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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).

Gavin Schmidt investigated the claim that tide gauges on islands in the Pacific Ocean show no sea level rise and found that the data show a rising sea level trend at every single 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 a threat to coastal habitation and environments, sea level rise corroborates other evidence of global warming 

The blue line in the graph below clearly shows sea level as rising, while the upward curve suggests 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 behavior is such an important signal for tracking climate change, skeptics seize on the sea level record in an effort to cast doubt on this evidence. Sea level bounces up and down slightly from year to year so it's possible to cherry-pick data falsely suggesting 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, don't be fooled by selective presentations.

graph from Church et al. (2008)

Other skeptic 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 geologic processes, a favorite distraction for skeptics to highlight. Not surprisingly, 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 upward trend.

Various technical criticisms are mounted against satellite altimeter measurements by skeptics. Indeed, deriving millimeter-level accuracy from orbit is a stunning technical feat so it's not hard to understand why some people find such an accomplishment unbelievable. In reality, researchers demonstrate this height measurement technique's accuracy to be within 1mm/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 above, 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 emphasizes uncertainty while ignoring an obvious trend, that's a clue you're being steered as opposed to informed. Don't be mislead by only a carefully-selected portion of the available evidence being disclosed.

Current sea level rise is after all not exaggerated, in fact the opposite case is more plausible. 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. IPCC synthesis reports offer conservative projections of sea level increase based on assumptions about future behavior 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 IPCC projections and strongly hints at acceleration while at the same time it appears the mass balance of continental ice envisioned by the IPCC is overly optimistic (Rahmstorf 2010).

Basic rebuttal written by doug_bostrom


Update July 2015:

Here is a related lecture-video from Denial101x - Making Sense of Climate Science Denial

This rebuttal was updated by Judith Matz on September 13, 2021 to replace broken links. The updates are a result of our call for help published in May 2021.

Last updated on 5 July 2015 by pattimer. 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

Comments

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Comments 126 to 150 out of 322:

    • Do you mean short-term as in the last La Nina?
    That's what the Colorado University Sea Level Research Group said. How short term that is remains to be seen.
      Are you sure you're taking everything into account with this back-of-the-napkin calculation?
    I think the "Back-of-the-Napkin" assessment is accurate I also think that with respect to the information given in the Executive Summary of the AR4's Chapter 5 it's not likely to be that far off the mark. The Chapter 5 Executive Summary quote is in regard to the empirical record and Table 10.7 is a projection, and the 6.8 mm/yr is worst case. Worst case is often what is reported in the popular press. So it ought to be realistic. So how realistic is it that in the next 89 years that the thermal expansion component of sea level rise will go from 0.36 mm/yr to 6.8 mm/yr?
  1. Steve Case - 'So how realistic is it that in the next 89 years that the thermal expansion component of sea level rise will go from 0.36 mm/yr to 6.8 mm/yr?" Well, observations show the thermal (steric) component of sea level is rising at 0.69mm per year over the last 6 years, so your calculations appear to be missing important details- I see a glaringly obvious one in your calculations. Unless you're going to develop back-of-the-napkin climate models, that's going to continue to be the case.
    • Well, observations show the thermal (steric) component of sea level is rising at 0.69mm per year over the last 6 years,

    Is rising 0.69 mm/yr or is 0.69 mm/yr? It does make a difference. In any case, do you have a link for that observation? Even at 0.69 mm/yr is it reasonable to expect a possible 6.8 mm/yr due to thermal expansion by 2100?

      so your calculations appear to be missing important details - I see a glaringly obvious one in your calculations.

    And that glaringly obvious one is?

  2. Steve: I think you are overestimating sea level rise. Envisat data, which at this time is the most advanced, iindicates a sea level rise of approx 1.78mm/yr if memory serves me.
  3. Re #129, You memory fails you. GSL is increasing at about 3.22 mm/yr, almost double what your memory thinks: Source]
    • Camburn ... I think you are overestimating sea level rise. Envisat data, which at this time is the most advanced, iindicates a sea level rise of approx 1.78mm/yr if memory serves me

    The IPCC tells us that Over the period 1961 to 2003, global ocean temperature has risen by 0.1°C from the surface to a depth of 700 m. The IPCC also tells us, in table 10.7, that by 2100 we can expect thermal expansion to account for as much as 6.8 mm/yr. I'm questioning if those two facts are compatible. The graph that Albatross put up is nearly a straight line. In order to achieve the 6.8 mm/yr it's going have to change. So, how likely is it that it will begin a sharp upward trend resulting in that 6.8 mm/yr contribution from thermal expansion the IPCC tells us could happen by 2100? As I pointed out earlier, 6.8 mm/yr is worst case, but that's what the popular press will report, so it ought to be reasonable. Is it?

