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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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How much is sea level rising?

What the science says...

Select a level... Basic Intermediate

A variety of different measurements find steadily rising sea levels over the past century.

Climate Myth...

Sea level rise is exaggerated

"We are told sea level is rising and will soon swamp all of our cities. Everybody knows that the Pacific island of Tuvalu is sinking. ...

Around 1990 it became obvious the local tide-gauge did not agree - there was no evidence of 'sinking.' So scientists at Flinders University, Adelaide, set up new, modern, tide-gauges in 12 Pacific islands.

Recently, the whole project was abandoned as there was no sign of a change in sea level at any of the 12 islands for the past 16 years." Vincent Gray).

At a glance

You'd think it would be obvious, wouldn't you? If ice (or snow) melts, you get water. Water flows downhill through gravity and collects wherever it can be retained. In areas that see regular winter snowfalls, the processes involved are familiar. Snow-capped mountains look photogenic but along comes the eventual thaw and the river levels rise sharply with all the meltwater.

Now apply the same basic principles to glaciers and ice-caps. It should not come as a surprise that exactly the same thing happens and where that meltwater collects is ultimately the oceans. Note here that we're talking about land-based ice, not sea-ice: sea-ice is already part of the ocean so does not affect sea levels as it forms and melts every year. But melt enough land-ice and you get very significant change indeed.

What do we mean by very significant? Well, let's look at the transition out of the last ice-age that dominated the last 20,000 years. It began with ice-caps over parts of Europe and North America and ended not so long ago with much of that ice gone but with sea levels having risen by more than 120 metres. If that's not significant, what is?

There's not enough ice left on Earth to raise sea levels by that whopping amount now, but there is enough to raise the oceans by more than 60 metres. Over what sort of time-frame? Well, we know that the current rate of sea level rise is some 3.7 mm a year, or nearly an inch and a half per decade. A lot of that is due to the expansion of the oceans - as things are warmed up they expand. But the rate is accelerating. How fast do we think it can get? 

We do have the past to consider: during the glacial meltdown of the past 20,000 years, there was a period ominously named Meltwater Pulse 1A that began some 14,700 years ago. During this enhanced period of melting, sea levels rose by between 16 and 25 metres in about 400–500 years. That's roughly 40–60 mm per year or 16-23 inches a decade.

Could such drastic rates of sea level rise happen again? Probably not but nevertheless it shows what is possible as ice-sheets collapse in a warming world. But even if sea level rise stays at its current rate (it won't), that's getting on for a two-metre increase over the coming 300 years and a one-half to one-metre increase over the next 100 years. Now go anywhere affected by tides and think about all the communities of people that live and work along the shore. Pick the biggest spring tides, take a look at where they reach at high water, maybe watch the waves and surge when a storm occurs, then imagine an extra two metres of water on top of that.

And try to imagine being the decision-makers in the coming decades and centuries, who will have to work out what best to do. What would you think of the people all those years ago, who went around pretending this was not happening? Not favourably, for sure - because of such behaviour, that is how history will remember them.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!


Further details

The climate myth set out in the coloured box above gives an insight into the minds of climate change deniers. Why? Because it's entirely made-up. It annoyed the Realclimate blog's Gavin Schmidt sufficiently for him to write an eloquent debunking in 2012 that is well worth reading because it demonstrates so clearly what we, the scientific community, are up against.

The claim that tide gauges on islands in the Pacific Ocean show no sea level rise is nonsense: the data presented in the Realclimate link above show a variably rising sea level trend at each station. But what about global sea level rise?

Sea level rises as ice on land melts and as warming ocean waters expand. As well as being an existential threat to coastal habitation and environments (think about many of the world's capital cities here), sea level rise corroborates other evidence of global warming 

The black line in the graph below (fig. 1) clearly shows sea level is rising; its upward curve shows how sea level is rising faster as time goes on. The upward curve agrees with global temperature trends and with the accelerating melting of ice in Greenland and other places.

Because sea level behaviour is such an important signal for tracking climate change, the misinformers seized on the sea level record in an effort to cast doubt on this evidence. As fig. 1 clearly demonstrates, sea level bounces up and down slightly from year to year so it's possible to cherry-pick data and falsely suggest the overall trend is flat, falling or linear. You can try this yourself. Starting with two closely spaced data points on the graph below, lay a straight-edge between them and notice how for a short period of time you can create almost any slope you prefer, simply by being selective about what data points you use. Now choose data points farther apart. Notice that as your selected data points cover more time, the more your mini-graph reflects the big picture. The lesson? Always look at all the data rather than being fooled by selective presentations.

