measured by the retreat in glaciers and breaking off of ice shelves, it is possible that we are starting to see this effect shortly.

The increase in levels of the oceans should not be particularly afected until now, however, as until now, Greenland and Antarctic ice packs have not been appreciably melting. A mountain glacier here or there is what we have seen so far, as the melt zone has migrated north and south. But its what happens when the major land-bound ice packs get melted – THAT will be the major impact, when and if it happens. We should know in about 10-20 years if this is happening.

By then of course, it will be too late.

46. Douglas Hoyt

An update on sea level rise from co2science.org. It is 1.35 mm/yr, not the 3 mm/yr that Topex gets.

Global Positioning System Adjustments to Tide Gauge Estimates of Global Sea Level Trend
——————————————————————–
Reference
Woppelmann, G., Miguez, B.M., Bouin, M.-N. and Altamimi, Z. 2007. Geocentric sea-level trend estimates from GPS analyses at relevant tide gauges world-wide. Global and Planetary Change 57: 396-406.
What was done
The authors describe a technique they developed for utilizing Global Positioning System (GPS) data, which they obtained from numerous GPS stations situated in close proximity to various tide gauges around the world, to correct the tide gauge records and thus obtain what they call a “set of ‘absolute’ or geocentric sea-level trends.” Based on a number of criteria that had to be met by both the tide gauge and GPS stations, they ultimately used paired data sets from 28 locations that covered a time span of 5.9 years (1999.0-2005.7) to derive their final mean global result, after which they compared it with what they call the “most quoted” tide-gauge results of Douglas (1991, 1997, 2001), which had been corrected for the most common form of vertical land motion by means of theoretical models of Glacial-Isostatic Adjustment (GIA).

What was learned
Whereas the data of Douglas yielded a mean global sea-level rate-of-rise of 1.84 ± 0.35 mm/year after correction for the GIA effect (Peltier, 2001), Woppelmann et al. obtained a much lower mean value of 1.35 ± 0.34 mm/year when employing their correction for measured GPS vertical velocities. The sizable difference between these two results raises the question of how they compare with results obtained from other ways of estimating global sea level trends. In this regard, the four researchers note that Mitrovica et al. (2006) recently indicated there is a 1 mm/year contribution to sea-level rise from the melting of global land ice reservoirs, as well as a 0.4 mm/year contribution from thermal expansion of the global ocean (Antonov et al., 2005). Together, these two numbers yield a value of 1.40 mm/year for the global ocean’s total sea-level mean rate-of-rise, which is much closer to the 1.35 mm/year result of Woppelmann et al. than to the Douglas-Peltier result of 1.84 mm/year.

What it means
The mean global sea-level rate-of-rise calculated by Woppelmann et al. appears to resolve the “sea-level enigma” noted by Munk (2002), who called attention to the sizable discrepancy that existed at the time of his writing between estimates of climate-related contributions to sea-level change and what the observed value was thought to be. Now, there is no longer any discrepancy between these two numbers. What is more, the global ocean’s mean rate-of-rise is now seen to be much slower than what was previously believed to be the case.

References
Antonov, J.I., Levitus, S. and Boyer, T.P. 2005. Themosteric sea level rise: 1955-2003. Geophysical Research Letters 32: 10.1029/2005GL023112.

Douglas, B.C. 1991. Global sea level rise. Journal of Geophysical Research 96: 6981-6992.

Douglas, B.C. 1997. Global sea level rise: a redetermination. Surv. Geophys. Res. 18: 279-292.

Douglas, B.C. 2001. Sea level change in the era of the recording tide gauge. In: Douglas, B., Kearney, M. and Leatherman, S. (Eds.), Sea Level Rise: History and Consequences, Academic Press, San Diego, CA, USA, pp. 37-64.

Mitrovica, J.X., Wahr, J., Matsuyama, I., Paulson, A. and Tamisea, M.E. 2006. Reanalysis of ancient eclipse, astronomic and geodetic data: a possible route to resolving the enigma of global sea-level rise. Earth and Planetary Science Letters 243: 390-399.

Munk, W. 2002. Twentieth century sea level: an enigma. Proceedings of the National Academy of Science, USA 99: 6550-6555.

