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NASA Mission Takes Stock of Earth's Melting Land Ice

Posted on 10 February 2012 by John Hartz

This article is a reprint of a news release posted by the US Jet Propulsion Laboratory on  Feb 8, 2012

In the first comprehensive satellite study of its kind, a University of Colorado at Boulder-led team used NASA data to calculate how much Earth's melting land ice is adding to global sea level rise.

Using satellite measurements from the NASA/German Aerospace Center Gravity Recovery and Climate Experiment (GRACE), the researchers measured ice loss in all of Earth's land ice between 2003 and 2010, with particular emphasis on glaciers and ice caps outside of Greenland and Antarctica.

The total global ice mass lost from Greenland, Antarctica and Earth's glaciers and ice caps during the study period was about 4.3 trillion tons (1,000 cubic miles), adding about 0.5 inches (12 millimeters) to global sea level. That's enough ice to cover the United States 1.5 feet (0.5 meters) deep.

"Earth is losing a huge amount of ice to the ocean annually, and these new results will help us answer important questions in terms of both sea rise and how the planet's cold regions are responding to global change," said University of Colorado Boulder physics professor John Wahr, who helped lead the study. "The strength of GRACE is it sees all the mass in the system, even though its resolution is not high enough to allow us to determine separate contributions from each individual glacier."

NASA GIF

Average yearly change in mass, in centimeters of water, during 2003-2010, as measured by NASA’s Gravity Recovery and Climate Experiment (GRACE) satellites, for Greenland and Antarctica and their peripheral glaciers and ice caps, all the world’s glaciers and ice caps (excluding Greenland and Antarctica), for the Indian subcontinent, and changes in ice thickness (in centimeters per year) averaged over each of the world's ice caps and glacier systems outside of Greenland and Antarctica. Blue represents ice mass loss, while red represents ice mass gain.

About a quarter of the average annual ice loss came from glaciers and ice caps outside of Greenland and Antarctica (roughly 148 billion tons, or 39 cubic miles). Ice loss from Greenland and Antarctica and their peripheral ice caps and glaciers averaged 385 billion tons (100 cubic miles) a year. Results of the study will be published online Feb. 8 in the journal Nature.

Traditional estimates of Earth's ice caps and glaciers have been made using ground measurements from relatively few glaciers to infer what all the world's unmonitored glaciers were doing. Only a few hundred of the roughly 200,000 glaciers worldwide have been monitored for longer than a decade.

One unexpected study result from GRACE was that the estimated ice loss from high Asian mountain ranges like the Himalaya, the Pamir and the Tien Shan was only about 4 billion tons of ice annually. Some previous ground-based estimates of ice loss in these high Asian mountains have ranged up to 50 billion tons annually.

"The GRACE results in this region really were a surprise," said Wahr, who is also a fellow at the University of Colorado-headquartered Cooperative Institute for Research in Environmental Sciences. "One possible explanation is that previous estimates were based on measurements taken primarily from some of the lower, more accessible glaciers in Asia and extrapolated to infer the behavior of higher glaciers. But unlike the lower glaciers, most of the high glaciers are located in very cold environments and require greater amounts of atmospheric warming before local temperatures rise enough to cause significant melting. This makes it difficult to use low-elevation, ground-based measurements to estimate results from the entire system."

"This study finds that the world's small glaciers and ice caps in places like Alaska, South America and the Himalayas contribute about 0.02 inches per year to sea level rise," said Tom Wagner, cryosphere program scientist at NASA Headquarters in Washington. "While this is lower than previous estimates, it confirms that ice is being lost from around the globe, with just a few areas in precarious balance. The results sharpen our view of land-ice melting, which poses the biggest, most threatening factor in future sea level rise."  

The twin GRACE satellites track changes in Earth's gravity field by noting minute changes in gravitational pull caused by regional variations in Earth's mass, which for periods of months to years is typically because of movements of water on Earth's surface. It does this by measuring changes in the distance between its two identical spacecraft to one-hundredth the width of a human hair.

The GRACE spacecraft, developed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., and launched in 2002, are in the same orbit approximately 137 miles (220 kilometers) apart.  The California Institute of Technology manages JPL for NASA.

For more on GRACE, visit: http://www.csr.utexas.edu/grace and http://grace.jpl.nasa.gov .

For more information about NASA and agency programs, visit: http://www.nasa.gov .

JPL is managed for NASA by the California Institute of Technology in Pasadena.

