Will advances in groundwater science force a paradigm shift in sea level rise attribution?

by Jim Steele

 A better accounting of natural groundwater discharge is needed to constrain the range of contributions to sea level rise. The greater the contribution from groundwater discharge, the smaller the adjustments used to amplify contributions from meltwater and thermal expansion.

In a 2002 paper, what is frequently referred to as “Munk’s enigma”, Scripps Institution of Oceanography’s senior researcher bemoaned the fact researchers could not fully account for the causes of sea level rise. He lamented, “the historic rise started too early, has too linear a trend, and is too large.” Early IPCC analyses noted about 25% of estimated sea level rise was unaccounted for. Accordingly, in 2012, an international team of prominent sea level researchers published, Twentieth-Century Global-Mean Sea Level Rise: Is the Whole Greater than the Sum of the Parts? (henceforth Gregory 2012). They hoped to balance struggling sea level budgets by re-analyzing and adjusting estimates of the contributions from melting glaciers and ice caps, thermal expansion, and the effects of dam building and groundwater extraction. However, a natural contribution from any imbalance in groundwater re-charge vs discharge was never considered. Yet the volume of freshwater stored as groundwater, is second only to Antarctica’s frozen supply, and 3 to 8 times greater than Greenland’s.

At the risk of oversimplifying, the effects of groundwater storage can be differentiated between shallow-aquifer effects that modulate global sea level on year to year and decade to decade timeframes, versus deep aquifer effects that modulate sea level trends over centuries and millennia.

Researchers are increasingly aware of natural shallow groundwater dynamics. As noted by Reager (2016) in A Decade of Sea Level Rise Slowed by Climate-Driven Hydrology, researchers had determined the seasonal delay in the return of precipitation to the oceans causes sea levels to oscillate by 17 ± 4 mm [~0.7 inches] per year. Reager (2016) also argued decadal increases in terrestrial water storage driven by climate events such as La Nina, had reduced sea level rise by 0.71 mm/year. Likewise, Cazenave 2014 had published according to altimetry data, sea level had decelerated from 3.5 mm/yr in the 1990s to 2.5mm/yr during 2003-2011, and that deceleration could be explained by increased terrestrial water storage, and the pause in ocean warming reported by Argo data.

Improved observational data suggest during more frequent La Nina years a greater proportion of precipitation falls on the land globally and when routed through more slowly discharging aquifers, sea level rise decelerates. During periods of more frequent El Niños, more rain falls back onto the oceans, and sea level rise accelerates. In contrast to La Nina induced shallow-aquifer effects, deep aquifers have been filled with meltwater from the last Ice Age, and that water is slowly and steadily seeping back into the oceans today.

Munk’s “Too Linear Trend” Enigma and Deep Groundwater Discharge

Hydrologists concerned with sustainable groundwater supplies and drinking water contamination, have been in the forefront of analyzing the volume and ages of the world’s groundwater, providing greater insight into deep aquifer effects. Gleeson (2015) determined, “total groundwater volume in the upper 2 km of continental crust is approximately 22.6 million cubic kilometers, twice as much as earlier estimates. If all 22.6 million cubic kilometers of freshwater stored underground reached the oceans, sea level would rise 204 feet (62,430 millimeters). Via various isotope analyses and flow models, Jasechko (2017) estimated that between 42-85% of all groundwater stored in the upper 1 kilometer of the earth’s crust is water that had infiltrated the ground more than 11,000 years ago, during last Ice Age.

Clearly the earth’s groundwater has yet to reach an equilibrium with modern sea levels. With deep aquifer discharge primarily regulated by geological pore spaces (in addition to pressure heads), the slow and steady discharge of these older waters affects sea level rise on century and millennial timeframes. And, although freshwater discharge from deep aquifers may be locally insignificant relative to river runoff, deep aquifer discharge when integrated across the globe could account for the missing contribution to the sea level rise budgets.

Unfortunately, quantifying the groundwater discharge contribution to sea level rise is extremely difficult, suffering from a low signal to noise problem. That difficulty is why natural groundwater contributions are often ignored or brushed aside as insignificant. Although GRACE satellite monitoring of gravity changes offers great promise for detecting changes in terrestrial groundwater storage, GRACE cannot accurately separate the relatively small discharge of deep aquifers from large annual changes in shallow groundwater. In periods of heavy rains, groundwater increases will mask deep aquifer discharge. And during a drought, any deep groundwater discharge will likely be attributed to the lack of rain.

However, estimates of groundwater re-charge via isotope analyses can provide critical information regards rates of groundwater re-charge and discharge.

Using the abnormal levels of tritium released during nuclear testing in the 1950s, plus carbon­14 dating, researchers have categorized the time since groundwater had last left the surface into 25, 50, 75 and 100-year old age classes. As expected, the youngest water is concentrated in the shallowest aquifer layers and the proportion of young water decreases with depth. The estimated volume of 25-year-old or younger groundwater suggests global groundwater is currently recharging at a rate that would reduce sea level by 21 mm/year (0.8 inches/year). Water cycle researchers (i.e. Dai and Trenberth) have made the dubious assumption that the amount of water transported via precipitation to the land from the ocean is balanced each year by river runoff. But if the tritium derived estimates are valid, balancing water cycle and sea level budgets becomes more enigmatic. Clearly a significant amount of precipitation does not return for decades and centuries.

Intriguingly, comparing the smaller volume of ground water aged 50 to 100-years-old versus the volume of water 50-years-old and younger suggests 2 possible scenarios. Either ground water recharge has increased in recent decades, or if recharge rates averaged over 50 years have remained steady, then as groundwater ages a significant portion seeps back to the ocean at rates approaching 1.7 mm/year, a rate that is very similar to 20th century IPCC estimates of sea level rise.

Groundwater discharge must balance recharge or else it directly alters global sea levels. When less than 21 mm/year seeps back to the ocean, then natural groundwater storage lowers sea level. When discharge is greater than 21 mm/year, then groundwater discharge is raising sea level. Without accounting for recharge vs discharge, the much smaller estimates of all the other factors contributing to sea level rise are simply not well constrained.

Higher rates of discharge could account for the enigmatic missing sea level contributions reported by the IPCC and other researchers (i.e. Gregory 2012). More problematic, if discharge proves to significantly exceed recharge, then estimates of contributions from other sources such as melting ice and thermal expansion may be too high. What is certain, the current estimates of contributions to sea level from melting ice and thermal expansion only range from 1.5 to 2.0 mm/year, and those factors by themselves cannot offset the tritium estimated 21 mm/year of groundwater recharge. So, what is missing in our current water cycle budgets?

The Importance of Submarine Groundwater Discharge (SGD)

The recharge-discharge imbalance can be reconciled if water cycle budgets included the difficult-to-measure rates of prolific submarine groundwater discharge (SGD). Freshwater springs bubbling up from coastal sea floors have long been observed. To reliably replenish drinking water, Roman fisherman mapped their occurrences throughout the Mediterranean. Moosdorf (2017) has reviewed the locations and many human uses of fresh submarine groundwater discharge around the world.

Recent ecological studies have measured local submarine groundwater seepages to determine contributions of solutes and nutrients to coastal ecosystems. But those sparse SGD measurements cannot yet be reliably integrated into a global estimate. Rodell (2015) notes that most water cycle budgets have ignored SGD due to its uncertainty, so Rodell’s water cycle budget included a rate of SGD equivalent to 6.5 millimeters/year (~0.25 inch/yr) of sea level rise. However, that estimate is still insufficient to balance current recharge estimates.

However, with improving techniques, researchers recently estimated total submarine groundwater (saline and fresh water combined) discharges suggesting a rate 3 to 4 times greater than the observed global river runoff, or a volume equivalent to 331 mm/year (13 inches) of sea level rise. Nonetheless more than 90% of that submarine discharge is saline sea water, most of which is likely recirculated sea water, and not likely to affect sea level. Only the fraction of entrained freshwater would raise sea level. To balance the 21 mm/year ground water recharge, between 6 and 7% of total SGD must be freshwater and that amount is very likely. Local estimates of the freshwater fraction of submarine discharge range from 1 to 35%, and on average just less than 10%. If fresh submarine groundwater discharge approaches just 7% of the total SGD, it would not only balance current groundwater recharge, but would steadily raise sea level by an additional 2 mm/year, even if there was no ocean warming and no melting glaciers. 

A Sea Level Rise “Base-flow” and Paleo-climate Conundrums

Hydrologists seek to quantify the aquifer contributions to river flow, otherwise known as the “base flow”. During the rainy season or the season of melting snow, any groundwater contribution is masked by heavy surface runoff and shallow aquifer effects. However, during extended periods of drought hydrologists assume the low river flow that persists must be largely attributed to supplies from deeper aquifers. Streams that dry up during a drought are usually supported by small shallow aquifers, while reduced but persistent river and stream flows must be maintained by large aquifers. Using a similar conceptual approach, we can estimate a possible “base flow” contribution to sea level.

