Sea level rise: isostatic adjustment

by Judith Curry

A discussion thread to ponder the uncertainties in glacial isostatic adjustment and the implications for past and future sea level rise.

I’m in the process of completing my report on the sea level rise, the preliminary notes for which were presented in my recent 7 part series Sea level rise acceleration (or not).  I very much appreciate all the input I received in the comments and via email.

While glacial isostatic adjustment was discussed (or at least mentioned) in several of these posts, I did not take a critical, skeptical look at what has been done.  Nor did I summarize the uncertainties and their implications for assessments of past and predictions of future sea level rise, particularly local sea level rise.

I realize we have discussed this before, but I want to make sure I am not missing the boat in some way.


The University of Colorado web page provides this explanation:

The correction for glacial isostatic adjustment (GIA) accounts for the fact that the ocean basins are getting slightly larger since the end of the last glacial cycle. GIA is not caused by current glacier melt, but by the rebound of the Earth from the several kilometer thick ice sheets that covered much of North America and Europe around 20,000 years ago. Mantle material is still moving from under the oceans into previously glaciated regions on land. The effect is that currently some land surfaces are rising and some ocean bottoms are falling relative to the center of the Earth (the center of the reference frame of the satellite altimeter). Averaged over the global ocean surface, the mean rate of sea level change due to GIA is independently estimated from models at -0.3 mm/yr. The magnitude of this correction is small (smaller than the ±0.4 mm/yr uncertainty of the estimated GMSL rate), but the GIA uncertainty is at least 50 percent. However, since the ocean basins are getting larger due to GIA, this will reduce by a very small amount the relative sea level rise that is seen along the coasts. 

This means that if we measure a change in GMSL of 3 mm/yr, the volume change is actually closer to 3.3 mm/yr because of GIA. We apply a correction for GIA because we want our sea level time series to reflect purely oceanographic phenomena. In essence, we would like our GMSL time series to be a proxy for ocean water volume changes. This is what is needed for comparisons to global climate models, for example, and other oceanographic datasets.

This correction is now scientifically well-understood and is applied to GMSL estimates by nearly all research groups around the world. Including the GIA correction has the effect of increasing previous estimates of the global mean sea level rate by 0.3 mm/yr.

Sea level budget

This figure of sea level budget from Chen et al. (2017) clearly illustrates the issue.

The unadjusted values show a deceleration in the rate of sea level rise, whereas the adjusted values show an acceleration. Chen et al. state:

the unadjusted GMSL exhibits a slightly decreasing rate of rise from about 3.5 mm/yr during the first decade to 3.0–3.3 mm/yr during the second. In contrast, the rate of the GPS-based adjusted GMSL rise increases by 0.5 mm/yr from about 2.4 ± 0.2 (1σ ) mm/yr in 1993 to around 2.9 ± 0.3 mm/yr in 2014 (2.8 ± 0.2 to 3.2 ± 0.3 mm/yr for the GIA-based adjusted GMSL). That is, the time-varying trend of the adjusted altimeter data suggests an acceleration in GMSL , with the dominant increase in the rate of rise occurring in the recent decade.

Tamisiea 2011 wrote a comprehensive review on on the GIA.  From the abstract:

Studies determining the contribution of water fluxes to sea level rise typically remove the ongoing effects of glacial isostatic adjustment (GIA). Unfortunately, use of inconsistent ter- minology between various disciplines has caused confusion as to how contributions from GIA should be removed from altimetry and GRACE measurements. In this paper, we review the physics of the GIA corrections applicable to these measurements and discuss the differing nomenclature between the GIA literature and other studies of sea level change. We then examine a range of estimates for the GIA contribution derived by varying the Earth and ice models employed in the prediction. We find, similar to early studies, that GIA produces a small (compared to the observed value) but systematic contribution to the altimetry estimates, with a maximum range of −0.15 to −0.5 mm/yr. Moreover, we also find that the GIA contribution to the mass change measured by GRACE over the ocean is significant. In this regard, we demonstrate that confusion in nomenclature between the terms ‘absolute sea level’ and ‘geoid’ has led to an overestimation of this contribution in some previous studies. A component of this overestimation is the incorrect inclusion of the direct effect of the contemporaneous perturbations of the rotation vector, which leads to a factor of ∼two larger value of the degree two, order one spherical harmonic component of the model results. Aside from this confusion, uncertainties in Earth model structure and ice sheet history yield a spread of up to 1.4 mm/yr in the estimates of this contribution. However, even if the ice and Earth models were perfectly known, the processing techniques used in GRACE data analysis can introduce variations of up to 0.4 m/yr. Thus, we conclude that a single-valued ‘GIA correction’ is not appropriate for sea level studies based on gravity data; each study must estimate a bound on the GIA correction consistent with the adopted data-analysis scheme.

Concerns about the analysis of satellite data for sea level rise were summarized in a previous post Sea level rise acceleration (or not): Part IV Satellite era record (scroll down towards the bottom), focusing on an exchange between Nils Axel Morner and Steve Nerem.

All this makes my head hurt.  The punchline of all this seems to be that if you assume that the ‘glass’ remains constant in size and shape, then the amount of water in the glass is increasing, at an apparently accelerating  rate.  However, if the glass is expanding in diameter, then the increase in the level of the water from increasing the amount of water in the glass rises more slowly.

West Antarctic Ice Sheet

This post was actually triggered by a recent article: Rising ground under West Antarctica could prevent ice sheet collapse.  This is based on a recent paper by Barletta et al. who found that the ground under the rapidly melting Amundsen Sea Embayment of West Antarctica is rising at the astonishingly rapid rate of 41 millimeters, or more than 4 cm, per year.  If this trend increases as the study projects, then the grounding line, which is the spot where the marine-based ice shelf of the Pine Island Glacier meets bedrock, will have risen by 8 meters, or 26.2 feet, in 100 years.  Such rapid rebound could stabilize the ice sheetby driving the grounding line for the marine ice sheet towards the sea, leading to less of the underside of the ice being exposed to the warm ocean.  However, the rising of the ground may have caused scientists to underestimate ice loss in the region by 10%, since the rising Earth partially hides the gravity signal coming from ice loss.


These new measurements of Glacial Isostatic Adjustment (GIA), the scientific term for uplift due to ice sheet unloading, are an important part of a wider story about the fate of the Antarctic ice sheets, said Doug Kowalewski, the Antarctic Earth Sciences program director in the National Science Foundation’s Office of Polar Programs (OPP).

“The observed GIA response captured by the POLENET array is an order of magnitude greater than previously thought. The upcoming challenge is to couple the GIA observations with ice-sheet models,” Kowalewski said.

While this is good news for the WAIS, it does not exactly inspire confidence in our quantitative understanding of the GIA.

Comparison with tide guages

Those that are skeptical of the satellite observations argue ‘but the tide guages.’  As reported in Part IV, there have been several studies that compare the tide guage with altimeter values during the period since 1993 and find good agreement:

Merrifield et al. (2009): After 1990, the global trend increases to the most recent rate of 3.2 ± 0.4 mm yr-1, matching estimates obtained from satellite altimetry.

Jevrejeva et al. (2014): There is a good agreement between the rate of sea level rise (3.2 ± 0.4 mm· yr-1) calculated from satellite altimetry and the rate of 3.1 ± 0.6 mm·yr-1  from tide gauge based reconstruction for the overlapping time period (1993–2009).

Hay et al. (2015): Our analysis, which combines tide gauge records with physics-based and model-derived geometries of the various contributing signals, also indicates that GMSL rose at a rate of 3.0 ± 0.7 millimetres per year between 1993 and 2010 . . . is also consistent with the estimate based on TOPEX and Jason altimeter measurements (3.2 ± 0.4 mm yr-1 for the period 1993–2010.)

Dangendorf et al. 2016our estimate of 3.1 ± 1.4 mm⋅y−1 from 1993 to 2012 is consistent with independent estimates from satellite altimetry.

So, what actually went into these analyses?  Dangendorf (2016) describes what they did:

Here we present a GMSL reconstruction that accounts for ocean volume redistribution, local observations [mostly global positioning system (GPS)] of VLM, and geoid changes caused by ongoing GIA, present-day ice melt, and TWS, including ground- water depletion and water impoundment behind dams. We base our approach on an area-weighting average technique and on recent scientific achievements made for each individual correction. Our tide gauge selection consists of 322 stations, for which VLM corrections with uncertainties of less than 0.7 mm/yr  are available. After accounting for VLM, each tide gauge is further corrected for geoid changes from ongoing GIA, glacier/ice-sheet melting, and TWS. The tide gauges are then grouped into six coherent regions objectively defined to account for water volume redistribution. Within each oceanic region, a regional mean sea level curve is built by recursively combining the two nearest stations into a virtual station halfway, until only one station is left. 