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Comments 51 to 67 out of 67:

  1. Tom Curtis @ 49

    Tom it is not me being the one lacking the understanding in this situation. I did explain it fairly well if you would take the time to read my post and not (-snipemotionally-) react to it.

    In post 31 I was addressing specifically your point in post 26. Reread the beginning of my post in 31, it is in this frame that I am bringing up the link to Texas. You make the claim in 26: "you make the assumption that extracted groundwater is not being replaced. That is not correct."

    In the Texas aquifier link I was showing you that I did understand the concept of withdrawal and recharge and I was showing how different aquifiers are being recharged at different rates. I chose the Ogallala aquifier to show you that some aquifiers recharge at very slow rates, it was not a deception I was making a specific point to address your claim in 26 the I made this assumption (which I did not) and that I was not correct in making this assumption which I had not made.

    Please read the post in 49 about the 8.9 figure. It was not included in my Texas link at all and is a totally seperate concept that has nothing to do with the link of the Texas aquifiers (again was only brought up to demonstrate that I did indeed grasp the concept of withdrawl vs recharge rates which you believe I do not understand).

    Please reread the posts if necessary but the 8.9 was a ratio difference between the work in KR's link that has the claim that withdrawal rates of water mining equal 61 km^3 per year but all other sources I look at indicate a much higher value than this.

    My original post was actually on topic, the defense of the original post has led to the off topic string of posts.

    My original post made the claim that even if all ice melting were halted the oceans would still continue to rise because of the water removed from deep sources that is not being replaced at the rate of removal and will find its way into the ocean as the ultimate water sink on the surface.

    Please follow the line of reasoning in my posts and you will see that it is not what you are claiming, mostly defending a postional statement that you have not proven wrong.
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    Moderator Response: [DB] Inflammatory trolling term snipped.
  2. Norman - "My original post made the claim that even if all ice melting were halted the oceans would still continue to rise because of the water removed from deep sources that is not being replaced at the rate of removal and will find its way into the ocean as the ultimate water sink on the surface."

    And that assertion is wrong. The link I provided to Milly specifically excludes ice melt both glacial and ice cap - discussing anthropogenic water movement. Their conclusion, including all the sources and sinks they could identify, the best information available, is that the best estimate for water usage contribution to sea level rise is: zero.
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  3. Norman @51, in your post @ 21 you claimed:

    "One problem is that even if the ice melting halted the oceans would continue to rise at about the same rate. The result of irrigation pulling water from aquifiers that had the water locked away and now going into the surface water balance."


    You quoted a figure from the total ground water used as irrigation and determined from that a projected increase in sea level. You did not mention recharge, and did not attempt to determine recharge before calculating the impact on sea level.

    In fact, you concluded that:

    "So the water added to the system via irrigation is fairly close to the amount of water added by melting ice. Meaning the sea water will continue to rise regardless if the ice melting stops and the problems of the future will still remain."


    For that to have been true, recharge must have been very small relative to withdrawals from ground water.

    If, as you now claim, "...I did understand the concept of withdrawal and recharge..." your failure to mention recharge in post 21, and your failure to allow for it in your calculation of the impact on sea level is a case of deliberate misrepresentation. You (claim you) knew about a relevant factor which would significantly effect your calculation, but chose neither to mention it nor to include it in your calculation. That, be definition, is telling a half truth, and a half truth is always a whole lie.

    You further state that "... I was showing how different aquifiers are being recharged at different rates." But you made no mention of different rates, and no mention of any aquifer other than the Ogallala aquifer. Generally when a person makes no mention of something, they are not trying to show people that thing.

    What is more, and this is the crux of the issue, you could have quoted the Edwards-Trinity aquifer* as easily as the Ogallala aquifer. That would as easily shown that you understood the concept and its relevance. It also would have suggested that recharge rates are over three times discharge rates, clearly indicating that may point @ 26 was well made, and that you did need to investigate and quote recharge rates in order to make the argument you were making. In fact any other choice of data from that site would have reinforced my point, and shown that failure to quote recharge rates was an obvious flaw in your reasoning. That is what makes it a cherry pick.

    Your continued defense of that cherry pick leaves no conclusion open except that it was a deliberate attempt to mislead.

    * The Edwards-Trinity aquifer is atypical of Texas aquifers in that it is the opposite extreme to the Ogallala aquifer. My point is that it is sufficient to show what Norman claims to have been his point, so there was no reason not to choose and discuss it. Certainly there was not reason not to discuss the state total, except of course, for the crucial point that it would have (again) shown the failure of Norman to present relevant data.
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    Response:

    [DB] "Your continued defense of that cherry pick leaves no conclusion open except that it was a deliberate attempt to mislead. "

    Agreed.  Back to Norman for a final plea.

