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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 276 to 300 out of 322:

  1. [JH] Recommended supplemental reading:

    Does NASA Data Show That Global Warming Isn’t Causing a Sea Level Rise? by Alex Kasprak, Snopes, Aug 1, 2017

  2. I guess Manhattan must be elevating to actually show a decrease in sea level since 2010.  And certainly no acceleration in sea level rise for more than 150 years.

    https://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8518750

    Response:

    [PS] Precisely what point are you trying to make here from the basis of a single tide station? The relevance to the article is not clear.

  3. George @277 , the tide gauge records collated by NOAA, for The Battery, on Manhattan, show a 400 mm rise in sea level during the past 160 years.   (Strangely, the record shows a gap from about 1879 - 1893.)   As you say, the reference no. is 8518750.

    Mean sea level rise approx 2.8 mm per year, over that 160 years. 

    Possibly Manhattan Island is developing a strong tilt in recent times, with the northern end of the island lifiting high?   I must look more closely at the Empire State Building, to see if it appears out of plumb.  My previous impressions were that it was nowhere like as bad as that skyscraper in Pisa (fortunately).

  4. George,

    While there is no rise since 2010, there is a large rise since 2008.  The long term rise is clear.  Do you have a reason for selecting 2010 or was it just to cherry pick your claim?

    Have you ever seen the escalator?

    escalator

    Do you think you could make a similar graph from the tide guage in New York?  

  5. Here are a couple more around the U.S.
    https://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=9413450
    https://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8449130

    There is certainly no acceleration in sea level rise and in fact a drop in sea level since 2010.
    My belief is that there has been additional snow and ice buildup causing the drop in sea level.  

    "Cherry Pick since 2010"?  Eight years of opposing data is not enough to make you question your hypothesis?

    Response:

    [DB] Multiple comments using the same failed rhetoric are unhelpful.  The facts are, global sea levels have risen since 2010.  Attempting to find a few areas where sea levels show different results is like using the existence of smaller waves at the oceanside following larger ones in an attempt to show that the tide has somehow stopped coming in.  It's a fallacy.

    Altimetric SLR

    We also know which of the components of SLR contribute to it most (mass increases vs thermal expansion):

    Mass increases

    And, from Hsu and Velicogna 2017, which areas will see more resultant SLR than others:

    SLR Fingerprints

    No amount of effusive prestidigitation (handwaving) can make that go away:

    Fake-skeptic SLR

    Please note that posting comments here at SkS is a privilege, not a right.  This privilege can be rescinded if the posting individual treats adherence to the Comments Policy as optional, rather than the mandatory condition of participating in this online forum.

    Please take the time to review the policy and ensure future comments are in full compliance with it.  Thanks for your understanding and compliance in this matter.

  6. George,

    Your first link (I cannot get the graph to copy here) is from Monterey Bay.  While it has a lower long range trend, the trend from 2010-present is very high, the opposite of your claim.  Your second graph, from Nantucket, shows a high long range trend but lower from 2010-present.  You must konw that individual locations have high noise and also land height change issues.  If that is the best you can find in the entire USA that indicates that sea level is rising rapidly.

    If you get some guages from Alaska they will actually show a long term decrease in sea level since there is strong isostatic lift (increase in land height) due to the melting of the glaciers from the ice age.  That does not mean the sea level is not rising, just that the land is rising faster.

  7. https://www.youtube.com/watch?v=EhW-B2udhQw

    7:00 no sea level rise in La Jolla, CA
    12:00 Topex/Poseidon Satellite measurements are crude
    12:43 ENVISAT, European satellite with higher resolution, much lower sea level rise, decrease since 2010

    How do you explain Manhattan?  Has the land elevated there?

    https://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8518750

    Response:

    [Rob P] - Not surprisingly, sea level at New York has risen over the long-term. In the short-term, fluctuations in the ocean circulation are having an effect. Now that ice mass loss from the Greenland ice sheet is fully underway it will be interesting to see how that alters sea level rise along the North American east coast. There's a recent paper on the subject here: Causes of accelerating sea level on the East Coast of North America (Davis & Vinogradova [2017])

  8. George,

    Manhattan is a very noisy record.  There are many short periods where it appears to not rise while the long term (actual) trend is increasing.  Since land elevation is a long term issue that would primarily afect the long term trend and not the noise.  Tamino has a lot of sea level analysis where he explains the statistics.

    The noise is affected by the weather and by issues like El Nino/La Nina.  Longer term processes like the Arctic ocellation would also affect the noise.

  9. George,

    I noticed that you did not link the graph for La Jolla.  Here it is.  Long term trend 2.17 mm/yr, not no sea level rise.  Read some of Tamino's stuf and you will be better able to determine if there is a trend from a graph.

  10. FFGeorge,

    The ENVISAT satalite has been shut down since April 2012.  How can you possibly suggest that it has more accurate data for the period 2010-2017 when it has not collected data for most of that time?  The video you linked is unreliable.

    You are choosing a time period that is too short to measure the sea level rise.  You are focusing on the noise and not the signal.

    Find a reliable source of information.  Read Tamino.

  11. I started at about post #7 with sea level rising at 2.46 mm per year. Eight years later, that may be 3 mm per year (3.46 +/- 0.4) or so ... so about 0.1 in per year ... less than a foot by 2100.

    California has accepted a new building code, expecting 10 feet by 2100.

    Does this make any sense? Should we all be investing in Dutch dike companies?

