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Why is future sea level rise still so uncertain?

Filed under: — gavin @ 12 May 2021

Three new papers in the last couple of weeks have each made separate claims about whether sea level rise from the loss of ice in West Antarctica is more or less than you might have thought last month and with more or less certainty. Each of these papers make good points, but anyone looking for coherent picture to emerge from all this work will be disappointed. To understand why, you need to know why sea level rise is such a hard problem in the first place, and appreciate how far we’ve come, but also how far we need to go.

Here’s a list of factors that will influence future regional sea level (in rough order of importance):

  • ice mass loss from West Antarctica
  • ice mass loss from Greenland
  • ocean thermal expansion
  • mountain glacier melt
  • gravitational, rotational and deformational (GRD) effects
  • changes in ocean circulation
  • steric (freshwater/salinity) effects
  • groundwater extraction
  • reservoir construction and filling
  • changes in atmospheric pressure and winds

And on top of that, the risks of coastal flooding also depend on:

  • tectonic/isostatic land motion
  • local subsidence
  • local hydrology
  • storm surges
  • tides

If that wasn’t bad enough, it doesn’t even get into why some of the bigger terms here are so difficult to constrain – but more of that below.

Meanwhile, note that the factors listed above involve the whole Earth system: the oceans, the cryosphere, the atmosphere, the solid earth and lithosphere, and a full range of scales, from the city block and shoreline, to ice dynamics that change over kilometers, to GRD footprints, to the whole global ocean. While each of these elements has a devoted scientific community, sea level rise cuts across all the disciplines. And similarly, while each of these elements has a specialized modeling capability, there is no single model that encompasses all of this (not even close – as yet).

What this means is that estimates of future sea level rise are mixes of information from multiple sources, tied together in more or less sophisticated frameworks (this is the approach in the IPCC SCROCC report and the upcoming AR6) that attempt to build a full uncertainty range from all the disparate sources of information (coupled ocean-atmosphere models, hydrology models, ice sheet models, solid earth models etc.). To reiterate, there is no ‘climate model’ prediction of global sea level rise, though the climate models we often discuss here (the CMIP-class of models), do provide some of the inputs. This means that links and feedbacks between these different elements are not always coherent – e.g. the estimates of groundwater depletion (used for irrigation) or glacier melt might not impact the soils or the freshwater budget of the downstream rivers and ocean.

Two elephant seals in the Southern Oceans arguing about marine ice cliff instability.

Yes, but what about West Antarctica?

The West Antarctic Ice Sheet (WAIS) is the elephant seal in the aquarium. Ever since the 1970s it’s been suspected that it was prone to rapid collapse because the bedrock on which it sits is below sea level (and in some places, thousands of meters below sea level). More recent research constraining Eemian sea level (~125,000 yrs ago) has confirmed that WAIS collapsed at that time, adding 3 or more meters of sea level rise to the contribution from a much reduced Greenland Ice Sheet. Moreover, present day observations from gravity sensors (GRACE/GRACE-FO) show large ice mass losses from WAIS – dominated by the rapid retreats of the Pine Island Glacier and Thwaites glacier, and concomittent decreases in ice sheet elevation (from IceSat2).

Simplified schematic of atmosphere-ocean-ice interactions (Zalasiewicz et al, 2019)

There are many interesting observations and non-observations from WAIS that make this a challenging problem. First, the melting of the ice shelves and the retreat of grounding line is being driven from below as slighty warmer circumpolar deep water (CPDW) has been pushed onto the shelf. The CPDW is thought to be affected by the shift in the westerly winds around Antarctica which have increased in recent decades due to a combination of greenhouse gas forcing and the polar ozone hole (Miller et al, 2006).

Additionally, it looks like the anomalous meltwater from WAIS is causing the local ocean to freshen, stratify and cool (see Rye et al. (2020) or Sadai et al. (2020). Both of these effects make a straightforward connection between global mean warming and WAIS mass loss tricky.

But there is more. For instance, the bedrock topography under the ice sheet is still being refined. The last major revision (BedMap2) was in 2013 (Fretwell et al., 2013), but many areas remain without good data and important revisions are still being made (Morlighem et al., 2020). Also, the topography of the ocean bottom under the ice shelves is still being discovered using autonomous underwater vehicles, for instance, under the Thwaites last year. Meanwhile Bedmap3 is underway...

Furthermore, one important factor in how WAIS will affect sea level is how fast the lithosphere will respond to changes in the ice loading (part of the GRD effects mentioned above). If the mantle is very viscous, then the response is slow and it doesn’t add much to the global sea level change. But if it’s less so, then uplift is more rapid, and it can add more SLR, faster. Unfortunately, It turns out that the specific conditions under WAIS are less viscous than was thought (Pan et al., 2021).

Recent advances

Given, then, that we don’t have a suite of models with all the effects that we can analyze to give us a measure of the uncertainty, what can we do in the meantime? First, we can analyze the models we have and estimate the structural uncertainty among them – for the processes they include. This is what Edwards et al., (2021) do. Using the ISMIP6 and GlacierMIP simulation data and a statistical emulator they map out the responses of these models to the global mean temperature change and ocean-driven melting in Greenland and Antarctica. The nice thing about this is that you aren’t tied to the emission scenarios that were initially used in the MIPs, but you can’t independently calibrate the projections to paleo-climate changes, and you are stuck with the models that were used, some of which are a little out of date.