  4. Tom Curtis @53

    "You quoted a figure from the total ground water used as irrigation and determined from that a projected increase in sea level. You did not mention recharge, and did not attempt to determine recharge before calculating the impact on sea level."

    Before my posting at 21, I had looked at this page. In post 21 I was not doing a highly detailed analysis, just demonstrating ball park numbers.

    "About 62 % of water used in agriculture, globally, comes from surface sources (e.g., rivers) while about 38 % comes from ground water (underground aquifers). However more of Earth's freshwater is in aquifers than in surface sources -- in fact, about 99 % of all liquid freshwater is in groundwater. (Issues in Ecol (9) 2001). Much (> 75 %) of this groundwater is "fossil water;" -- water that is not being recharged but is relic from wetter ancient climate conditions and from melting ice after the Pleistocene ice ages. Once we use it, it is "gone" for all practical purposes." source of quote.

    The Wikipedia article on irrigation gave the 545 km^3/year for irrigation. The above article made the claim that over 75% of the water used in irrigation was fossil water and is not being recharged at any appreciable amount (which is why I used the Ogallala Aquifier in my post to you, it is one of the types of Aquifiers that does not recharge very much and most the water withdrawn from it for agriculture will take a very long time to return).

    You call using the Ogallala Aquifier a "cherry pick", but I call it a demonstration of just how slow this type of aquifier fills up. The article I linked to above said over 75% of irrigation uses this type of aquifier.

    In your Post at 47 I am convinced that you and I are not making a communication link. "For what it is worth, the paper you link to estimates a global recharge rate of 15,200 km^3 per annum, and a withdrawal (abstraction) rate of 734 km^3 per annum. So withdrawal is only 5% of recharge globally, according to this paper. So, despite your continued cherry picking of the data, you have still not shown evidence that supports your claims, let alone establishes them."

    What I am talking about is removal of water from deep aquifiers that is not being replaced. If it is taken out from those aquifiers and not replaced, it is being added to the the surface water total amount.

    You are talking about groundwater recharge rate of 15,200 km^3 km/year (not recharge rates of deep aquifiers...a big difference) which makes sense it would recharge at this rate since this is the amount that is leaving the system (so it maintains balance)...

    "According to hydrologists and climatologists, about 15,000 cubic miles of water may evaporate from the earth's land sources each year. This includes water that moves through growing plants as transpiration. This value is less than 20% of the water that evaporates from all the seawater sources on earth." source.


    Finding the exact amount of water withdrawn from deep aquifiers minus replacement may not be possible. All sources I have researched would indicate it is much higher than the 61 km^3/year used in the paper KR linked to in previous posts but it has a large range. I can't agree with KR's sources as other peer-reviewed items state a much higher water removal.

    Tom, even when I completely explain the reason I gave you the Ogallala aquifier example you still call it a "cherry pick". Why do you keep making that claim and stating my intent is to mislead? The Ogallala aquifier was not used in my calculation. As you pointed out, they do not use any units on that web page. The purpose of bringing up that link was to give you a real example of the slow rate of recharge of a deep aquifier of which most irrigation uses (at least according to the source in the quote above making the claim over 75% of irrigation uses these slowly recharging wells).

    I think I have done a fairly decent job of research to show my point in global context. For reference check out the link in Post 43 and look at the table 7.4.
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  5. Norman @54:

    1) "Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations." Because it is located beneath the surface of the Earth, it is not subject to evaporation. The fact that one estimate of total evaporation from "land sources", ie, from lakes and rivers, is similar in magnitude to one estimate of total recharge of groundwater globally is coincidental, and irrelevant.

    2) "The water table is the surface where the water pressure head is equal to the atmospheric pressure (where gauge pressure = 0). It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity." Water tables may fall, but they may also rise. (Curiously, that can also be bad for farming. In large sections of Southern Australia, agriculture is threatened by rising water tables carrying salt to the surface.)

    Clearly concern about the viability of groundwater based irrigation is focused on those areas in which the water table is falling. But falling water tables are not universal, nor even necessarily typical. Indeed, I do not know the proportion of water tables world wide which are rising, or falling. The global balance of ground water is determined by the simple equation :

    dGW =Rn + Ra - Wn - Wa,

    where dGW is the change in ground water, Rn is the natural recharge, Ra is the artificial recharge, Wn is the natural withdrawals and Wa is artificial withdrawals.