AR6 WGI Chapter 2 Figure 2_28c

Fig. 1: sea level change, from IPCC AR6 WGI Chapter 2 section Climate Change 2021: The Physical Science Basis. Tide-gauge and, more latterly, altimeter-based estimates since 1850. The full image with all four panels and IPCC caption is available here.

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

Tide gauges must take into account changes in the height of land itself caused by local geological processes, a favourite distraction for deniers to highlight. It will come as no surprise to learn that scientists measuring sea level with tide gauges are aware of - and compensate for - these factors. Confounding influences are accounted for in measurements and while they leave some noise in the record they cannot account for the observed long-term upward trend.

Various technical criticisms are mounted against satellite altimeter measurements by deniers. Indeed, deriving millimetre-level accuracy from orbit is a stunning technical feat so it's not hard to understand why some people find such an accomplishment unbelievable. It's astonishing that in another breath they are happy to jump aboard an airliner, parts of which are engineered to a similar tolerance!

In reality, researchers demonstrate this height measurement technique's accuracy to be within 1 mm/year. Most importantly there is no form of residual error that could falsely produce the upward trend in observations. 

As can be seen in an inset of the graph in fig. 1, tide gauge and satellite altimeter measurements track each other with remarkable similarity. These two independent systems mutually support the observed trend in sea level. If an argument depends on skipping certain observations or emphasises uncertainty while ignoring an obvious trend, that's a clue you're being steered as opposed to informed. Don't be misled by only a carefully-selected portion of the available evidence being disclosed. Look at it all.

Current sea level rise is not exaggerated, in fact the opposite case is more plausible. For one, sea level rise is not the same everywhere. Many areas around the world already experience much faster rates of sea level rise than the average global rate shown in Fig 1.  As well, observational data and changing conditions in such places as Greenland suggest if there's a real problem here it's underestimation of future sea level rise. Past IPCC synthesis reports offered rather conservative projections of sea level increase based on assumptions about future behaviour of ice sheets and glaciers, leading to estimates of sea level roughly following a linear upward trend mimicking that of recent decades. In point of fact, observed sea level rise is already above older IPCC projections - and accelerating - while at the same time it appears the mass balance of continental ice once envisioned by the IPCC was overly optimistic (Rahmstorf 2010; Otosaka et al. 2023).

Fast-forward to 2023 and the recent IPCC AR6 Synthesis Report is a bit less nuanced:

Limiting global surface temperature does not prevent continued changes in climate system components that have multi-decadal or longer timescales of response (high confidence). Sea level rise is unavoidable for centuries to millennia due to continuing deep ocean warming and ice sheet melt, and sea levels will remain elevated for thousands of years (high confidence). However, deep, rapid and sustained GHG emissions reductions would limit further sea level rise acceleration and projected long-term sea level rise commitment. Relative to 1995–2014, the likely global mean sea level rise under the SSP1-1.9 GHG emissions scenario is 0.15–0.23 m by 2050 and 0.28–0.55 m by 2100; while for the SSP5-8.5 GHG emissions scenario it is 0.20–0.29 m by 2050 and 0.63–1.01 m by 2100 (medium confidence).

The report goes on to state, however:

The probability of low-likelihood outcomes associated with potentially very large impacts increases with higher global warming levels (high confidence). Due to deep uncertainty linked to ice-sheet processes, global mean sea level rise above the likely range – approaching 2 m by 2100 and in excess of 15 m by 2300 under the very high GHG emissions scenario (SSP5-8.5) (low confidence) – cannot be excluded.

If they cannot exclude such risks - and they know what they are talking about - can you?

Last updated on 20 August 2023 by John Mason. View Archives

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Further viewing

From Peter Hadfield (potholer54 on YouTube) published on Dec 5, 2021

Compare two photos 130 years apart and it looks as though sea levels haven't moved. So why all the fuss about rising sea levels and evacuating islands? This video closes the yawning gap between internet myths and science.


 

From Peter Sinclair (greenman3610 on YouTube) published on Sep 24, 2009

Denial101x lecture

Comments

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Comments 151 to 175 out of 322:

  1. "Looking at tidal guages and satillites, both at this time show a reduction in sea level rise. That puts the Von Schuckmann paper in question because for them to be correct, we should be seeing a steady if not increasing rate of rise." That's not right Camburn, check out the graph I provided @ 143 Von Schuckmann & Le Traon measure an increase in ocean heat down to 1500 metres over the 2005-2010 period, along with a corresponding rise in steric sea level. It's as one would expect.
  2. Rob: Envisat, which covers a larger area of the globe, does not agree with your graph, and when one adds the current data the GMSL is unchanged since 2004. Before you accuse me of cherry picking a satallite, the reason I use Envisat is because it covers more surface area and should be a better metric of what is going on. My question once again is, how is this possible? Is Evistat not correct? If it isn't, wouldn't someone that works there know and written about it?
  3. Re, "Envisat, which covers a larger area of the globe.." Please back up this assertion, you have made it several times now, and while it may be true, and if it is, please demonstrate quantitatively why and how this 'revelation' is important in the face of a myriad of other data. And please respond to the points made about OHC and sea level rise in the latest von Shuckmann paper. Do you deny that too? You are doing a sterling job of missing the point, and this time continuing to be in denial about sea-level rise.
  4. Re, "....and when one adds the current data the GMSL is unchanged since 2004.' Please quantify this statement and compare it with analysis of data from other observation platforms. Thanks.
  5. Whilst chasing down Camburn's unsubstantiated claims, I came across this comment on the Aviso website: "On the other hand the drift obtained with the Envisat MSL is more significant, approximately 0.45 mm/year. This is currently being investigated and could possibly be explained by stability problems for the correction of the wet troposphere and instrument corrections." They also say elsewhere on the page that: "During the first year (cycles 9 to 22) Envisat MSL global trend is not consistent to other flying satellites. This unexplained behavior is under investigation. Results plotted here are obtained after cycle 22 (beginning of 2004)." So while the Envisat coverage is better, north of 66 N and S, it appears that the data have unresolved issues. It would thus be unwise to place emphasis on these Envisat sea-level data until the drift issues have been identified and corrected. Now this is interesting, a so-called 'skeptic' identified those Envisat data and believed the results at face value, likely because those data told him what he wanted to believe. That is not skepticism, it is confirmation bias folks. And this is all ignoring the foolhardiness of looking at such short periods of time that are not statistically significant.
  6. Albatross: The Von Schuckman paper is one of the reasons I am questioning the results of the Evistat satillite. As I said, there is no physical reason for sea level to have been virtually flat for the past 6-7 years. I don't know how to post pictures. I have tried, but can't seem to get that to work yet. So, either there is someone wrong with the Evistat data, which I have not read about, or there is something that we don't understand.
  7. Albatross: Yep.....confirmation of bias, to question if the posted results are correct. That is really some bias. Thanks for the info on Envisat. They indiate that the results after cycle 22 should be viable...right? Are they?
  8. Albatross: Thank you for the link. After reading it, it appears that the error bars are so large for all satillite data at this point that it is unrealiable. "This demonstrates in two independent ways the reliability of the global MSL evolution deduced from the Topex and Jason-1 altimetry missions. Nevertheless, this budget should be refined further in order to estimate the impact of error sources which have not yet been taken into account such as the contribution of the ocean covered by ice and eventually the impact of very long ocean tide periods (18.6 years)." Certainly changes my view on the valilidity of salillite measurements of GMSL.
  9. Camburn, I doubt very much had those Envisat data been showing a faster rate of increase in the GMSL than the other products that you would have been so quick and eager to post them here. "So, either there is someone wrong with the Evistat data" Indeed there does appear to be an issue with those data. Please follow and read the link provided above. The drift issue (see below) applies to the data after 2004. As clearly shown in my previous post, the Envisat sea-level data have issues at this time and should not be considered reliable. [Source]
  10. Data from von Suckmann and Le Traon (2011), experts in this field, clearly contradict your claims Camburn: "Our revised estimation of GOIs [Global Ocean Indicators] 25 indicates a clear increase of global ocean heat content and steric height. Uncertainty estimations due to the data handling reveal that this increase is significant during the years 2005–2010 (this does not mean, of course, that these are long term trends). Global ocean heat content changes during this period account for 0.55±0.1W m−2 and global steric rise amounts to 0.69±0.14 mmyr−1." The steric rise has decreased recently, but it is certainly not "virtually flat" (whatever that is supposed to mean-- anything you want I guess).
  11. Camburn @158, "it appears that the error bars are so large for all satillite data at this point that it is unrealiable." Argumentum ad absurdum. Also, intriguing that you deduce that when their first line states: "This demonstrates in two independent ways the reliability of the global MSL evolution deduced from the Topex and Jason-1 altimetry missions." Your claim might apply to the Envisat data, but not the other satellite data. Note the excellent agreement between those data and the global tide gauge data shown in the post @151.
    Response:

    [DB] I appreciate the passion and conviction, but you are no doubt aware that all efforts to convince your primary target will bear no fruit.