Alternately, you can take a single ice sheet model with better calibration to paleo-climate changes and drive it with climate model-derived boundary conditions as is done by DeConto et al., 2021. This doesn’t give you an estimate of full structural uncertainty (which is high), but perhaps is more internally consistent. However, the calibration that has been done on this model is (a little) controversial, and it’s worth discussing why.

Back in 2015, Pollard et al. (2015) found that their ice sheet model was overall too stable in that it wasn’t able match the large sea level changes that have been inferred for the Pliocene 3 million yrs ago (~20 meters) Eemian 125,000 yrs ago (6 to 9 meters). They added two destabilizing mechanisms, hydrofacturing of ice shelves and something called marine-ice cliff instability (MICI) and tuned the parameters to match the target. They then used this tuned version for future projections. However, the number of potential issues in the model (or any model really) is large – from uncertainties in the bedrock topography, the boundary conditions at bedrock itself, grounding line parameterizations, the resolution, the ice rheology, the lithospheric response etc. And MICI itself is quite uncertain Clerc et al., 2020 and as Edwards et al note, no model that contributed to ISMIP6 included a MICI-like mechanism. There is no guarantee that the specific destabilizing mechanisms used were the actual mechanisms at play in the warmer period. There may be other (unexplored) variations in the ice model that could have provided as good a match and that would have different sensitivity in the modern.

To their credit, DeConto et al. have extended the calibration to Pliocene sea level, the Eemian and the rate of change observed since 1992, though the Eemian constraint is the most important. And they did vary the mantle viscosity in the sea level calculations consistent with the Pan et al values. Even better, they also explored the sensitivity to a southern ocean response to Antarctic meltwater based on Sadai et al. (2020).

The question then is whether these two approaches are consistent and/or complementary.

Total land ice contribution to SLR (Edwards et al., 2021)
Antarctic contributions to sea Level scenarios from DeConto et al (2021)

So what do they show?

As one might expect, there are a lot of moving parts in these results. Many things have been varied. But there are some notable contrasts. First off, the main results for Antarctica in Edwards et al surprisingly suggest very little sensitivity to forcing scenario – basically just a continuation of the current rates of melt, which contrasts strongly with the DeConto et al result suggesting a threshold effect by 2060 between SSP1-26 (consistent with 2ºC) and SSP2-45 (or higher). Edwards et al. also look at some more ‘low probability/high impact’ runs (their ‘simulations for the risk averse’) which are more similar to the DeConto et al. results (around 20 cm from WAIS by 2100).

Remember that the biggest uncertainty is still the emission scenario, and the higher the scenario in terms of global warming, the more uncertain the ice sheet contribution is. Another key point made by DeConto et al. is that the world doesn’t stop at 2100. The consequences of even stable temperatures post-2100, has very large long term implications for sea level. For instance, even a 2ºC eventual warming is associated with around 1 meter of SLR just from WAIS by 2300.

Work to be done

These two papers illustrate the fundamental ingredients that will (eventually) get us to a more reliable estimate of SLR. The structural uncertainty explored by Edwards et al is broad, still incomplete, but essential. The calibration against past change in DeConto et al is also essential, even if the structural uncertainty they explore is narrower. A combined approach would be enlightening – using the DeConto et al model for the current ISMIP6 protocol, and extending that project to include the Eemian as an out-of-sample test might help.

Ice sheet science and the consequent sea level rise, like many cutting-edge topics, generally has a widening of uncertainty when the tools and theory start to really kick off. It is only later that this uncertainty is constrained as more observational data is brought to bear. Then, and not before, will projections start to narrow.

Until then, the most productive way to reduce uncertainties might just be to reduce emissions.