After all this, one is still left with the argument ‘but the tide guages.’

Local sea level rise

What does all this mean for local sea level rise? Pretty much nothing, apparently, with regards to recent and historical local sea level rise. Looking at raw, local tide gauge data in many locations shows much lower values over the past 3 decades than 3.2 mm/yr  (JC’s anecdotal eyeball estimate), with the exception of regions that are sinking from geological processes or land use practices.

What matters to local decision makers is their local rate of sea level rise, relative the local coast (whether it is rising or sinking for whatever reason).  Understanding the causes of their local sea level rise helps them understand what they can do to address the problem.

Projections of future local sea level rise are of course also relevant.  But such projections should account for the lessening of local sea level rise  by enlarging the ocean basins.


Assuming that the uncertainty in GIA adjustments are ‘in the noise’ of global sea level rise may not be entirely justified.  The adjustments to the satellite data that emerged in the discussion between Morner and Nerem do not inspire confidence in the estimate of sea level rise from satellite data, and the low level of stated uncertainty strains credulity.

I would appreciate any additional insights you have on this topic, recent references, etc.



121 responses to “Sea level rise: isostatic adjustment

  1. Reblogged this on Climate Collections.

  2. It sorta looks as if someone is trying a bit too hard to make the GPS corrected tide gauge readings and the satellite readings of increased sea level look as if the satellites are not reporting an artifact of their inaccuracy.

    • It is worse than that.

      If the ocean floor is sinking 0.3 mm/y the land surface is rising 0.7 mm/y (all that magma goes somewhere). If the volume of the ocean was constant the sea level relative to land would drop 1 mm/y.

      The University of Colorado GMSL is an estimated change in ocean volume.
      The UC GMSL would report 1 mm/y if there was no sea level rise.

  3. In addition to the many complexities hurting all of our heads, this may be referring to another issue (or I misinterpret):

    “The altitude of the satellite is established with respect to an ellipsoid, which is an arbitrary and fixed surface that approximates the shape of the Earth. The difference between the altitude of the satellite and the range is defined as the sea surface height (SSH) (Fig. 1B). Subtracting from the measured SSH a reference mean sea surface (e.g. the geoid), one can obtain a ‘SSH anomaly’. The global average of all SSH anomalies can be plotted over time to define the global mean sea level change, which can be considered as the eustatic, globally averaged sea level change.

    The shape of the geoid is crucial for deriving accurate measurements of seasonal sea level variations (Chambers, 2006). According to Rovere et al. (2016) measurements of paleo eustatic sea level (ESL) changes bear considerable uncertainty. Further, sea level changes on Earth cannot be treated as a rigid container although eustasy is defined in view of Earth as a rigid container. In reality, internal and external processes of the earth such as tectonics, dynamic topography, sediment compaction and melting ice all trigger variations of the container and these ultimately affect any sea level observation.”

    The study is Why would sea-level rise for global warming and polar ice-melt? By Aftab Alam Khan published in Geoscience Frontiers

    • interesting paper (my head hurts even more)

      • Doesn’t the low rate of SLR during the deglaciation following the LIA before 1950 also imply a large change in basin?

      • And doesn’t the GAT change and melting imply a larger forcing than recent decades?

    • ‘an ellipsis, which is an arbitrary and fixed surface’

      Well, maybe not so fixed. An aspect crucially important to calculating uncertainties of GIA.
      The pdf below includes published results of calculations of the major semi axis of the world geodetic ellipsis WGS84. The calculated results show a progressive change between 1992 and 2003 that implies that the ellipsis increased by 30cm over that period. This in the very least raises uncertainties that are relevant to the calculation of GIA.

      Warning, this article is presented in the context of an alternative paradigm which some readers my find offensive or upsetting. It’s main purpose was to call for a recalculation of the major semi axis, which has not been done in 13 years, to determine if the length of the semi axis has changed. An issue of uncertainty.

      • Earth expansionists! Got to love them. They are an alternative to plate tectonics. No reason to be offended or upset. In most branches of science, the minority opinion is not cause for alarm. I find that the amount of sea floor spreading is larger than the expansion (if any), but I have no issue with listening to them with an open mind. I even knew a couple in my college days. Science is furthered, not compromised by alternative paradigms.

  4. The elephant in the room is clearly Greenland and the growth rate of its contribution which is increasing by 10% per year (a 7-year doubling time) averaged over the last 20 years. At this growth rate, it will contribute 10 mm/yr well before 2050. Other factors like GIA will pale in comparison by then.

  5. What about other sources (i.e. non-glacial rebound) of changes in bottom bathymetry? Are changes in the sea floor known to millimeters or centimeters? These changes could be from plate tectonics as well as elevation/depression over time of the bottom due to mantle activity deeper down.

    Not my area of expertise, but I recall papers on this when I was Editor-in-Chief of the US National Science Report to the IUGG (1991-1994) for the American Geophysical Union. Read each of the papers including those on solid Earth issues.

    • David L. Hagen (HagenDL)

      rpielke Good question. Erosion sediments are an interesting example.
      The Bengal Fan extends 3,000 km and is up to 16.5 km thick.
      Curray, JR, Emmel FJ, Moore DG. 2002. The Bengal Fan: morphology, geometry, stratigraphy, history and processes. Marine and Petroleum Geology. 19:1191-1223.

      PS Bengal Fan sediments now indicate insolation changes.
      200,000 years of monsoonal history recorded on the lower Bengal Fan – strong response to insolation forcing

      The Bengal Fan monsoonal record shows very clear and strict responses to insolation forcing in the lower part from ~200 ka to the Younger Toba Tuff during Marine Isotope Stage (MIS) 7 – 5, and less distinct response patterns after deposition of the ash during MIS 4 – 2, consistent with lowamplitude changes in insolation.

      Two-stage opening of the Dover Strait and the origin of island Britain Nature Communications volume 8, Article number: 15101 (2017)

      Late Quaternary separation of Britain from mainland Europe is considered to be a consequence of spillover of a large proglacial lake in the Southern North Sea basin. Lake spillover is inferred to have caused breaching of a rock ridge at the Dover Strait, although this hypothesis remains untested. Here we show that opening of the Strait involved at least two major episodes of erosion. Sub-bottom records reveal a remarkable set of sediment-infilled depressions that are deeply incised into bedrock that we interpret as giant plunge pools. These support a model of initial erosion of the Dover Strait by lake overspill, plunge pool erosion by waterfalls and subsequent dam breaching. Cross-cutting of these landforms by a prominent bedrock-eroded valley that is characterized by features associated with catastrophic flooding indicates final breaching of the Strait by high-magnitude flows. These events set-up conditions for island Britain during sea-level highstands and caused large-scale re-routing of NW European drainage.

      J. Collier A megaflood in the English Channel 2017

      The data showed a set of six bowl-shaped depressions 5–10 km long, 4–6 km wide and up to 120 m deep. Importantly, the holes were in exactly the right place – at the foot of the chalk outcrop where the escarpment would have been (figure 5). Carving such a set of holes into solid bedrock requires the force of water that would result from overspill from a 200–300 m high precipice. Initially this would have been the most spectacular waterfall in modern Britain, until eventually removal of the lip of the dam gave way to a full-scale collapse of the barrier and the contents of the lake thundered down onto the dry, tranquil English Channel valley below.

    • What was the change in sea floor volume from the Sumatra earthquake in 2004 or the Japan one in 2011? They must have been large from the tsunami they created. Were they factored into the correction or too small?

  6. I worked for government for 5 years – on first moving to north Queensland – as the engineer in charge of beaches. I then went off and built a marina in the Whitsundays and project managed a $500M mixed urban coastal development – including storm surge inundation mapping. Well – someone had to do it.

    Sea level rise at my place as predicted by ‘coastadapt‘ with a low emissions scenario. There are a number of components – ocean expansion with warmth, balances between ice and water and groundwater and surface water. The balances add up to some 0.4m. This is not in any sense difficult to adapt to – development set backs, retaining mangroves and dunes, ubiquitous engineering safety margins on floor levels, tsunami and storm surge warning systems. escape routes and emergency responses.