Peltier, W.R. 2001. Global glacial isostatic adjustment and modern instrumental records of relative se3a level history. In: Douglas, B., Kearney, M. and Leatherman, S. (Eds.), Sea Level Rise: History and Consequences, Academic Press, San Diego, CA, USA, pp. 65-95.

Reviewed 8 August 2007

47. Willis Eschenbach

Mike, thanks for your post. I’m not sure exactly what claim you’re making here. You seem to be saying that if you apply heat to ice, there is a time lag between the application of the heat and the melting, which you say is called “latent heat”.

This is not the case. Actually, latent heat is merely the energy required to melt the ice. It does not involve a time lag of any kind, and is not a “period of absorption as the ice takes up the heat”.

Are the major land-bound ice packs in any danger of melting? I don’t find any reputable scientist saying that, although it features in works of popular fiction such as “An Inconvenient Truth”.

w.

48. MarkW

Mike,

That scenario is true in a lab, for very small amounts of ice.

Out in the real world, ice is a pretty good insulator, and if the temperature is sufficient to melt the ice, then the outermost layer of the ice will absorb that heat as it melts. Very little is transferred into the ice.

Second, you assume that the vast majority of the ice in the arctic and antarctic are just below freezing. Nothing could be further from the truth. Most of antarctic is 10′s of degrees below freezing.

As to calving glaciers. That’s what happens when a glacier meets the ocean. It is not evidence that the world is warming.

Additionally, there aren’t any glaciers in the arctic, the ice up there is sea ice. Since it’s already floting, it’s melting won’t affect sea levels.
If you have problems with this, might I suggest you reference any first grade science book. As for Antarctica, the glaciers down there are on balance, growing, not shrinking. The latest studies of Greenland find that the glaciers there are gaining mass as well.

49. Gunnar

Mike, to add one more point to what Willis and MarkW have correctly said on this forbidden topic:

It takes a large amount of energy to melt ice. It’s not just air at a certain temperature. Air doesn’t have much mass, so it doesn’t have much energy. If there is enough energy to melt a small amount of ice, that energy has to come from somewhere, which means that the air loses energy, bringing it’s temperature back down again. To melt a large amount of ice, you would have to keep applying energy. But the increased energy is also being drained by other factors, such as increased precipitation.

That’s why people say that the more likely scenario is that a change in ocean and air currents (ie, a change in weather) directed warmer equatorial waters more directly into the narrow bering strait, to cause the arctic melting.

RE: #46 – Consider the hydrologic reality of just how long it is taking for all of the remnent glacial melt water from the end of the Pleistocene to actually reach the ocean. Here’s but one example, water held in aquifers. Clearly, the effects of the great melt have been greatly prolonged by the innate holding capacity of water retention features on and in the lithosphere. Another example, muskegs and bogs. Flow rates out of those are …. positively glacial …. LOL!

51. Posted Nov 16, 2007 at 5:21 PM | Permalink | Reply

Steve #32 mentions the spectre of an Ice age onset, implicated in the flattening global sea level rise graph.
Can anyone reference data that shows the maximum global sea level achieved prior to the last Ice age onset?

52. D. Patterson

For the sake of accuracy and a reminder to readers who are not familiar with such matters, it should be noted that the term, “mean sea level”, denotes an imaginary sea level used by convention for various purposes.

The sea level in the real world is not one sea level for the entire world. Instead, the world’s seas have a variety of different sea levels which undergo constant change in every minute of every day. The waters of the Pacific Ocean are at a slightly higher altitude than the waters of the Atlantic Ocean. The water at the Pacific Ocean end of the Panama Canal tend to be around 20 centimeters higher than the water at the Atlantic Ocean of the canal. The Pacific Ocean perpetually spills from its higher altitude into the lower Atlantic Ocean off the southern coasts of South America.

Gravitational waves from the Moon and from the Sun create tidal high and low variations in the topography of the seas. Gravitational waves from the Earth and its oceans also cause variations in the topography of the seas. Weather conditions such as air and sea temperatures, atmospheric pressures, and wind conditions cause sea topography changes in tens of meters in altitude. Seasonal changes in precipitation patterns and freshwater discharges vary sea topography.

In order to calculate a global sea level value, scientists apply adjustments to the raw observational data in order to derive an adjusted and calculated mean value to represent all of the varying altitudes of the planet’s seas.