    Response:

    [DB] And yet, per Nerem et al 2018:

    "Global sea level rise is not cruising along at a steady 3 mm per year, it's accelerating a little every year, like a driver merging onto a highway, according to a powerful new assessment led by CIRES Fellow Steve Nerem. He and his colleagues harnessed 25 years of satellite data to calculate that the rate is increasing by about 0.08 mm/year every year—which could mean an annual rate of sea level rise of 10 mm/year, or even more, by 2100."

    "This acceleration, driven mainly by accelerated melting in Greenland and Antarctica, has the potential to double the total sea level rise by 2100 as compared to projections that assume a constant rate—to more than 60 cm instead of about 30." said Nerem, who is also a professor of Aerospace Engineering Sciences at the University of Colorado Boulder. "And this is almost certainly a conservative estimate," he added. "Our extrapolation assumes that sea level continues to change in the future as it has over the last 25 years. Given the large changes we are seeing in the ice sheets today, that's not likely."

    And:

    "the observed acceleration will more than double the amount of sea-level rise by 2100 compared with the current rate of sea-level rise continuing unchanged. This projection of future sea-level rise is based only on the satellite-observed changes over the last 25 y, assuming that sea level changes similarly in the future. If sea level begins changing more rapidly, for example due to rapid changes in ice sheet dynamics, then this simple extrapolation will likely represent a conservative lower bound on future sea-level change."

    SLR acceleration

  12. Chez Provence: You wrote:

    California has accepted a new building code, expecting 10 feet by 2100.

    Please document and link to the source of this claim.

  13. w6g-9-2018-exhibits.pdf

    prepare-for-10-feet-of-sea-level-rise-california-commission-tells-coastal-cities/

  14. Thanks for the Nerem reference. This may be a local politics thing ... In the draft report of the California Coastal Commission, they acknowledged the 800mm rise shown by, Nerem ... added their own sense, suggesting that the most likely will be 1.2 m, worst case 2 m ... and proposed regulation for 3 m. Starting point is fig 4 on page 46 of the w6g reference above.

  15. ChezProvence: Thank you for providing the documentation per my request.

    The headline of the Scientiic American article:

    Prepare for 10 Feet of Sea Level Rise, California Commission Tells Coastal Cities 

    The sub-headline of the article qualifies the headline: 

    Though an extreme scenario, it should be factored in to coastal infrastructure planning, new guidance suggests

    That is quite different than your statement:

    California has accepted a new building code, expecting 10 feet by 2100.

  16. ChezProvence: Furthermore, the head-line and sub-headline of the SA article do not comport with the facts set forth in the first three paragraphs of the article:

    California coastal cities should be prepared for the possibility that oceans will rise more than 10 feet by 2100 and submerge parts of beach towns, the state Coastal Commission warns in new draft guidance.

    The powerful agency, which oversees most development along 1,100 miles of coast, will consider approving the guidance this fall. A staff report recommending the changes was released last week.

    Earlier commission guidance put top sea-level rise at 6 feet by 2100. But according to the new report, there’s the “potential for rapid ice loss to result in an extreme scenario of 10.2 feet of sea level rise” by the end of the century.

    As Yogi Berra was wont to say, "It ain't over until the fat lady sings!"

  17. I encounter some extreme fringe RWNJ deniers on various investor sites. They literally don't care if the West Coast or Northeast have issues with SLR "because Democrats live there" (no, I'm not kidding). So I would like to put it in terms that they might care about. At approximately what year does SLR become "a problem" for Florida (that big swing state needed to win elections)? The Houston Ship Channel (which would be supremely ironic)? Has there been any science done at that kind of level?

  18. I think Miami is already struggling with sealevel rise. Cant help with Houston Ship Channel sorry.

  19. AFT: Try https://sealevelrise.org/states/florida 

  20. The deniers are saying the satellite equipment that can only measure distances in centimeters cannot produce sea level measurements in millimeters. Can someone address this or provide a link where this is addressed. I can’t find anything on this. Thanks.

  21. Hank: Sea level is a population parameter that is estimated by combining multiple sample measurements of it. The Law of Large Numbers explains that the precision of the combined estimate increases with the number of sample measurements. Look up Law of Large Numbers in a textbook or in Wikipedia, then prove it yourself using a spreadsheet. There is a tutorial on satellite measurement of sea level linked right above the image at the bottom of This NOAA page, though currently it does not work, probably due to the government shutdown.

  22. Thanks Tom. As an engineer I’m familiar with the Law of Large Numbers and thought that might be at least part of the explanation. I look forward to reading the tutorial if the government ever opens.

    Response:

    [DB] The Internet Archive has a backup of the tutorial page, here.

  23. Just what I was looking for. Thank you.

  24. Do an Earth mean sea level has any real meaning ?

    https://www.psmsl.org/products/trends/

    Relative Sea Level Trends

    Response:

    [DB] As a professional nautical cartographer, I can assure you that mean sea level has a concrete meaning.  If you have an actual question, please be more specific.

    Reduced image width (keep image widths below 500 to avoid breaking page formatting).

  25. Sealevel rise is not even across the globe.

    Source:

    Note that sealevel measured from satellite altimetry is based on height change with respect to the reference ellipsoid, avoiding the issue of subsidence or tectonics which plague tide guages (though both measurements systems yield comparable results).

    Sealevels are falling close to melting ice thanks to reduced gravitional attraction and isostatic rebound. See here for more detailed explanation.

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