    My place is set into a granite hill some 15m above mean sea level – which I can see over the mangroves. It is secure against flooding, fire, storm surge and anything but the largest tsunamis. For which – as a good coastal engineer and environmental scientist over decades – I have escape plans. I plan for tsunamis rather than sea level rise.

  7. The economic impact of sea level rise in 2100, relative to 1900, as projected by FUND3.9 , is -0.03 % of global GDP.

    It’s trivial.

  8. This article covers a recent study that finds the level of uncertainty in GIA amounts have been underestimated.

  9. “What matters to local decision makers is their local rate of sea level rise, relative the local coast (whether it is rising or sinking for whatever reason). Understanding the causes of their local sea level rise helps them understand what they can do to address the problem.”

    The city of Bangkok has had cumulative subsidence since 1900 of 1250 mm. At times in the early 1980s the annual rate of subsidence was 120 mm. I was stationed there in 1968 and there was clear evidence in buildings and roadways of that sinking. It has gotten only worse since. A 2015 report projects that additional subsidence will be 190 mm by 2025.

    Over the last 25 years some 100 skyscrapers have been built in Bangkok. There are more large buildings in the planning stages. Even in the early 1990s when the first of those buildings were being designed, local officials knew of the City’s history of subsidence. While some reductions in groundwater abstraction have helped to curtail the rate of subsidence, those measures can do only so much. Placing millions of tons of concrete on the City’s unstable soils only exacerbates the inherent problems they face.

    Who becomes legally culpable in 2100 for those sinking skyscrapers? The world community for its share thru AGW or the City of Bangkok for its short sighted development policies?

    • If they are not sinking deep piles – it would be a surprising engineering design decision.

      • That’s true, Chief, but I was thinking about the “sea level rise” and the attribution between natural rise of the ocean,the AGW component and subsidence. I wasn’t focused on the leaning towers as they have had in, I think, São Paulo.

        Change of subject. I hope you will continue to discuss the possible changes in the north as you’ve done above. The entire AO, NAO, AMO, AMOC etc, is fascinating. I think JimD is getting a little bit out over his skis. Skeptics will never win the debate, though. If the Arctic Sea Ice extent begins to show recovery and the Antarctic sea Ice declines, then that will be the new poster child. If Al Gore’s house is covered with 50 feet of glacial material, then they will say it would have been 100 feet except for CO2. Like Roseanne Rosannadanna said, it’s always something.

      • My non-engineering brain just got your point about compaction. Accepted.

      • This is getting interesting. I just looked at a few sources and they indicate bedrock under Bangkok ranges from 500 to 2000 meters. Good question about how deep those pilings could or would go.

      • Most (if not all) pilings are shallow relative to 500 to 2000 meters. Pilings would normally be used in soils with cohesion (clays). Spread footings would be used in soils that lack cohesion (sands). Without access to the soil report, I would not try to guess the type of footings in an area even knowing that the area is subsiding.

        There continue to be issues with buildings sinking. About 1998 there was a high rise building in Las Vegas (casino) that had more than tolerable displacement during construction due to the engineer thinking the hard pan there (it is considerable in thickness) would support the building. It did not.

        However, I would like to think engineers are getting better. In fact the poster child for the need for foundation engineering, the leaning tower of Pisa, was saved by engineers pumping grout below the structure to prop up one side and to bring it back to historical leaning amounts. I remember reading the reports. They could have corrected the leaning more than they did, but they felt that maintaining historical accuracy was important. Also the construction of the structure tried to compensate for previous deviations meaning that there is no “upright” for the structure anyway. The building is doomed to fail eventually, and so will need further intersessions on its behalf in the future if it is to be maintained as a historical landmark.

  10. David L. Hagen (HagenDL)

    curryja Thanks for insightful perspectives. Here are some large isostatic changes that might be of interest.
    Large step changes in lithospheric thickness.
    Continental margins show large lithospheric changes. Do these impact the Glacial Isostatic Adjustments?
    Shahraki, M., Schmeling, H. and Haas, P., 2018. Lithospheric thickness jumps at the S-Atlantic continental margins from satellite gravity data and modelled isostatic anomalies. Tectonophysics, 722, pp.106-117.

    We analyzed satellite derived geoid data and, after filtering, extracted typical averaged profiles across the Western and Eastern passive margins of the South Atlantic. They show geoid jumps of 8.1 m and 7.0 m for the Argentinian and African sides, respectively.

    Isostatic river displacement
    Pico, T., Mitrovica, J.X., Braun, J. and Ferrier, K.L., 2018. Glacial isostatic adjustment deflects the path of the ancestral Hudson River Geology. 2018 May 30.

    Quantifying the pace of ice-sheet growth is critical to understanding ice-age climate and dynamics. Here, we show that the diversion of the Hudson River (northeastern North America) late in the last glaciation phase (ca. 30 ka), which some previous studies have speculated was due to glacial isostatic adjustment (GIA), can be used to infer the timing of the Laurentide Ice Sheet’s growth to its maximum extent. Landscapes in the vicinity of glaciated regions have likely responded to crustal deformation produced by ice-sheet growth and decay through river drainage reorganization, given that rates of uplift and subsidence are on the order of tens of meters per thousand years. We perform global, gravitationally self-consistent simulations of GIA and input the predicted crustal deformation field into a landscape evolution model. Our calculations indicate that the eastward diversion of the Hudson River at 30 ka is consistent with exceptionally rapid growth of the Laurentide Ice Sheet late in the glaciation phase, beginning at 50–35 ka.

    The “Zanclean deluge” Megaflood filled the Mediterranean
    The Zanclean megaflood may have caused one of the highest rate of isostatic adjustment.
    Garcia-Castellanos, D., Estrada, F., Jiménez-Munt, I., Gorini, C., Fernández, M., Vergés, J. and De Vicente, R., 2009. Catastrophic_flood_of_the_Mediterranean_after_the_Messinian_Salinity_Crisis Nature 462(7274):778-81 · December 2009

    The Mediterranean Sea became disconnected from the world’s oceans and mostly desiccated by evaporation about 5.6 million years ago during the Messinian salinity crisis. The Atlantic waters found a way through the present Gibraltar Strait and rapidly refilled the Mediterranean 5.33 million years ago in an event known as the Zanclean flood. The nature, abruptness and evolution of this flood remain poorly constrained. Borehole and seismic data show incisions over 250 m deep on both sides of the Gibraltar Strait that have previously been attributed to fluvial erosion during the desiccation. Here we show the continuity of this 200-km-long channel across the strait and explain its morphology as the result of erosion by the flooding waters, adopting an incision model validated in mountain rivers. This model in turn allows us to estimate the duration of the flood. Although the available data are limited, our findings suggest that the feedback between water flow and incision in the early stages of flooding imply discharges of about 10^(8) m(3) s(-1) (three orders of magnitude larger than the present Amazon River) and incision rates above 0.4 m per day. Although the flood started at low water discharges that may have lasted for up to several thousand years, our results suggest that 90 per cent of the water was transferred in a short period ranging from a few months to two years. This extremely abrupt flood may have involved peak rates of sea level rise in the Mediterranean of more than ten metres per day.

    Devon M. Burr, Paul A. Carling, Victor R. Megaflooding on Earth and Mars, Baker 2009

    1.4.2 Laurentide Ice Sheet: ice-marginal lakes

    “The greatest megafloods developed from the last of the ice-marginal lakes, a union between Lake Agassiz in south-central Canada and Lake Ojibwa in northern Ontario. The redulting megalake held about 160000 km3 of water, which was released subglacially about 8200 years ago under the ice sheet and into the Labrador Sea via the Hudson Strait (Clarke et al., 2004).

    note 8 mentions of “isostatic”.

  11. thank you for this interesting and comprehensive lecture

  12. Averaged over the global ocean surface, the mean rate of sea level change due to GIA is independently estimated from models at -0.3 mm/yr.

    The special words are “GIA is independently estimated from models”, You can trash that as not really meaning anything based on actual data.

    • My non-scientist brain has never seen (or heard) an explanation of GIA that makes any sense. Until someone can help me comprehend this phenomenon, I will assume it’s another product of models that’s intended to add another jimmied-up adjustment to climate data, this time to add a positive adjustment to slr.