    Artificial recharge includes such measures as pumping water into oil wells to sustain well pressure, and the flooding of old mines. Natural withdrawal consists of natural springs and the like. To have a reasonable estimate of global dGW you need a reasonable estimate of all four relevant factors. Instead of providing them, you have consistently proceeded under the assumption that:

    dGW =~= Wa.

    Quite frankly, that is like assuming that all you need to know to know if a population is rising or falling is the number of homicides.

    As it stands I know of at least three areas in the world with rising water tables (Southern Australia, Tasmania and Nigeria), and have no reason to think they are the only ones. I also know that there are rising water tables in Texas, although on average ground water in Texas is decreasing. Given that natural recharge may be up to 20 times greater than artificial withdrawals globally, you are certainly not entitled to assume that areas in which ground water is building up exceeds areas in which ground water is depleting by a sufficient factor that it can be neglected.

    As it happens I think there is good reason to think global change in ground water is negative. In many aquifers, increased recharge will simply result in increased discharge from water seeps and springs, resulting in little net change. But that is not certain, there is certainly no justification for assuming, as you consistently have, that global change in groundwater is approximately equal to human withdrawals.

    That much is very clear, and very simple. What is more, consideration of the simple equation above shows very clearly that you have not done "...a fairly decent job of research to show my point in global context." Neglecting three terms of the equation is not fairly decent research, and constitutes ignoring the global context.

    Turning now to your misrepresentations:

    1) Patricia Muir, ie, your source, do not state that "... over 75% of irrigation uses these slowly recharging wells" (your claim). Rather she states that:

    "About 62 % of water used in agriculture, globally, comes from surface sources (e.g., rivers) while about 38 % comes from ground water (underground aquifers). However more of Earth's freshwater is in aquifers than in surface sources -- in fact, about 99 % of all liquid freshwater is in groundwater. (Issues in Ecol (9) 2001). Much (> 75 %) of this groundwater is "fossil water;" -- water that is not being recharged but is relic from wetter ancient climate conditions and from melting ice after the Pleistocene ice ages. Once we use it, it is "gone" for all practical purposes."


    Read it carefully. The claim is that >75% of ground water is fossil water, but she earlier indicates that only 38% of water used in agriculture comes from groundwater directly contradicting your claim. She never mentions what proportion of groundwater extraction comes from fossil water.

    Indeed, another of your sources (linked in post 43, as it happens) informs that total world water consumption is 3,560 km^3/year (table 7.3; 2,480 km^3/year for agriculture), and that non-renewable water extraction from ground water is 200 km^3/year, yielding only 5.6% of total world consumption coming from non-renewable ground water (or 8% for agriculture assuming all non-renewable ground water extraction is used for agriculture).

    It should be noted that much of the non-renewable ground water extraction is not from "fossil water", but simply from ground water which is being exploited faster than in can be replenished due to the sheer scale of exploitation, as is occurring in India. As can be seen from the graph below (fig 3 from the previously linked paper), ground water recharge is more than capable of replenishing more than a years withdrawal in a year in northern India, but on average recharge is less than withdrawal so the total groundwater is reduced, in this case by 109 km^3 over the period of study (or 17.7 km^3/year):



    It follows that the point you were trying to make with your cherry picked example is false.

    With brings us back to the cherry pick. So, please, if you learn nothing else, learn this:

    1) When presenting data, always present the data which is most representative of the sample from which you drew the data, of the sample which is worst for the point you wish to make (if you do not present all the data);

    2) If for some reason you cannot follow rule one, always explain that the data you present is not representative, and is more favourable for your case than the other data, and state very clearly why you never-the-less regard it as important to present that sample rather than some other sample form the data (or all of the data).

    If you do not follow rules (1) and (2) you are cherry picking. End of story. There are no subtleties about this.

    Applying these rules to what you did, it is clear that your chosen sample was neither representative (it was the most extreme case), nor the worst for your case. It is equally clear that you did not explain that when you presented it. Ergo, you cherry picked.

    Sometimes we all cherry pick by accident. I expected you to respond to my challenge by pointing out that you had been lazy, and had just picked the first entry on the table. Had you said that, and apologized for the unintentional deception, that would have been the end of the matter. But you have dug your heals in either because you are so intent on deception you do not recognize how transparent you have been, or because you are so foolish that you genuinely do not know what cherry picking is. In either case it makes no difference for the reader, your word, and your data is not to be trusted because you will not, or are incapable of handling it with integrity.

