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How much will sea levels rise in the 21st Century?

What the science says...

Select a level... Basic Intermediate

Sea levels are rising faster now than in the previous century, and could rise between 50cm to 1.5 metres by 2100

Climate Myth...

Sea level rise predictions are exaggerated

"Professor Niklas Mörner, who has been studying sea level for a third of a century, says it is physically impossible for sea level to rise at much above its present rate, and he expects 4-8 inches of sea level rise this century, if anything rather below the rate of increase in the last century. In the 11,400 years since the end of the last Ice Age, sea level has risen at an average of 4 feet/century, though it is now rising much more slowly because very nearly all of the land-based ice that is at low enough latitudes and altitudes to melt has long since gone." (Christopher Monckton)

Measuring Sea Levels

Sea levels are rising due to thermal expansion and melting of land-based ice. Global warming is causing the oceans to absorb a lot of extra heat (up to 90%). This makes the volume of water expand, and sea levels rise. The Greenland and Antarctic ice caps, and many of the world’s glaciers, are all slowly melting. The runoff feeds into rivers and directly into the oceans. This too adds to sea levels.

Prior to the use of satellite systems, measurements were taken using tide-gauges, devices that measure the height of a water level relative to a fixed point on land. Global estimates of sea level rise were subject to substantial differences in measurement from different parts of the world.

Sea levels change all the time. They are affected by seasons, astronomical tides, storm surges, currents and density, among other influences. Tidal gauges reflect these short term influences, introducing a large margin of error.

The IPCC Fourth Assessment Report described studies that estimated sea level rise for the 20th century between 0.5 and 3.0 mm a year. The most likely range, according to the IPCC, was between 1.0 and 2.0 mm a year.

Satellite altimetry since 1993 provides a more accurate measure of global sea level rise. Three different satellites take measurements: TOPEX/Poseidon (launched 1992), Jason-1 (launched 2001) and Jason-2 (launched 2008).

Figure 1: Source - CSIRO

The IPCC projections are derived from climate models. Using both tide gauge and satellite data, we can see that sea levels are rising. Unfortunately, sea level rise is already tracking the worst-case projections, as this graph shows:  


Figure 2: Sea level change. Tide gauge data are indicated in red and satellite data in blue. The grey band shows the projections of the IPCC Third Assessment report (Allison et al. 2009).

In fact, the climate models underestimated the rate of sea level rise because the rapid melting of the ice sheets and glaciers was not incorporated in the last IPCC report. (It was left out because the data were not considered sufficiently robust).

Damaging Potential

Rising sea levels are widely considered to be the greatest threat posed by climate change. They threaten low-lying countries with inundation, forcing inhabitants to migrate.  Coastal cities and ports could be flooded, as could cities sited near tidal estuaries, like London. Many nuclear installations are built by the sea so they can use sea water for cooling.

The potential for sea level rise is enormous. This is because the ice caps - Greenland and Antarctic - contain huge amounts of fresh water - around 70% of all the freshwater on Earth. Estimates suggest that if the Greenland ice sheet was to melt away to nothing, sea levels would rise around 6 metres. To put that a different way, a loss of just one per cent of the Greenland ice cap would result in a sea level rise of 6cm. 

If the West Antarctic Ice Sheet (WAIS) were to melt, this would add around 6 metres to sea levels. If the East Antarctic Ice Sheet (EAIS) were to melt as well, seas would rise by around 70 metres.

In a process that is accelerating, all three ice caps are losing mass. While nobody is suggesting any of the ice caps will melt away to nothing, only a small amount of melting would cause great problems.

A 1% loss of ice from these three sources would produce a likely increase in sea levels of around 76cm. With the thermal expansion implied by such melting, and contributions from melting glaciers, the oceans would actually rise far more.

Predictions for future sea levels

Future sea level rises depend on a number of factors. The amount of CO2 emitted will determine how much global warming takes place. The amount of ice that melts will vary according to the amount of global warming. The same is true of thermal expansion.

Previous estimates of sea level rise have been based on a set of possible outcomes called emissions scenarios. These theoretical scenarios range from emissions which fall very quickly, to emissions that continue to rise even faster than they have already. Scientists then calculate possible outcomes for each scenario.

In the next IPCC report (AR5), due in 2014, a new method has been used. Emission scenarios have been replaced by Representative Concentration Pathways (RCP). Four trajectories were chosen, based not on emissions, but possible greenhouse gas concentrations in the year 2100. From the concentrations, the RCPs project a ‘forcing’ for each pathway (the amount of warming); 2.6, 4.5, 6.0, and 8.5 Watts per metre squared. Each pathway is named after it’s forcing e.g. RCP4.5. The lowest emission scenario is also referred to as RPC3PD, because it posits a peak warming of 3 w/mby 2070 (~490 ppm CO2 and equivalents), and a reduction to 2.6 w/m2 by 2100. (PD stands for Peak/Decline). 

A draft version of the next report from the IPCC (AR5), due for publication in 2014, was recently leaked. Although the information is subject to change, the draft report says sea levels are likely to rise by between 29 and 82 centimeters by the end of the century, (compared to 18-59 centimeters in the 2007 report).

Other recent studies have projected comparable sea level increases. Jevrejeva (2011) for example modelled sea level rise using RPC scenarios. This table shows best and worst cases (RPC3PD and RCP8.5), with two in between. The figures for each projection are listed in this table:

Table 1: Projected sea level rise (m) by 2100 for the RCP scenarios. Results presented as median, upper (95% confidence interval) and lower (5% confidence interval) limits, calculated from 2,000,000 model runs. Sea level rise is given relative the period 1980–2000. (Jevrejeva 2011)

Another study (Rahmstorf 2011) obtained much the same results:

Figure 4: Sea level hindcasts and projections for different models calibrated with different temperature and sea level data. The error bars on the right indicate 90% confidence intervals (5–95 percentile, using the GISS temperature dataset); for the proxy-based projection the uncertainty is as presented in Kemp et al., 2011. (Rahmstorf 2011)

What's in the pipeline? 