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  5. M. Morlighem, E. Rignot, T. Binder, D. Blankenship, R. Drews, G. Eagles, O. Eisen, F. Ferraccioli, R. Forsberg, P. Fretwell, V. Goel, J.S. Greenbaum, H. Gudmundsson, J. Guo, V. Helm, C. Hofstede, I. Howat, A. Humbert, W. Jokat, N.B. Karlsson, W.S. Lee, K. Matsuoka, R. Millan, J. Mouginot, J. Paden, F. Pattyn, J. Roberts, S. Rosier, A. Ruppel, H. Seroussi, E.C. Smith, D. Steinhage, B. Sun, M.R.V.D. Broeke, T.D.V. Ommen, M.V. Wessem, and D.A. Young, "Deep glacial troughs and stabilizing ridges unveiled beneath the margins of the Antarctic ice sheet", Nature Geoscience, vol. 13, pp. 132-137, 2019.
  6. L. Pan, E.M. Powell, K. Latychev, J.X. Mitrovica, J.R. Creveling, N. Gomez, M.J. Hoggard, and P.U. Clark, "Rapid postglacial rebound amplifies global sea level rise following West Antarctic Ice Sheet collapse", Science Advances, vol. 7, pp. eabf7787, 2021.
  7. T.L. Edwards, S. Nowicki, B. Marzeion, R. Hock, H. Goelzer, H. Seroussi, N.C. Jourdain, D.A. Slater, F.E. Turner, C.J. Smith, C.M. McKenna, E. Simon, A. Abe-Ouchi, J.M. Gregory, E. Larour, W.H. Lipscomb, A.J. Payne, A. Shepherd, C. Agosta, P. Alexander, T. Albrecht, B. Anderson, X. Asay-Davis, A. Aschwanden, A. Barthel, A. Bliss, R. Calov, C. Chambers, N. Champollion, Y. Choi, R. Cullather, J. Cuzzone, C. Dumas, D. Felikson, X. Fettweis, K. Fujita, B.K. Galton-Fenzi, R. Gladstone, N.R. Golledge, R. Greve, T. Hattermann, M.J. Hoffman, A. Humbert, M. Huss, P. Huybrechts, W. Immerzeel, T. Kleiner, P. Kraaijenbrink, S. Le clec’h, V. Lee, G.R. Leguy, C.M. Little, D.P. Lowry, J. Malles, D.F. Martin, F. Maussion, M. Morlighem, J.F. O’Neill, I. Nias, F. Pattyn, T. Pelle, S.F. Price, A. Quiquet, V. Radić, R. Reese, D.R. Rounce, M. Rückamp, A. Sakai, C. Shafer, N. Schlegel, S. Shannon, R.S. Smith, F. Straneo, S. Sun, L. Tarasov, L.D. Trusel, J. Van Breedam, R. van de Wal, M. van den Broeke, R. Winkelmann, H. Zekollari, C. Zhao, T. Zhang, and T. Zwinger, "Projected land ice contributions to twenty-first-century sea level rise", Nature, vol. 593, pp. 74-82, 2021.
  8. R.M. DeConto, D. Pollard, R.B. Alley, I. Velicogna, E. Gasson, N. Gomez, S. Sadai, A. Condron, D.M. Gilford, E.L. Ashe, R.E. Kopp, D. Li, and A. Dutton, "The Paris Climate Agreement and future sea-level rise from Antarctica", Nature, vol. 593, pp. 83-89, 2021.
  9. D. Pollard, R.M. DeConto, and R.B. Alley, "Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure", Earth and Planetary Science Letters, vol. 412, pp. 112-121, 2015.
  10. F. Clerc, B.M. Minchew, and M.D. Behn, "Marine Ice Cliff Instability Mitigated by Slow Removal of Ice Shelves", Geophysical Research Letters, vol. 46, pp. 12108-12116, 2019.

67 Responses to “Why is future sea level rise still so uncertain?”

  1. 1

    Shorter term uncertainty in SLR has a lot to do with uncertainty in predicting ENSO. In many places one can track El Nino La Nina cycles via tidal gauges.

  2. 2
    Piotr says:

    I like the “list of factors that will influence future regional sea level” particularly with their order of importance. A few comments/questions:

    – “ steric (freshwater/salinity) effects” – a new rejoinder to MA Rodger’s “the dissolving of salt into water has zero direct impact on volume”, but this time from somebody he does … NOT dismiss for his “pedantic nonsense” ;-)

    – “changes in ocean circulation” vs. “changes in atmospheric pressure and winds” – wouldn’t most of the ocean circulation be wind-driven? Or do you, by “atmospheric pressure and winds”, mean ONLY effects of these on the storm surge, i.e. excluding their effects on currents ?

    If the latter – then “atmospheric pressure and winds” may indeed be at the bottom of the ranking for the influence on the average SL (as their effect would mostly average out) – but LOCALLY and in the short term (weather) – THIS IS the one type of SL rise that we will be noticing the MOST:
    – it was the storm surge that drowned New Orleans, not the mean SLR
    – future storm surges may be higher (stronger hurricanes), the hurricanes may be moving slower (=>bigger chance that storm surge is there during the high tide),
    AND the storm surge+high tide will ride on top of the already elevated mean sealevel.

  3. 3
    RUSSELL says:

    How dare you suggest that 41 & 43 areunwise to persevere in wintering in slightly soggy Boca Grande ?

    The Gasparilla Island higlands are today only a few feet lower than the high ground on Galveston, when that charming town went glug glug a century ago

  4. 4
  5. 5

    KIA 4: Just what I’ve been saying all along!

    BPL: At no point does that article say sea level rise isn’t happening, isn’t going to be very large, or isn’t going to be a vast and destructive problem. So it isn’t what you’ve been saying at all.

  6. 6
    aden says:

    Why has the rotation speed of the earth increased when the research papers predicted the opposite?

  7. 7
    Ric Merritt says:

    Just in case this is unclear to anyone:

    If someone has your head in a vise, and efforts to remove your head from the vise are failing, and your enemy closes the vise a quarter turn each day, and you’re not sure whether they may increase that rate, it’s not a whole lot of comfort to think “hey, maybe they’ll just keep it at the daily quarter turn”. That’s already bad enough. One day your skull will crack.

    Regional variations in sea level, land subsidence, etc are well known. In the many places where the sea is winning, the current rate is already too costly to bear much longer. The homes and infrastructure already in place near sea level are “your head”. A rising sea will damage or destroy it, or impose costs that increase implacably. The current rate of rise is already too much, and any more will just be worse.

    Similar reasoning applies to wildfires, droughts, floods, bad weather of various kinds, stress on agriculture, and hot days that just kill outright. (I feel that last one is underappreciated.) Not to mention all the other human factors, conflicts, and resource problems not falling directly under the climate heading.

    And, they don’t come at you one at a time like Bad Guys in a cheesy movie. They gang up unfairly, interact, and play dirty.