Any effort to determine a value or values for changes in the volume of seawater represented by the sea levels must rely upon accurate methods of measuring sea levels and sea basin capacities.

53. John Serink

Hi All:

I am no expert in this field but do deal with equipment and such that is sold to hydrographers.
I had a chat with some of the guys that work for the Chief Hydrographer of the Singapore Maritime and Port Authority earlier this year and they all fell over laughing when I asked them about sea level. Their response was the Minitry had come back to them THREE times when they reported NONE of the tide gauges around Singaproe had shown any changes in Sea Level. They have records going back to when the British ran the port over 60 years ago, it has not changed.

So my question to all of you is, if sea level is rising at X mm/year (insert a number X depending upon who you read), where is it rising? Its falling in the Hudson’s Bay in canada and is static in Singapore, so where is it rising?

Cheers,
john

54. welikerocks

53. Hi John, I don’t know! It’s not rising on the island of Oahu where my father in law lives either. (And Oahu is sinking geologically speaking) His beach front properity is growing not disappearing.

And Surfer Magazine has an article on a “Secret Surf Spot” in the new issue, and it’s a spot my husband surfed when he was a kid located somewhere in So. California (got to keep it secret you know). The picture of the spot in the article shows that the shoreline has not changed in 30 yrs. And it shows the same rock sticking out of the water inside, and same rock sticking out the water outside the break. Go figure. It’s was a really fickle break my husband says, and this is important: it only broke sweetly for surfing at minus tide. So the conditions are the same to this day, no rise in sea level- or it wouldn’t be the subject of a Secret Spot.

55. Dennis Wingo

John #53

I think that it is falling in the Hudson bay as the land there continues to rebound from the Laurentide ice sheet’s weight removal.

An interesting study that I have been doing is to use Google Earth Pro and look at shorelines on islands around the world. From just an eyeball view it looks like there is either no change or a slight decrease in ocean level.

It is a lot of fun to see what these islands look like from above.

FWIW

56. D. Patterson

53 John Serink says:
December 16th, 2007 at 9:54 pm

So my question to all of you is, if sea level is rising at X mm/year (insert a number X depending upon who you read), where is it rising? Its falling in the Hudsons Bay in canada and is static in Singapore, so where is it rising?

Cheers,
john

The rising sea levels are claimed to be occurring at rates measured in one or more tenths of a millimeter per year. Meanwhile, natural changes in local absolute sea level occur in measures of tenths of a meter or meters in hours and days. The judgement exercised in reducing the absolute measures to mean measurements can introduce errors which are a magnitude or magnitudes greater than the reported increases in mean global sea levels.

54 welikerocks says:
December 17th, 2007

Alleged changes of sea level at one or more tenths of a millimeter per year would go unnoticed over a period of decades at a beach. Local temperature changes and winds would conceal such a minor difference.

There are not any glaciers getting bigger any more., so that we can assess the precision of Dr Kasers claim (particular given that it is based on an extrapolation)? Im particularly interested in knowing how hes managed to get round all the worlds glacier to confirm this highly precise measurement. Perhaps like Father Christmas he has a sled and some reindeers.

It’s the magic dust, dude! A little bit for the reindeer, a little bit for Santa Claus, a little bit for the reindeer, a little bit more for Santa Claus . . .

58. Pat Keating

41 42 Steve Alan

What time should we come over?

59. frost

Re 31:

I looked up this posting to get some ammunition to argue AGW consequences with a friend who is most concerned about a sea level rise inundating the Ganges delta. In particular I wanted to find the graph showing sea level rise since the end of the last glacial maximum, as shown in #31. However, while I was looking for this data I came across a similar graph on this NASA web page.

The curious thing is that the NASA graph shows a dashed line over the last 2000 years with a slight but noticeable upward curve in the most recent period. There is no explanation given for what the dashed line means and there is no upward curve in the globalwarmingart.com image here. Hence the NASA graph seems to be more alarmist than it needs to be. That wouldn’t be news but I thought it might be of interest to this audience.