When the continental ice sheets began to melt as the earth transitioned from its Ice Age maximum to our present warm interglacial, sea level began to rise from depths ~130 meters lower than today (see graph below). Melting continental ice sheets drove much higher rates of sea level rise than seen today, ranging from 10 to 40+ mm/year. Approximately 6,000 years ago, a consensus suggests the last of the continental ice sheets had melted completely, the earth’s montane glaciers had disappeared, and Greenland and Antarctic ice sheets had shrunk to their minimums. The earth then entered a long-term 5000-year cooling trend dubbed the Neoglaciation. Although sea level models forced only by growing glaciers and cooling ocean temperatures would project falling sea levels, proxy evidence enigmatically suggests global sea level continued to rise. Albeit at reduced rates, global sea level continued to rise another 4 meters (Figure 1 below). Although there is some debate regards any continued contribution from Antarctica and “ocean siphoning”, according to Lambeck 2014 about 3 meters of sea level were added between 6.7–4.2 thousand years ago. That continued sea level rise could be explained by aquifer discharge, suggesting a minimal “base flow” of ~1.2 mm/year from groundwater discharge.

Similarly, during the Little Ice Age between 1300 and 1850 AD, montane glaciers as well as Greenland and Antarctic ice sheets, grew and reached their largest extent in the last 7,000 years. Ocean temperatures cooled by about 1 degree. Yet inexplicably, most researchers estimate global sea level never dropped significantly. They report sea levels were “stable” during the Little Ice Age, fluctuating only by tenths of a millimeter. That stability contrasts greatly with the recent rising trend, that has led some to attribute the current rise to increasing CO2 concentrations. However Little Ice Age stability defies the physics of cooling temperatures and increasing water storage in growing glaciers that should have caused a significant sea level fall. However, that seeming paradox is consistent with a scenario in which a “base flow” from groundwater discharge would offset any transfer of waters to growing Little Ice Age glaciers.

Once the growth of Little Ice Age glaciers stopped, and groundwater base flow was no longer offset, we would expect sea levels to rise as witnessed during the 19th and 20th centuries. Such a scenario would also explain Munk’s enigma that sea level rise had started too early, before temperatures had risen significantly from any CO2-driven warming.

Interestingly, assuming a ballpark figure of a 1.2 mm/year groundwater base flow, unbalanced groundwater discharge could also explain the much higher sea levels estimated for the previous warm interglacial, the Eemian. Researchers estimate sea levels ~115,000 years ago were about 6 to 9 meters higher than today. That interglacial has also been estimated to have spanned 15,000 years before continental glaciation resumed. Compared to our present interglacial span of 11,700 years, an extra 3,300 years of groundwater discharge before being offset by resumed glacier growth, could account for 4 meters of the Eemian’s higher sea level. 

Recent glacier meltwater contribution to sea level is likely overestimated?

In addition to a groundwater base flow driving the current steady rise in sea level, meltwater from retreating Little Ice Age glaciers undoubtedly contributed as well. But by how much? Researchers have estimated there was greater glacial retreat (and thus a greater flux of meltwater) in the early 1900s compared to now. So, current glacier retreat is unlikely to cause any acceleration of recent sea level rise. Furthermore, we cannot assume glacier meltwater rapidly enters the oceans. A large proportion of meltwater likely enters the ground, so it may take several hundred years for Little Ice Age glacier meltwater to affect sea level.

How fast can groundwater reach the ocean? Groundwater measured in the Great Plains’ Ogallala Aquifer can flow at a higher-than-average seepage rate of ~300 mm (~1 foot) in a day, or about the length of a football field in a year. For such “fast” moving groundwater to travel 1000 kilometers (620 miles) to the sea, it would require over 10,000 years! Most ground water travels much slower. The great weight of the continental glaciers during our last ice age, applied such great pressure that it forced meltwater to into the ground at much greater rates than currently observed recharge. And that Ice Age meltwater is still slowly moving through aquifers like the Ogallala.

(However, its release to the ocean has been sped up by human pumping. Recent estimates suggest that globally, human groundwater extraction currently exceeds rates of water capture from dam building, so that groundwater depletion is now accelerating sea level rise.)

How much of the current meltwater can we expect to transit to the ocean via a slow groundwater route? That’s a tough question to answer. However, thirteen percent of the earth’s ice-free land surface is covered by endorheic basins as illustrated by the gray areas shown in the illustration below. Endorheic basins have no direct outlets to the ocean. Water entering endorheic basins only return to the sea via evaporation, or by the extremely slow route of groundwater discharge. Any precipitation or glacial meltwater flowing into an endorheic basin could require centuries to thousands of years to flow back to the oceans.

For example, in 2010-2011, researchers reported that a La Nina event had caused global sea level to fall by the equivalent of 7mm/year (~0.3 inches/year). That dramatic drop happened despite concurrent extensive ice melt in Greenland and despite any base flow contribution. As described by Fasullo (2013), GRACE satellite observations detected increased groundwater storage caused by higher rates of rainwater falling on endorheic basins, primarily in Australia. Although satellite observations suggested much of the rainwater remained in the Australian basin, sea level resumed its unabated rise as groundwater base flow contribution would predict.

To balance their sea level budgets, researchers assert melting glaciers have added ~0.8 mm/year to recent sea level rise. The 20th century retreat of most glaciers is undeniable, but we cannot simply assume all 20th century glacier meltwater immediately reached the oceans. The greatest concentration of ice, outside of Greenland and Antarctica, resides in the regions north of India and Pakistan, in the Himalaya and Karakoram glaciers. Most melt water flowing northward enters the extensive Asian endorheic basins. Likewise, some of the Sierra Nevada meltwater flows into Nevada’s Great Basin, and some Andes meltwater flows into the endorheic basins of the Altiplano and Lake Titicaca as well as the Atacama Desert. It is very likely much of the current glacial meltwater will then take decades to millennia to reach the ocean and has yet to impact modern sea levels. If the glacial melt water contribution to sea level is overestimated, then, the unaccountedfor contribution to sea level rise becomes much larger than initially thought.

Accurate Attribution of Groundwater Discharge and Recharge Will Constrain Sea Level Contributions

Using a combination of GRACE gravity data that measured changes in ocean mass, altimetry data that measured changes in ocean volume and Argo data that measured heat content, Cazenave (2008) used 2 different methods and both estimated the contribution from increased ocean heat to be about 0.3 to 0.37 mm/year. Jevrejeva (2008) calculated a similar heat contribution. Other researchers suggest thermal expansion contributes 1.2 to 1.5 mm/year (i.e. Chambers 2016). Such large discrepancies reveal contributing factors to sea level rise are not yet reliably constrained.

One of the great uncertainties in sea level research are glacial isostatic adjustments.

Researchers have subjectively adopted various Glacio-isotatic adjustment models with recommended adjustments ranging from 1 to 2 mm/year. For example, although GRACE gravity estimates had not detected any added water mass to the oceans, Cazenave (2008) added a 2 mm/year adjustment, as illustrated from her Figure 1 below. Other researchers only added a 1 mm/yr adjustment.

In the Gregory (2012) paper Twentieth-Century Global-Mean Sea Level Rise: Is the Whole Greater than the Sum of the Parts? researchers suggested the sea level budget could be balanced and the IPCC’s unaccounted for contribution to sea level rise could be explained by making 5 assumptions:

  • Assume the contribution from glacier melting was greater than previously estimated.

But greater melting rates were documented for the 30s and 40s, and the likelihood that some glacier meltwater is still trapped as groundwater, suggests the glacier meltwater contribution has been overestimated.

  • Assume an increased contribution from thermal expansion.

But ARGO data suggests the contribution from thermal expansion has been decreasing and plateauing.

  • Assume Greenland positively contributed to sea level throughout the entire 20th century.

Greenland has undoubtedly contributed to episodes of accelerating and decelerating sea level changes, but the greatest rate of Greenland warming occurred during the 1920s and 30s. Previous researchers suggested Greenland glaciers have oscillated during the 20th century but had been stable from the 60s to 1990s. Although there was increased surface melt in the 21st century, culminating in 2012, that melt rate has since declined. And according to the Danish Meteorological Institute, Greenland gained about 50 billion tons of ice in 2017 which should have lowered sea level in 2017. Clearly Greenland cannot explain the enigmatic steady 20th century sea level rise.

  • Assume reservoir water storage balanced groundwater extraction.

But net contributions from groundwater extraction vs water impoundments and other landscape changes are still being debated. For the period 2002–2014 landscape changes have been estimated to have reduced sea level by −0.40 mm/year versus IPCC estimates of contributing 0.38 mm/year from 1993–2010 to sea level rise.

  • Assume the remaining unaccounted contribution to sea level rise is small enough to be attributed to melting in Antarctica.

Debatably, Antarctic melting is too often used as the catch-all fudge factor to explain the unexplainable. Furthermore, there is no consensus within the Antarctic research community if there have been any human effects on Antarctica’s ice balance. Regions that are losing ice are balanced by regions that are gaining ice. Claims of net ice loss have been countered by claims of net ice gain such as NASA 2015. Additionally, unadjusted GRACE gravity data has suggested no lost ice mass and all estimates of ice gains or loss depend on which Glacial Isostatic Adjustments modelers choose to use. We cannot dismiss the possibility that unaccounted for groundwater discharge has been mistakenly attributed to hypothetical Antarctic melting?

A better accounting of natural groundwater discharge is needed to constrain the range of contributions to sea level rise suggested by researchers such as Gregory 2012. The greater the contribution from groundwater discharge, the smaller the adjustments used to amplify contributions from meltwater and thermal expansion. Until a more complete accounting is determined, we can only appreciate Munk’s earnest concern. How can we predict future sea level rise if we don’t fully understand the present or the past?

Moderation note:  As with all guest posts, please keep your comments civil and relevant.




115 responses to “Will advances in groundwater science force a paradigm shift in sea level rise attribution?

