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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


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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: 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.

    [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.

    [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. 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 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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