The 'pipeline' is a term used to describe the slow reaction of the oceans to heating (inertia). Even if we were to stop emitting greenhouse gases tomorrow, the oceans would continue to rise, driven by the heat already stored. (90% of all the sun's energy falling on the surface of Earth is absorbed by the oceans as heat). This sea level rise is said to be 'in the pipeline'.

A paper published in PNAS - Levermann (2013) - has found that greenhouse gases emitted today will cause sea levels to rise for several centuries. For every degree of warming, sea levels will rise by more than 2 meters in the next few centuries. The Earth's temperature has already risen 0.8 degrees C over pre-industrial temperatures. 

Jevrejeva (2011) also found increased rates of sea level rise, even if emissions were to stabilise at 490 ppm by 2070 following the scenario in RPC3PD (RPC2.6):

Table 2: Projected sea level rise (m) by 2500 for the RCP scenarios. Results presented as median, upper (95% confidence interval) and lower (5% confidence interval) limits, calculated from 2,000,000 runs of the model. Values of sea level rise are given relative the period 1980–2000.


Based on the new mid-range IPCC  RCP4.5 scenario - around 650 ppm CO2 and equivalents producing a forcing of approximately 4.5 watts/metre - the most likely sea level rise by 2100 is betweem 80cm and 1 metre.  Longer term, sea levels will continue to rise even after emissions have been reduced or eliminated.

Basic rebuttal written by GPWayne

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 12 July 2015 by MichaelK. 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.


1  2  3  Next

Comments 1 to 50 out of 102:

  1. I have been looking for more information in this area as most sea level graphs only go back 15,000 years to the end of the last ice age. 125,000 years ago the earth had 300ppm of CO2 and a temperature 5c warmer than now and sea levels rose 6 to 9 meters. We now have CO2 at 390ppm and rising so what can we expect from sea levels? 6 to 9 meters would be very modest. There needs to be more information on this. A sea level rise of one meter wipes out Holland, London, Florida, and many other industrial areas so we need to know how soon.
  2. Not to blow my own horn, but there's a fairly extended (some say positively puffy) article on London and rising sea level here: Grappling With Change: London and the River Thames From all accounts London will cope w/1m, it's the upside of uncertainty in projections that inspires consternation. Other places are a different story w/1m. The common thread is that of getting in line for lots of money, early.
  3. Has there been a response to the issues raised by Dr. Nils-Axel Mörner? He does seem to be a very experienced expert on sea levels. Am interested in evaluating his comments on sea level inferred from earth's rotation rate and other approaches. He seems quite convinced that the claims of AGW vis a vis sea levels are spurious. Feedback welcome. The interview is at
  4. #3: "evaluating his comments ... " An interview that starts off with "there's no one who's beaten me" didn't do much for his credibility. When I got to "if the radius of the Earth increases, because sea level is rising, then immediately the Earth’s rate of rotation would slow down", I lost interest. Assuming the earth to be a uniform sphere (its not) one meter of additional radius would increase the earth's rotational inertia by a factor of 1.00000031, slowing the rotation rate in proportion. But the mass of water that moves outwards is much much less than the mass of rock that stays put, so the effect would be far less. His use of the familiar ice skater analogy is hardly appropriate in this context: rather than extending her arms changing her rotation rate, this is more like a drop of water on the tip of her nose. Then there's Wikipedia: Mörner has written a number of works claiming to provide theoretical support for dowsing. He was elected "Deceiver of the year" by Föreningen Vetenskap och Folkbildning in 1995 for "organizing university courses about dowsing...". As I said, I lost interest.
  5. Zoltan @ 3 -"He does seem to be a very experienced expert on sea levels." And water divining too. Which doesn't really say much for his credibility either. In fact he wrote some garbled paper trying to scientifically provide evidence for water divining, thereby effectively ending all credibility. But why rely on the word of one rather confused man, when we have satellite altimetry data and tidal gauges?:


    [DB] Updated graphic from this url:

  6. Sea level rise has historically been at 2mm/year. Has that changed?
  7. Harry Seaward, have a look at the graph immediately above, in Rob Painting's post, and you will see the current rate shown. However, looking at the graph today, the rate has gone up to 3.1mm/yr. (If, like me, you get a mainly blank page at that link, just scroll down)
  8. The difference between the two graphs is actually due to the 'Inverse Barometer' being applied or not.
  9. Harry, if you check Rob's graph (comment 5) you will see that the rate since the 90's (when satellite measurements of sea level become available) is around 3mm/year. So the indications are that the rate of sea level rise has increased from the 20th century average of 1.6mm/year. Some of the world experts on sea level rise are Australian scientists at CSIRO, they have good webpage with some good information on SLR here.
  10. I'm looking at a TOPEX/Poseidon Jason-1/2 (CSIRO)chart showing 200 mm of rising ocean level over 130 years. This equates to a 1.54 mm per year rise. There is not much of an uptick in the curve corresponding to the increased levels of CO2. Let me check Rob's graph. Yes, it now shows 3.0 mm rate of rise. Almost double. Now I will go back to the latest CSIRO to see if they have similar data. Darm, you guys are making a believer out of me yet!
  11. Hey, At first, I was a GW skeptic, but then in the past year or so, I've really begun to study this data, and I'm convinced now that not only is GW real, but it's probably worse that what has been predicted. I'll just link to a few obvious sources for paraphrase and reference of data. Ok, anyway, what I noticed several months back is the simple fact that each year you have a net melting, whether sea ice or land-locked ice caps, it would be obvious that the change in albedo of that area of "net melted ice" should "pay" for it's own melting within a certain number of years. I assumed it would be an exponential, and was playing around with a bunch of different numbers for the exponential growth, but I didn't know exactly what numbers to use, until a few weeks ago. Suffice it to say that one of the articles I linked to above shows how the five year average rate of melting of ice in greenland is doubled in ten years. As it turns out, just recently, it was discovered that the rate has actually quadrupled in about 10 years! Well, what curve does that follow? And is it related to the PIOMAS data? Well, yes it is! Greenland and Sea Ice are treated as two seperate entities, but they follow the exact same curve: A power series. IN the article above, "Lou" mentions what appears to be a linear progression for average annual net melting of Greenland as: 200, 220, 240, 260, 280. But these were not measurements, these were his rough estimates based on 5 year total loss data, going all the way back to 1996 @ 96km^3 to 280km^3 in 2008. Well, what I would suggest is this is not a linear function. The numbers appear linear because he "reconstructed" the annual rates by just assuming it's increasing, but the increase isn't linear, it's exponential. In 12 years it increase from 96 to 280(or 300), but assuming this is exponential increase, then we have: 280/96 = 2.916 12th root of 2.916 = 1.0933 we have the form: c*n^x x = time (delta) in years. n = 1.0933 c = 96 (initial melt rate) Now if we actually plot these numbers for whole number X, starting at 0: 96, 105, 115, 125, 137, 150, 163, 179, 195, 214, 234, 256, 279, 300,..., c*n^x.... is very close to linear: 100, 120,140,160,180,200,220,240,260,280,300... You can see how if you were trying to "post-dict" this from field observations with normal noise in raw data, you might mistake this for a linear relationship due to errors in instrumentation, rounding, etc. But what you find with the Piomas sea ice data is the same. If you take the 5 year running average of the data (the 10 year running average is too "back heavy" to be useful,) and starting from the last time there was a volcanic rebound in the 5 year average data: 5 year running average of Piomas volumetric sea ice data, starting with 1990: 90 14.86 91 14.38 92 14.32 93 13.78 94 13.58 95 13.08 96 13.12 0.04+ 97 12.78 98 12.64 99 12.10 00 12.06 01 11.78 02 11.28 03 11.02 04 10.82 05 10.46 06 9.82 07 8.96 08 8.34 09 7.74 10 6.78 11 5.84 Now, this is no big deal, its an exponential, which they calculated on the site, but the kicker here is that the 5 year average is itself "back heavy" by about 3 years. If you put this data in a graphing calculator and do a regression, you'll find that the five year running average is zero within 8 years. (I interpret negative numbers on this curve after the "0" as additional net losses to Greenland.) But what I noticed is you can smooth out the raw data from Greenland and the Sea Ice by simply noticing that they are the same thing, and adding the net losses together. The average net annual loss in sea ice in the past 5 years was: 9000 - 4300 = 4700 4700/5 = 940km^3 The net annual loss from Greenland is currently "somewhere" around 300km^3. 940 +300 = 1200km^3 annual loss. If you then assume the entire ice mass is following about the same curve, you can start with 1200 as the coefficient, c, above, to run a series to see the rate of melting. After all, the cumulative energy which is currently going into melting Sea Ice will have to go "somewhere" once the Sea Ice is melted. The obvious place is the ice on Greenland land mass... Since I know from the data that the exponent is certainly somewhere between 1.072 and 1.15, you can calculate the minimum and maximum times of Arctic Sea Ice melt (5 to 8 years,) and the minimum and maximum times of Greenland meltdown... Yes, I've done this, and God help us all, it's much faster than anyone publicly claims. NOw to show how well this works predictively, we can take the piomass data and pick two "good", adjacent data points which are not corrupted by the volcanic rebound peaks (or alternatively pick two adjacent 5 year running averages...) Take the difference between 86 and 87: 15.9-15.2 = 0.700 (thousands) Now, let's pick an exponential, say 1.15, a big one, and project the curve forwards. 2011 - 1987 = 24 years -0.700 * 1.15^24 = - 20.03 Well, you say that's too much? Well, not hardly, we have to add back the volcanic rebounds of years following major volcanoes: 86 1.4 (columbia) 91 1.4 Pinatubo 94 1.4 (unknownst ot me) 96 2.5 (Monsurat) 01 1.2 Hekla 07 0.6 Furnas (I think) Total: 8.5 Now -20 + 8.5 = -11.5 And of course, This is statistically close to the real data set's end: 15.9 -11.5 = 4.4 1986 minus 1.15 exponential projection to 2011, and adjusted for volcanic winter rebounds... Very close to the actual 2010 and 2011 data of 4.4 and 4.3 respectively... Therefore, 1.15 is probably the correct exponent when you factor out volcanism, but the real exponent with volcanism is a bit lower than that... This suggest Greenland is melting much, much faster than anyone publicly claims, as in possible total meltdown within the century, and that is NOT an exaggeration... To top it all off, World population growth is 1.1% per year, and then you figure all the countries modernizing, the net CO2 production will probably increase at a rate of about 22% per decade for at least the next 2 or 3 decades...Which gives something link another 90PPM CO2 by 2040, or around +57PPM by 2030...
  12. 11, Wade, Hansen argued your case in Paleoclimate Implications for Human-Made Climate Change (2011). The bulk of the paper tries to compare current events to the last time this happened (although over much longer time frames) in the Cenozoic, Holocene and Pliocene, when sea levels rose 15m to 25m. You would be most interested in section 6, however, on sea levels, where he argues that the increase is probably not linear, but instead with a potential doubling every ten years, with all of the nasty implications that you yourself have tuned into.
  13. Now remember, I'm not an expert and don't claim to be. I'm just johnny come lately looking at some data and stuff... Now Sea level rise from 1995 to 2005 was around 30mm to 40mm, depending on who's data you believe, and 20CM in the last several decades of recorded history. Thermal expansion of water suggests we should get about 7cm of sea level rise per degree celsius of temperature increase of the ENTIRE HYDROSPHERE. We have it that Sea Surface Temperatures average has increased by about 0.9...but that is just the SST, that is not the average of the entire water collumn... Which is what is misleading about this. The oceans do not top heat very well. The majority of the depths of the oceans is in total darkness, and most of the heat concentrates near the surface, sort of like your swimming pool, the top few inches are hot, but the lower levels are cooler. So in reality, almost no thermal expansion actually happens unless you heat the entire water collumn by an average of 1C, but to do that, you'd really need to heat the surface temps by an average of about 2C or 3C, if not more than that, to make up for the fact hot water doesn't mix well in the deep oceans. At any rate, the amount of heat required to heat the hydrosphere by the average 1C to cause 7CM of thermal expansion (as vertical sea level rise) is 4200 * 1.4*E21 Joules. This is equal to 391 days worth of the entire solar constant, if all energy went to nothing other than raising the temperature of water, which is completely ridiculous and we obviously know isnt happening. Anyway, by the time you take this into consideration, and SST has only risen about 0.9C average in the past century, then thermal expansion is probably no more than like 3cm or 4cm, but whatever. Let's give them 7cm from thermal expansions, just for the sake of argument...that's still leaves about 13cm from melting glaciers and ice caps during the modern records, and what? At least 20mm to 30mm in the past 10 years from melting Greenland and the West Antarctic sheets alone... If I calculate that out based on approximate surface of the ocean, I get a volume of 7.6485E12 meters cubed. This is 7648.6 kilometers cubed worth of ice melted in the past 10 years. Keep in mind, I'm just using "round" anecdotal numbers. Sn = 120* sum(1 + 1.1 + 1.1^2 + 1.1^3 + ... ... + 1.1^n) 120 being about the "known" annual net melting of 2001... I got a total, using round numbers, of 2100. Ok, well, admittedly, that's only around 1/4th of the total we need, however, we didn't consider Antarctica is probably melting at about the same rate, and we didn't consider other ice melting and snow packs melting earlier, and things of that nature. If you double it to make up for Antarctica probably melting similarly, that gives around 4200. Then double it again to make up for the fact field researchers and satellites may be missing some of the action when looking directly at the glaciers, (but the sea levels catch all whether or not man does).... So I explained at least half the Sea level rise of the past decade as definitely being from "known" ice cap melt in Greenland and Antarctica, and assume field researchers and satellite interpretations have missed as much as half of the losses.... Even if I'm off by 50% one way, or 100% the other way, it only makes a 5 to 10 year difference in the long term projection of when Greenland totally melts... At any rate, it shows that the Sea level rise data relates very, very well, almost exactly 1 to 1 with then measured melting rates of Greenland over the past 10 to 20 years....
  14. Sea level is rising. But rising at a fairly constant rate: And we should remember that during the Holocene Climatic Optimum, Greenland encountered significantly more summer sunshine for thousands of years around six thousand years ago, but this did not effect sea level:

    [DB] Note: This comment was moved from the Climate and Sea Level: An Emerging Hockey Stick thread to this one.

  15. It is clear in the above post's graphs and elsewhere, sea level rise has been accelerating through the past 100 years - I presume that ClimateWatcher's first graph, covering just 23 tide records, is an unrepresentative sample. The thrid graphic presented by ClimateWatcher is, to me, one of the scariest graphs in climate science, but I suspect ClimateWatcher does not realise why. It shows Meltwater Pulse 1A, a sea level rise of about 20m in <~500 years, which happened abruptly at some point during the melt of the last great ice sheets (though two great ice sheets remain). Thus the graph shows what is possible when you begin to melt a big ice sheet - sudden pulses of accelerated sea level rise. There was little warning as to the onset of the Pulse 1A, no gradual ramping up to it. Of course, something like that might not happen this time, or it might be thousands of years down the line. But the climate forcing this time is much bigger, and who'd like to deal with a sea level rise rate of >~60mm/yr? Wetsuit fitting sessions for St Mark, Galileo, the Statue of Liberty, the Old Course and anything else within a short distance of the coast? Or invest in a sea wall manufacturing company...
  16. As I understand it the Greenland Ice Sheet is unlikely to collapse because it is surrounded by coastal mountains. The Antarctic sheets are however a different story.
  17. Greenland inner plateau is high as well. However, you dont need to melt all of it to get very wet.
  18. The GIS is drained very effectively by many marine-terminating ice-streams which penetrate into the heart of the sheet. Thus, decadal doublings of mass loss which can raise global sea levels by several meters per century have been observed in the paleo record. So even if the GIS takes several centuries to largely collapse, the ramifications of the collapse will still be felt this century. By us, our descendants and our civilization. The West Antarctic Ice Sheet (WAIS) is another story...
  19. CW#14:"Greenland encountered significantly more summer sunshine for thousands of years around six thousand years ago, but this did not effect sea level:" Excellent point! We're seeing more melting now than we did 6kya, yet (according to your unsubstantiated statement) we're now seeing less sunshine. Wonder what must be different now compared to then. Could it be that there's something in our atmosphere now that is keeping things warmer? Something that wasn't present in as large a concentration during 6kya?
  20. Mods: Rob Painting's graphic @ 5 must have been moved. When I try to display it, I see "The requested URL /files/current/sl_global.jpg was not found on this server." On topic, am I right in thinking that the rate of melt of the ice sheets will increase as they lose mass: ie the more they melt, the faster they melt? Something about mass relative to surface area, if I recall my high-school physics from 45 years ago.