  8. 8
    Mark A. York says:

    I had a condo on Little Gasparilla Island that was only assessable by boat, private ferry, personal etc. The complex was built in an ancient coastal intrusion watercourse and in a Coastal Barrier Island Protection Zone therefore the owners didn’t qualify for FEMA flood insurance. I saw frequent storms that pushed bay water 3/4 of the width of the island. Everything was on 15 foot stilts but still. It will go under easily.

  9. 9
    Pete Wright says:

    As a related aside, could someone describe what happens to the underwater ice immediately below a marine ice cliff when the 100m+ ice cliff above it collapses, as in the MICI scenario. I just can’t quite visualize what happens next. Thanks

  10. 10
    Robert L. Bradley Jr. says:

    And if anyone thought the science was settled, much less in favor of climate alarmism…. and forced energy transformation.

  11. 11
    Stan Chrzanowski says:

    Since ice (water in a solid state) can exist at any temperature from 0°C (32°F) down to absolute zero, does anyone know if the Antarctic ice cap (over a mile thick on average) is warming internally, i.e. heading upward toward 32°F?

  12. 12
    Eric Steig says:

    Gavin, a minor correction. Pollard et al. 2015 really didn’t use the Eemian as a calibration target, because we don’t actually know for certain (though I agree it’s virtually certain) that the WAIS Collapsed at that time. Their calibration was to the Pliocene, when we have more confidence that the WAIS was gone. This raises the problem, though, that the uncertainties in forcing are larger. Deconto and Pollard (2016) actually found for the Eemian that WAIS didn’t collapse in their model set-up, even with MICI, unless significant ocean thermal forcing occurred (equivalent to warming CDW by 2-3°). All of which to say is that your bottom line is correct: reducing emissions is the best way to reduce uncertainties.

    [Response: I think the graph in the SM in this paper shows that the Eemian constraint is important: – gavin]

    [Response: No disagreemnt from me. The Eemian is the most important paleo constraint we have, in my view. – eric]

  13. 13

    “We can’t control the whether, we can only control the when”

  14. 14
    RUSSELL says:

    Be of good courage, Mark.

    Geophysicists may fear Boca Grande becoming the next Galveston, but others blame the rising tides on the astrology of the Galactic Bulge

  15. 15
    nigelj says:

    R.M. DeConto et alia discuss sea level rise here:

    Some very sobering sea level rise predictions buried in the text.

  16. 16

    a 6: Why has the rotation speed of the earth increased when the research papers predicted the opposite?

    BPL: WHAT research papers? [CITATION NEEDED], as it always says in Wikipedia.

    The rotation speed of the Earth would have sped up as more mass from the melting polar caps moved toward the equator. What’s more, this would have been predicted ahead of time.

  17. 17

    RM 7,

    That’s an excellent, if chilling, analogy. May I use it?

  18. 18
    MA Rodger says:

    aden @6,
    You ask “Why has the rotation speed of the earth increased when the research papers predicted the opposite?”
    I think you need to be a bit more precise as to the period of this rotational acceleration and perhaps also the particular research papers you say predicted deceleration.

    The planet Earth’s rotation is decelerating, this due to the tidal forces acting as a brake (which also results in the moon moving into a more distant orbit). This is surely a wondrous development. The original rotational speed of planet Earth gave a Length Of Day of something like 6 hours. So without deceleration, the terrestrial day would have remained a quarter its actual present length, the sun would rise and you’d hardily have brushed your teeth before night falls and its time for bed.
    The present rate-of-shrinkage in the LOD has been assessed at roughly 0.02 seconds per millennium which is roughly what the tidal forces should deliver. I think folk see a potential wobble in that rate with LOD roughly static for 1000 years then shrinking by 0.03 seconds over 500 years. (See for instance Fig 2 from Nelson et al (2003) ‘The Leap Second: Its History and Possible Future.’)
    Note that Nelson et al (2003) does project a future with an increasing LOD, suggesting we would need 2 leap second per year by 2100 to cope with this deceleration. But also note in that Fig2 that we are potentially in one of the periods when the LOD is increasing less dramatically than the average.

    Over a shorter period, the wobbles of LOD have been showing a decreasing trend (thus the spin of the planet has been accelerating) as shown in this Wikithing graphic of LOD 1962-2018 and we haven’t needed to add a leap second to the calendar since 2016. We even hear said “Before 2020, the shortest day occurred in 2005. However, this record has been broken 28 times in the last 12 months.” and also that 2021 will see further acceleration apparently suggesting the need to enact negative leap seconds, not positive ones. However this record-breaking-speak applies only over 60 years of LOD measurement. The predicted -0.05ms average LOD for 2021 compares with annual averages of perhaps -0.5ms back in the 1940s [as shown in Fig 19 of Stephenson et al (2016) ‘Measurement of the Earth’s rotation: 720 BC to AD 2015’].

    This account may explain why you have found some contradiction between LOD and ‘predictions’ of LOD. But without knowledge of the actual research papers and the period of ‘rotation speed of the earth’ you have in mind, it isn’t possible to give a more direct answer to your question.

  19. 19
    Mal Adapted says:

    Robert Bradley:

    And if anyone thought the science was settled, much less in favor of climate alarmism…. and forced energy transformation.

    Again with the luckwarmism. Sorry, but uncertainty still isn’t our friend.

    If anyone is wondering why Dr. Bradley keeps posting zombie denialist memes here, the most likely explanation is that he’s paid to do it.

  20. 20

    “Water vapor, and not CO2, is the most important greenhouse gas.”