      • Soils have spaces between the particles. These spaces contain air and/or water. When weight is place on soils, over time these spaces contract. This is called soil compaction. Soil compaction is a function of water content, time, weight and vibration. Water content vs compaction is a curve that the compaction goes up for low water content and then down for high water content. The point at which the compaction is the greatest is called the optimal water content. The amount that soils compact over time depends on the soils cohesion. Soils with no cohesion compact fairly linearly with time to a point where compaction is no longer possible (theoretically). Soils with cohesion compact less and less with time. The amount of weight that is placed on the soil will impact the amount of compaction. This weight can be other soil, ice, water, buildings, etc. When the weight is removed, over time the soils can uncompact (rebound). One way to envision this is with water infiltration. The water gives the soil buoyancy and expands the pore space. Another way to look at this is with expansive soils. Clay soils can expand with huge forces when they come into contact with water pushing the soil above them up.

        The soils in Michigan, for instance, have measurable rebound due to ice retreat. During the last ice age, the soils were compacted due to the weight of the ice over them. The ice melted, and the soils are currently in rebound. Much of the desert areas (as well as some other areas) that are heavily populated have measurable subsidence due to ground water removal. This is the case for Tucson, and Phoenix Arizona and for Las Vegas, Nevada for instance.

        GIA is real, the problem is in calculating it in areas that do not have good historical records. The sea floor, for instance is a huge unknown. We know that the sea floor is constantly moving (we can see that the floor is youngest at the spreading centers and gets older further out towards the continents). However, we do not have good data on specifics such as island creation, how hot spots affect sea floor elevations, etc.

      • atandb. I understand the idea of compaction and rebound. What eludes me is why the oceans basins get larger, and that scientists can understand this to the degree that they attach a specific number to it. Before you know it, an adjustment is made without comment and it becomes set in stone. The UCAR statement is obviously an attempt to do this.

      • I agree, I would not put a number on GIA nor the sign of the number, except in specific locations that have good historical records. Stating that the ocean volume is getting larger would require more information than I am aware exists.

  13. The real problem is not glacial isostatic adjustment. That is a trivial problem. Isostasy is the notion is the notion that equilibrium will be achieved between the plastic levels of the mantle and the less buoyant oceanic crust and the more buoyant continents.

    It never will. Even as the Canadian Shield rebounds from the weight of glaciers, the western US is rising as well, and it had much less ice. I just returned from a second 20 day trip down the Grand Canyon in 7 months. The record is crystal clear. Transgression after transgression, through the Carbo-Permian glaciation and not. At orbital scales and much bigger scales.

    Tectonic forces rule the displacement of water to land, and the reverse.

    • Didn’t you get the memo from Mike Mann? No palaeo data earlier than 40kya is reliable. And CO2 stayed at 280 from creation and the garden of Eden till we bit the apple of the industrial revolution.

      That’s us told. Stick to the hymn-sheet if you know what’s good for you.

    • Snowfall rules the displacement of water from ocean to land. Thawing rules the displacement of water from land to ocean. Nothing else matters much, no mater what causes it.

      • There is an excellent section through the Carbo Permian glaciation in the Grand Canyon, and another in the Honaker Trail formation exposed in Cataract Canyon and also along the San Juan river. As you suggest, there are small scale marine to fluvial oscillations embedded in every member of these formations, likely due to ice-ostacy. But superimposed on these are large scale marine transgressions. Melt all the ice on the planet today and you still won’t get a seaway through central North America.

        At orbital scales of less than a half million years, nothing but ice matters for sea level oscillations of a few hundred feet. When you start trying to correct for glacial rebound, you enter a realm where tectonic forces capable of oscillations of thousands of feet are on the same order.

  14. However, if the glass is expanding in diameter, then the increase in the level of the water from increasing the amount of water in the glass rises more slowly.

    … or, the glass isn’t really getting bigger and changes in sea level are increasing but at a decreasing rate.

  15. What sort of adjustment must we make for billions of cubic feet of lava flowing into the ocean from the Kilauea volcano eruption…?

  16. Steven Mosher

    Gosh, I remember when I left grad school to enter industry.
    Applying statistics to literary texts had been easy, but in industry the guys
    were all talking about kalmen filters and other things I did not understand.

    It never occurred to me to ask a random sampling of people to help me.
    I sought out a few experts, they gave me text books, I studied. Then they
    quizzed me until I proved that I understood. Since I knew less than they knew, they decided when I had mastered the topic. not me.

    There is no shame in asking for help, but there are proven ways that are more effective, GENERALLY, than others.
    the “wisdom” of crowds has some appeal.
    Not in this case. no harm in asking denizens, but you might cover more ground if you sat down with folks published in the field. Its a better form of aspirin for the head hurting.

    • I’ve read all the literature and the assessments. This is a check on ‘groupthink’ by the establishment scientists publishing on this topic.

    • afonzarelli

      Mosher, that is your problem. You trust the experts. Kind of like when you say that Svalgaard is your go to guy on solar. Are you aware that Dr S does not believe that the oceans are warming? How can you have any faith in the man’s assessment of any solar/climate connection when he doesn’t even think that the oceans are warming? (and one has to wonder where else your shallow faith has led you astray)…

  17. 4TimesAYear

    Reblogged this on 4TimesAYear's Blog.

  18. Bias in Estimates of Global Mean Sea Level Change Inferred from Satellite Altimetry

    Estimates of regional and global average sea level change remain a focus of climate change research. One complication in obtaining coherent estimates is that geodetic datasets measure different aspects of the sea level field. Satellite altimetry constrains changes in the sea surface height (SSH; or absolute sea level), whereas tide gauge data provide a measure of changes in SSH relative to the crust (i.e., relative sea level). The latter is a direct measure of changes in ocean volume (and the combined impacts of ice sheet melt and steric effects), but the former is not since it does not account for crustal deformation. Nevertheless, the literature commonly conflates the two estimates by directly comparing them. We demonstrate that using satellite altimetry records to estimate global ocean volume changes can lead to biases that can exceed 15%. The level of bias will depend on the relative contributions to sea level changes from the Antarctic and Greenland Ice Sheets. The bias is also more sensitive to the detailed geometry of mass flux from the Antarctic Ice Sheet than the Greenland Ice Sheet due to rotational effects on sea level. Finally, in a regional sense, altimetry estimates should not be compared to relative sea level changes because radial crustal motions driven by polar ice mass flux are nonnegligible globally.

    It will be hilarious to watch the wording in this study get beaten and abused.

  19. David Wojick

    As several people have mentioned, the SLR community seems to be either ignorant of, or ignoring, the tectonics community. Tectonic velocities routinely average around 5 cm per year, all over the globe. Here is a nice notional global map of this:

    A Google images search on tectonic motion gives many more.

    Given these huge motions and the enormous forces they produce, it is all but impossible that the ocean basin not change its shape over time. That the constant volume elevation might increase by a mere 2-3 mm per year is not at all surprising. GIA has nothing to do with this.

    Thus this looks like yet another case of the climate change activist scientist community ignoring natural variability that may well explain all of the change we see. Perhaps the tectonics people simply do not want to be seen as meddling in SLR, but they do have models and one wonders what these might say about tectonic SLR changes.

    • David Wojick

      There is also a good bit of vertical displacement in this dynamics. For example, the Himalayas continue to rise more than 1 cm a year. 3 mm starts to look small.

    • David Wojick

      It seems I have identified yet another fundamental issue that is beyond discussion. I shall add this to my list.

      There is in philosophy of science and math a sub-field called “fundamentals” which I did a lot of work in. The idea is to find the often unstated assumptions that underlie a field. In the SLR case it is that the very thin film of rock, water and air that covers the 8000 mile diameter dynamic molten ball is not affected by said ball. What a hoot!

  20. It seems that the SLR is accelerating. But the total volume of the ocean’s basins is more.

    SLR = Water in the basin change plus basin changes. So are we after the SLR or the SLR we would’ve got except for basin changes?

    For policy, one is more useful. For policy, acceleration has a meaning. Using Chen’s figure 4 in the article, we don’t have, for policy, acceleration. We have people wanting to say acceleration and saying it, when for policy, it is not.

    The climate scientists can balance their books on their own time. Sure, they want to count all the water, it’s good practice. But then to twist those books for policy is wrong. And the climate scientists ought to say so. You can say the volume is accelerating. Then the next question is, what does that mean for Oceanside, Red State? With or without ocean basin expansion?

    There’s me and the ocean. If the ocean is going to get me I don’t want to hear about volume changes of the basin. I want to know which decade the ocean is going to get me. I don’t want an adjusted number that keeps track of volume for the models. Don’t add in stuff that will not impact me just so you can balance your books. Keep that behind the curtain and give me information that has value. Don’t wander off into the weeds, or tell me a story about your Aunt Jenny, give me value.