  12. Camburn - It should be clear to you by now that Envisat data is still being calibrated, and is not currently a reliable data set. As opposed to the Jason/TOPEX data, which have much smaller drifts when calibrated against tide gauge data. Hence the Envisat dataset is not (yet) a basis for disputing sea level rise. I believe that over the next few years the various instrumental issues with Envisat will be identified and corrected for, much as satellite surface temperature records have been. As was noted earlier by another poster, though, I suspect you presented the Envisat data as something that agreed with your preconceptions. You did not take sufficient care to ensure that this was quality data, and certainly did not take into consideration the statistical significance of it given the short timeline. You need to pay more attention to the possibility of confirmation bias.
  13. Don't blame poor Camburn. He's just echoing the siren calls of the great minds of denialism skepticism, like that Arctic ice prognosticator of prognosticators Steven Goddard. Goddard has a post about how the evil scientists that launched and run all of these nefarious, one-world-government-oriented satellites have hidden the decline in sea level rise by using a hard-to-notice color (yellow) for the Envisat data on their graphs. Evil, yellow-wielding scientists! Curse them and their foul color choices! He fixed that on his blog (by changing the one he likes, Envisat, to blue, while one he doesn't like, Jason-1, to the yellow that was originally assigned to Envisat... I don't know why he didn't do away with yellow completely and use black, maroon, dark green, dark gray, or any other clearly visible color -- pot, meet kettle kind of thing): Of course, the fact that none of them seem to notice how closely all of the other data sets agree, while Envisat is a clear outlier that is off throughout its existence, doesn't appear to enter their observations or logic at any point. It couldn't possibly be that the Envisat data as currently badly calibrated, could it? I can see the post a year from now, when they sort it out and the cry becomes that they "homogenized" the data to look the way they want it to. You can't win with some people (some = those with a serious confirmation bias wired into their nervous systems).
  14. I don't read Mr. Goodards blog, and I, up till a few weeks ago, have very seldom read Wattsup blog. As far as denialist, you will have to do better than that.
  15. Camburn - Envisat has a drift problem as pointed out by Albatross @ 159, & Sphaerica @ 163, whereas ARGO, JASON, TOPEX (now defunct) and tide gauges all show rising sea level trends. Von Schuckmann and Le Traon in fact use the AVISO satellite altimetry data to validate their 'box-averaging' method. So any contradiction is purely imagined on your part. Is sea level rising long-term? Yes. But look at the satellite, tide gauge and ARGO data - there is considerable year-to-year variability. What do you think that means?
  16. Camburn, when the data for Jason and Envisat are compared over the same latitudes and over areas deeper than 1000 meters, Envisat still shows a negative trend relative to Jason for Mean Sea Level, along with much larger semi-annual fluctuations in sea level (see the first graph for "Cross comparison of performances".) At the same time, Envisat is known to have major instrument problems (from the same link):
    "USO anomaly: In February 2006, the RA-2 Ultra Stable Oscillator (USO) clock frequency underwent, for an unknown reason, a strong change of behavior. The anomaly consists in a bias, superposed with an oscillating signal with an orbital period. Auxiliary files are distributed since mid 2006 allowing the users to correct the range from this anomaly. The anomaly periods are detailed beside Loss of the S-Band: On the 17 January 2008, a drop of the RA2 S-band transmission power occurred. There is thus no more dual frequency altimeter both in Side A and Side B"
    Further, Jason is known to agree with buoy data, while Envisat disagrees. This is true not only for sea level, but also for wave height:
    "Collocation criteria of 50 km and 30 min yield 3452 and 2157 collocations for Jason-1 and Envisat, respectively. Jason-1 is found to be in no need of correction, performing well throughout the range of wave heights, although it is notably noisier than Envisat. An overall RMS difference between Jason-1 and buoy data of 0.227 m is found. Envisat has a tendency to overestimate low Hs and underestimate high Hs. A linear correction reduces the RMS difference by 7%, from 0.219 to 0.203 m."
    The logical conclusion is that the difference between Envisat and Jason is due to instrumental error in Envisat.
  17. To all: I have no problem that Envisat has errors. IF you note, on my original post, I pointed out that the rise in Envisat exceeded the rise of the other metrics. Anyways, I had asked repeatedly if the data was good data. I had a hard time believing that a major organization would present data publically with known errors, (at least to me now). Envisat should not be avaialbe to the public until these issues are addressed and corrected in my opinion. One would expect AVISO to be a credible source....it now appears that I have to view everything with a skeptic eye. Thank you all for pointing this out.