    And of course humans can influence the water vapor content of the atmosphere.

    We are doing it every day since centuries. Millions km² of rainforest mostly eliminated by slash and burn together with ~ 1.5 million km² of urban sealed area, inevitably means that much less water evaporates over these areas and that precipitation and service water quickly flow off into the sea via the sewer system and rivers.

    The longstanding global drainage of moors and wetlands also significantly reduces their ability to evaporate water. Spreading deserts rapidly increase these areas with reduced evaporation.

    A large part(23,4%) of the solar energy specified in the averaged radiation balance with ~ 80W / m² is converted into water vapor. Here is the immensely important coupling and interface between the radiation balance and the water cycles. The radiative forcing or the net balance of water vapor is cooling and negative due to the cloud formation., evaporation and climate
    – CO² out of the atmosphere
    – H²O into the atmosphere
    is a holistic climate protection.
    Over the 70% ocean area the volume of evaporation is very likely to increase with increasing air and water temperatures, but it looks like the 30% land area with the spreading deserts and the causes described above tend to be the other way around.

    The flow of energy from the surface in height and width takes place less and less with water vapor, but increasingly in the form of hot and dry air.
    Rainforests transport clouds and rain inland and deserts, conversely, spread blue skies and drought.

    In theory, a lowering of the sea level rise would even be conceivable. To do this, we “only” have to bring our rainwater from the roof surfaces and additionally a small percentage of the flowing water of rivers either to evaporation (via plants) or to store it in the groundwater. The question: How do we bring falling groundwater levels, global cloud cover loss, drought, temperature records and rising sea levels together ? – has a very simple answer: rain barrels and cisterns with overflow on unsealed terrain and artificial irrigation of the agricultural and forest areas in the summer drought through the water management-controlled expansion of irrigation systems.

    More information:

  21. 21
    sidd says:

    Re: mechanism of ice cliff collapse

    Parizek (an usual suspects) 2019 on collapse via listral slumping
    doi: 10.1130/G45880.1


  22. 22
    Mr. Know It All says:

    8 – Mark A. York
    “Everything was on 15 foot stilts but still. It will go under easily.”

    Some Gulf Coast land is subsiding – is Gasparilla Island subsiding?

    Easy solution: attach pontoons at the bottom of the homes (at the top of the stilts). When the sea rises, they will float (best if the stilts come off at that point), and can be moved to a safe location. I said easy. I didn’t say cheap, but with some thought that might be achieved as well. Humans adapt.

    16 – BPL
    “The rotation speed of the Earth would have sped up as more mass from the melting polar caps moved toward the equator.”

    No. Mass moving toward the equator would slow the rotation, the same way that ice skaters slow their rotation as their arms/legs are extended; their rotational speed increases as they draw their arms/legs in closer to the axis of rotation.

  23. 23
    Tim McDermott says:

    KIA 22

    Have you ever seen a video of a hurricane landfall? If your house on 15 ft stilts gets hit with a 20 ft wave, you don’t have a house anymore. As a rule of thumb, a cubic meter of water masses a metric ton.

  24. 24
    Arup Kumar Chattopadhyay says:

    Everyone has perfectly stated their views, most of which are important.
    Now, I’m sending you one more clue, which may encourage you all to think..
    It’s based on Groundwater over-exploration and resulted wobbling.
    Out of our 7.4b population, about 7.0b stayes in Northern hemisphere, and since 1860 (i.e. since onset of metallurgy based development through industrialisation, we have over-explored the deep layer aquifer. The estimated value of this layer(in terms of H2O is 914 trillion Km3.. Where the estimated exploration is about 60-40%, with a recharge of about 3-5% since 1860. So if we consider the net loss of underground water store to be 35% since then, it accounts 30-32 trillion Km3. This mass has found its course of deposition to mostly in southern hemisphere, adding about 15 trillion million tonnes of weight to southern hemisphere, withdrawing it sporadically from different regions in northern hemisphere. This has gradually created an uneven imbalance in gravitational mass. This may have created the beyond estimated wobbling of our planet around its axis. So due to this wobbling coupled with other stated factors, might have created more uneven sea level rise in different coastal regions. So it be very difficult to the authoritative organisations to exactly predict, how this sea level rise will make a total disruption of coastal lands.

    If anyone has any proper idea, please share.

  25. 25
    nigelj says:

    Regarding the rate of spin of the earth on its axis.

    “But surface rearrangements are happening right now as well: as glaciers and icecaps melt, particularly over land masses. The Antarctic ice sheet, for example, is the largest single mass of ice on Earth, which contains 30 million cubic kilometers of ice: about 30 quadrillion tons of material. It’s located, on average, at an elevation of between 8000 and 9000 feet (2400-2700 meters) above sea level. Every time some of that ice melts or calves into the ocean, it not only causes sea levels to rise, it redistributes Earth’s mass so that it’s closer to the central rotational axis. Changes in ice and water storage on Earth may be responsible for both the current speed-up in Earth’s day, (conservation of angular momentum law presumably, Im not a physics guy) as well as newly observed wobbles in Earth’s rotation.”

  26. 26

    RLBJ 10: And if anyone thought the science was settled, much less in favor of climate alarmism…. and forced energy transformation.

    BPL: Complete sentences are your friend.

  27. 27

    MS 20: humans can influence the water vapor content of the atmosphere.