  21. Snowfall rules the displacement of water from ocean to land. Thawing rules the displacement of water from land to ocean. Nothing else matters much, no mater what causes it.

    Snowfall rules the ocean level fall. Thawing rules the ocean level rise.

    An ice machine requires energy to operate it and energy removed. This is the only way ice machines operate. The amount of energy that must be removed to produce ice is well known. The energy must be input and removed.

    Snowfall happens when earth albedo is low so that the solar energy can get in and this happens when earth is warmer with high IR out. Ice is produced in large quantities when these conditions are met.

    Snowfall does not happen when earth albedo is high so that the solar energy cannot get in. Ice is not produced when earth is cold and IR out is low. Low energy in and low energy out does not, can not, produce ice. Earth is cold in cold times because ice extent is large, ice is reflecting and thawing and the oceans and earth are cold with low IR out.

    Snowfall happens in warm times and results in ocean drop. Thawing happens ice cold times. Reflecting happens in cold times. Oceans rise in cold times. Warming occurs because of ice retreat.

    We warmed out of the Little Ice Age because it did not snow enough. We cooled out of the Medieval Warm Period because it snowed too much. We will warm out if this modern warm period because it is snowing enough and it will snow too much to stay warm.

    If you want to understand temperature regulation, look to the abundant water on and inside earth and the wonderful properties of water and how it changes states and the changes in the amount of energy stored in each state.

    When Mother Earth is too warm, she thaws the oceans and produces snowfall. When Mother Earth is too cold, she freezes the oceans and does not produce snowfall. The temperature that oceans freeze and thaw is the thermostat setting.

    When continents drifted and warm tropical ocean currents were allowed to flow more in cold polar regions, that supported more snowfall until it supported major ice age cycles. Ice ages, especially the major ice ages. sequestered some of the ice, increasingly in each cycle, in cold places and removed water from taking part in the next cycle. The amount of ice that was reflecting and thawing increased in cycles. The amount of water and ice involved in each cycle is less in the cycles of the recent ten thousand years. That is why we have a new normal and major ice ages will not happen.

    • Solar in powers evaporation. IR out provides energy dissipation.
      Snowfall can only occur in warm times when albedo is low and energy is coming in and being dissipated. Cold times are cold because ice is reflecting and thawing. There is little energy in and little energy dissipated, little ice is being produced in cold times.

      Dr Curry, I would like you comments.

    • Ice core records show the most ice accumulation in the warmest times.
      Ice core records show the least ice accumulation in the coldest times.

      This proves the ice production is more when there is more solar in and more IR out.

  22. Water should find it’s own level.
    Which is a complex blend of gravitational forces.
    These include the variation in external gravity from the moon and sun and planets in their elliptical orbits.
    The variation of the Earth’s gravity with it’s rotational speed. Here extremely small fractions of a second speed up or slow down could produce significant height changes.
    The variation of the earths gravity due to the solid part’s composition and shape.
    The reduction of the earths gravity due to atmospheric pressure changes.
    The change in water mass due to different salt concentrations and temperature variations.
    Not to mention the surface tension variation due to different salt concentrations and temperature variations.
    While one’s head may hurt with the concept of glacial rebound adjustments they could be safely ignored. Or one must add the reminder that the actual rise is lower than that given in GIA figures.
    Satellites and tide gauges measure pretty much the same thing, the height of the surface of the water, just relative to different bases.
    Sea level [tides] can vary by meters in their rise and fall in different parts of the world by local topography, but every spot should vary about a known mean with enough observations.
    I do not really mind which mean we use as long as the measuring methods are consistent, rigorous and reproducible .

  23. Still interesting to note that at NOAA’s Tide and Currents site, it still states:
    ” given that the absolute global sea level rise is believed to be 1.7-1.8 millimeters/year.”

  24. Is promoting vegetarianism a form of colonialism?

    “That’s why peoples living in deserts, scrub, & dry grasslands aren’t vegetarian. They’d starve. They kept close to the animals that can digest what grows there: ruminants.”

    What’s natural is hunting animals and then eating them. That’s harmony. Growing crops rearranged all kinds of Carbon.

    Consider the Inuits. You should be a vegetarian. The Alaskans make a big deal over yanking salmon out of rivers and don’t spend so much time trying to grow tomatoes.

    There’s certainly plenty to criticize. We can consider how we end with McDonald’s cheeseburgers. Agriculture has a number of areas with the potential for improvement.

    When things should be local, hunters and fishermen never stopped doing that.



    Tide gauge sea level and satellite sea level are not the same thing. One is shoreline measurements, the other is mid-ocean measurements. The mid-ocean measurements are at the mercy of thermal expansion and winds. Shoreline measurements are also at the mercy of winds, but not thermal expansion. See Ole Humlum’s discussion of this.

  26. Judith explains: “This means that if we measure a change in GMSL of 3 mm/yr, the volume change is actually closer to 3.3 mm/yr because of GIA. We apply a correction for GIA because we want our sea level time series to reflect purely oceanographic phenomena.”

    However, 3.3 mm/yr is not a volume change, it has the wrong units. All that consumers of IPCC reports need to know is the rise in GMSL, because that is the only thing people will experience. The experts who are interested in proving the change in GMSL can be explained by observed changes in volume (steric expansion, ice cap melting, etc.) and assumed changes in volume (GIA) should convert GMSL into volume and not confuse the public with a LARGER number that is based on assumptions.

    Which value is easiest to understand and reliably measure reliably measure 3.0 mm/yr (the distance) or 3.3 mm/yr (the volume)? I would certainly use the former and criticize the IPCC for using the latter.

    Don’t forget, the latest figures for the satellite altimetry era are lower 2.4 and 2.7 mm/yr (+/-0.4 mm/yr).

    • I also suspect that measuring SLR in terms of volume compounds errors. For example, let’s assume that we knew that the height of the surface of Antarctica was not changing. Of course, glacial isostatic rebound means that the land under Antarctica has risen and some volume of water has been added to the ocean. Since rebound is highly uncertain, the volume change is highly uncertain. However, the rise in GMSL must be zero, because the mass/volume that is pushing up under Antarctica is exactly the same mass/volume that the ocean floor near Antarctica has sunk.

      Since experts use a single unchanging global GIA adjustment no matter what assumptions are made about rebound around Antarctica, “alarmist” researchers can pick a large amount of rebound and exaggerate the change in ocean volume AND GMSL. (Sorry for the paranoid tone, here.)

    • Arguably, users of IPCC reports should be more interested in tide gauge data (or the change in satellite altimetry along the coasts.) Tide gauges are located where people are and where damage from rising SLR will occur. Local SLR has two components, a global component from climate change and a local component from natural and anthropogenic vertical land motion. Policymakers need to know two or three of these values, not just the global value.

      The global component of local SLR depends on which ice caps are melting, so GMSL from satellite altimetry is somewhat misleading as a metric.

      Satellite altimetry can achieve great precision in a decade, but it is prone to large systematic error in processing the data. Tide gauge data is less precise, but more relevant and reliable. IMO, a set of tide gauges corrected for VLM by GPS should be the main source of information and supplemented by the satellite altimetry record.

      • The global component of local SLR depends on which ice caps are melting, so GMSL from satellite altimetry is somewhat misleading as a metric.

        Oceans are connected, water from any ice cap or river that dumps into the oceans raises all the oceans. When one ice cap loses ice volume and a different ice cap or glacier gains ice volume they all sum together. With large outflows, there may be some time for things to even out, but they do even out and correct measurements would average out correctly. If you measure all the pieces correctly and accurately the sum is correct. If the measurements have errors that are much larger than the differences you need to know, the result does not really tell you anything. They just make up a number that supports their cause and they can’t prove it right, but no one can prove it wrong.

      • Popesclimatetheory wrote: “Oceans are connected, water from any ice cap or river that dumps into the oceans raises all the oceans.”

        Due to the gravitational attraction of ice caps, the amount of sea level rise varies with location depending on which ice cap melts.

        The Moving Boundaries of Sea Level Change: Understanding the Origins of Geographic Variability, MARK E. TAMISIEA and JERRY X. MITROVICA
        Vol. 24, No. 2, SPECIAL ISSUE ON Sea Level (JUNE 2011), pp. 24-39

        I wasn’t convinced until I did a thought experiment: What if the mass of all of ice in Greenland lay in the center of the island? What is the relative force of gravity from the Earth pulling downward compared with the horizontal plug of the gravity from the ice near the coast of Greenland? The relative forces determine the “slope” of the ocean near Greenland. A very small slope near Greenland becomes a significant change in height over a thousand kilometers of ocean or more.