  1. Sea levels rising – NOT happening FAKE news.


    Open this link and a map will appear with numerous multi colored arrows. Click on an arrow and the data for that location will appear, e.g. Miami. In the pop up window select “linear trend”.

    2.39 mm/y, that’s 0.094” 3/32 of an INCH each year!!!! OOOOHHHHH SCARY!!!!

    Which is NOT actually measured but computer MODELLED!!!!

    0.78 ft over 100 YEARS or a WHOPPING 9 inches!!!!

    Alarmists pushing the dangers of sea level rise are nothing but a pack of lying weasels!!!

    • Have you considerd that you might be more effective in the long term, not posting the first reply? You could compose your thoughts in a Word document and just come back in an hour or two, and then reply.

      • Indeed Russell, we skeptics exhibit the courage to reveal the falsehoods of “cli-fi” and the cli-fi spin that denigrates the scientific process.

        After reading your link piping you own silly post, I would advise everyone not to worry if they too missed it. Nothing of value for this topic, nor for anyone one interested in climate science.

      • Really, Jim –

        Four decades should have taught you that more self-publicatiion is not about to wiin you much street cred in a world with tens of thousands of non-pay-for-play science journals.

        Why don’t you move up to managing the fire pits at the Ahwanee?

      • Russell,

        The depth and thoughtfulness of your scientific rebuttals is enlightening

      • I think he is famous for it. But you have to know that Nicky’s views are a bit bugs bunny?

      • Are we missing something , or is this the full extent of Robert Ellison’s
        bibliography :

        A climate computing revolution (2010), Quadrant Online.
        Decadal ENSO Variability (2009), Energy & Environment.
        ENSO Variation and Global Warming (2007), American Thinker.
        Changing our approach to the environment (2005), The Environmental Engineer, Engineers Australia.

        As with Steele, he seems to prefer pal review to peer review.

      • lmfao – I have been a professional hydrologist, engineer, hydrodynamic modeler, environmental scientist, technologist and natural philosopher for decades. My special topic is biogeochemical cycling – the movement of water, nutrients and pollutants around the planet. And especially at that ecotone between urban, industrial, agricultural and and mining development and the natural world.

        An environmental scientist works in a multi-disciplinary setting to solve ‘wicked problems’ that have social, scientific, economic, technological and cultural dimensions. I used to think I was a dilettante because my interests were so broad. Now I might know something just from persistence. And I did predict the hiatus publicly in 2007. I have evolved since then – I am predicting that the intrinsic component of warming in the 20th century will be reversed this century. It is the way the best climate science is heading.


        If Russel wants to know what I have been thinking about – he need only click on my name. He could also try one of my FB pages. The name comes from a Japanese word – the duck is just cool.


        Natural philosophy is one thing – endlessly fascinating. You have to love it for the sake of pure knowledge. Something lacking with much of the climate rabble. But the AGW ‘problem’ is not a ‘problem’ for science alone – and it has been ‘solved’ in a multi-faceted approach – some people just haven’t got it yet. Russel is still fighting the climate war like some ragged and more than faintly ludicrous soldier who doesn’t know the war is over.

      • Every time Russ comments it is enlightening.

  2. Can you comment on the paper by Mitrovica et al., “Reconciling past changes in Earth’s rotation with 20th century global sea-level rise” ?

    • Harold I cannot comment on MItrovica et al’s analysis with any authority. They are looking at rotational effects that Munk addressed and GIA adjustments. Its difficult to analyze those GIA models and for this essay on addressing groundwater effects, their analysis was not directly relevant.

      But what is clear from their paper is the “sea level budget” is problematic and unsettled. Changes in one estimation force changes in every other. Instead of raising contributions from meltwater and thermal expansion like Gregory 2012 suggested, Mitrovica chose a lower estimates of total GMSL in order to fit their calculations.

      Here is what they wrote

      “A recent probabilistic analysis of a global database of tide gauge
      records (22) has estimated a GMSL rise of 1.2 ± 0.2 mm/year in 1900–
      1990. The Fifth Assessment Report of the Intergovernmental Panel on
      Climate Change estimated three contributions to GMSL rise over this
      period: melting of glaciers (0.7 ± 0.1 mm/year, as noted previously) (18),
      thermal expansion (0.4 ± 0.1 mm/year) (10), and net anthropogenic
      storage of water on land (−0.11 ± 0.05 mm/year) (10).

      These signals add to a GMSL rise of ~1.0 mm/year, and the consistency of this value with the new probabilistic estimate suggests that the 20th century sea-level budget can be closed without additional contributions from polar ice
      sheet mass loss (22).

      That is, if we accept the new GMSL estimate over the period 1900–1990, we need not consider any melt signal in addition to the glacier contribution shown in Fig. 1 (B and C).

      In contrast, an earlier analysis of the global tide gauge records estimated a GMSL rate of 1.5 ± 0.2 mm/year for 1900–1990 (10, 23), a value that would likely require additional ice melting beyond the glacier contribution cited by
      Vaughan et al. (18).”

  3. This post has already been up at wuwt for a couple of days. Do you want us to replicate our comments?

    • jim

      to answer my own question I will ask something to see if you can provide a reply.

      Do we know the sources of all groundwater and its life cycle from ground to air and back underground again?

      Does that life cycle vary in length?

      I ask that, as when at Roman Bath a few moths ago all the literature, including in the museum, said the hot water in the baths started off life 10000 years ago in the nearby Mendip hills.(yes 10000 years!)

      IF it can take a very long time for groundwater to appear should we take into account the period of time from when it came? For example, there may have been an excessively wet or dry period 10000 years ago or 5000 years ago or 500 years ago.

      We need to know how much water is entering the system at any one time and how long it takes to re-emerge in order to be sable to judge whether it is contributing more or less than normal in any one year.

      As an afterword I read once that the atmosphere contains the equivalent of 5cm of water spread evenly over the globe. Is that normal or does it vary noticeably? A few years ago the excessive rain in Australia was said to have changed the sea levels..


    • Hi Tony,

      You ask, “Do we know the sources of all groundwater and its life cycle from ground to air and back underground again?”

      The short answer is no! The degree of uncertainty in recent water cycle budgets illustrates the lack pf precision in estimating all the factors affecting sea level.

      Rodell 2015 calculated “Annual precipitation, evapotranspiration, and runoff over the global land surface are estimated to be 116,500 +/- 5,100, 70,600 +/- 5,000, and 45,900 +/- 4,400 km3/year, respectively, after optimization.”

      Given 1 km3 = 1 Gigaton of water, and about 362 Gt is the global sea level equivalent of 1 mm, then their lowest range of uncertainty for each factor is +/- 12 mm of sea level. Within their uncertainty bounds, almost any theory of the causes of sea level rise can find some level of statistical support. So we need to be skeptical of any sea level calculations and attribution.

      Regards groundwater, there are similar large uncertainties. However the efforts to understand groundwater supplies and contamination are adding increased precision, at least on local and regional scales. Reading the tritium based estimates of groundwater ages triggered this analysis. Water aged 50 years and younger should average out most of the annual and decadal fluctuations of shallow aquifer effects. Given the uncertainty, their estimation that groundwater is being recharged on average of about 21 mm/year, requires a better understanding of groundwater discharge, and this is only now being addressed by investigations of submarine groundwater discharge. If recharge exceeds discharge it is possible that GRACE pre-adjustment data showing no mass gain are an accurate accounting and all the adjustments are pure fabrication.

      I don’t claim to know what the best calculus will prove to be. The essay only emphasizes 1) the great uncertainties in sea level adjustments and its contributions and 2) that groundwater recharge/discharge must be added to the debate on 20th century sea level rise and on paleoclimate sea level estimates. I used Lambeck’s paleoclimate estimates but his work is not accepted by many paleoclimate researchers.

      Much to be debated.

  4. Jim, very nice post,permabookmarked for future use. More unsettled science. My own view is that net groundwater is real but a minor contributor to delta sea level rise. I have three lines of reasoning.
    1. Two sets of papers purporting to explain the supposed slowing of SLR in the Jason 2 record are fatally flawed. Exposed them is essay PseudoPrecision in ebook Blowing Smoke. Likely answer is just Jason 2 instrument drift. This is only short term, not long term contributions.
    2. The two major global drawdowns of paleogroundwater are the Ogallala aquifer in the US and central/southern India’s cratonic system. Both are depleting since decades due to intensive agricultural irrigation. But the estimated annual drawdowns are SLR rounding error not visible in the tide gauge records before/after center pivot irrigation was developed.
    3. Using corrected (published 2013) Grace info for Antarctica, is is possible to get closure between long record vertical land motion diff GPS corrected tide gauges and the sum of ice sheet loss from Grace and thermosteric rise from ARGO. Wrote that up in guest post here, “Sea level rise, acceleration, and closure”. Which suggests any net groundwater contribution is small.

    • Rud says “Using corrected (published 2013) Grace info for Antarctica, is is possible to get closure …….suggests any net groundwater contribution is small.

      It may or may not be true that groundwater make no significant controversy union and your example illustrates my concerns. Estimates of groundwater contributions are assumed based on adjusted data for other contributions such as Antarctica so that by subtraction they leave no room for a groundwater contribution.