  18. 167, Camburn, First, if they did hold back the data until they were certain it was well calibrated, there would be a great hue and cry that they were hiding something, so they can't win. Secondly, scientists, the ones who actually use this stuff, know very well all of the details involved, what to trust, when to be skeptical, and so on. That you are naive about it is meaningless. Thirdly, the information that you failed to find is all available on the Internet. You only had to take the time to look yourself, instead of excepting it to be spoon fed, and then complaining that you felt cheated. This last point is, time and again, the problem at the heart of so called "skeptics." For all of their skeptical attitude, they stop the very moment they find something that supports their desired belief, and anything after that is just plain annoying, or part of a vast conspiracy, or incompetence, or whatever the denial flavor of the month is. So your rather arrogant sounding "aha" attitude is nothing but bluster and implied recriminations. The only thing wrong here is your apparent feeling (shared by too many "skeptics") that science exists to satisfy and/or entertain you personally. It does not.
  19. Camburn @167, the proper thing to do when you have flawed data is to report both the data and the flaws. So called "skeptics" have been very critical when climate scientists have supposedly done otherwise, as, for example, with "hide the decline". Of course, they did not do otherwise in that case; and it would be wrong for AVISO to not publish their envisat data, so long as they also publish their reasons for thinking it may be flawed. The problem here is not with AVISO but with people such as Steve Goddard, who purport to have a scientific education, and hence should be aware of the pitfalls and qualifications that exist in the data, but who publish a cherry picked selection of the data to a popular audience without any mention of the problems that may be involved. That is, IMO, dishonest. It deliberately cultivates misunderstanding in order to persuade people to a view point that is almost certainly false.
  20. Scientists conduct proper research Deceivers misrepresent that research 'Sceptics' rejoice that global warming is false Actual sceptics point out that they've been hoodwinked 'Sceptics' complain about the scientists. Not the people who tricked them Par for the course. It always makes me think that at some level 'skeptics' must KNOW their position is nonsense. Otherwise they'd feel some sense of outrage at being lied to. The only conceivable reason that 'skeptics' haven't run off frauds like Goddard, Monckton, and so forth after their numerous blatant falsities have been revealed is that they WANT to be deceived. Why else keep going back to people you know are lying to you?
  21. You may be interested in this paper, if not for the specifics of the Australian measurements, for the international references. http://www.jcronline.org/doi/full/10.2112/JCOASTRES-D-10-00141.1
  22. Eric the Red, you may be interested in the analysis of this paper How not to analyze tide gauge data. While this analysis isnt published (though I am encouraging the author to do so) it is basically the same cherry pick as H&D. See here for published criticism of this kind of cherry pick.
  23. I was curious about the history of the Sea Level Estimates published on the web by Colorado University. Here's the current estimate, 2011 release #2, of 3.2 mm/yr: I used The Internet Wayback Machine and searched on: [http://sealevel.colorado.edu/] [take me back] I found the following series of CU Sea Level Estimate pages: YYYY MM DD; Rel #; rate mm/yr 2004 02 15; rel 1; 2.8 2004 12 23; rel 4; 2.9 2006 04 10; rel 5; 2.9 2007 09 08; rel 2; 3.0 2007 04 27; rel 3; 3.2 2008 02 10; rel 2; 3.2 2008 09 08; rel 3; 3.2 2009 01 24; rel 4; 3.3 2009 11 02; rel 2; 3.2 2010 04 13; rel 4; 3.1 2011 01 08; rel 5; 3.1 2011 07 18; rel 1; 3.1 2011 07 19; rel 2; 3.2 So I plotted them all out: I added in red what the time line would have been if GIA hadn't been added starting in May of 2011
    Response:

    [DB] If you have a point with this exercise please be more transparent and just state it.  As it stands right now, you don't.

  24. "Including the GIA correction has the effect of increasing previous estimates of the global mean sea level rate by 0.3 mm/yr. (Source) Doesn't this mean that, to illustrate the 2011 new releases GIA correction, you should have done exactly the opposite : let the blue line after 2011, and substract 0.3 mm/yr before ? But I agree that the influence of this correction should be discussed to determine if the nino variations are the only driver of the recent global sea level drop.
  25. # 174 Papy Your source has this interesting statement: In essence, we would like our GMSL time series to be a proxy for ocean water volume changes. In other words they aren't really measuring sea level anymore. They aren't measuring sea level relative to the center of the Earth, nor are they measuring sea level relative to the shore line. So, if I want to sea what sea level is relative to the center of the earth, I need to subtract the GIA from those last two data points. Indeed, that's what Colorado U said to do back in May when they announced that they were adding the GIA correction. They said: Simply subtract 0.3 mm/year if you prefer to not include the GIA correction. (Link) Why might you want to not include the GIA correction? If you wanted to know what sea level is and not ocean water volume.

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