      • Due to the gravitational attraction of ice caps, the amount of sea level rise varies with location depending on which ice cap melts.

        If an ice cap melts, it raises all the connected oceans, it could vary some, but all rise, the earth gravity is so much larger than ice cap gravity, your differences would be really small.

    • “However, since the ocean basins are getting larger due to GIA, this will reduce by a very small amount the relative sea level rise that is seen along the coasts.”

      Trite quibbles and an unsupported narrative from Frank? Not interesting at all – but we should recognize the nature of these supercilious comments superficially in the objective idiom of science. They are intended to create an impression of incompetence for people who really don’t know any better. It is quintessentially tribal and not a pursuit of dialogue in the service of an evolving understanding.

      There is an immense disparity of knowledge and intellect between Judith and a Frank encouraged in blogospheric echo chambers to believe in his intellectual and moral superiority over outsiders. Sorry Frank – it ain’t so.

      • Robert: I provided some reasons why why the consensus presentation of SLR may be flawed. Unfortunately, your kind words didn’t provide any useful information as to why my thoughts were incorrect.

        I was sure Judith understood why local SLR depended on which ice cap was melting and why glacial rebound had such a large impact on the estimate of ice volume lost from so I didn’t bother to provide her with a references to this subject. At an earlier post, I did provide a number of references illustrating the potential for systematic errors in satellite altimetry.

    • (Sorry for the paranoid tone, here.)

      No, you’re not.

      Don’t forget, the latest figures for the satellite altimetry era are lower 2.4 and 2.7 mm/yr (+/-0.4 mm/yr).


      • JCH: I was rushed when writing the above comment and recognized it’s tone was injudicious. I didn’t have time to revise.

        According to this paper (which sounds familiar), I should have said 2.6 and 2.9 mm/yr or perhaps the estimate of some other group was slightly lower. Needless to say, I’d choose to correct using GPS estimates of VLM rather than a GIA model.

        The recent detection of acceleration was the result of a correction of a systematic error that lowered the rate of SLR by about 50% during the first five years. The CU website has not reduced the rates of SLR it cites for the five groups to reflect this correction, including their own, which is down from 3.4 to 2.9 mm/yr in Nerem 2018. I presume that no one citing rates above 3 mm/yr now.

        Unabated global mean sea-level rise over the satellite altimeter era
        Christopher S. Watson, Neil J. White, John A. Church, Matt A. King, Reed J. Burgette & Benoit Legresy
        Nature Climate Change volume 5, pages 565–568 (2015)

        The rate of global mean sea-level (GMSL) rise has been suggested to be lower for the past decade compared with the preceding decade as a result of natural variability1, with an average rate of rise since 1993 of +3.2 ± 0.4 mm yr−1 (refs 2, 3). However, satellite-based GMSL estimates do not include an allowance for potential instrumental drifts (bias drift4,5). Here, we report improved bias drift estimates for individual altimeter missions from a refined estimation approach that incorporates new Global Positioning System (GPS) estimates of vertical land movement (VLM). In contrast to previous results (for example, refs 6, 7), we identify significant non-zero systematic drifts that are satellite-specific, most notably affecting the first 6 years of the GMSL record. Applying the bias drift corrections has two implications. First, the GMSL rate (1993 to mid-2014) is systematically reduced to between +2.6 ± 0.4 mm yr−1 and +2.9 ± 0.4 mm yr−1, depending on the choice of VLM applied. These rates are in closer agreement with the rate derived from the sum of the observed contributions2, GMSL estimated from a comprehensive network of tide gauges with GPS-based VLM applied (updated from ref. 8) and reprocessed ERS-2/Envisat altimetry9. Second, in contrast to the previously reported slowing in the rate during the past two decades1, our corrected GMSL data set indicates an acceleration in sea-level rise (independent of the VLM used), which is of opposite sign to previous estimates and comparable to the accelerated loss of ice from Greenland and to recent projections2,10, and larger than the twentieth-century acceleration2,8,10.

      • 1993 to 2014 is the rate to 2014. AVISO cites Watson et el in their processing and corrections section.

        Their current rate is 3.32 mm/yr:

      • JCH: If you look carefully at your graph, you’ll see a relatively straight line through the data of slope 3.32 mm/yr – no acceleration. The people who are reporting acceleration (like Nerem 2018) have visible curvature in their plots and that arises from the previously mentioned large correction before 2000. As best I can tell, there could data sets showing acceleration with overall rates for the entire satellite era of 3.0 mm/yr or less and older(?) sets that are linear and higher.

        As you see above, if you correct calibration sites for VLM with GPS or a GIA model, you also get different answers.

        Looking more carefully, Nerem (2018) appears to have detected acceleration by correcting for Pinatubo and ENSO, not by incorporating the systematic correction linked in my previous comment. That acceleration is 0.084 mm/yr or a huge 2 mm/yr over 25 years. Perhaps Nerem doesn’t accept the correction other are using.

        FWIW, Chen et al mentioned by Judy just below Figure 4 in this post also claims SLR rising from 2.4 to 2.9 mm/yr (1993 to 2014) using GPS (instead of modeled GIA) for calibration. Systematic errors in processing satellite altimetry data can easily shift SLR outside the confidence interval derived from noise. Which is one of the reasons why I preferred tide gauges. But, as Judy complains, obtaining a “global” tide gauge signal today involves processing the data though the GIA models with large correction factors at some sites.

  27. As a land dweller, I’m not interested in absolute ocean volume changes, only sea level relative to land, even if some sea level changes vis-a-vis land is due to subsidence. Therefore, I think the GIA adjustment isn’t necessary for most of us. It is important in an academic sense, not a practical, useful sense.

  28. This means that if we measure a change in GMSL of 3 mm/yr, the volume change is actually closer to 3.3 mm/yr because of GIA. We apply a correction for GIA because we want our sea level time series to reflect purely oceanographic phenomena. In essence, we would like our GMSL time series to be a proxy for ocean water volume changes. This is what is needed for comparisons to global climate models, for example, and other oceanographic datasets.

    In other words, they make GIA to be whatever it takes to make their SLR theories match what they think the data should be. In their words: “This is what is needed”

  29. There seem to be very large deep aquifer on every continent that hold a great deal of water. Some measurements (and probably, mostly hypothetical figuring) says that drainage to oceans can be as slow as 10,000 years for any given bit of water. Glaciers melt, rain falls, some of the water is sequestered in these aquifers.

    In terms of sea level models’ calculations, could this be relevant?

  30. The focus should be on the financial effects of sea level rise. Fact is its creeping along so slowly it will have practically no incremental financial effect than it has now. 99 year land leases cost virtually the same as a fee simple purchase the difference amortized over a hundred years pounds it into insignificance. Contrary to markets environmentalists argue for very low discount rates all they have to do is convince people that money today isn’t much better than money tomorrow. Good luck with that. Its doubtful anybody will do anything but talk about that its somebody else’s money that isn’t important today. 3mm/year works out to about the average over the entire Holocene. Today here on the West Coast the original mammal hunters to cross the Bering Strait land bridge 11,000 years ago have their communities out in about 350 meters of water.

  31. It is amazing just how much is unsettled or unknown in an allegedly long-settled area of “science.”

  32. Judith: I presume your journey’s through the SLR literature have taken you to Munk (2002). If I understand correctly, melting of polar caps results in mass moving further from the axis of rotation and a slowing of the rate of planetary rotation. Munk was able to show that little SLR could have come from melting of polar ice caps (and that the rise in ocean heat content and therefore steric expansion wasn’t large enough to explain observed SLR.)