      Also, the agricultural drawdown of aquifer has had a recent small effect on sea level acceleration, but that drawdown does not reflect the slow steady small discharge from global deep aquifers

      • Jim, I agree with your comments. Said so at first. Irrigation drawdown is from (by economic definition) from relatively shallow paleowater aquifers. My sisters Northwest Washington state cattle ranch has the deepest water well I ever heard of, about 750 feet. We helped her drill it when the 450 foot well failed.
        So no clue about what deeper, longer time aquifers might mean. But, I simply cannot see a bigger groundwater delta in the available SLR data post center pivot irrigation. So, remain in your ‘unsettled science’ camp while also remaining in the ‘skeptical, but only big stuff’ camp outside groundwater delta SLR. Of such issues is one or more future PhD theses comprised. Regards.

      • Jim, a further belated thought contributing to my ‘deminimus’ view. ‘Fast’ changes are theoretically credible for shallow rainfed aquifers based on precipitation variance (my debunked Australia example in essay PseudoPrecision), or in shallow (hence tapped for irrigation) paleowater aquifers like the Ogallala. But there is no credible mechanism to posit decadal or centennial change in net groundwater for deep paleowater aquifers, as that waternet flow is a function of geological porosity, permeability, and osmotic pressure. Which on centennial scales hardly change at all except in very tectonically active terrestrial regions like Alaska.

      • At the cost of becoming annoying, I owe Judith and her denizens here one further thought. Starting with my first post here in 2011 on a deliberate NRDC presentation misleading Congress (my Denizens 2 road to Damascus moment comment) I have been adimantly against junk science. But this climate ‘war’ is much larger, because mostly political. Now in my decades long ‘political’ corporate combat arena, elevator speeches and simple talking points have always prevailed. Even Fortune 50 Board members do not get nuanced factual subtleties.. So, to ‘win’ a policy or corporate strategy you have to follow the simple, irrefutable ‘KISS’ principle: Keep It Simple, Stupid.
        So this explains my comments here as well as elsewhere. Object is to win, not be scientifically precise in every detail.

      • Rud, I agree when you say deep aquifers ” on centennial scales hardly change at all except in very tectonically active terrestrial regions like Alaska.”

        I do not argue that deep aquifer discharge is changing. I only suggest it provides the “base flow” that is not accounted for in water cycle and sea level budgets. And the base flow needs to be quantified.

        The question that needs answering, is not if deep aquifer discharge is changing, but 1) how much does deep aquifer discharge contribute to the ocean, and 2) does it balance recharge?

      • It is easy to over simplify geological stratigraphy. In the basement is rock under pressure such as the pore sizes are too small to hold water. Where the underlying rock is heated – mostly by decay of radioactive nuclides – they are sometimes known as hot dry rock.

        Above are sometimes very complex strata that hydrologists define in terms of porosity. Porosity determines flow paths and rate of flow.

        But each of the flows will connect with rivers, lakes and oceans and flow as long as the hydrostatic pressure is positive – if there is a ‘head’ to drive it.

  5. I suppose we also have to account for salt water produced with oil and gas, as well as the water pumped from coal beds, and mines, which is usually sent to the sea (the exception being onshore areas where salt water is injected in disposal wells). Plus we have to account for the water vapor released by burning hydrocarbons. For example hexane is C6H14, when burned it releases 7 water molecules. I suspect the volumes are negligible.

  6. The value of this excellent piece is that it introduces yet more questions and variables toward having a better understanding of the earth’s natural systems. Contributions to SLR might turnout to be minimal. Or maybe not. But until we have a better grasp than we do now, the level of uncertainty remains legitimately high.

    Estimates of the level of geothermal heat in West Antarctica have increased dramatically in the last few decades. The assumptions about deep aquifers could be altered significantly in the future as well.

  7. Debatably, Antarctic melting is too often used as the catch-all fudge factor to explain the unexplainable.

    In addition to all the knowns and unknowns including what we don’t know we don’t know, etc., there’s all those fudge factors. Freeman Dyson says all of the data has been fudged.

  8. Very interesting article Jim. A couple of comments.

    If we discount any anthropogenic effect we can assume that any changes in underground water net flux are only due to changes in global precipitation. As the planet has been cooling slightly for the past 5000 years, we can assume a small decrease in global precipitation and therefore a net draw from millennial storage contributing towards sea level rise. But for the past 300 years the trend must have reversed as warming should increase precipitation, so we can assume a net contribution to centennial storage. Since millennial storage and centennial storage must show opposite natural trends, I would guess that non-anthropogenic underground water storage changes are probably too small to be important. As far as I know precipitation changes are not big either. Therefore I would think that we only have to worry about human extraction of underground water, and we should be able to measure or estimate that.

    Glaciers have been melting since 1850, but the melting has been accelerating, so their contribution might be more linear than you assume over the past 170 years. Also a significant proportion of glaciers end at sea or close enough to it, and their melting goes directly to sea without going through underground storage.

    We really don’t know what sea level has been doing during the Holocene. The figure that you use from Lambeck et al., 2014 is from a high-viscosity lower mantle model, and therefore should not be taken as evidence. Their figure 1A shows their data with error bars and it is compatible with a Holocene highstand that exists in many regions but not all.

    A different model by Grinsted et al., 2009 based on temperature reconstruction proposes that sea level decreased towards the LIA nadir and increased afterwards. And after all, sea levels must depend on temperature.

    • Javier I am well aware of the Grinstead model and believe it makes more sense from a thermodynamic perspective than does Lambeck’s. The problem with discussing contributions to sea level change is that there are several conflicting calculations. If the Grinstead model is correct, then there would be little need to account for a groundwater base flow.

      That said the question I raised is driven by recent isotopic analyses of the rate of groundwater recharge that left the surface 50 to 100 years ago. If those results prove to be reliable, even within the bounds of its uncertainty, then there must be a significant supply of groundwater discharge that is not yet being accounted for, and must be before we can dismiss its effects.

      If recharge exceed discharge it would confirm the GRACE raw data that no additional mass has been added to the oceans. That would call into question the algorithms that calculate total sea level rise.

      If discharge exceeds recharge, then suggests other contributions are overestimated.

      You state, ” a significant proportion of glaciers end at sea or close enough to it, and their melting goes directly to sea without going through underground storage.”

      I dont argue that a healthy proportion of meltwater does not quickly enter the sea. Only that a healthy proportion enters the ground and the a count needs to be addressed.

      In the Jasechko 2017 paper “Substantial proportion of global streamflow less than three months old” they condoled “This young streamflow accounts for about a third of global river discharge, and comprises at least 5% of discharge in about 90%of the catchmentswe investigated.We conclude that, although typical catchments have mean transit times of years or even decades, they nonetheless can rapidly transmit substantial fractions of soluble contaminant inputs to streams. Young streamflow is less prevalent in steeper landscapes,”

      That substantial proportion of young water in stream flow is expected from dynamics of shallow aquifers and vadose zone dynamics.

      However it is reasonable to infer that if young stream flow is less prevalent in steeper landscapes (i.e. glaciated basins) then a significant proportion of recent glacier meltwater does not enter the oceans for centuries.

  9. Pingback: Will advances in groundwater science force a paradigm shift in sea level rise attribution? — Climate Etc. – NZ Conservative Coalition

  10. Terrestrial water storage is removing water from sea levels slightly more than thermal expansion is adding to sea levels.

    Terrestrial Water Storage: -0.71 mm/yr (2002-2014)

    Reager et al., 2016
    “We found that between 2002 and 2014, climate variability resulted in an additional 3200 ± 900 gigatons of water being stored on land. This gain partially offset water losses from ice sheets, glaciers, and groundwater pumping, slowing the rate of sea level rise by -0.71 ± 0.20 millimeters per year. These findings highlight the importance of climate-driven changes in hydrology when assigning attribution to decadal changes in sea level.”
    Thermal Expansion: 0.64 mm/yr (2005-2013)

    Llovel et al., 2014
    “Over the entire water column, independent estimates of ocean warming yield a contribution of 0.77 ± 0.28 mm yr−1 in sea-level rise … the deep ocean (below 2,000 m) contributes −0.13 ± 0.72 mm yr−1 to global sea-level rise [0.64 mm/yr total].”

  11. A lot of mixed units rolling around here. A useful aide-memoire is that 360 cubic kilometres or 360 gigatons added or removed changes sea level by 1mm.

    • Excellent metrics contribution. The estimated annual sum of Ogallala and India cratomic aquifer depletion is ~50 cubic km of water per year. Rounding error.

      • I just did a ball park estimate for the water vapor we get from burning oil and gas, plus the produced water I think we dump in rivers and oceans from oil and gas production, and I get at best 20 cubic km. Therefore the total from all these sources, fresh water plus oil and gas plus coal degas and mine dewatering must be less than 100 cubic km. To that we have to add the water vapor from burning forests, but that’s tiny.

        So I wonder, what about water going in and out of aquifers exposed to the ocean? Evidently rising sea level pumps water into these aquifers, rising continents increase flow into the ocean, dropping continents retain water, etc.

        I have to conclude I just wasted 30 minutes of time.

      • We should also consider increasing water stored in biomass on land. How much more water is stores in plants, soil, and animals each year? What do drawdown of co2 and changes in oxygen production imply?

    • Isn’t each next mm more water volume?

      • Maybe. Or less ocean basin volume based on plate tectonics. Hypothetical example. We know the Atlantic is widening thanks the seafloor spreading at the mid Atlantic rift. More ocean volume. But we also know that rift is driven by upflowing magmatic basalts creating the midAtlantic rift ridge. Less volume. Net, dunno. And so goes settled science.
        Now, with respect to thismhypothetical, we probably DO know. The tectonic net ocean volume change is so slow it is in the rounding error (GIA per U C is 0.3mm/ye and that is only a modeled guesstimate. The major SLR contributors are ice sheet mass loss and thermosteric rise. Delta groundwater is surely something, as Jim points out. But even he says must be within the 25% ‘irreconcilability’. I dont thinkmwe know exact global SLR within 25%. The diff GPS vertical land motion long record tide gauges number about 70, with a strong northern hemisphere Atlantic basin bias. Judith’s uncertainty monster strikes again.