60. John Lang

This sea level expert says there has been a little chichanery going on with how TOPEX’s measurements are calibrated.

http://www.mitosyfraudes.org/Calen7/MornerEng.html

61. Geoff

bump

62. John S.

63. Posted Jun 13, 2008 at 11:44 AM | Permalink | Reply

John S–

About a year ago, Bad Behavior didn’t like me either. I read the message, clicked the links and discovered it was because a spammer had taken out an account with my ISP. So, I forwarded the information to my ISP, they cancelled his account, informed the entities that track the spammers, and “Voila!” Bad Behavior no longer disliked me. :)

64. John Lang

Sea level seems to be falling right now, although there is enough variation in the data to consider the current decline to be temporary. But it is falling.

Same data adjusted for changes in pressure across Earth (not that I expect the average atmospheric pressure across the whole planet varies by very much hence the need for this adjustment is questionable.)

65. Geoff

bump – see Wunsch Dec ’07

66. Geoff

Journal of Climate

67. Geoff Sherrington

So you know where your taxes are going for Climate Change aka Global Warming, here is a June 20 2008 Lanch Advisory from NASA.

I read into this that an accuracy of sea level measurement of better than a few inches has not yet been obtained. But that might be jumping to conclusions. Note also the word “precision”, when what is needed is “accuracy”.

“NASA partnered with European scientists to launch an ocean research satellite from California early Friday, giving forecasters a new tool to make more accurate predictions of weather patterns and climate change.

“The \$432 million Jason 2 satellite blasted off aboard a Delta 2 rocket at 12:46 a.m. PDT (3:46 a.m. EDT; 0746 GMT) from Vandenberg Air Force Base, Calif.”

“Jason 2 carries a suite of instruments built by U.S. and French scientists to measure the distance between the orbiting spacecraft and the ocean surface. Scientists expect a precision of between one and two inches.”

“Researchers will incorporate real-time data from Jason 2 into their computer models to improve weather and ocean forecasts on scales ranging from a few days to more than a year.”

68. D. Patterson

Given the fact that ocean and sea waves have peaks and troughs with elevations differing by measures of feet and meters and not one or two inches, the need for computing average wave heights and sea levels from the satellite observations presents an opportunity custom-made for using adjustments of the raw observations in the service of manipulating the reported results. GIGO!

69. Geoff Sherrington

Re # 68 D. Patterson

On the other hand, I have seen reports that whales and subs can be detected from the portion of their bow waves that disturbs the surface. When an outsider gets close to military stuff, it can be difficult separating fact from anti-spy fiction. Personally, I find it obscene that \$432m can be spent on ostensible climate change studies like this when disease reduction and malnutrition are more humane imperatives.

Who gave the final approval to this launch and experiment? More money than sense?

70. Willis Eschenbach

\$432 million is cheap, and produces valuable scientific information. For example, the sea level has actually been decreasing lately, for the first time in the satellite record. I am very interested in seeing whether this continues, and Jason 2 is the only way to do that.

On the other hand, hundreds of billions are going to Kyoto, which produces absolutely nothing …

w.

71. D. Patterson

Jason 2 can produce scientific results worth every penny of the money spent upon it. However, the usage of this project with respect to reporting sea levels to a given accuracy must be an irresistable temptation to manipulate the calculation of the reported values in support of the Global Warming lobby and agenda. The Global Warming lobby knows few people understand how the satellite results must be analyzed to derive methematically interpreted results for sea level heights, because the topography of the sea surface is highly irregular. Once the mainstream media broadcasts the falsely manipulated results of an allegedly scientific space research project to the general public, it is going to be an exremely tough and uphill battle to correct the misinformation in the public’s mind. So, who can and will hold the Jason and Jason 2 projects accounatable for the accuracy of the calculated results in their sea level reports?

72. Geoff Sherrington

Re # 70 Willis Eschenbach

Oh that I was as confident as you that we can detect if sea level is changing, in any direction. Have you ever examined the angular momentum effect on Earth’s rotational velocity? Is it an adequately sensitive measurement? (I feel that rock events near the tropics, like the Himalayas uplift, would need a big correction to Ocean data, but I have not done the calculations ab initio, only looked at those of others).

73. D. Patterson

Dr. Nils-Axel Mörner has commented that the measurements of Earth’s rotational speed confirms there has not been enough change in the Earth’s size to account for more than a 1.1mm sea level increase at the very most and very likely to be less or decreasing. What is your impression of his works and commentaries regarding sea level changes?