    So learn, apologize and move on. Or dig your heals in further and show you have no place in discussions that value rationality. Your choice!
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  6. Readers - The preceding exchanges with Norman can perhaps be most useful as a demonstration in cherry-picking.

    When you see someone making an assertion without qualifications, when you see someone base their argument on a single number without looking at or discussing whether that is representative, and (in this particular case) when the single factum presented is an extreme that appears to support their argument, when a more complete look at all of the data demonstrates the opposite: Then - you should suspect cherry-picking.

    Norman - As I have noted, and as Tom Curtis has so very clearly demonstrated, you have repeatedly selected single numbers from only one side of the water usage mass balance equations, the withdrawal side. And those numbers are extrema, outliers, which you have presented without context or even mention of the averages. All in pursuit of your first, unsupported/unsupportable assertion - claiming that groundwater withdrawal was sufficient to cause sea level rise even without cryosphere melt. That assertion is clearly incorrect when all of the data, including groundwater replenishment and external constraints on the mass balance, is viewed.

    Your repeated presentations of this flawed argument indicate (IMO) either an inability or unwillingness to actually consider the data, and readers should keep that in mind.
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  7. Tom Curtis @55 and KR @56

    Before you continue to believe my argument to be flawed.

    Please read this material and remember what I had claimed in Post 21. Maybe you will find my thinking ability is not so poor after all and that I do have a valid point.

    "Because most of the groundwater released from the aquifers ultimately ends up in the world’s oceans, it is possible to calculate the contribution of groundwater depletion to sea level rise. This turned out to be 0.8 mm per year, which is a surprisingly large amount when compared to the current sea level rise of 3.1 mm per years as estimated by the IPCC. It thus turns out that almost half of the current sea level rise can be explained by expansion of warming sea water, just over one quarter by the melting of glaciers and ice caps and slightly less than one quarter by groundwater depletion. Previous studies have identified groundwater depletion as a possible contribution to sea level rise. However, due to the high uncertainty about the size of its contribution, groundwater depletion is not included in the latest IPCC report. This study confirms with higher certainty that groundwater depletion is indeed a significant factor." source.

    Please note I stated that groundwater use of aquifiers was close to the same amount of SLR from ice caps and glaciers and this material says the very same thing.
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  8. Norman - Let's look at all the data. I'm using Milly 2010 as the reference, rather than the dozens of papers they reviewed. This is the data I pointed Norman to, the data from which he quoted but a single number for a particular, quickly depleting, aquifer.

    Primary among Norman's omissions is the expansion of reservoir filling - both direct containment and in the rise of local water tables around reservoirs.

    I invite everyone to view this summary - and compare it to Norman's cherry-picked presentation of just aquifer depletion, just one side of the equation. Groundwater adds to sea levels (as per your reference), but reservoir filling subtracts from it - and they appear to cancel out.

    Norman, you continue to present just one side of the picture - and hence you are distorting it.

    ---

    External constraints - Some uncertainties, for example the recent GRACE data indicates that ice cap contributions may be ~10% lower than previously thought.

    Table 8.1 Sea-level rise (mm/year) / 1961–2003a / 1993–2003b / 2003–7c
    1. Observed / 1.8 ± 0.3 / 3.1 ± 0.4 / 2.5 ± 0.4
    2. Thermal expansion / 0.4 ± 0.06 / 1.6 ± 0.25 / 0.35 ± 0.2
    3. Glaciers / 0.5 ± 0.1 / 0.8 ± 0.11 / 1.1 ± 0.25
    4. Ice sheets / 0.2 ± 0.2 / 0.4 ± 0.2 / 1. ± 0.15
    5. Sum of 2 + 3 + 4 / 1.1 ± 0.25 / 2.8 ± 0.35 / 2.45 ± 0.35

    Note that this leaves ~0.05mm/yr +/- 0.35 unaccounted for over the last eight years, including the GRACE data. There is very little room for water usage contributions!

    Now looking that the Milly summary of ground water contributions, excluding cryosphere contributions:

    Estimated potential contributions of changes in terrestrial water storage to sea-level change during the decade of the 1990s. Trends assigned “medium confidence” are probably of correct sign and order of magnitude. Trends assigned “low confidence” cannot be constrained by available data to be smaller than multiple tenths of a millimeter per year in magnitude, nor are data sufficient to be sure that any of these terms is large enough to be a factor in sea-level rise. “Essentially unidirectional” trends are those whose sign and order of magnitude are probably dominated by decadal and longer timescales, as opposed to interannual variations.