      • I mean simply that the sea surface increases with rising sea level.

  12. Global models underestimate large decadal declining
    and rising water storage trends relative to GRACE
    satellite data

    Assessing reliability of global models is critical because of increasing reliance on these models to address past and projected future climate and human stresses on global water resources. Here, we evaluate model reliability based on a comprehensive comparison of decadal trends (2002–2014) in land water storage from seven global models (WGHM, PCR-GLOBWB, GLDAS NOAH, MOSAIC, VIC, CLM, and CLSM) to trends from three Gravity Recovery and Climate Experiment (GRACE) satellite solutions in 186 river basins (∼60% of global land area). Medians of modeled basin water storage trends greatly un- derestimate GRACE-derived large decreasing (≤−0.5 km3/y) and in- creasing (≥0.5 km3/y) trends. Decreasing trends from GRACE are mostly related to human use (irrigation) and climate variations, whereas increasing trends reflect climate variations. For example, in the Amazon, GRACE estimates a large increasing trend of ∼43 km3/y, whereas most models estimate decreasing trends (−71 to 11 km3/y). Land water storage trends, summed over all basins, are positive for GRACE (∼71–82 km3/y) but negative for models (−450 to −12 km3/y), contributing opposing trends to global mean sea level change. Im- pacts of climate forcing on decadal land water storage trends exceed those of modeled human intervention by about a factor of 2. The model-GRACE comparison highlights potential areas of future model development, particularly simulated water storage. The inability of models to capture large decadal water storage trends based on GRACE indicates that model projections of climate and human- induced water storage changes may be underestimated.

  13. rainfall – evapotranspiration – infiltration – runoff = zero

    What I always loved about hydrology is how simple it is and how it all adds up. I have been waiting for GRACE to have a record long enough to be interesting. Could we balance the core hydrological equation over land using GRACE? It is not there yet – however.

    “The 13-year record of GRACE time-variable gravity solutions provides a revolutionary means for measuring water mass movement and redistribution in the global water cycle and offers a unique tool for monitoring long-term groundwater storage change at continental to global scales (Famiglietti 2014). GRACE measurements have captured significant groundwater depletion in many aquifers or regions globally, including NWI (and neighboring eastern Punjab Province in Pakistan), HPA, and Central Valley in the USA, the NCP in China, the Middle East, and the southern MDB in Australia. Among those, the NWI and Middle East regions show the most significant and persistent groundwater depletion over the past decade, with rates as large as 20.4 ± 7.1 km3/year and 25 ± 3 km3/year, respectively, for the period 2003–2012 (Chen et al. 2014; Joodaki et al. 2014). The Central Valley is also losing a large amount of groundwater with estimated
    depletion rates range from 4.8 ± 0.4 to 7.7 ± 0.7 km3/year, depending on the time span of the studies, and GRACE estimates agree well with in situ well data (Famiglietti et al. 2011; Scanlon et al. 2012). Even though the estimated Central Valley groundwater depletion rates appear not so significant compared with those for NWI and the Middle East, the current record-breaking severe chronic drought in California is only expected to worsen the already dismal situation there.” https://cloudfront.escholarship.org/dist/prd/content/qt4h04788b/qt4h04788b.pdf

    Rainfall over land seems to have been in decline over several decades. This is the major cause of the land/ocean temperature divergence – despite Jimmy’s typically one eyed narratives.

    But whether this implies a reduction in rainfall over both land and oceans or just a change in the patterns of where rainfall happens is another question. Possibly the latter is more important.

    Irrigation while extracting from groudwater stores adds to the evapotranspiration component – a local and regional effect adding to global convection. Total groundwater extraction for irrigation is some 545 km3/yr. – of the 22.6 million cubic kilometres total. Irrigation may be regionally significant for aquifer levels. Some of Elinor Ostrom’s – Nobel Prize wining economist – early work was on polycentric governance of Californian aquifers.

    Infiltration and exfiltration seem to be components of interest in this. Conceptually there is a hydrostatic pressure between the surface of aquifers and outflows to oceans are regulated by pressure and pore size – like turning a tap to higher or lower flow. I have worked on northern Australian aquifers where there are quick flows through bauxite deposits – and in catchments with micro infiltration through indurated coastal silts. Outflow adds to mass in the oceans – changing flows could compound changing sea levels.

    Infiltration is what is most in our hands, We are at the start of a global geoengineering project with a promise of immense, broad ranging benefits.

    • Robert I Ellison

      Thanks! Some pretty good slow banjo picking’.

      To me, the residual soybean crop cover water retention demonstration was most informative. Leave the stalks and empty pods on the ground until the next planting season. Which reminds me that globally, crop residue is burned by the majority of developing nations agriculturalists. Why do they still do that?

    • Robert what is the meaning of your comment, “Rainfall over land seems to have been in decline over several decades. This is the major cause of the land/ocean temperature divergence – despite Jimmy’s typically one eyed narratives.”

      First in the context of the essay, there is no discussion of “land/ocean temperature divergence”

      Second are you complaining that to focus on groundwater effects as one missing factor in the complexities of sea level rise is “one eyed ”

      What are you trying to say?

      • Sorry -it’s a different one eyed Jimmy. I like your post a lot and I think you are on the right track. My humble apologies for the confusion.

        It has been drier on land in recent decades. This has had impacts on terrestrial water stores as well as on soil moisture and thus reduced latent and increased sensible heat flux – biasing the surface temperature record – e.g. http://onlinelibrary.wiley.com/doi/10.1029/2004EO210004/abstract

        As well as contributing to declining TWS – rather than increasing as Reager et al find. Chen et al using GRACE find a TWS decline adding to SLR. There is another comment that will be unmoderated in due course.

        Again -my sincere apologies.

      • Reager focuses on the big picture, which is the total land storage component is subtracting from sea level over the Grace era. That is likely been driven by the negative PDO, which is ended in 2015.

        Greenland gained about 50 billion tons of ice in 2017 which should have lowered sea level in 2017. Clearly Greenland cannot explain the enigmatic steady 20th century sea level rise. – from the article

        This is an odd leap. 20th-century sea level rise has a Greenland component. Greenland’s 2017’s outcome, possibly an outlier, would have nothing to do with that.

        Estimating the sources of global sea level rise with data assimilation techniques

      • “20th-century sea level rise has a Greenland component.”

        How uncertain should you be about that?

        According to GISP2, Greenland summit ice accumulation is positively associated with temperature:

        And that’s why they had to dig down so deep to recover the WWII Glacier Girl.

      • thx for this ref

      • A component can be either positive or negative, so I’m pretty certain.

      • JCH says “This is an odd leap. 20th-century sea level rise has a Greenland component. Greenland’s 2017’s outcome, possibly an outlier, would have nothing to do with that.”

        JCH, I am not arguing that Greenland is not a component of 20th century sea level rise. I only argue that its contribution is variable, as opposed to Gregory et al’s suggestion it has contributed steadily.

        The reference to the 2017 ice gain is simply a detail in that variability.

        The best studied Greenland glacier, the Jakobshavn, began retreating from its Little Ice Age maximum with it fastest observed retreat of 500 meters per year between 1929 and 1942. The rapid retreat was amplified when the glacier’s terminal front became ungrounded from the ridge. The glacier then stabilized, and even began advancing between 1985–2002.

        Greenland melting of the 21st century has been correlated with a change in the North Atlantic Oscillation shifting and centering a high pressure system over Greenland, causing clearer skies and increased insolation. That culminated in peak surface melt in 2012, but the melt rate has decreased since then culminating in the 2017 ice gain.

        Although Greenland has undeniably retreated from its Little Ice Age maximum, it has not been a steady rate of change.

      • As my reference shows, for the ~40 years of the 20th century Greenland steadily reduced sea level, and subsequently has steadily increased sea level. They’re saying the 2017 exception is so small it would require ~80 of those in a row just to get back to 2002.

      • Thanks Robert for the clarification. Much appreciated.

      • afonzarelli

        Sorry -it’s a different one eyed Jimmy

        (Robert, i think you may have just bungled your apology here! Seems JimD has a knack for causing trouble without even showing up)…

  14. Absent dimensional analysis in support of his rather fantasic assertion, Jim Steele seems to be literally splitting hairs when he asserts:

    “Greenland gained about 50 billion tons of ice in 2017 which should have lowered sea level in 2017. Clearly Greenland cannot explain the enigmatic steady 20th century sea level rise.”

    A billion tons of ice is a cubic kilometer, and dividing 50 km3 into the > 300,000,000,000,000, square meter area of the oceans offsets net rise by < 150 microns — rather less than the diameter of a human hair.

    Perhaps he should compare notes with Oakes Spalding.


    • In context it means that the variability of Greenland ice melt isn’t the source of a steady 20th sea level rise. But then these odd, angry brain farts do happen aye?

    • Russel, Such an odd fact to glom onto. Are you deflecting?

      Indeed 50 Gt changes sea level by about 0.14 mm.. That figure should not be any more of a “fantastic assertion” then claims that Greenland is raising sea level by 0.3 mm or that the width of a human hair threatens humankind. Yet Greenland’s contribution is what sea level researchers are using to project future sea levels as coastal towns prepare their adaptation plans. So who is splitting hairs?