74. Geoff Sherrington

Re # 73 D. Patterson

I did not derive my comments from Morner. I have skimmed his work and studied others and am left with the impression that those who venture into this minefield are not fully eqipped to survive. That is, there are myriads of subtle effects, some operating on a long time scale, some short, that presently make for a lack of confidence in all estimates of sea level change.

For example, if you state that Earth’s rotation is altering, you need to state a frame of reference. Stars? Universe expanding. Atomic clocks? Fairly recent. Old Greenwich? A ball dropping down a tower at Neap tide. Satellites? Circular arguments in calibration, still developing stellar reference maths.

This is only a small bit about one of the myriad factors. Compounding the galaxy of errors and uncertainties, I suggest you have to be brave to be dogmatic. The “authorities” produce data in conflict.

Having said that, I share your fear of the potential misuse by climate people of the data to be collected by Jason 2, whose real purpose is probably military.

75. Geoff

Wunsch:

Estimates made here produce a global mean of about 1.6 mm yr−1, or about 60% of the pure altimetric estimate, of which about 70% is from the addition of freshwater. Interannual global variations may be dominated by the freshwater changes rather than by heating changes. The widely quoted altimetric global average values may well be correct, but the accuracies being inferred in the literature are not testable by existing in situ observations. Useful estimation of the global averages is extremely difficult given the realities of space–time sampling and model approximations. Systematic errors are likely to dominate most estimates of global average change: published values and error bars should be used very cautiously.

76. Geoff

Wunsch:

At best, the determination and attribution of global-mean sea level change lies at the very edge of knowledge and technology. The most urgent job would appear to be the accurate determination of the smallest temperature and salinity changes that can be determined with statistical significance, given the realities of both the observation base and modeling approximations. Both systematic and random errors are of concern, the former particularly, because of the changes in technology and sampling methods over the many decades, the latter from the very great spatial and temporal variability implied by Figs. 2 , 6 and 8 . It remains possible that the database is insufficient to compute mean sea level trends with the accuracy necessary to discuss the impact of global warming—as disappointing as this conclusion may be. The priority has to be to make such calculations possible in the future.

• Geoff

Re: Geoff (#76), The Wunsch article can be found here.

Ref: Wunsch et.al., 2007, Decadal Trends in Sea Level Patterns: 1993–2004; Journal of Climate, Vol. 20, pages 5889-5911

I’m surprised more people are not familiar with this paper.

• Geoff Sherrington

Re: Geoff (#79),

It has been added to and overtaken by
http://www.ocean-sci.net/5/193/2009/os-5-193-2009.pdf
“A new assessment of the error budget of global mean sea level rate
estimated by satellite altimetry over 1993–2008″

• Geoff
Posted Jul 3, 2009 at 7:43 AM | Permalink

Hi Geoff, thanks for the reference, and don’t overlook this one on the 1950-2003 period, ” Two-dimensional reconstruction of past sea level (1950–2003) from tide gauge data and an Ocean General Circulation Model”. Interestingly they do not give an average sea level increase over the period (which overlaps by 10 years the period of the paper you referenced) buy eyeballing the graphs it doesn’t look like much more than 1.5 mm/year. In the new paper, they claim 3.11 mm/year for the whole period 1993-2008, but only 1 mm/year for 2005-8.

Looks like there is still work to be done and Wunsch’s comment that “the determination and attribution of global-mean sea level change lies at the very edge of knowledge and technology” still stands.

• Willis Eschenbach

Re: Geoff (#79), thanks for the fascinating link. For me the money quote was:

At best, the determination and attribution of global- mean sea level change lies at the very edge of knowledge and technology. The most urgent job would appear to be the accurate determination of the smallest temperature and salinity changes that can be determined with statistical significance, given the realities of both the observation base and modeling approximations. Both systematic and random errors are of concern, the former particularly, because of the changes in technology and sampling methods over the many decades, the latter from the very great spatial and temporal variability implied by Figs. 2, 6, and 8. It remains possible that the database is insufficient to compute mean sea level trends with the accuracy necessary to discuss the impact of global warming—as disappointing as this conclusion may be. The priority has to be to make such calculations possible in the future.