    BPL: Only locally and temporarily. The water content of the atmosphere is set passively by the ambient temperature. Google “Clausius-Clapeyron law.”

  28. 28

    KIA 21: No. Mass moving toward the equator would slow the rotation, the same way that ice skaters slow their rotation as their arms/legs are extended; their rotational speed increases as they draw their arms/legs in closer to the axis of rotation.

    BPL: You got that right and I, the physicist, got it wrong. Color me embarrassed.

  29. 29
    zebra says:

    re Rotation,

    And then, we have the jet stream. Speed or slow Earth’s rotation and you would expect a change there as well.

  30. 30
    Piotr says:

    zebra(29) And then, we have the jet stream. Speed or slow Earth’s rotation and you would expect a change there as well.

    “Alex, what is how many zebras can dance on the head of a pin”?

    Melting of the whole Greenland ice-sheet would slow the Earth rotation by 2 milliseconds per day ( Which means that the rotation speed of Earth (and Coriolis effect) would change by … 2 millionth of a per cent…

    On the other hand, the reason for the Jet Stream, the temperature difference between a pole and mid-latitudes, may change quite a bit (Arctic amplification!)

  31. 31
    MA Rodger says:

    Arup Kumar Chattopadhyay @20,
    So you are saying that since 1860AD (in roughly the last 1½ centuries) humanity has sucked 30 trillion cu km of water from aquifers and that water is now sloshing round the oceans destabilizing the rotation of the planet on its axis.
    Thinks – There are seven billion humans running round the planet today and back 1½ centuries ago there was just one billion. So I’d reckon that 1½-century interval could be considered as comprising half a trillion man.years. And you say those pesky folk have collectively drained 30 trillion cu km of water? That would average out at 60 cu km by each human each year. Now, I know I drink a lot of tea, but I don’t think it is anything like that much.
    And thinks – The oceans stretch across 361 million sq km of the planet so an addition of 361 cu km raises sea levels by a whole 1mm. So if you poured 30 trillion cu km into the oceans, I’m thinking we would have surely noticed.

  32. 32

    Stan C., #11–

    Is the Antarctic ice sheet warming internally?

    Dunno, but there’s this on the metrology:

    However, I would expect, on the limited reading I’ve done as an interested layperson, that the threat to the ice sheets isn’t that they’ll melt en bloc and in situ. Increases in glacial outflow and net accumulation rates will presumably be much faster in effect than heat conduction through that mile-plus of ice, and hence will be more significant drivers of ice wasting.

  33. 33

    Regarding the rate of spin of the earth on its axis, most of the modulation in the rate has to do with tidal torque. And since the tidal torque is cyclic relating to the long periods in the lunar orbit, the majority is reflected in the measurements of length-of-day (LOD) — maintained at in Paris. It’s precise enough that one can actually extract the lunar nodal cycle of 18.6 years from the LOD measurement.

    But that’s just the solid earth’s inertial response to a torque. What’s more complex is the fluid response, which because it is not fixed wrt the mantle, will slosh in place. This takes some math to model correctly and has implications for climate, as I presented at last month’s European Geophysical Union meeting — summarized here w/links

  34. 34
    Karsten V. Johansen says:

    It seems to me that your article underestimates the influences of what a recent analysis call interacting tipping elements, see: “Interacting tipping elements increase risk of climate domino effects under global warming”, Wunderling et al. 2021, . Especially your article concentrates solely on the WAIS and does not consider what is happening with increased mass loss from the Greenland ice sheet and the coupling mechanisms between these two key elements, and not the least the also coupled warming effects of the rapidly diminishing (both in area and volume) sea-ice-cover of the Arctic ocean, resulting in rapidly decreasing overall albedo in the Arctic, and not the least from that especially the interacting processes of 1) rapidly decreasing snowcovered area also in time, 2) increased warming and thawing of arctic permafrost, both land-based and subsea, and 3) resulting increasing release from the thawing permafrost of both methane and carbon dioxide, including from rapidly growing wildfires in the woodlands and tundra peatlands (some of which now linger subsurface through the winters in dried-out peatlands and spontaneously flare up again in springtime, reportedly in Siberia).

    There are a whole lot of coupled feedback-mechanisms here which the IPCC until now to my knowledge have grossly underestimated and/or not considered at all. Not the least the albedo-reducing effects of long-distance transport of soot and ashes from wildfires onto the glacier and sea-ice surfaces, observed especially in the summer of 2012 on the Greenland ice sheet, see: “Climate change and forest fires synergistically drive widespread melt events of the Greenland Ice Sheet”, Keegan et al. 2014, , and in during the enormous australian wildfires 2019-20 on the glaciers in New Zealand and (as far as I remember) on the Antarctic Peninsula.

    Also not considered in your comments is this new theme: what does the lowering of the ice-sheet surface, resulting from increasing mass loss, mean for the mass balance of the Greenland Ice Sheet, see “Critical slowing down suggests that the western Greenland Ice Sheet is close to a tipping point”, Boers & Rypdal 2021, : “We reveal early-warning signals for a forthcoming critical transition from ice-core-derived height reconstructions and infer that the western Greenland Ice Sheet has been losing stability in response to rising temperatures. We show that the melt-elevation feedback is likely to be responsible for the observed destabilization. Our results suggest substantially enhanced melting in the near future.” (From the abstract). Similar processes are well-known from evidence (conf. landforms like systems of parallel meltwater channels in the scandinavian mountain range showing the gradually lowered surface of the cold-based central parts of the ice-sheet) considering the later phases of the down-wasting of the last great ice sheet in the central scandinavian peninsula.