      Besides, as pointed out to you, in the context of the essay I was merely pointing to that Greenland does not supply a constant rate of sea level rise. Nor does it always add to sea level, but can lower sea level.

  15. “The 100 km^3/year groundwater loss over land will contribute ~ 0.27 mm/year to the global sea level rise. The actual total groundwater depletion rate over the world could be significantly higher than the above estimate, as many other aquifers or regions with relatively small magnitudes of groundwater depletions are not included.”

    The SLR budget is not balanced – but now we may be a little closer. Although I will have to ponder the Reager et al study linked above by Richard. From the NASA ‘Sea Level Rise Portal’.

    Mean sea level rise from altimetry – 3.2 +/- 0.5 mm/ yr

    Ocean mass from GRACE – 1.8 +/- 0.3 mm/yr – includes Greenland and Antarctic ice loss

    Steruc height from Argo – 0.8 +/- 0.2 mm/yr

    Greenland mass loss from GRACE – 286 +/- 21 km^3/yr

    Antarctic mass loss from GRACE – 127 +/- 39 km^3/yr

    Ice mass loss can be converted to sea level rise at the well known conversion rate of 360 km^3/mm – but it is already included in the total ocean mass gain – although that doesn’t quite add up either. See I said hydrology is easy and it almost adds up. Not that sea level rise is more than a smidgen – but groundwater is interesting.

  16. From a layman… Are there (deep) underground aquifers under the oceans? Is all the water in underground aquifers fresh water?

    • Groundwater in coastal areas can be depleted and allow ocean water into them. The term for this is saltwater intrusion, and a Google search will lead to documented examples of this. So the answer to the second part of your question is yes. The first part of your question would depend on what you think of as deep. Deep as in this post is not likely to be the same thing as deep as in under the ocean as the ocean has depth itself. However, the land at the bottom of the ocean is obviously saturated, and there are cracks and vents for the water to penetrate so there is water for some depth below the ocean/land contact. Exactly how deep and how much water will depend on local conditions, just as it does for groundwater in a continental area.

    • The USGS has a good illustration of the freshwater submarine discharge

  17. In the 1990s, I recall an estimate of “impervious surface” in the US to be the same area as Ohio. I’m guessing that in the quarter century since, that are has increased further. This would indicate an increase in runoff at the expense of groundwater uptake.

    Global ground water use appears to continue to accelerate.

    And dam building, and with it impoundment, has all but ceased over the last fifty years.

    • Lots of dams still being built just not many in N. America
      The Mekong delta is a good example of what happens when you convert a major river to hydropower.
      “Mekong River’s sediments fell from 65 to 75 percent compared to the total in the 1990s, and by half over the last few years… Mekong Delta is very likely to receive between 10 and 20 percent of the nutrient-rich sediment compared to what it used to get in the last century once all the hydropower plant projects on the Mekong River are finished.
      Lots of side effects, some that seem to affect the mass balance of surface water.

      This was interesting… Good use of AI and big data:
      “To satisfy our hunger, we humans catch something on the order of one trillion fish ever year — a yield that amounts to more than 90 million tons of animal flesh… China, Spain, Taiwan, Japan and South Korea accounted for 85 percent of the observed fishing on the high seas during 2016.”

      • You highlight the problem with accounting for sediment contribution to sea level. Erosion happens but dams have slowed the normal sediment supply to deltas. So determining the net effect of sediments is very difficult.

    • I suspect groundwater extraction would/has contributed to sea level rise. The problem is there have been various estimates, and the question of net contribution is affected by estimates of groundwater recharge. Any extracted water that recharges the same aquifer at the same depths would have not a sea level effect. But such a balance is unlikely, and estimates of recharge by extracted water are likely confounded by natural recharge dynamics.

      • Irrigation is by far the largest use of groundwater – averaging 70% globally.

        In the US in US gallons.

        And more generally in rational units.


        It is allocated and managed wherever I can think of. Total extraction is about a 1000 km^3 and this number is reasonably well constrained. If we assume that 30% quickly flows to oceans – then this is less than a millimeter.

        Irrigation is designed to have a small flow through into deeper soils to wash through accumulated salts. Other than that – about 30% lost of sprays evaporate and the rest in evaporation from soils and transpiration by plants. It ends up in the atmosphere.

        Recharge by rainfall is the process of interest. In a rainfall/runoff model I would assume – unless I had better information – 25mm initial and 2.5mm continuing losses to deeper horizons. All over the globe from Melbourne to Souel we are designing water sensitive urban landscapes. Water use is minimized through treatment and reuse of both sewage effluent and stormwater. Excess stormwater from hardened surfaces is increasingly infiltrated into groundwater stores – sometimes to be reused. Flash flooding downstream and pollutant exports are minimized. This is the essence of water efficient and water sensitive design.

        But it is agriculture where the great gains are to be made. Management of cover and soil organic content increases infiltration and water holding capacity – it holds back water and reduces erosion. Productivity is the objective and CO2 sequestration (perhaps 100 GtC) a secondary effect. We can hold back water in the landscape lifting water tables and providing moisture for vegetation growth. Increased infiltration creates ground water stores for later seepage into streams as baseflow – dry weather flow – important for so many reasons. This is one of my favorites.

        The Anthropocene in the 21st century is brilliant.

      • One interpretation of these charts with the phaseout of the impoundments impacting SLR so the groundwater contribution goes from a net negative to a net positive, is that what has been perceived in some quarters as an acceleration in the SLR Rate from AGW is really just more groundwater making its way to the ocean. The estimates of the exact amount are all over the board, including one paper that says the IPCC has overstated the contribution.

        Who knows what the facts are. One thing for certain, there is more to learn than what we have already learned. Just one more reason to jack up the uncertainty level. That would be the rational thing to do.

      • “so the groundwater contribution goes from a net negative to a net positive”

        That’s certainly what it indicates to me.

        But as you say, there’s uncertainty with the estimates.

      • Total land storage is currently net negative, and the satellite-era rate has accelerated.

      • Land storage seems to be in decline – with seemingly conflicting GRACE results – by conservation of mass it ends up in the oceans.

      • Total land storage is currently net negative

        With respect to what year?
        Probably more water is dam impounded than was so in 1945.
        Probably less water is dam impounded than in 2000.

        Once dams fill, they no longer provide long term net change.

        Then some other things happen.

        Sediment infill is one.
        Increased withdrawal is another.
        Senescence and removal is another.

        But since large dam building has practically ceased, dams would not appear to be a significant factor, unless rates of removal increase.

      • This is a list of estimated global contributions to SLR from various papers over the last several years.


  18. Jim Steele & Dr. Curry ==> For what it is worth; I have let this whole issue percolate in my mind for the last week or so — a method that usually results in my coming to a conclusion … sometimes not.
    Readers here and at WUWT may have read my series on SLR, Tide Gauges, and all over the last year or two. But here is my bottom line on Sea Level Rise and its Acceleration (which technically means just “change in speed or rate” – plus or minus):

    Mankind has no chance of understanding this issue until we can reliably, accurately and precisely measure the actual height of the sea surface above the geoid at a sufficiently large number of locations properly spaced around the Earth using high-quality GPS@TG (GPS at TIde Gauge) instruments capable of both measurement on the scale of millimeters and the same scale of correction for vertical movement of the tide gauge itself. With such a network of instruments, we can derive some idea of actual short-term absolute SLR — it will be many years more before medium-range estimates can be made (20-30 years) and longer still before multi-decadal and longer cycles can be discovered and accounted for.

    All the attempts to calculate or derive SL change from anything other than actual physically measured change in the height of the surface of the seas themselves is a fools errand and results in and imaginary metric biased by the scientific worldview of the research team. I say imaginary because these efforts include literally imagined corrections: “If the volume of the seas hadn’t expanded, then SL would have been X mm more, so we’ll add that in…” Satellite calculations contain many imagined corrections and adjustments of unknowable factors (sea height under storm conditions, tidal effects known only to cm scale even when measured, etc). These imaginary corrections (rank guesses) are used to arrive at fractional millimetric global results.

    Science requires measurement and it is not measurement when the calculation includes guesses concerning confounders orders of magnitude greater than the effect being measured.

