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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 101 to 125 out of 322:

  1. daniel at 00:36 AM on 14 July, 2010 "The 1 sigma bounds are irrelevant Peter". This is not science, it is not recognisable statistics either. Irrelevant, or inconvenient? It fits the 1 sigma bounds where it is. It does not elsewhere.
  2. 20 Andrew Hobbs at 21:06 PM on 13 June, 2010 Thank you for your post. Especially in light of no one else elaborating on the statement made in "The Skeptical Argument," and that I've been trying to find something on that charge for a little while: ~ ~ ~ "Scientists from Flinders University, Adelaide, certainly DID NOT abandon the project. " "In 2003 the University decided to cease the operations of the National Tidal Facility Australia (NTFA). ... The operation was transferred to the Commonwealth Government effective from 1 January 2004." "It is possible to access their latest results on the Australian Bureau of Meteorology website at the web page for the South Pacific Sea Level and Climate Monitoring Project. " "These results support the general rate of global sea level rise noted elsewhere." ~ ~ ~ Beyond that, earlier a comment was made: "... my comments have been deemed inappropriate by a rather draconian comments policy." Well, I for one, found this back and forth discussion another wonderful (and educational) example of how science should be discussed. Too bad such a sight can't be found in the AGW Hoax blogosphere. My point is that I'm sure it is the "draconian comments policy" that makes such discussion possible so thank you John for sticking to your guns.
  3. What is the maximum possible sea level rise if all of the glaciers and ice sheets melted, and how much sea level rise can we get from thermal expansion? I read in "Global Warming FOR DUMMIES" that the maximum possible sea level rise from global warming is 650ft(200m) is this correct?
  4. Re: Karamanski (103) Not accounting for an additional rise due to an unknown level of thermal expansion, if it all goes at some unknown point in the future, Greenland contains enough water to raise sea levels by 7.2 meters while Antarctica (WAIS + EAIS) has enough to raise sea levels by 61.1 meters for a total of 68.3 meters (224 feet). Dunno where you got those figures (not cited in my powerpoint of the same name), but that total amount is approximately the vertical interval between the lowest of the sea levels during glacial max and that if all the ice melted. Perhaps that is what they meant. As far as thermal expansion, my understanding is that per each 1 degree C of ocean temperature rise will be accompanied by 1 meter sea level rise just from thermal expansion. Unless memory is deserting me. The Yooper
  5. Originally posted in the front-page article about Greenland ice loss. The moderator determined it was off-topic and that this would be the better place for the discussion. How is the short-term (last decade) accelerating land-ice loss (in Greenland and elsewhere) reconciled with sea level rise not accelerating? Does thermal expansion/contraction dominate over this time scale, is there too much error in the measurements, or is this truly something not clearly understood because of insufficient data like the energy budget? I guess the question is more broad in the sense that I wonder if the temperature, land-ice, and sea-level rates of change are fully reconcilable with available data.
    Response: [Daniel Bailey] Thank you for setting a positive example!
  6. PDT: I have no idea why sea level rise does not show an acceleration as a consecuence of accelerating melt in Greenland and Antartica. However, the University of Colorado data seems odd to me, because (to the delight of the folks at WUWT) shows instead a deceleration of sea level rise. I suggest to follow the CSIRO and AVISO data and graphs: http://www.cmar.csiro.au/sealevel/sl_hist_last_15.html http://www.aviso.oceanobs.com/en/news/ocean-indicators/mean-sea-level/products-images/index.html That show a nearly constant trend of aproximately 3.2 mm/yr unlike the University of Colorado (U. of C.) that show a deceleration and a lower mean (linear) trend: 3 mm/yr, that seems to coincide with the AVISO trend when Glacial Isostatic Adjustement (GIA) is not applied, so I suspect that the U. of C. do not apply GIA in their product. Note to the moderator: how can I post IMAGES and ACTIVE LINKS here at skepticalscience?
    Response: [Daniel Bailey] Try here. Remember to use the image width tag if the image width is more than 450. Use the Preview function to make sure everything looks right before posting. Thanks!
  7. So, is there simply no answer to my question (post 105), or is the question so undeserving as to not warrant a response? I didn't really find anything on a Google search. It seems like sea level should be predictable from temperature change and land-ice loss. Has someone looked at that? Perhaps it's the other way around, one could measure the average sea temperature by a combination of land-ice loss and sea level rise. Anyone?
  8. I believe the accepted term for the topic of my question is "sea level budget" and the first link given by Google for this is this one, from a website that claims higher atmospheric CO2 is a good thing for us. Seriously, the climate science community needs to figure out how to make sure the first links for searches on climate science are to actual science.
  9. Chemist1 - Glacial isostatic adjustment is a known issue, and sea level rise estimates are corrected for it. Your claims that sea level rise cannot be measured are unjustified; if you disagree, please provide references.
  10. #30 under One of the best climate change ads I've seen les at 07:47 AM on 21 March, 2011 I wasn't sure because the first data points on both are not the same as yours... That's because folks at University of Colorado at Boulders for some obscure reason have omitted the first three data points at the end of 1992 from the graphs, although it's included in the text files. If you give the comparative fit qualities, we can all judge whether a linear fit is not appropriate compared to your function... You miss the point. A linear fit is insufficient to raise alarm, it only implies a 27 cm rise by 2100 which is entirely manageable. For a disastrous multi-meter sea level rise you'd need acceleration but you simply don't have it.
  11. For a disastrous multi-meter sea level rise you'd need acceleration but you simply don't have it. What we would EXPECT is surely what models predict. Looking at say Vermeer 2009 I dont think we do expect to much acceleration yet. 2050 will be different.
  12. 110 - no I don't miss the point. You presented some new and significantly different numbers without details (the fitted functions, confidence etc.). You can't expect that to go unchallenged, surely. A challenge to which you are failing to rise.
  13. Well, no defence of your numbers. I think we can take them as false and without credibility.
  14. Jay - Googling "average ocean depth", as I noted earlier, provides the average depth of 3790 meters in the summary of the first link.
    Response:

    [DB] Fixed link.