    Table 8.2 1990s sea-level trend (mm/year) / Essentially unidirectional?

    Medium confidence

    Reservoir filling: −0.25 yes
    Groundwater mining: +0.25 Yes
    Fifteen largest lakes: +0.1 No
    Climate-driven change of snow pack, soil water, and shallow groundwater: −0.1 No
    Atmospheric water storage: −0.05 Yes (under projected warming)

    Low confidence, but possibly substantial magnitude
    Irrigation: <0 Yes
    Dam-affected groundwater: <0 Yes
    Permafrost thaw and drainage: >0 Yes
    Lake-affected groundwater: ? No
    Wetland drainage: >0 Yes
    Deforestation, urbanization: ? No

    Low confidence, probably not substantial magnitude
    Post-glacial desiccation on millennial scale: >0 Yes
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  9. KR @58

    "Norman, you continue to present just one side of the picture - and hence you are distorting it."

    Are you certain of this. You use this one source which uses a super low figure for water depletion that no one else seems to agree with (you can check my previous links on this if you so choose). I am not using one data point (Ogallala aquifier) to make a point. In the links I have posted, they all deal with estimates of global water depletion from aquifiers.

    Your article would be correct if the water depletion was at the very low value of slightly more than 61 km^3 per year but I have listed more than one source that shows it to me much higher and they are including recharge rates.

    They have a medium condifence for Groundwater mining even though no other source I linked to is even close to this low level. That is why they do not find any change in SL from water mining. They are using the super low value of 0.25 SLR even though other experts in the field have this number much higher. For irrigation alone the figure was around 245 km^3.

    Wouldn't it be a "cherry pick" to use just one source of data as your refute of mine and then claim I am wrong, when your data source is considerably lower than other researchers in the same field?
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  10. Note: This will be my last post on this conversation, as it is both off-topic and, in my opinion, settled.

    Norman - The figures for groundwater depletion definitely have uncertainties. I have seen figures from 0.15 to 0.8mm/year, although the 0.8 you point to is, again, on the upper border.

    Where you are seriously distorting the data is in not recognizing or incorporating other factors, such as reservoir impoundment, or as Tom Curtis has shown, groundwater replenishment.

    I'll leave the replenishment portion to Tom Curtis, who has shown a great deal of the data. On impoundment, Church et al 2001 estimate a net water usage contribution of -1.1 to 0.4 mm/yr contribution, with impoundment ~-0.3 (Table 11.8), and Chao et al 2008 show an average rate of impoundment of -0.55 mm/yr.

    Groundwater mining, on the other hand, has been estimated at 0.2-0.3mm/yr (Vemeer & Rahmstorf 2009) - just about equal to impoundment.

    So yes, you are cherry-picking, not presenting all of the data. You only once mentioned increases in impoundment, dismissing it offhandedly (when it is of equal scale, and opposite in sign), and have only presented groundwater mining without replenishment.

    And what's worse, you continue not to recognize your cherry-picking. I no longer have any expectation that you will.
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  11. KR @60

    Since you are done posting on this topic. I still feel the need to defend myself from your claim that I am not taking in groundwater replenishment. Also on the impoundment equation, unless they use groundwater specifically for filling of a reservoir, the -0.25 given for impoundment would include all sources of water not just ground water. Reservoirs are generally filled by river flow and the source of this preciptiation is not singular to groundwater, melting ice will also contribute via evaporation of ocean water.

    Anyway here is the link that shows water abstraction and recharge rates on a global scale. This piece does address clearly Tom Curtis's objection.

    Nonrenewable water abstraction.

    Another article from the American Geophysical Union that is supporting the point I had made. American Geophysical Union paper.

    Considering there are experts in the field that are indicating that a quarter of current SLR may be caused by groundwater mining, maybe you should not be so convinced my position is wrong. It could be wrong but you should be open to that as a real possibility and in the future with more study I believe it will be demonstrated that the position I have taken is the correct and scientifically supported one. Wait and see but keep an open mind to this possibility before you slam the messenger. Thanks.
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  12. KR @58, for the first time I am going to disagree with you (but not by much). Specifically, I am suggesting that Church et al, 2011 probably gives more accurate figures than Milly et al 2010. There results are as follows:


    The figures are not strictly comparable due to differing time periods, so convenience I have calculated Milly's figures for the 1993-2007 interval as a weighted average ((2*1993-2003 +2003-2007)/3). I have also combined contributions from all forms of ice melt, again for convenience of comparison. Finally, I have placed the difference between the equivalent Milly and Church figures (Milly - Church) in brackets after each figure:

    Observed: 2.9 mm/year (-0.32 mm/year)
    Thermal Expansion: 1.18 mm/year (+0.3 mm/year)
    Glaciers & Icesheets: 1.5 mm/year (-0.23 mm/year)

    In each case Milly's results are within the error bounds of Church et al's analysis, hence the small disagreement. In both cases, the GRACE analysis discussed in the OP strongly suggests that they have overestimated the contribution of ice melt. Specifically, over the period of the GRACE analysis, total ice melt contribution to sea level was 1.5 mm per year. Over the most comparable period from Milly et al (2003-2007) the combined ice contribution was 2.1 mm per year, suggesting Milly has over estimated the ice contribution by 40%, while Church has overestimated it by 61%. That would suggest that Church et al's residual for tidal gauges and satellite measurements should be around 1.35 mm per year, which is a large hole in their budget.

    It should be emphasized that these figures are approximate only because, firstly the periods of analysis do not strictly correspond, and secondly because of the short duration of the GRACE study which means it is significantly influence by short term effects. In particular, the GRACE analysis includes the very wet Asian Monsoon of 2010 which is likely to have contributed substantially to snow fall in the Himalayas, significantly altering the glacial mass balance compared to the preceding decade. Never-the-less there is clearly still some way to go before we can be entirely confident in Sea Level budgets.

    Finally, you will have noticed that Church et al show a greater contribution to sea level rise from ground water depletion than to Milly et al, but that net contribution from terrestial storage is negative. Church's estimate is based on that in Konikow 2011, with Konikow being a co-author of Church et al. (More on Konikow 2011 later.)

    I notice that Norman now pins his confidence in Wada et al, 2010. In doing so, he ignores the careful analysis by Wada comparing (surprise, surprise)recharge to abstraction (withdrawals). Further, he quotes a document that concludes global groundwater depletion was 243-323 km^2/year with an annual contribution to sea level rise of 0.8 mm/year as supporting his claims that groundwater depletion was about 545 km^3/year, and the sea level contribution was 1.52 mm/year. He is also citing a paper that claims that groundwater depletion averages at 40% of total withdrawals in support of his methodology of ignoring recharge. Apparently he has no sense of irony.

    Given Norman's reliance on Wada (a distinct improvement from his previous position if he actually accepts their results), it is worthwhile quoting Konikow's critique of Wada et al:

    "The first two estimates are based on a limited number of direct aquifer evaluations. The estimate of Wada et al.[2010] is derived using an indirect, flux‐based water budget approach that assumes that groundwater depletion is equal to the difference between natural recharge and withdrawals—an approach that is not based on observations of groundwater conditions. Recharge values are derived from global‐scale modeling designed to estimate “diffuse” recharge from climatic data and soil properties [Döll and Fiedler,2008]. This methodology does not calculate recharge from surface‐water bodies, nor adjust depletion estimates in accordance with Theis’ [1940] principles, which are applicable regardless of climate (Wada et al. [2010] only allow this for humid climates). Even in the Nubian Aquifer system—the classical example of a fossil groundwater aquifer having no modern recharge—about 25% of the total withdrawals in 1998 were offset by (and derived from) reductions in natural discharge from the system (such as to springs and oases) [CEDARE, 2001]. The global modeling approach to estimating natural recharge also does not account for “non‐natural” non‐diffuse recharge, such as leakage from canals, sewers, or pipelines, or from artificial recharge—none of which depend on climate and soil characteristics inherent in their recharge estimation model. Hence, the flux‐based water budget approach of Wada et al. [2010] can substantially overestimate groundwater depletion.

    Problems with the approach of Wada et al. [2010] are
    illustrated by examining their results for areas in the US where depletion data exist. Figure 2 of Wada et al. [2010] shows highest rates of depletion in four areas in the US (red zones, rated at 300–1000 mm/yr of depletion), which appear to include the Los Angeles and San Diego areas of southern California. In the Los Angeles area, depletion is closely tracked by local agencies. These data and analyses (see auxiliary material) indicate that from 1961 to 2008 the cumulative change in storage was an increase of ∼0.20 km3, and in 2000 was a decrease of ∼0.04 km3/yr. This corresponds to a rate of depletion of less than 20 mm over the area of resolution of the map of Wada et al. [2010]. In the San Diego area, there is no large‐scale development of groundwater, and no reported depletion problems of significance."