    • Steven Mosher

      The only problem is this: If you wait until you have data that satisifies the precisionists, it will be too late to correct the problem should it exist. We know it is getting warmer; we know this will lead to SLR, all other things being equal; we have, broadly speaking, two methods of predicting SLR: simple linear extrapolation; extrapolation via a physics model. We know neither of these approaches will ever be accurate to a millimeter or centimeter for that matter. Still, we make decisions every day about building in locations that require estimates of future SLR. Those decisions cannot wait for a precisionist answer. So lets make you the planner Kip. The proposal in front of you is whether or not to develop a property. Take treasure Island in San Francisco. You have to decide. Given all the data you have, there is no time to wait 20 years to collect better data, given all that data and 2 ways of predicting the future Sea level in that location, which answer do you use and why? do you use a simple linear model that says sea level will rise a foot there, or do you plan for 3 feet? or do you plan for 6 feet just to be super safe? There are real practical problems and practical decisions that are made every day. They are made under uncertainty. We shoot the precisionists and make informed decisions cogniscent of our ignorance and attuned to the risks. We know that if we designed a perfect observation system and waited 30 years that we would have less uncertainty. That is a given. It’s trivially true and beside the practical point. We make decisions every day with bad data, incomplete data, bad assumptions, over simplified models, etc. When we make these decisions the first casuality is the precisionist in the room. We already know what he is going to say, we know it better than him. Being a precisionist is a luxury, folks who have to actually work for a living and live with the responsibility of deciding under uncertainty and risk, have no patience for them

      • Mosher ==> You have not been following the conversation, apparently. It is NOT I who is the “precisionist” — it is those who purport to produce scientifically accurate and precise statements of “SLR” from data not suited for purpose, use wild guesses in place of real data, and use the resulting nonsense for political purposes.
        All of my work on SLR has focused on the need for local planners to use their own, actual-measurement Local Relative Sea Level data for planning and emphasized that that is the ONLY information pertinent to their needs, allowing that they might consider the real long-term global absolute SLR information as a guideline for longer term planning.
        The latest data shows your Treasure Island subsiding at 10 mm/yr. A far greater threat than the actual rising of the surface of the sea itself along the Pacific coast of California.
        Continuing to insist that the world’s planners use data that WE KNOW IS WRONG instead of the data that we know is right — actual measurements of things we can see and touch and changes that are physically being experienced — is the apex of scientific hubris and a gross misuse of science.
        There are things we know about Sea Level and its potential for change. We don’t need to make things up — just use real data.
        Despite giving in to the temptation to use “the scariest scenario”, at least this paper starts out with real data: Global climate change and local land subsidence exacerbate inundation risk to the San Francisco Bay Area

      • After all these years and all the empty blog science comments, mosh’s argument still breaks down into chicken littleism as it’s foundation.


      • Engineers do not design and build to precise levels. Practical engineering is based on a hierarchy of risk, stochastic analysis of wave and flood risk – among other risks – safety margins and contingency planning.

        There is a problem with stochastic analysis – it is based on the wrong paradigm.

        “The type of change that can be predicted with precision is usually trivial.
         Also, decision making under certainty is mostly trivial.
         History teaches that while understanding and prediction are good advisers for decisions and actions, neither of them is a
         According to Aristotle, what is needed as a guide to human
        decisions and actions is Orthos Logos (Recta Ratio, or Right
         Science, including hydrology, can contribute to societal progress
        by promoting Orthos Logos.”


        Mosh has never distinguished himself in Orthos Logos.

  19. Judy’s penguin tweet showed me how to tweet – so I tweet again.

    To get back on topic – I noticed this on my long neglected tweetery.

    Restored soils and ecosystems on land conserve the freshwater resource on which terrestrial life depends – and in oceans protect the diamond sparkling, dancing, kaleidoscopic patterns of life itself.

  20. Geoff Sherrington

    That needed stressing.
    We do not even know the constancy of the walls and bases of the oceans that form the vessel whose surface height we seek to measure and explain. Geoff.

  21. nobodysknowledge

    I don`t understand this groundwater discharge. As if water is poured out of earth. I can understand that the upper layers can be emptied in dry periods. But it seems that they are filled up again. There is some seasonal variation in gravitation many places. The idea of discharge that increases sea level will presuppose that there is a net emptying, that the amount of water in is less than water out, and that there is no water saturation deep down. There is much water quite down to the core of the earth, but I have always thought that this is in a kind of equilibrium.

    • When we pump water from a deep aquifer we can (and usually do) pump it out faster than what infiltrates back in. It is groundwater mining. Many communities mine groundwater in this way until they become a certain size to make treatment plants economically feasible. Good examples of this are Las Vegas, NV and Phoenix, AZ. Both communities have pumped large amounts of water from the ground to irrigate and provide their communities with drinking water. Phoenix has pumped so much water out of the ground, that the ground has actually subsided feet in elevation, and I suspect Las Vegas has as well. Both communities now have treatment plants that allow them to use surface water and reuse sewer water. Both communities now recharge groundwater by injection into wells. However, I suspect that both communities are still using more water than they inject, as well as using more than what they inject plus what water infiltrates naturally into the aquifer. Regardless, for a good number of years both communities pumped considerably more water out than was being replaced, and there are smaller communities in both states that are currently drawing the water levels down.

      • I linked to the the USGS tool that has 2017 data. I don’t need an abstract – that I cannot locate a doi for – to tell me that compaction and subsidence is happening. And you still haven’t named the tome you took a screenshot of.

        If you had a viewpoint informed by a depth of knowledge – or even less stridently expressed as a would be climate warrior with always the same off point bombastic rants – or perhaps showed signs of earnestly reasoning about topics – instead of googling and pasting abstracts – it might be a different story. It ain’t.

      • … whoops wrong place…

    • Some soils compact after the fossil water is mined and they no longer will hold as much water. The Houston area has this problem.

      • Yes, and coastal areas have the potential of saltwater intrusion as well to worry about when they extract more fresh water than infiltration.

      • “Conversely, when the pore pressure recovers (i.e., increase due to water level recovery), the support provided by the skeleton is gradually transferred to the pore pressure, which in turn leads to soil expansion (i.e., uplift) [37].” http://www.mdpi.com/2072-4292/8/6/468/htm

        In particularly reactive soils the problem of sequential compaction and recovery makes for some interesting urban topology.

      • Galveston County has heavily regulated groundwater mining for a long time. It has significantly limited subsidence. in some areas it is described as halted. I’ve never heard of an uplift in the Houston area. They would probably hold a parade.

      • There is compaction of the coastal and lacustrine silts simply from mechanical loading from the city above. But if water is removed as well – nature abhors a vacuum.

        It generally takes a lot of effort to understand specific groundwater regimes. A persistence in investigating in depth (pun intended) is something missing to any substantive degree. You are too far behind the curve – and imagine that 10 minutes on the internet makes you a professional. I’ll help – here knock yourself out.


        Many wells seem to be recovering – some not. But as long as there is pore connectivity – the ‘skeleton’ is the key – increased hydrostatic pressure from increased water levels will translate to increases in pore pressure and ultimate soil expansion. It can takes decades I presume.

        Your reference relater to dewatering of silts and clays for engineering foundations. Usually dewatering by mechanical loading. It can take decades and these things are never unloaded.

      • I link and quote a relevant 2016 Beijing study – he gives a screenshot of a tome without even saying what it comes from. It’s a game of intellectual hide the weasel. Now that’s a double entendre.

      • My reference is from a report of the USGS on subsidence in Houston and Galveston counties.

        But of course, an arrogant and condescending pile like you knows better.

      • Subsidence Rates in Southeast Texas as Determined by RTK GNSS Measurements of Preexisting Survey Markers


        This study determines the rates of subsidence or uplift in coastal areas of SE Texas by comparing recent GNSS measurements to the original orthometric heights of previously installed National Geodetic Survey (NGS) benchmarks. Understanding subsidence rates in coastal areas of SE Texas is critical when determining its vulnerability to local sea level rise and flooding, as well as for accurate survey control. The counties covered are Chambers, Galveston, Hardin, Jefferson, Liberty, Orange, and parts of Jasper and Newton counties. These counties lie between an earlier subsidence study conducted in Louisiana and an ongoing subsidence study of several counties around the Houston metropolitan area. The resurveying methods used in this RTK GNSS study allow a large area to be covered relatively quickly with enough detail to determine subsidence rates that are averaged over several decades. This information can be used to place more targeted GNSS observation stations in areas that appear to be rapidly subsiding. By continuously, or periodically, measuring the elevations at these targeted stations, current subsidence rates can be determined more accurately and at lower cost than by scattering a large number of GNSS stations over a wide area. This study was conducted using a Trimble R8 GNSS system on all NGS benchmarks that were found in the study area. Differential corrections were applied in real time using a VRS network of base stations. This system yields a nominal vertical accuracy of 1.5 to 2.0 cm for each 2 to 5 minute reading. Usually three of these readings were measured on each benchmark and averaged for the final result. A total of 367 benchmarks were resurveyed, most of which were suitable for vertical change rate calculations. Original NGS elevations were subtracted from the new elevations and divided by the time between the two elevation measurements to determine the average subsidence or uplift rate of the benchmark. Benchmarks used for determining the vertical change rates were monumented between1931 and 2006, thus yielding rates averaged for 5 to 80 years. Besides the errors inherent in RTK GNSS measurements, other sources of error for vertical change rates include inaccuracies in the original elevations published by the NGS and uncertainties about the year in which those original elevations were measured. Initial results show as much as -0.86 m of subsidence over a 58 year period on one benchmark in Jefferson County 30 km north of the coast, and up to +0.23 m of uplift over a 60 year period on one benchmark in Jasper County approximately 130 km north of the coast. Overall, preliminary results of the study show near zero vertical change rates to a maximum of -15.3 mm/yr subsidence in Chambers, Galveston, Liberty, and Jefferson counties, with the highest rates of subsidence in Jefferson and Chambers counties. Parts of Galveston, Orange, and Jasper counties show subsidence rates up to -9.1 mm/yr, but also show uplift rates up to +4.8 mm/yr. Potential causes of vertical change in the study area include expansion or contraction of near-surface clays due to changes in water content, compaction of near-surface to deeper sediments, growth faulting, groundwater, oil, or natural gas extraction or injection, and to a much smaller extent, tectonic effects.

      • https://judithcurry.com/2018/03/04/will-advances-in-groundwater-science-force-a-paradigm-shift-in-sea-level-rise-attribution/#comment-867994

        If you have something you want to make a point about – something quite unlikely I know – quote the passage or simply reference. As it is you litter posts with entire abstracts. It’s like a science totem. And try to read more than the abstract. It takes a lot of time and effort to get good at even reading science. Friendly advice.