    Twentieth century sea level: An enigma
    Walter Munk
    PNAS May 14, 2002. 99 (10) 6550-6555;

    Changes in sea level (relative to the moving crust) are associated with changes in ocean volume (mostly thermal expansion) and in ocean mass (melting and continental storage): ζ(t) = ζsteric(t) + ζeustatic(t). Recent compilations of global ocean temperatures by Levitus and coworkers are in accord with coupled ocean/atmosphere modeling of greenhouse warming; they yield an increase in 20th century ocean heat content by 2 × 1023 J (compared to 0.1 × 1023 J of atmospheric storage), which corresponds to ζgreenhouse(2000) = 3 cm. The greenhouse-related rate is accelerating, with a present value ζ̇greenhouse(2000) ≈ 6 cm/century. Tide records going back to the 19th century show no measurable acceleration throughout the late 19th and first half of the 20th century; we take ζ̇historic = 18 cm/century. The Intergovernmental Panel on Climate Change attributes about 6 cm/century to melting and other eustatic processes, leaving a residual of 12 cm of 20th century rise to be accounted for. The Levitus compilation has virtually foreclosed the attribution of the residual rise to ocean warming (notwithstanding our ignorance of the abyssal and Southern Oceans): the historic rise started too early, has too linear a trend, and is too large. Melting of polar ice sheets at the upper limit of the Intergovernmental Panel on Climate Change estimates could close the gap, but severe limits are imposed by the observed perturbations in Earth rotation. Among possible resolutions of the enigma are: a substantial reduction from traditional estimates (including ours) of 1.5–2 mm/y global sea level rise; a substantial increase in the estimates of 20th century ocean heat storage; and a substantial change in the interpretation of the astronomic record.

    A little checking shows that Mitrovica (2015) claims to have resolved Munk’s enigma by the always popular technique of tweaking three unrelated phenomena, including reducing SLR for 1900-1990 to 12 cm. However, according to Figure 4 in this post, the contribution from polar melting has increased over the last 25 years and that should predict increased slowing of the planet’s rotation since Monk’s work was done. Unfortunately Mitrovica et al didn’t apply their new model to the IPCC-assessed sources of recent SLR and predict the required slowing of rotation.

    Reconciling past changes in Earth’s rotation with 20th century global sea-level rise: Resolving Munk’s enigma
    Jerry X. Mitrovica1, et al
    Science Advances 11 Dec 2015:
    Vol. 1, no. 11, e1500679
    DOI: 10.1126/sciadv.1500679

    In 2002, Munk defined an important enigma of 20th century global mean sea-level (GMSL) rise that has yet to be resolved. First, he listed three canonical observations related to Earth’s rotation [(i) the slowing of Earth’s rotation rate over the last three millennia inferred from ancient eclipse observations, and changes in the (ii) amplitude and (iii) orientation of Earth’s rotation vector over the last century estimated from geodetic and astronomic measurements] and argued that they could all be fit by a model of ongoing glacial isostatic adjustment (GIA) associated with the last ice age. Second, he demonstrated that prevailing estimates of the 20th century GMSL rise (~1.5 to 2.0 mm/year), after correction for the maximum signal from ocean thermal expansion, implied mass flux from ice sheets and glaciers at a level that would grossly misfit the residual GIA-corrected observations of Earth’s rotation. We demonstrate that the combination of lower estimates of the 20th century GMSL rise (up to 1990) improved modeling of the GIA process and that the correction of the eclipse record for a signal due to angular momentum exchange between the fluid outer core and the mantle reconciles all three Earth rotation observations. This resolution adds confidence to recent estimates of individual contributions to 20th century sea-level change and to projections of GMSL rise to the end of the 21st century based on them.

  33. Geoff Sherrington

    The term ‘ocean container’ is used here for brevity to describe the rock walls and floors of oceans that constitute the ‘cups’ in which ocean levels are measured for rise and fall.
    Overall, the stability of the basal, non-sedimentary rocks of the ocean floors is not known, for each of: major element composition; water content; motion; and mineral assemblage. This is so for the three main units – soft rocks that rise to form mid-ocean ridges, the ridges themselves and their extensions that form ocean floor according to generalized plate tectonic theory.
    The dimensions of each of these units will change with temperature through their overall cooling regime. Their heat sources include mantle heat such as residual, radiogenic, endo- and exothermic metamorphic heat and the water in contact. Dimensions will also change with hydration/dehydration, more so if fracturing allows ‘free’ water to be taken in or expelled. (The process of dehydration is commonly invoked, for example in eclogite formation).
    At the present time, observational data does not allow a conclusion that the volume of water that ocean containers can hold is stable, increasing or decreasing or if dimensions change at rates comparable to those associated with ocean level changes.
    For example, dimensional change from lateral ocean floor spreading astride mid-ocean ridges has been estimated to reach 10 mm per year, but there seems no similarly well-known assessment of vertical movement. So, at least some movement is in the vertical dimension of interest, with contemporary ocean level change estimates around 3 mm per year. However, rate of change needs quantification as well as the present state and the usual state.
    Apart from continental influences such as at deltas, the wider ocean floors support sedimentary deposits that are geologically thin. It is likewise not known if the volume of these sediments changes significantly with time in the same sense as compared with dimensions of ocean level change. These sediments can be expected to change with time by compaction, metamorphism and the balance of deposition/erosion (+ dissolution). There is also physical dewatering of sedimentary piles, some of it as step changes following shock. Further, there is a volume change as some of the descending sedimentary precursor material changes from suspension to solute.
    River deltas are a known and studied example of a first-order effect that will change the water-holding dimension of oceans. While estimates can be made of the volume of incoming sediment from the sum of all rivers, less is reported about the volume of dust that falls on oceans and its solubility. Likewise, less is known about the dimensions of compensatory mechanisms that raise land levels to provide a source to be depleted to make such deltas and dust.
    Finally in this broader view, there is subduction at continental margins, a mechanism that reduces the area of some ocean floors. Study of earthquake epicentre depths allows inferences that subduction has a vertical component of several hundred kilometres, but the dimension, if any, of this vertical movement is unstated with respect to the volume of ocean contained. One can envisage subduction without effect on ocean container volume; but also with changes. That is, if one accepts the popular concept of subduction.
    There is more. The dimensions of the ocean container are known to be affected on a small scale that might be safe to ignore, by encroachment of grounded ice displacing water formerly present; and the converse.
    For decades now, I have been blogging about how unscientific it is to assume properties of the deeper half of the ocean. It is sparsely sampled. The words here are only part of the known unknowns. Some do not even have the sign of change known.
    With widespread lack of accurate information, there has been a tendency to assume some changes to be lost in the noise, to be of that increasingly-common category where as if by divine guidance, the plus will cancel the minus and the hypothesis can proceed to proof.
    Proper, hard science does not work by guess and convenient supposition.
    Consequently, it is premature to guess at values for glacial isostatic adjustment before the stability of the ocean container is quantified in detail and with observations that close. Geoff.

    • Informative comment. Much to think about. Main takeaway:Unknowns are extensive.

    • Makes sense to me. How can we possibly know enough about changes in the “ocean container” to talk about a specific adjustment.? I guess it takes quite a bit of modelling assumptions.

      A plain English explanation by Prof. Nerem might help.

  34. Geoff Sherrington

    From the University of Colorado web site citation –
    “ … the ocean basins are getting slightly larger since the end of the last glacial cycle.”
    In hard science, what does this mean?
    There is more, “some ocean bottoms are falling relative to the center of the Earth”. This is attributed, in part at least, to the movement of mantle material to compensate for a reduced load now that continental ice deposits have melted. How do we know that this mantle material moves as described? We can make some suppositions and model the global gravity pattern from sources like the Grace satellite system. We can look at changes in magnetic patterns, but this is complicated because we cannot sample the actual material that moves to divide its magnetism into the components used geophysically. (Induced, remanent, etc. and especially on directionally-oriented samples). Bathymetry and seismic interpretation and echo sounding are further available tools. However, major concepts can change quickly over time.
    In a 2016 paper, M.J. Hoggard et al wrote –
    “A sufficiently accurate grid of crustal thickness throughout the oceanic realm is not yet available. As a result, residual topographic estimates determined from ship-track observations are not isostatically corrected for anomalous crustal thickness.”
    In March 2017 they noted that –
    “Over a period of a million years, which is our standard unit of measurement, the movement of the mantle can cause the surface to move up and down by hundreds of metres.” “Although we’re talking about timescales that seem incredibly long to you or me, in geological terms, the Earth’s surface bobs up and down like a yo-yo.”
    M.J. Hoggard et al. ‘Global dynamic topography observations reveal limited influence of large-scale mantle flow.’ Nature Geoscience (2016). DOI: 10.1038/ngeo2709.
    For reference, a vertical movement of 1000 metres in a million years equates to 1 mm per year. This is in the ball park of inferred ocean level change of 3 mm per year particularly if the short term rate of change can be larger than the million-year average rate.
    If Hoggard’s work is confirmed, one can return to the University of Colorado quotes and note that vertical crustal movements caused by vertical mantle material movement, are plausibly likely to have horizontal movements as well. A convective cell pattern is usually invoked. How does one distinguish these horizontal motions from those proposed as compensatory for ice mass loss? Does one effect dominate the other?
    It is confusing to read a core statement like this: “the ocean basins are getting slightly larger”. Larger with respect to what? The base moving down w.r.t earth’s centre? The walls moving further apart? The lip of a basin rising to contain more water volume? Rising w.r.t what? Is this “slightly larger” a reversible effect that predictably will change or stop? When, why? How larger is “slightly”? “Slightly larger” with respect to what? Beforehand? How long beforehand?
    Did any other reader bog down in frustration realising that the full quote, the first line of their web page, is more fully “The correction for glacial isostatic adjustment (GIA) accounts for the fact that the ocean basins are getting slightly larger.”
    Fact? Why is this a fact and not a thought bubble? Geoff.