    [DB] Graphic updated.

  21. I keep reading about the comfortable 2m upper boundary of SLR this century, but can't shake the images from Greenland of roaring rivers discharging meltwater this past summer. With the fantastic shrinkage in arctic sea ice volume, and this past year loss of area, I'd be interested in seeing a followup post on the prospects for nonlinear SLR. I got interested in this when searching for comments on Pfeffer's kinematic constraints paper from 2008, and stumbled onto this excellent blog post: Would be interested in the SkepSci crew's take on those questions.
  22. So, you have a prediction for sea level rise of between 750mm and 2,000mm, but have observed rates of 3.2 mm/yr.  100 yrs X 3.2 mm/yr = 320 mm.  So, essentially, you are predicting a substantial increase in the rate of rise.Looking at the graph of sea level rise for years 1880-2000,there does not seem to be much chance of your prediction coming true. 

    A gradual, steady increase from 3.2 to 11.8 mm/yr by 2100 would give you an increase of 750 mm after 100 years, but it would take a steady increase to 36.8 mm/yr by 2100 to give you a 2 M rise.  I realize you are not advocating for a linear increase, but the math is simpler and the principle remains the same.


    Bottom line, I don't see any evidence that these increases are occurring, so I don't see the predictions happenning.

  23. Kevin @22:

    Um, you did look at figure 2, that shows the rate of change increasing? Tamino's blog also has a recent post discussing some of this. And you realize how the rate of increase is going to depend on both warming of the oceans and increased loss of land ice, and future predictions of this don't depend on the past trend alone?

    First, you ignore the fact that the rate of increase has gone up over the last hundred years, then you do a linear extrapolation, then you admit that a linear extrapolation is not appropriate, but then you claim that the principle is the same and go ahead and do it anyway, because "the math is simpler"????

    Bottom line: you don't see any evidence because you're working so hard not to see it.

  24. Kevin @22, unless serious efforts to reduce carbon emissions are in place soon, the temperature difference between the end of this century and now will be approximately that between the coldest period of the Last Glacial Maximum and the Holocene average.  That temperature difference was enough to cause a 100 meter rise in sea level in 8,000 years, the equivalent of a 12.5 mm per year rise.  Given that, a rise of  0.785 meters (increase of annual rate to average rate of deglaciation over the century), or 1 meter (increase to deglaciation rate over fifty years, and constant thereafter) are likely.

    Given that the Earth warmed gradually after the LGM so the actual differential in temperature during the last deglaciation was less than what we will experience, and given that periods of much faster melting occurred durring the last deglaciation, sea level rises of 2 meters are a distinct possibility.

  25. I would agree with the Post 14 statement that the rate of rise - using a consistent measurement method - is constant. What tidal guage data set/type, or satelite data, do give different estimates, but none appear to show a change in rate. Can't take one data set in C and then go to F and say you have a temp acceleration, as an example of the same..

  26. Elsewhere wideEyedPupil comments:

    "Interested in comment from scientists on the Media watch story "AN ALARMING STORY" on 10 March about sea level rise, describing reportage of a 6 metre sea-level rise as alramist because they omitted the 4014 prediction-come-trueth date."

    The Media Watch (ABC, Australia) show has several problems, but arguably that is not one of them.  As can be seen from the main post above, expected sea level rises by the end of this century vary from 0.57 to 1.1 meters, depending on the scenario, with confidence intervals of 0.81 to 1.65 meters for the warmest scenario (table 1).  Those values are from a single study, and are higher than the IPCC values, who give a likely range of 0.45 - 0.82 meters for the warmest scenario by 2081-2100.  That is, its upper 66% confidence range almost coincides with the lower 95% confidence range of the study above.  I have heard several times that scientist making emperical projections of sea level rise think the IPCC relied to heavilly on models, and gave too low a value, but only a few expect sea level rises above 2 meters as even an upper bound.  Those few (best typified by Hansen), argue not that very high sea level rises are likely, but that they are possible, and sufficiently probable that they should be taken into account in establishing climate policy.  For what it is worth, I disagree with those very few, but several SkS regulars agree with them.

    Given that background, it is at minimum careless sensationalism to not mention the timescale involved, particularly given that a more or less specific time was given the the paper being reported on.

    Having said that, the Media Watch article is rife with inaccuracies itself.  To start with (and most germaine), the two thousand year interval in the study was chosen as a period in which equilibrium will have been reached.  That means they are predicting the sea level rise will be reached by 4014 AD, but do not specify that it will not be reached before than.  Potentially much before them.  In fact, while I consider it unlikely that the full sea level rise will be reached by 2100, it is certainly possible that it could be reached by 2500, and probable that it will reached by 3000 AD.  Indeed, technically the article does not preclude Hansen's worst fears being realized, and the full sea level rise being reached in as little as 150 to 200 years.  So, if leaving out the date is careless sensationalism, not specifying that the paper is stating the latest possible date for  the realization of sea level rise must be considered careless soft pedalling of a real threat.

    Even worse, is Media Watch's describing a 6.9 Meter rise in Sea Level as "a worst case scenario".  In fact, the paper in question mentions the number 6.9 exactly once.  In table 1 it shows as the median (not worst case) percentage of the current population displaced by sea level rise with a temperature of 3 C (again, not the worst case examined).  So it is neither a worst case, nor even a value for sea level rise.