As the person who wrote the original post lo these many years ago, I must say that this has to rate as one of the most honest assessments of the state of the science that I have seen.

Since that time, the data have become available on the internet, making my digitization unnecessary. It is worth noting that the recent data shows a levelling off of the rise. Given the history, I suspect this will not last. But it clearly indicates that the many projections of an increasing rate of sea level rise have no observational support.

The map shown above illustrates another important point in the discussion. The tides have a very long and complex cycle. It is well known that no matter how accurate your measurements are, you need about a half century of data to give you an accuracy of ± 1mm in sea level rise. This is because of the non-repeating cycle of the tides, which only return to near (not exactly) where they started after about 50 years. In addition, there is a “sloshing” of the water in the various oceanic basins. As a result, our current satellite record of 17 years is far from adequate for any analysis of long term trends.

Finally, I am quite curious about the accuracy of the maps produced using the satellite data. While they are accurate in some areas, in others they seem to be unsupported by the local tidal data. Anthony has a discussion of one example at WUWT. It is worth noting in this context that to measure sea level to the nearest 1 mm, the measurement must be done to an accuracy of one part per billion. This is difficult to do even in a laboratory, much less from a satellite with a host of potential errors (satellite elevation, size of footprint, atmospheric delay, instrument stability over time, etc.).

77. Reference

new map pinpoints areas of sea level increase

Warming water and melting land ice have raised global mean sea level 4.5 centimeters (1.7 inches) from 1993 to 2008. But the rise is by no means uniform. This image, created with sea surface height data from the Topex/Poseidon and Jason-1 satellites, shows exactly where sea level has changed during this time and how quickly these changes have occurred.

• nevket240

Re: Reference (#77),

I wonder what effect the “ring of fire” is having on the detected sea level. From Wikipedia

Q//As well as the sideways movement between the plates, the sea floor is estimated to have risen by several metres, displacing an estimated 30 km3 (7 cu mi) of water and triggering devastating tsunami waves. The waves did not originate from a point source, as was inaccurately depicted in some illustrations of their paths of travel, but rather radiated outwards along the entire 1,600 km (994 mi) length of the rupture (acting as a line source). This greatly increased the geographical area over which the waves were observed, reaching as far as Mexico, Chile, and the Arctic. The raising of the sea floor significantly reduced the capacity of the Indian Ocean, producing a permanent rise in the global sea level by an estimated 0.1 mm (0.01 cm or 0.0001 m).[14]//unQ

Accounted for or not?? Too many of the hot spots are in areas of repeating plate movemnets.
regards

• DeWitt Payne

Re: nevket240 (#84),

Sea floor movement correction to global sea level is referred to as Glacial Isostatic Adjustment (see here for example). Land covered by glaciers kilometers thick at the end of the last ice age was depressed causing a corresponding increase in the sea floor height. Now that those glaciers are gone, the surface is rebounding, causing a corresponding reduction in sea floor height. 30 km3 of water seems like a lot but it’s vanishingly small compared to the volume of the earth ocean as a whole.

78. Posted Jul 2, 2009 at 3:40 AM | Permalink | Reply

The satellite data must go through some tricky manipulations to be able to detect a 3 cm change. Consider the beam diameter at sea level of 300 mi. From the curvature of the earth alone the height difference from the center to the edge is about 2 3/4 mi.

If the beam diameter was only 30 miles there would be about a 150 ft difference – center to edge.

The corrections have to swamp the data.

79. Ausie Dan

I have just unwrapped the latest copy of NewScientist and have read the cover with horror and alarm “Sea Level rise – it’s worse than we thought” page 26 on 4th July 2009. – Over to you guys.
Regards for your good work – keep it up.
Dan

1. [...] Analysis of the Topex Sea Level Record [...]

2. [...] [...]

4. [...] will not affect coral atolls, and provide evidence for the human alteration of the Tuvalu reefs. An Analysis of the TOPEX Sea Level Record :: Satellite-measured sea level data Floating Islands :: Shows why tropical coral atolls [...]

5. [...] to even talk about millimeter changes. There are so many inputs and so many adjustments that the final results claimed are unjustified. Current estimates place sea level rise at 3 mm but as Carl Wunsch says, It [...]