  4. Steve: The transition from XBT data to ARGO data showed a huge step rise in OHC. We know because of instrument splicing, changes in models etc that XBT data had huge error bars. The results to date of ARGO data would indicate that the XBT data had a strong negative bias in measurement. With that in mind, and the fact that co2, because of its emissions spectra does not penetrate beyond the skin of the ocean. the idea of a 6.8 mm/yr thermosteric rise in sea level to 2100 is virtually impossible.
  5. Albatross: Note I said Envisat. Multiple sat observations of sea level
    Response:

    [DB] You continue to be disingenuous with your graph.  Envisat data is actually shown here:

    Envisat

    [Source]

  6. Camburn, I am well aware of what you said. You continue to be incredibly disingenuous. You are cherry picking a satellite dataset that only starts in 2004. There are multiple satellite datasets going back to circa 1993, yet you choose one dataset that presents the answer that you want, and then present a trend that is probably not statistically significant give the limited time window.
  7. Albatross: My memory was wrong in that it is 1.02MM/yr. as DB shows. Take a look at the coverage of Envisat does, verses the other satillites. Envisat is suppose to be the widest coverage. This is all the data from this satillite as this is the age of this satillite. The thing to watch in the long run being it has better coverage of the globe is to see if a divergence develops. I presented what it shows. I wanted to show them all. You will see that early it showed an increased rate of rise, and now it shows more of a decreased rate in rise. Are those slight divergences because of the coverage above 70 degrees? This thread is about sea level rise...right? And one has to look at all the data available....right?
    Response:

    [DB] "This thread is about sea level rise...right?  And one has to look at all the data available....right?"

    Excellent point.  One in which the entire thrust of your point is lacking in.  So, let's look at ALL of the data, shall we?  You mean like this, right?

    SLR

    Or this, right?

    SLR

    Or this, right?

    SLR

    Or this, right?

    SLR

    Multiple sources, using the all of the data available, rightly show the long term trend is far worse than your dissembling, cherry-picked case.

  8. Steve Case- And that glaringly obvious one is? The global ocean is a lot deeper than 700 mtrs. The executive summary in the IPCC document you cited says: "The oceans are warming. Over the period 1961 to 2003, global ocean temperature has risen by 0.10°C from the surface to a depth of 700 m. Consistent with the Third Assessment Report (TAR), global ocean heat content (0–3,000 m) has increased during the same period, equivalent to absorbing energy at a rate of 0.21 ± 0.04 W m–2 globally averaged over the Earth’s surface. Two-thirds of this energy is absorbed between the surface and a depth of 700 m" What do you think happens to that leftover third? And regardless it doesn't explain the discrepancy between your calculations and actual observations.
  9. Camburn Your data and examples are so very clearly cherry-picked that I find it increasing difficult to consider this an error. I rather hate to say it, but I've come to the conclusion that you are deliberately distorting the data to make your point - that you are trolling. Unless you significantly improve the quality of your posts, I see no reason to take them seriously.
  10. KR @137, I concur. DB @135, Thank you.
  11. Rob Painting - The Question I have asks if it's reasonable to project a 6.8 mm/yr thermal component to sea level rise by 2100. Adding in that leftover third and something less than a half for the salinity portion of steric rise won't change the overall gap between the current assessment in the Executive summary and the projection in table 10.7 by very much. Your actual observations link was a link to method, not data. So, is it reasonable or is it an exaggeration to project that the thermal component of sea level rise by 2100 might be over ten to nearly 20 times what it is today?
  12. Steve Case - "Your actual observations link was a link to method, not data" Now Steve that's being a little bit silly. Data is useless without analysis. I'm sure you know this. The point was that your simplistic calculations bore no to relationship to reality. "So, is it reasonable or is it an exaggeration to project that the thermal component of sea level rise by 2100 might be over ten to nearly 20 times what it is today?" Well climate modelling sure suggests an increase in the thermal component. It's to do with the greater temperature rise expected this century. Much more than the 20th century. Like this study for instance: Note the inset portion, where the thermal component reaches 6mm per year by 2100.
  13. So I present data from a new satillite and that is suppose to be bad? And from that data we can see that MSL rise has slowed. Do we know why it has slowed? All satillite data shows that it has slowed. That is why I posted the link to all of the current measureing satillites. Ya know, to make an observation supported by all metrics, and then be told that I am cherry picking? A valid question is, the major temp metrics all show wraming, yet MSL is not responding....why?
  14. "Your actual observations link was a link to method, not data"

      That's being a little bit silly. Data is useless without analysis.

    Analysis without any data is even more useless.