    The actual values for sea level rise used in the paper comes from another paper from the same authors plus others.  That paper indicates a median sea level rise of 2.3 Meters per degree C increase in temperature.  It does not specify the error, but it is shown in figure Figure 2 E:

    The worst temperature case looked at in the original paper is a 5 C rise, and as can be seen, even with a 4 C rise, the worst case (95%) at even 4 C is well above 12 meters.  Even the median case at 5 C is an 11.5 meter sea level rise, so that Media Watch has stated as a worst case a value 40% less than the median value of the highest temperature examined.

    What is worse is that while 5 C is at the upper end of the likely range (66% confidence interval) for BAU (RCP 8.5) as given by the IPCC, that is just for warming until 2100.  By 2400 warming could procede well beyond that point so that 5 C may be the worst case examined, but it is not by any stretch of the imagination a worse case scenario.

    Consequently, while Media Watch's limited point is fair, in making it they have made far worse errors in the opposite direction - errors that in fact contradict the study they are reporting on rather than merely eliding ambiguous information.

    (Having looked at this, I will be notifying Media Watch of these issues.)


    [RH] Tweaked image width.

  27. Has anyone encountered informaiton showing how much water is pushed to other parts of the ecosystem whenever there is a loss of rainforest, or deforestation in general, whether to desertification or increased agricultural/farming practices etc.. i.e. 130000 to 150000 km loss per year is a lot of moisture pushed into other parts of the planets storage capability! without having done the research I would imagine the quantity over the past 60 years is enough to skew the data?

    I only today read about the relationship of human pumping of groundwater to increased sea level rise.    snippet "because most of the groundwater released from the aquifers ultimately ends up in the world's oceans, it is possible to calculate the contribution of groundwater depletion to sea level rise. This turned out to be 0.8 mm per year, which is a surprisingly large amount when compared to the current sea level rise of 3.3 mm per years as estimated by the IPCC. It thus turns out that almost half of the current sea level rise can be explained by expansion of warming sea water, just over one quarter by the melting of glaciers and ice caps and slightly less than one quarter by groundwater depletion. Previous studies have identified groundwater depletion as a possible contribution to sea level rise. However, due to the high uncertainty about the size of its contribution, groundwater depletion is not included in the latest IPCC report. This study confirms with higher certainty that groundwater depletion is indeed a significant factor"

    This got me wondering about the ground biomass canopy and animal life storage capacity of the vast forest losses each year.


    (Rob P) - See the SKS rebuttal: Sea level fell in 2010. There is a large year-to-year , and decadal-scale, exchange of water mass between the continents and ocean mainly due to rainfall patterns forced by La Nina & El Nino. The strong La Nina dominance over the last decade or so has stored greater-than-normal water mass on land. See Jensen (2013) - Land water contribution to sea level from GRACE and Jason-1 measurements & Baur (2013) - Continental mass change from GRACE over 2002–2011 and its impact on sea level - free copies are available online.

    This is part of the reason for the smaller-than-anticipated sea level rise in recent times - since the early 2000's anomalous water mass, equivalent to 0.2mm of sea level rise per year, has been stored on land. This is consistent with the increase in land vegetation (Net Primary Productivity) during that time. See: Bastos (2013) - The global NPP dependence on ENSO: La Niña and the extraordinary year of 2011

    No surprise that water availability impacts plant growth. But a return to El Nino-dominant conditions (the positive phase of the Interdecadal Pacific Oscillation) hints at major problems in the near-future. Sea level should rise more sharply too as the water mass drains from the continents.   

  28. Gary Marsh

    What the IGRAC page is missing is another change to the land water balance which is empoundment - the building of surface water storages. Some time back I read a study - I don't recall now where it was - that estimated the increase of surface water storage in dams etc. Serendipitously this roughly balances out the loss of groundwater.


  29. Glenn Tamblyn

    You are correct, I mistakenly thought the resevoir and surface water effect was taken into account in this study. The following article from the National Geographic News updates the information somewhat, whilst raising further points for consideration :)   It also mentions the forest effect, though having not found figures for this I am going to estimate an average of 1cubic metre height of water lost per square metre of forest/rainforest loss, to take into account water held in ground, biomass, roots, animals, above surface trees plants and atmospheric humidity, this would equal one cubic kilometre of water every 1000 kilometres of forest lost, times this by 130 000 square kilimetres lost per year = 130 cubic kilometres of extra water per year that ends up largely in the sea. I would apreciate informed comments as to how far off my estimations are and as to if there is any significance to this quantily of yeatly increase affecting sea level rise...   Mind you that last part I should be able to find out myself.. it's the per square kilometre water storage capacity of forest and attendents that are hard for me to assess.

  30. In case my last direct tinyurl link breaks, you can use this one but National Geographic will want you to sign in with email or facebook to read the article.

    To sumarise a snip from the article referring to the work of a team of Dutch scientists led by hydrologist Yoshihide Wada 

    "Newly constructed reservoirs above ground can offset the net loss of water underground. These, Wada said, trap water that would otherwise reach the sea. Before 1990 or so, he added, that offset was large enough that the United Nations' Intergovernmental Panel on Climate Change never took groundwater depletion into account in predicting 21st-century sea-level rise. But that offset is no longer as significant as it once was, Wada said. "There are not so many places where people can build new reservoirs," he said. "They are already built."

    Already, he and his colleagues have found, groundwater depletion is adding about 0.6 millimeters per year (about one-fortieth of an inch) to the Earth's sea level. By 2050, he said, the triple pressures of growing population, economic development, and higher irrigation needs due to a warming climate will increase that to 0.82millimeters per year—enough to raise sea levels by 40 millimeters (1.6 inches) above 1990 levels. Between 2050 and 2100, according to some estimates, sea levels would rise even faster. To put that in perspective, he said, groundwater depletion adds about 25 percent to projected rates of sea-level rise, making it the largest contributor from land to sea-level rise other than the melting of the Greenland and Antarctic ice sheets. Even the melting of glaciers in the world's high mountains won't contribute more to rising sea levels, Wada said."