    Generally it seems to me that the global warming modelling attempts are suffering from one inevitable weakness: *the current growth rate of greenhouse gases in the atmosphere has no *known* precedents in the whole paleoclimatic history* – according to some estimates it is around 15 (fifteen) times higher than even during the end-permian times 252 myrs BP when enormous events of magma release leading to the build-up of the siberian traps during some ten thousands of years, burned through vast sediment beds of oil and coal, producing the greatest of the five known mass-extinction events. Hence we can not possibly know if the global system will react on this full-scale experiment with some new processes with no predecessors in the paleoclimatic history. We also cannot estimate the scale of possible consequences of this. There may be hidden tipping points in the system.

    Often it seems to me that the modelling attempts are suffering from a well-known weakness in the field of economic modelling: too much fascination with the pure mathematics and too little consideration of the limitations due to the modelling presumptions and gross simplifications, including especially: too weak overall/holistic knowledge of the facts from the historic/the paleoclimatic legacy and the involved complex social/natural (physical, chemical and biological) processes.

  35. 35
    Mr. Know It All says:

    25 – nigelj
    “Changes in ice and water storage on Earth may be responsible for both the current speed-up in Earth’s day, (conservation of angular momentum law presumably, Im not a physics guy) as well as newly observed wobbles in Earth’s rotation.””

    Incorrect. All of the ice in the Antarctic is relatively close to the earth’s axis of rotation because of the high latitude. As the ice melts, its mass will be distributeded fairly evenly around the world’s oceans, most of which are farther from the axis of rotation than where the ice is currently. This will produce a slower rotation, which is what has been happening.

    Exhibit 1:

    “As glaciers melt and sea levels rise, relatively more mass is flowing (in the form of meltwater) from near the poles to closer to Earth’s equator. That’s slowing the Earth down and gradually lengthening our days.”


    Exhibit 2: (real scientists will like this one)

    “The mass loss from these glaciers over the period 1900–1990, including those in the periphery of the Greenland Ice Sheet, is equivalent to a global mean sea-level (GMSL) rise of 0.7 ± 0.1 mm/year (18). Including this melt signal slows the rotation rate of Earth (because mass moves away from high latitudes) and leads to a significant misfit to the satellite geodetic estimate of the J2 rate. Furthermore, as noted by Munk (1), including any additional polar ice mass flux to increase the total 20th century GMSL rise to ~2 mm/year would add a signal of ~4 × 10−11 year−1 to the J2 rate for each millimeter per year of equivalent GMSL rise (19) and would further increase the misfit to the J2 rate. TPW driven by modern glacier melting is predicted to be relatively small (blue arrow, Fig. 1C), but polar ice sheet melting would likely introduce a significant misfit to the TPW observation because mass flux from either the West Antarctic or the Greenland Ice Sheet equivalent to a GMSL rise of 1 mm/year would drive a polar wander speed in excess of 1° My−1 (20). In any case, it is clear that any significant level of modern mass flux from glaciers or ice sheets would destroy the GIA (VM1)-based fits to the J2 rate and (likely) the TPW rate summarized in Fig. 1; thus, the 20th century enigma in GMSL rise (1) is defined.”


    Title is: “Reconciling past changes in Earth’s rotation with 20th century global sea-level rise: Resolving Munk’s enigma”

  36. 36

    #35, KIA–

    Fine, apparently, but we care in this context because–?

    The Mitrovica et al. paper linked says, inter alia:

    We limit our discussion to estimates based on observations up to 1990 to avoid signals associated with the onset of major polar ice mass flux and the acceleration of mountain glacier melting beginning in the early 1990s and continuing to the present.

    So, nothing specifically to do with anything that’s happened in the last 30 years.


    This value maps into an associated rate of change in Earth’s rotation rate… equivalent to an increase in Earth’s rotation period (or length of day) of ~6 millionths of a second per year.

    It’s great that we no longer need to lose sleep over Munk’s Enigma–although for myself at least the lost sleep is surely less than the increase in Earth’s rotation period–and quite wonderful that such minute changes can be accounted for with sufficient precision. But here it seems rather a sidebar item at best.

  37. 37
    nigelj says:

    Mr. Know It All @35, you’re right (for once) melting glaciers would cause the earths spin to slow down as water moves towards the equator. I must have been asleep. However while the earths spin has largely been slowing down long term due to tidal forces and melting glaciers, the earths spin HAS actually sped up since 2020 as below for whatever reason. This happens sometimes for short periods.

  38. 38
    Jean-François Fleury says:

    Question and comment to E. Steig and G. Schmidt. 1) Is there any sediment cores collected under Ross Ice-Shelf or elsewhere which could answer the question of the persistence or not of the WAIS during Eemian? 2) I have no doubts that we are going to reduce our emissions but by force. Oil producers are in disarray. Just take a look at the contents of the website peakoilbarrel. That’s instructive.