    • I agree with Geoff: the Colorado web page is sloppily written. But they have an informative picture in their header. (OT, but may be of interest to some readers). The picture shows the west coast of France a little south of the city of Brest (google Tas de Pois). The flat upper surface of the peninsula in the distance was cut across folded Paleozoic quartzite strata by prolonged marine erosion during a period when local sea level was approximately 70 metres higher than now. A marine erosion surface at around this level is widespread along the Atlantic fringe of Europe and may represent higher eustatic (i.e.worldwide) sea level before the accumulation of thick permanent ice in Antarctica.

  35. In the latest Nature paper about Antarctica that has created a lot of fuss recently, half of the claimed ice mass loss was due to the GIA adjustment!
    I wrote a comment under the article:

    The authors have not responded.

  36. Dr. Curry ==>
    1. GIA “adjustment” is not an adjustment to GMSL — it is not an adjustment to sea level at all. It is, as you say, an adjustment to ocean(s) volume. The only justifiable reason to mention it is if one is attempting to guesstimate some change the volume of water in the Earth’s oceans — there are legitimate reasons for doing so, but not when
    stating Sea Level Rise — it is NOT a rise in sea level and to add it to calculate GMSL is propagandistic.

    2. Local/regional governments should jump on the “CGPS@TG [same structure]” effort, immediately. This means financing or cajoling NOAA to install a permanent official Continuous GPS station on the same structure (pier, dock, wharf) alongside of the longest operating Tide Gauge in their area so that Local Relative Sea Level change can be accurately calculated and Absolute Sea Level change for their area can be known. What a local county or state government needs to know is How Much, How Fast , and in What Direction is sea level changing HERE. They need to know also, is the water rising/falling and at what rate AND is the land rising/falling at what rate.

    3. When there are enough CGPS@TG [ss] stations and they have all operated long enough (three years minimum is the standard, I believe), then we can calculate what Absolute Sea Level is doing regionally and by ocean.

    4. Any other measurement efforts have only scientific interests (not policy interest) or propaganda intent.

    5. Satellite measurement, as currently done, may be only showing us that the system of measurement is biased a bit to the “up” side — and that the bias isn’t changing much. The uncertainties in the individual steps in determining a “global mean sea level” are known to be orders of magnitude (a hundred, a thousand, ten thousand) times greater than the suspected actual change in sea level, almost none of the uncertainties can be assumed to be random error (as in: not biased in some way). Satellite GMSL will tell us if the seas suddenly begin to rise by a foot per year, but can tell us nothing in the millimetric range.

    • nobodysknowledge

      GMSL = fake sea level rise. What matters is SSH = sea surface hight.

    • nobodysknowledge

      And I think there are great uncertainties in how much the ocean floor is sinking.

  37. Global SLR is as useful as the GMST. It tells us we won. We need a number that says, We won. Now what do they mean for the city of Oceanside, Red State? Who knows? We know we won but what’s coming as far as local SLR and temperatures? Who knows? It’s like telling poor people free markets work. Global GDP is up. The distribution of the money doesn’t matter, we won. Free markets all the way. When poor people complain, revolt in some poor country, we tell them world GDP is up, Everything will be Okay and what’s your problem?

  38. I have what is a completely lay person thought on this. It seems to me that GIA is wholly unimportant assuming that the expected changes are more or less constant over the anticipated timelines regards to climate change. I mean, the real importance of measuring sea level in the first place is because of its impact on coastal sea levels. So, if GIA has been occurring since the last ice age and will continue past the horizon of our current climate projection timelines, and it has been fairly constant, does it really matter? The reduced level of coastal sea levels is what is important. Trying to attribute an increased or decreased level is only important to folks trying to argue the political aspects of CO2. So if I say sea level is rising by 3mm/yr and someone pushing the agenda of a CO2 impact says 3.3mm/yr, that’s a nice selling point for the newspapers but makes no difference to the people living on the coast. There level is only increasing at 3mm/yr (ignoring local differences of course).

  39. Hello,

    I thought it would be useful to prepare an accessible document outlining in colourful graphs the climate change that has occurred specifically in Ireland since 1800 and compare the period 1800-1950 to 1950-2017 as it will pique the interest of a lot of Irish. I spent many weeks searching for, collating, formatting and updating climate info (temps, rainfall, wind etc.) and preparing the presentation (30 slides). I have run it by friends who say it is very interesting and understandable (I’ve avoided complex stats). I’d be interested in the comments of the readership here on the document and how it could be improved and circulated.



  40. Kenneth Bramwell

    Can i point out the obvious? Sea “Level”.

    Since when was a level a volume?

    Sea level matters a lot. Sea volume?? Not so much. No matter how correct GIA is as a concept, it’s just an irrelevant abstraction when the debate and concern is about sea level at the coasts.

  41. Pingback: Weekly Climate and Energy News Roundup #320 | Watts Up With That?

  42. Pingback: Weekly Climate and Energy News Roundup #320 |

  43. I hope everybody is aware that there is GNSS … apart from more relevant civil and military applications, we also use GPS every day … we know, the system is not perfect, as technicalities still produce estimates of the subsidence of an antenna still suffering of errors of may be 1-2 mm/year …. but these errors are nothing compared with the gross inaccuracy of GIA computations that are outrageous … I suggest stop talking about the wrong GIA correction, and just use the subsidence rate from GNSS ….

    by the way, if the GNSS antenna is not co-located with the tide gauge, but several km apart, I would not suggest to use the antenna subsidence rate as a good estimate of the sinking of the tide gauge instrument ….

    For the lovers of the GIA correction I suggest a visit to New Orleans …. Some areas are sinking at about 50 mm/year ….but the single cell of the GIA gives nothing ….

    Conclusion: correction of sea level data by GIA is legitimate may be in cucu-land, where the most part of the climate studies are correct …

  44. Steve Case

    Colorado University used to put a note on thier main page “GIA corrected” LINK

    But in January 2016 the notation was dropped: LINK

    One would think that at the time there would have been a great hue and cry when CU did that. But as near as I can tell absolutely nothing was said from the skeptical side of the coin back then. This discussion doesn’t seem to mention that fact either. Today the ordinary person who views the CU Sea Level Research Group web page
    has no clue that an adjustment of 0.3 mm/yr has been added to the graph on their main page. Indeed a search for “GIA” turns up just one reference in a side box:

    GMSL Rates
    CU: 3.4 ± 0.4 mm/yr
    AVISO: 3.3 ± 0.5 mm/yr
    CSIRO: 3.3 ± 0.4 mm/yr
    NASA GSFC: 3.4 ± 0.4 mm/yr
    NOAA: 3.2 ± 0.4 mm/yr (w/ GIA)

    So considering the history, this little discussion is a tempest in a teapot.

  45. For the greenhouse theory to operate as advertised requires a GHG up/down/”back” LWIR energy loop to “trap” energy and “warm” the earth and atmosphere.

    For the GHG up/down/”back” radiation energy loop to operate as advertised requires ideal black body, 1.0 emissivity, LWIR of 396 W/m^2 from the surface. (K-T diagram)

    The surface cannot do that because of a contiguous participating media, i.e. atmospheric molecules, moving over 50% ((17+80)/160) of the surface heat through non-radiative processes, i.e. conduction, convection, latent evaporation/condensation. (K-T diagram) Because of the contiguous turbulent non-radiative processes at the air interface the oceans cannot have an emissivity of 0.97.

    No GHG energy loop & no greenhouse effect means no CO2/man caused climate change and no Gorebal warming.

  46. You didn’t accurately address the rebuttal to the “but the tide gauges” argument. You just quoted a paper without showing a flaw in the paper. And no, your fallacious argument from personal incredulity is not convincing.