  15. Jay, NSIDC says at least 70 meters. As others have pointed out, it was very easy to find. If you don't trust authority to do the calculation properly...a simplistic way to calculate it is to multiply the average depth of the ocean (3790m) by the ratio of the fraction of earths water crrently in land ice (0.02) vs seawater (0.97). You get about 70-80 m. It's a rounded estimate and doesn't account for thermal expansion, salinity effects on density, changes to shorelines etc, but it gets you in the ball park. It also says nothing about time scales of melting.
  16. Okay so that would be a 2% rise in average sea level, that is reasonable. I think Robert Laughlin's take on sea level is the most accurate, however. "the amount of water on the earth hasn’t changed significantly over geologic time, and that the rise and fall of the oceans is adequately accounted for by the waxing and waning of the polar ice sheets and slow changes in ocean basin volumes. The sea level has had a complex and interesting history, but it has never deviated more than 200 meters from its present value." Also "The last glacial melting, cross-dated at 15,000 years ago by the radiocarbon age of wood debris left by the glaciers as they retreated, occurred rapidly. The sea rose more than one centimeter per year for 10,000 years, then stopped. The extra heat required for this melting was 10 times the present energy consumption of civilization. The total melt­­water flow was the equivalent of two Amazons, or half the discharge of all the rivers in all the world." So we can conclude that our energy consumption is far too low to significantly impact sea levels.
  17. Dr. Jay >So we can conclude that our energy consumption is far too low to significantly impact sea levels. Your conclusion is invalid. The heat energy that drives global warming comes from the sun, not from human energy consumption. Humans emit CO2 which increases the amount of solar energy retained by the earth. The "waste heat" produced by humanity is indeed too small to have a significant effect on global temperatures, a topic that is covered in the waste heat post.
  18. @e Did you mean the waste heat is too small to have an impact on "global sea level"?
  19. Jay - That's what 'e' said. Note, however, that human energy use is 1% of the energy trapped by anthropogenic greenhouse gases - it's 2 orders of magnitude smaller. See the interminable waste heat thread for details. Hence the greenhouse forcing is 10x what you describe in your post, more than sufficient to be an issue. Nobody is predicting complete melt of the Antarctic ice caps, mind you. More appropriate comparisons are with peak Holocene or Eemian conditions: global temperatures ~2°C warmer, 4-6 meter higher sea levels, which would take quite some time to occur. And it looks like we're committing to an even higher temperature with AGW.
  20. @Dr. Jay, Sea level rise is caused by increasing global temperatures and ice melt (which itself is caused by increasing global temperatures), so my comment is transitively relevant to global sea levels.
  21. KR>Hence the greenhouse forcing is 10x what you describe in your post, more than sufficient to be an issue. Actually it's 100x more, sufficient indeed.
  22. e - I was discussing that in the light of Jay's claim that industrial energy was 1/10 that involved in the last peak interglacial sea levels, and that AGW provides energy 10x greater than that - 100x overall. Jay - Robert Laughlin's take on climate appears to be a mix of Climate's changed before and It's not bad. Both arguments are discussed here, and shown to be wrong, and Laughlin himself has been roundly criticized for his illogical stand on these matters. Personally, I would not rely on him as a climate expert.
    Response:

    [DB] Fixed text.

  23. The Chapter 5 Executive summary of the IPCCs AR4 Says: The oceans are warming. Over the period 1961 to 2003, global ocean temperature has risen by 0.1°C from the surface to a depth of 700 m.
    globmaritime.com Says: At temperature 15°C, and atmospheric pressure, the coefficient of thermal expansion is... 0.000214 per degree Celsius for average seawater.
    The National Climatic Data Center Says: Average annual sea surface temperature is 16.1°C
    engineeringtoolbox.com Has a nice Online Thermal Cubic Expansion Calculator: 700 meter column V0 - initial volume (m3, ft3, gallons ..) 0.000214 β - volumetric expansion coefficient (1/oC, 1/oF) 16.0°C t0 - initial temperature (oC, oF) 16.1°C t1 - final temperature (oC, oF) Which yields: Change in Volume - dv = 0.015m (column)
    From above 2003 minus 1961 equals 42 years and it follows that 0.015 m divided by 42 years equals 0.36 mm/yr
    Table 10.7 from the IPCC's AR4 Says: By 2100 we can expect thermal expansion to account for as much as 6.8 mm/yr.
    That is nearly 20 times the rate (calculated above) over the last 40 years or so.
    Colorado University Sea Level Research Group Says: The rate of sea level rise over recent years has been less than the long-term average believed to be due to the recent La Nina's.
    In other words, the rate of sea level rise has decreased in recent years due to lower temperatures. So, how likely is it that the current decreasing rate in sea level rise will do a turn around resulting in values represented in Table 10.7 from the IPCC's AR4?
  24. Steve, are you sure you're taking everything into account with this back-of-the-napkin calculation? Applying a simple thermal expansion formula to a global average affected by regional ENSO, large-scale circulation, and isostatic rebound issues is a sketchy proposition. Why not take a look at what the professionals are saying.
  25. Steve Case -"So, how likely is it that the current decreasing rate in sea level rise will do a turn around resulting in values represented in Table 10.7 from the IPCC's AR4?' What decreasing rate?. Do you mean short-term as in the last La Nina?

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