  39. 39

    @ Barton Paul Levenson
    The Clausius-Clapeyron law does not explain the global loss of water vapor and cloud cover meassured 1983-2010 by NASA satelitte:, evaporation and climate

    We as humanity are able to change a rainforest into desert – that`s for shure.
    Note that the water cycle, water vapor and cloud albedo can be influenced by many anthropogenic behaviors. The volume of runoff, soil moisture, groundwater and evaporation via plants determine the rise in sea level, cloud formation, albedo and earth temperature. (make use of google translator if needed) best regards

  40. 40

    MS 39: The Clausius-Clapeyron law does not explain the global loss of water vapor and cloud cover meassured [sic] 1983-2010 by NASA satelitte [sic]

    BPL: Sure it does. That’s the period of the “pause,” when surface temperatures were briefly stalled in their long climb and all the deniers were saying global warming had ended.

  41. 41
    Poh Poh Wong says:

    King tides are important too. Coastal states with king tide initiatives should continue to monitor such events to improve and verify the sea-level rise models and to indicate significance of local factors, if any. As sea-level rises, king tides will be increasingly higher. Today’s king tides will be tomorrow’s normal high tides. Ray & Cartwright (2007) computed times of peak astronomical tides (PAT) in each century from 0-3,000 AD. In the last century, the PAT was in 1974; in this century the PAT is 2036. Besides, as the lunar nodal cycle over a period of 18.61 years is the main force influencing high tides on decadal timescales, nodal modulations will peak before 2036.

  42. 42

    @ BPL 40 According to the theory (Clausius-Clapeyron equation)
    there should be per 1 ° C temperature rise 7% more precipitation will fall.
    However, this increase in precipitation is not uniform distributed.
    We find the greatest increase in rainfall at the heavy rain events.

    How do you explain the decrease of ~ 2mm absolute water vapor content in the atmosphere 1983-2010 ?

    Everyone knows the ice albedo effect. The cloud albedo effect is still largely unknown.

  43. 43
    Zach says:

    I think we each have a responsibility to make wise decisions and care for the earth that we have been given however, I am not concerned with the what if game. The Lord has promised that there will never be another global flood. All of the scientists are chasing wind, trying to figure out a solution to a problem while looking at the wrong data. Look beyond the physical for the questions that matter most. Seek Him and He will draw near to you.

  44. 44
    Steven Emmerson says:

    Matthias Schürle @ 42 wrote:

    How do you explain the decrease of ~ 2mm absolute water vapor content in the atmosphere 1983-2010?

    According to the peer-reviewed paper “”, there was no decrease during that time period.

  45. 45

    @StevenEmmerson 44

    5.5 ISCCP
    The International Satellite Cloud Climatology Project (ISCCP) provides cloud properties over
    a period of more than 35 years (Rossow and Schiffer, 1991; Rossow et al., 1996; Rossow and
    Schiffer, 1999). This project was established in 1982 as part of WCRP to collect weather
    satellite radiance measurements (from geostationary and polar orbiting satellites) and to
    analyze them to infer the global distribution of clouds, their properties, and their diurnal,
    seasonal and inter-annual variations. The resulting data records and analysis products are
    being used to study the role of clouds in climate, both their effects on radiative energy
    exchanges and their role in the global water cycle. This project and its results are considered
    to be the state of the art today on what can be derived from routine weather satellite data.
    ISCCP is the only other existing TCDR for cloud physical property products (here we mean
    products CPH, LWP and IWP). However, it has the disadvantage that it is based on different
    satellite types – polar and geostationary – of which most of the latter do not contain the
    necessary narrow-band channels for accurate retrieval of LWP and IWP.

  46. 46
    Piotr says:

    Re: Matthias Schürle (45)
    Where in the quoted by you text, there is a proof for your earlier contested claim, namely:
    Matthias Schürle(42) How do you explain the decrease of ~ 2mm absolute water vapor content in the atmosphere 1983-2010 ?

  47. 47

    MS 42: How do you explain the decrease of ~ 2mm absolute water vapor content in the atmosphere 1983-2010?

    BPL: Don’t know, don’t care. Whatever the observation, it doesn’t overturn basic physical chemistry.

  48. 48

    #45, Matthias S.–

    Your reply to Steve is non-responsive, as while the bona fides of the project may be just as stated, it is concerned with *cloud* climatology, providing 6 data products:

    Fractional Cloud Cover CM-11015 (CFC)
    Joint Cloud property histogram CM-11025 (JCH)
    Cloud Top level CM-11035 (CTO)
    Cloud Phase CM-11045 (CPH)
    Liquid Water Path CM-11055 (LWP)
    Ice Water Path CM-11065 (IWP)

    (Of course, it was evident right there in the name: “The International Satellite Cloud Climatology Project.”)

    Not one of those products has to do with water vapor, which was the topic at hand. Apparently you were a little phased out.

  49. 49
    Steven Emmerson says:

    Matthias Schürle’s #45 posting doesn’t provide evidence of a decrease in atmospheric water vapor.

  50. 50
    Piotr says:

    Matthias Schürle (42, 45): “How do you explain the decrease of ~ 2mm absolute water vapor content in the atmosphere 1983-2010 ? “

    In addition to your proof of that statement not containing this number,
    now MARodger in Unforced Variations 1 Jun 2021 refers to: Pascolini-Campbell, M. et al. (2021) ‘A 10 per cent increase in global land evapotranspiration from 2003 to 2019’ [Links to the abstract and CarbonBrief article in MAR post]

    So the only way this could be linked to “~ 2mm absolute water vapor content” would be if you had greatly increased precipitation. But warmer temps. mean _lower_ relative humidity (even at the same absolute water content), hence MORE difficult to make rain.

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