  22. I ran some numbers on the DEM (Digital Elevation Model) data used for Greenland and concluded that the precision needed to account for sea level rise attributed to the “melting” of the Greenland ice sheet was beyond the precision achievable by the satellite instruments,

    Something like 0,5 mm +/-5 mm means the ice sheet could be gaining or losing mass. (figures for illustration only). Whenever you see the attribution to Greenland or Antarctica you have to consider the error bars. Journalists ignore these, so you have to go at least to the abstract, but some abstracts do not show the error bars.

    I have used DEM data from the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer), a high resolution Japanese imaging instrument that is flying on the Terra satellite. As I recall the resolution is 15 meters (for land only). This is the level of resolution needed to attribute sea level changes to glaciers, but unfortunately the instruments that record ice mass / elevation do not have such high resolution.

    I have no experience modeling mass gain/loss of continental glaciers and hope the modelers know what they are doing, But I have found disturbing some statements to the press by academics who describe the dynamics of continental glaciers in terms usually reserved for mountain glaciers.

    And worse. much worse. Our knowledge of glacier movement has advanced much further than Horace-Bénédict de Saussure (1740–1799). We no longer hold that continental glaciers slide downslope like toboggans lubricated by a layer of melt-water.

    It is still possible to watch or read an entire lecture/article on the Greenland glaciers without discovering that Greenland itself is so depressed by the weight of the ice that the island forms a basin with its lowest point below sea level.

    (Compare the epicenter of the Laurentide Ice Sheet: Hudson’s Bay is still below sea level and is still rebounding by isostatic adjustment.)

    From the lowest level of the Greenland ice-sheet melt-water would have to flow uphill to reach the sea. Not to say this is impossible, but surely the mechanism would be worth mentioning in a lecture or article.

    • “….would be worth mentioning…..”

      That observation applies to just about anything having to do with climate issues, whether they be lectures, articles or IPCC reports.

      But if they attempted to provide context or perspective then that might generate questions. Why run the risk of legitimate questions?

      Two recent examples: An article in the Guardian spoke about the “record” low level of sea ice in Antarctica. A group of scientists were perplexed by the low 2 million sq k when only 4 years ago there was a “record” high level of 20 million sq k. Denizens get it since they follow the charts with its swings from austral summer to austral winter. They also know the difference between sea ice and ice shelves and the continental ice Sheet and all the dynamics involved in each and the importance and unimportance of data for each. And they know the data relates to the satellite era. Denizens can form their own opinion on the significance of the “record” low.

      But for the average reader, without any background, the takeaway could be interpreted as a breathtaking change. There was no effort to provide context or background.

      Yesterday I reread the IPCC5 section on glaciers. I could have missed it but I saw no mention of the possible role of geothermal activity in Greenland or Antarctica. Not a sentence. It might turn out that those rifts and hot spots are not significant to contributions to SLR, but why not at a minimum mention that this factor could be involved with the inherent instability of West Antarctica and should be adding to the uncertainty in calculating future ice loss?

      Journalists could at times be given a pass for their ignorance of the issues. The professionals deserve no such pass. Such omissions warrant misfeasance.

  23. Geoff Sherrington

    I have not put the following mechanism into context of size yet, but it is another mechanism that might not be part of the SLR balance. My colleague John Elliston has just published a book on geological mechanisms involving mineral particles of colloidal size. In a river delta like the Mississippi, water and fine particles in various extents of hydration can coexist until a shock like an earthquake can causes liquefaction and large scale flow under gravity. There are changes in the balance of free and fixed water that will be involved in closing the sea level equations. As noted, very little measurement, uncertainty if it counts in real life.
    This is the more philosophic point. One can try to optimise the contributions of competing processes so all adds up to 100%. But, this fails if there is a significant competing process that is not included because the process is unknown or unquantified. Pulses of dewatering in sediment piles is a case.
    I grin at my old mate Mosher dismissing these as unicorns. The wider problem in climate work is that this bit by bit attribution with residual unicorns is a widespread but faulty process as shown by earth radiation balances, sea level change, ice mass balances, CO2 budgets, accuracy of Argo floats etc.
    Maybe this is the only possible approach given the impossibility of replication of many processes, but the faulty results should not be proclaimed with the certainty that encourages policy changes of large consequence. Geoff

    • Curious George

      At the first glance the liquefaction is just a separation of a liquid and solid component. I don’t see a change of volume of water. Not unlike a thawing iceberg.

      • Geoff Sherrington

        Volume of hydrated minerals is less than volume of dehydrated plus freed water. Not a big difference, but there. Geoff.

    • ‘Not only sands and gravels
      Were once more on their travels,
      But gulping muddy gallons
      Great boulders off their balance
      Bumped heads together dully
      And started down the gully.
      Whole capes caked off in slices.
      I felt my standpoint shaken
      In the universal crisis.
      But with one step backward taken
      I saved myself from going.
      A world torn loose went by me.
      Then the rain stopped and the blowing,
      And the sun came out to dry me.’

      H/t Robert Froast.

  24. Tom and Jerry – the GRACE satellites – are such beautiful instruments. They move as a pair in orbit around the Earth and track gravity by measuring the distance between to an accuracy of 10 microns. They are due to be crashed into the Earth soon. GRACE-FO will have a greater precision.

    If we are looking at climate change – we need a millennia of data at a bare minimum. But these beautiful instruments can tell us amazing things.

    • we need a millennia of data at a bare minimum.


    • “Since “panta rhei” was pronounced by Heraclitus, hydrology and the objects it studies, such as rivers and lakes, have offered grounds to observe and understand change and flux. Change occurs on all time scales, from minute to geological, but our limited senses and life span, as well as the short time window of instrumental observations, restrict our perception to the most apparent daily to yearly variations. As a result, our typical modelling practices assume that natural changes are just a short-term “noise” superimposed on the daily and annual cycles in a scene that is static and invariant in the long run. According to this perception, only an exceptional and extraordinary forcing can produce a long-term change. The hydrologist H.E. Hurst, studying the long flow records of the Nile and other geophysical time series, was the first to observe a natural behaviour, named after him, related to multi-scale change, as well as its implications in engineering designs. Essentially, this behaviour manifests that long-term changes are much more frequent and intense than commonly perceived and, simultaneously, that the future states are much more uncertain and unpredictable on long time horizons than implied by standard approaches. Surprisingly, however, the implications of multi-scale change have not been assimilated in geophysical sciences. A change of perspective is thus needed, in which change and uncertainty are essential parts.” (Demetris Koutsoyiannis, 2013)

      There is an intractable agnotology –
      a culture of ignorance – in would be climate warriors. It means that they cannot progress in right reasoning. This is a political problem for the progress of science and society. JCH has to deny a throw away statement that was based on a millennia and a half of climate data – because it is not in accordance with the ideology of certain catastrophy. With of course nothing but a blanket denial.

  25. There is a fatalism to the NY Times story of San Francisco sinking into the ocean that is at odds with millennia of water engineering. The future we can cope with. In terms of opportunity cost it is best not to cope with it too soon – or on the basis of improbable projections and night terrors.


    • The fascinating implications of this study is that the SF tide gauge suggests RSL has been rising at about 2 mm/year, although since 1980 that rate of rise has decelerated. This study on land subsidence suggest the land has been sinking at a rate of just less than 2 mm/year. Thus any contribution from meltwater and thermal expansion is nearly none!

      It suggests there has been no rise in actual sea level. Grace data from 2003 to 2008 resulted in no change in ocean mass. If that data is correct, then whatever river runoff and ground water is seeping back to the ocean, it is being balanced by terrestrial water storage. That storage is predicted by the hypothesis that La Nina conditions cause more rain to fall on land.

      It also illustrates that sea level rise rates are driven by subjective adjustments. As my analysis reports, depending on which researchers employ which models, and which adjustments to the GRACE data are employed, then sea level rise can vary from 0 to 2 mm/year. What to trust?

  26. Geoff Sherrington

    I do not think Grace is magical. Ingenious, yes, but a panacea, no.
    Grace data need more than known equations of physics. Cannot tell the difference between a heavy shallow mass and a little lighter, slightly deeper mass, for a start. It needs subjective assumptions to frame the math to allow solutions at times.
    If climate research has taught us anything, it is to beware the important assumption. That is where big lots of money are linked. Geoff

  27. Interesting post. Led to a thought bubble.
    Why do we have water on the surface anyway?
    Meteorites have water in them but all through them, some are ice.
    I guess the proximity to the sun melts them and they freeze last on the outside.
    On a bigger rock like the earth why does the water not just blend in with the rest of the substrate and just make a layer of wet mud miles deep?
    Are we just a test tube with different elements and molecules at different surface levels based on their meltability and gaseability?
    I mean water should sink and permeate and go through the ground to the lowest permissible level.
    Does the level of permeability and density deeper down really stop water going down?
    Should we consider the ocean as just an accidental condensate of the water in the air in which case if it gets a lot hotter it will all go into the atmosphere and the sea level could fall.
    After the ice all melts of course.

  28. Ta. See it has made WuWT as well. Lucky it is enclosed in carbon as well

  29. Groundwater is a particularly interesting question given that human influence may increase dramatically over the next 100 years. I often wonder if the 2100s might see 100B people living at 5-10x today’s economic consumption, taking on megaprojects like damming the Drake Passage to fuel their thirst for energy and to combat falling sea levels :)

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