    Konikow uses empirical measurements of groundwater depletion in the US to calibrate his estimates. While superior to Wada et al, this approach of assuming the USA is typical of global ratios between depletion and withdrawals is dubious. Consequently we should also expect further improvements on Konikow's, and hence Church et al, 2011's, estimates of groundwater depletion.
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  13. Norman @61, Bierkens and Beek, the authors of the poster to which you linked, are co-authors of Wada et al. They use a slightly refined version of Wada et al's method, adding only the use of water demand as a proxy for abstraction. As such, the are subject to the same criticisms as Wada et al as detailed in the quote of Konikow in my preceding post. Read that quote carefully. Better yet, read Konikow 2011 carefully and pay attention to everything.

    Finally, water held in dams is water not being held in the ocean. It does not matter where the water comes from.
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  14. Tom Curtis @55

    Are you certain of your claim in point 1)?
    "Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations." Because it is located beneath the surface of the Earth, it is not subject to evaporation"

    Here is a study that directly contradicts your view.
    "Soil evaporation is a significant loss or depletion from the water balance. Most often, this water balance component is lumped together with plant transpiration into the collective term “evapotranspiration (ET).” However, because evaporation and transpiration are distinctly different phenomena, it is useful to consider evaporation explicitly and separately." source.

    I am sorry to continue to pursue this line of thought but you do question my integrity and indicate I am a dishonest person your quote: "But you have dug your heals in either because you are so intent on deception you do not recognize how transparent you have been, or because you are so foolish that you genuinely do not know what cherry picking is. In either case it makes no difference for the reader, your word, and your data is not to be trusted because you will not, or are incapable of handling it with integrity."

    I do like your points Tom but it is unpleasant that you think the worst of me.

    The final point. I reread the post you are bringing up and making the claim I am dishonest. Post @31 here is my claim in that post: "This means that the water pumped out of this aquifier will indeed add to the surface water amount. Yes it will add to the surface storage, the atmosphere and yes the ocean as well."

    There is nothing false or misleading in this statement. It is a factual comment based upon the evidence presented. The water pumped out of the Ogallala Aquifier will increase surface water storage. What is misleading in that comment or point? That is the only point I made in comment@31. I did not use this example to calcualte SLR, I only may the postive statement that from this particualr aquifier, it will add to the surface water.
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  15. Norman#61: Your AGU reference points up a major flaw in your argument.

    “The rate of depletion increased almost linearly from the 1960s to the early 1990s,” says Bierkens. “But then you see a sharp increase which is related to the increase of upcoming economies and population numbers; mainly in India and China.”--emphasis added

    Here's a graph of sea level rise:


    -- source

    The sharp increase in groundwater withdrawal does not appear in the sea level curve; groundwater cannot be a significant factor.

    This off-topic distraction must cease.
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  16. muoncounter @65

    Ok, I am done. Sorry for the off-topic chatter. Daniel Bailey does frequently warn me to stay on topic.

    Tom Curtis @63, Thanks for the link to the Konikow paper, I did read it.
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  17. Norman @64, where you have a shallow water table, you can dig a hole, and when you get to the point where the bottom of the hole fills with water, you have reached the water table. Above that point the soil may well be moist, and water from that soil will evaporate, or be taken up by roots and transpirated. Where the water table is shallow enough, the water in the soil will be replenished by capillary action, thus allowing some of the water in the water table to escape by a combination of wicking and evaporation/transpiration.

    Likewise, if the water table is very shallow and breaks the surface in a low lying area, it can form a lake or soak, from which evaporation will escape directly.

    Finally, a deep penetrating cave or mine shaft can penetrate the water table such as at Weebubbie Cave, thus allowing evaporation to escape:

    Cave Diving in Australia - Weebubbie Cave from oxy-doc on Vimeo.



    However, the total evaporation from these effects is small in relation to the total amount of ground water, and escape by these mechanisms is small relative to both the total land surface evaporation and relative to total artificial and natural withdrawals from the water tables (although for some shallow water tables it may be a major or dominant form of water loss).

    The extent of evaporative loss of ground water is certainly not sufficient for you to use total land surface evaporation as a proxy for natural ground water losses, still less identifying them as you did @54.

    This response is not an invitation to continue the conversation, but merely to clarify a point on which I was insufficiently clear. If you would like me to think well of you, stop cherry picking. It is your most persistent and unendearing feature in post after post and topic after topic on this site.
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