      The point was that your simplistic calculations bore [no] relationship to reality.

    What doesn't bear any relationship to reality is the mismatch of claims within the IPCC's AR4.

    So, is it reasonable or is it an exaggeration to project that the thermal component of sea level rise by 2100 might be over ten to nearly 20 times what it is today?

      Well climate modeling sure suggests an increase in the thermal component.

    Climate modelers can most likely make sure their models do whatever they want.

      It's to do with the greater temperature rise expected this century.

    We are over ten years into the century and certainly sea level is not demonstrating any positive change in trend. this graph

    certainly doesn't and if you plot out the tide gage data from PSMSL you will find that the timeline over the last 120 is nearly as straight.

      Much more than the 20th century. Like this study for instance: Note the inset portion, where the thermal component reaches 6mm per year by 2100.

    The IPCC no doubt got their value for table 10.7 from such a study. I assume they got the value for the observed 0.1°C over 42 years in that 700-meter layer of ocean from a legitimate source.

    I'm questioning whether or not it's reasonable that the empirical record described in the Chapter 5 Executive Summary of the AR4 could lead to the worst case projected outcome in table 10.7. If it's reasonable, then the annual rate of sea level rise, and it's claimed that it's mostly thermal expansion, has to change very dramatically in the next few years. The only place I see that happening is in the models. World temperatures have been on an upward trend for 120 years but the sea level trend during that time has remained relatively constant. It's on course for about 275 mm or less than a foot.

  15. Steve Case -"Analysis without any data is even more useless." So ARGO is now useless because the data do not match your preconceived notions? You're not making any sense whatsoever. "Climate modelers can most likely make sure their models do whatever they want" This comment is skirting dangerously close to a violation of the comments policy. No comments of scientific malfeasance please. As well as breaking this forum's rules, it just demonstrates you have no rational argument to make. " I assume they got the value for the observed 0.1°C over 42 years in that 700-meter layer of ocean from a legitimate source." Ditto, my comment above. "The only place I see that happening is in the models." Note that the actual sea level rise is at the upper end of IPCC projections: "World temperatures have been on an upward trend for 120 years but the sea level trend during that time has remained relatively constant. It's on course for about 275 mm or less than a foot.' So you didn't even bother to read the post you are commenting on? Did you not notice the graph in the post above?. Just to refresh: That steadily rising curve, that's an acceleration in the long-term rate of sea level rise. It doesn't mean sea level won't slow-down or speed-up on short timescales however.
  16. "Climate modelers can most likely make sure their models do whatever they want." Another baseless assertion. Please explain then why skeptics cant use the models to make anthropogenic warming go away? Camburn, so you would bet on that being a long term trend?
  17. scaddenp: I would not bet on that being a long term trend at all. What I would like to know, being Envistat covers more of the globe and has demonstrated a slowing of MSL rise, why? Physically, it does not make sense.
  18. Fair enough, good questions and I would like to know some answers as well. I found some other interesting puzzles with spatial distribution of sea level rise that dont have easy answers either. However, I would guess at short term variability, which is what Trenberth is also interested in.
  19. scaddenp: Being no one that reads this seems interested, I will make a stab at it. According to ARGO data, the OHC of the top 700 meters has a cooling bias at present. The sea level rise has slowed, which would confirm that data. I think the ocean is stabalized and that evaporation is enough to keep the temperature flat.
  20. scaddenp: Nice that your brought up short term variability. The amount of thermal energy in the top 700 meters of the oceans dwarfs all the thermal energy of the atomosphere. At this time, the atmosphere has shrunk br approx 150 miles, which is a huge amount. My point is tho, that for the ocean to have even a minor change overall in temperature requires either recieving a lot of energy or expending a lot of energy. It is almost ocmical to see the step change in OHC graphs. The amount of energy required to either heat or cool the oceans that fast in that short of a time frame has not been observed. And it most certainly would have been observed.
  21. Given the Von Schuckmann and La Traon paper on 0-2000m, I will wait till there has been a full analysis of Argo before leaping to conclusions on that. I had been discussing the question of sealevel with local professor of surveying. He had been studying 100 year records for Australia and NZ, together with continuous GPS stations at some guages over last 15 years or so. Interesting questions. In short, there are many contributors to short term sea level change. He lacks confidence in the satellite reference frame being accurate enough for short term conclusions, preferring 50 year trends for tide gauge data and maybe 15 for satellite. I havent had time to look at the papers he has sent me yet.
  22. scaddenp: 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. We are not observing that. The amount of energy required for thermal expansion is huge to say the least. There has been no spike in energy, and it appears there has been a decrease in energy which is not being measured. There is something here that is being totally missed and I have no idea what it is.

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