  31. BTW I can't see a facility to edit our posts, my last one double entried when my web browser had to "recover the webpage"...    sorry!


    [JH] Your duplicate post has been deleted.

  32. Based on my estimation above (see 29.) 130 cubic kilometres of water directly lost each year to deforestation, spread over the world ocean surface of aproximatly 361 million square kilometres would equate to aproximately a 0.3mm rise per year, this allows for a percentage that would end up in rivers, reservoirs the atmosphere and the ground. I'm not a scientist or a skilled resercher so my quantities and sums must be checked, this is a significant figure so surely it is being accounted for somewhere and I'm just not finding it?


    (Rob P) - No, the scenario you conjured up isn't accounted for. Not sure why this would surprise you given that you seem unwilling to read the scientific literature on sea level rise and provide zero supporting evidence for your scenario.  

  33. Gary Marsh @32, observations of the carbon budget show that plants represent a net sink of CO2, ie, that on average there is more plant matter on Earth at the end of each year than at the start.  That means that plants are an increasing reservoir of water rather than, as you would have it, a decreasing reservoir.  Absent other effects, the increase in net plant mass would tend to decrease sea level rise.

  34. Tom Curtis 33.   do you have a data source for year after year plant matter increase?

  35. Thanks for the responce, Tom. I forgot to come back and check up till now. There were three things that made me uncomfortable with the kind of (smug) over-confidence of the reportage:

    1. was the certainty that 6 metres would take 2000 for sure which was why I asked it here. Polar ice melt in Arctic has outstripped previous IPCC AR high sensativity senarios since positive feedbacks like melt water fluid dynamics wasn't included. Surge factors of storms at kingtide can have a SL rise multiplier effect up to even 100x, although presumably that's more about inland effected areas than actual rise on the land/sea edge.

    2. unknown timelines for under-researched 'methane burbping' of frozen gases in Arctic sea bed, tundra and Antarctic sea ice. Sensitivity of these gases to sea warming is somewhat in dispute and atmospheric GHG levels, and ocean warming pathways are still very much dependant on future human carbon intensive activity levels. The amounts of methane and COx stored frozen in these places dwarf the so-called remaining carbon budget of 565Gt (Meinshausen 2ºC concept). It's not clear to me the likely size or time of the earliest of these 'burps' but there is already wide columns of these gases rising into the atmosphere. It's not clear to me how much they would accelorate sea level rise.

    3. the most critical problem with the MW report was the (blyth) omission of the fact that while the Opera House may not see sandbagging/re-footing for well beyond a millenia the climatic tipping point that will guarenty that consequence is likely to be yesterday, today or some time in the next few decades (Kevin Anderson, Tyndal Climate Centre). So urgency is justified (in preference to scoffing). That certainly sents alarm bells ringing for me even if MW think they; have better things to think about in 2 thousand years. The consequence of that level of sea rise on cities and agriculture (in combination with a warmer more extreme climate) will be way more significant than the damages bill to the Opera House of course.

    Please comment on issue of climatic tipping points regards polar ice melt and attendant methane/COx leaking, Tom.

  36. Gary Marsh @34, the easiest one to consult is the IPCC:

    You will see that "Net Land Flux", ie, the balance between "Gross photosynthesis" and "Total respiration and fire" sequesters 2.6 +/-1.2 Petagrams C per annum.  From that we must subtract the 1.1 +/- 0.8 Petagrams emissions from "Net land use change" (which includes deforestation).  That yields a net sequestration of 1.5 +/- 1.44 Petagrams C per annum.  The uncertainty is at the 90% confidence level, indicating that there is a better than 95% chance that the net flux sequesters a small amount of CO2 annually, and a remote chance that the flux is effectively neutral.

    It should be noted that there has been a net reduction of the carbon reservoir in plants and soil of 30 +/- 45 Petagrams of Carbon, equivalent to approximately 15 ppmv.  It is therefore, likely that the net flux has not always sequestered CO2 over the last 264 years, but currently with tropical deforestation partially balanced by reforestation in the NH, and with the additional effects of CO2 fertilization, the reverse is the case.

  37. Tom Curtis  - It appears that the information you've provided from the IPCC is refferring to Carbon and CO2. The scenario I proposed for consideration concerns the direct transfer of H2O/water, it being a quicker and more direct contributer to sea level rise when it is released via deforestation, tropical and otherwise. I appreciate there are an enourmouse amount of variables to be considered when attempting to quantify the water holding capacity of the myriad types of forest, especially when factoring in attendent animal life from microble to mammal, the subterranian trunk and canopy and micro atmospherical climate which will hold significant quantities of water when forested and much less when deforested! add all these factors together and there will be a net movement of WATER. Although related this is a different process from the movement of Carbon, certainly it would appear to have a much more immediate effect. So again I ask if anyone can show me the data or studies if they even exist.


    (Rob P) - You were provided with peer-reviewed literature in your comment @ 27, however you have not bothered to read any of it, or make any attempt to understand it.

    There has been a net growth in total biomass of land-plants over the recent decade, hence the uptake of carbon and water by plants has likewise grown.

    You are now in slogan-chanting territory and any further repetition of this meme, without any supporting evidence, will be deleted

  38. Gary Marsh @37, your initial premise is that there has been a reduction in plant mass.  That is shown to be false by the IPCC data.  If you now want to alter your premise by detailing water content of different sorts of plant mass, you need to actually provide detailed information on the relative water contents of different forms of plants, plus the relative growth or loss of those different plants.  You may then get an argument up that supports some measurable impact on sea level rise, (though I doubt it).  But if you don't do that legwork, you have nothing to discuss.  Your theory becomes "If all these complex and unmeasured factors come out just right, then changes in the biosphere are increasing sea level through loss of water."  To which is is sufficient to respond, "If they come out wrong, then you have the opposite, or no, effect".  The later is far more probably sight unseen than the former.  

  39. Looking at Post #5's Graph above, the 2006 peak is about 2mm below the 2011 valley. I would draw a new best fit curve starting in 2006 that shows an 8 mm rise in 6 years, or 1.33 mm/yr. With all that I've read lately about the cold 2012-13 and 2013-14 northern winters, I'd venture to say 2013 and 2014 would follow the 1.33 mm/yr line. Hardly the makings of flooding Florida, where I lived for 17 years in a house that is 14 feet above sea level. There's only so much water in the Olagalla aquifer, and when it is 70% empty in 2060, the rate of draw from it falls off a cliff. Then there's the huge increase in Great Lakes water levels this year. An unbelievable record increase in Lake Ontario and 14 inches added to Superior. Just Superior's gain offsets 7/33 of all land based melt from Antarctica. (cubic miles fraction for 1 year)


    [JH] Please explain exactly how you did your "curve fitting" and provide the sources for the data that you have included in your post. Until you comply with this request, your future posts will be deleted.

  40. Jetfuel...your approach would almost certainly seriously underestimate the sealevels for 2012 and 2013 presented in the updated graph in the OP, since starting in 2006 looks like it would give you a steeper slope than the 3.2 mm /year overall average.  Which is why we don't draw regressions on small subsets of the data, especially cherrypicked ones.  Why would you take the trouble to go through the comments and ignore the updated graph anyway?  

    With regard to lake levels, there has been little net change in level of the Great Lakes over the time frame of the sealevel observations.  That includes this year.  You must be thinking about seasonal changes, but those are irrelevant to sea level change since they are ephemeral.  Also this year does not seem unusual when you look at the data.

    BTW moderators, the link to the updated version of the fisgure in comment 5 appears to be broken.


    [DB] Fixed.

  41. jetfuel @39, Stephen Baines @40, here is the most recent update of sea level increase from the University of Colorado:

    As you can see, the trend from 1993 is still 3.2 mm per annum.  Clearly jetfuel's prediction of a trend of approximately 1.33 mm per annum is inaccurate.  I suspect Stephen Baines prediction of an increased trend since 2006 is also inaccurate, but that is not so obvious.  (It is more likely to have been accurate to early 2013 as in the OP.)

    Looking at the great lake data, Lake Ontario rose 0.11 meters between April 2013 and April 2014 inclusive, but fell 0.05 meters from May 2013 to April 2014, the actual one year "rise".  Even the former is no where near record breaking, being near one eigth the 0.86 meter rise from Dec 2012 to July 2013, although that does have a large seasonal component.  There have been larger seasonal and annual increases in the past. (For data, follow Stephen Baines' link.) 

  42. Thanks TC for the updated graph.  Yes I was referring to the trend line you would get from the graph in the OP.  It's not surprising that with more data you get reversion to the mean trend line.

    The recent large fluctuations around that mean trend are pretty interesting though.  I remember the decline was attributed to La Nina transporting water to temporary storage on land, but I haven't read anything really recent on that.  Even the large La Nina in 98-99 didn't have as big an effect.  I should look it up.

  43. Stephen, a significant part of the dip in 2011/12 ended up in Australia. Lake Eyre and several other lakes in Central Australia filled for the first time in years - flamingo heaven. Then slowly evaporated away over the next 2 years.

  44. jetfuel wrote: "Looking at Post #5's Graph above, the 2006 peak is about 2mm below the 2011 valley. I would draw a new best fit curve starting in 2006 that shows an 8 mm rise in 6 years, or 1.33 mm/yr."

    The human eye is only too good at finding patterns in noisy data, even when they don't actually exist.  That is why statisticians have invented methods for this problem, variously known as "breakpoint analysis", "broken stick regression", "segmented regression" etc.  What these methods do is determine whether the improvement in the fit of the model justifies the additional model complexity introduced by adding a breakpoint, which introduces at least two additional parameters to the model.

    If you don't follow standard statistical practice in this way and just pick the breakpoints by eye, you will generally end up overfitting the data and drawing meaningless conclusions based on the noise.  It is the sort of thing that is a recipe for confirmation bias.  So while you might do that, a scientist probably would know better.

  45. @ comment 5, is there any particular explanation for the drop in sea level circa 2011 in both the original graphic and the updated graphic? I looked up sunspots and there is some correlation but could that even make sense why it should?

     Are there any other explanations that work better?

  46. bozzza:


    sorry....0.13 meters to 11.5 35 feet...


    [JH] Link activated.

  48. Rhoowl, assuming that this is in response to my comment here, given those specific values you are presumably referring to 'table 2' in the basic version of the article above. Of course, that table shows those two values as sea level rise by 2500 for two completely different emissions scenarios at opposite extremes of the uncertainty ranges... do you not have any idea what you are talking about here? Because that's the most charitable explanation I can think of for such a blatantly ridiculous argument.

  49. Rhoowl - Do you understand the difference between different emissions scenarios and the uncertainties (including modeled natural variation) for a single scenario? Your comment seems to indicate that you do not. 

  50. I have a slightly off-topic, but to me pressing question about the IPCC graph displayed in #36: The net land flux is shown to be increased by 2.6 +/- 1.2 PgC(arrow downwards), however the Vegetation reservoir became de(!)creased ( -30 +/- 45 PgC). I can't see were the additional 'land' Carbon is ending up. This seems inconsistent. Is there a missing number in the graph?


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