Below is a GRACE satellite map. The Earth looks like a warty ball, with red bumps and blue pits that represent measured fluctuations in the planet’s gravity. Note Greenland in the red. We’ve covered GRACE before, suggesting it may not be a good tool to measure ice loss in Greenland. See this WUWT story.
The red spots represent measurements where Earth’s gravity is stronger. The blue ones are where it is measured to be weaker. The universal force of gravity itself does not vary, but the pits and bumps are a local indication that Earth’s mass distribution isn’t smooth and uniform. As seen on the image above, tectonic mountain building in South America produces red zones; elsewhere, tectonic movements produce thin, blue, ones.
Even more interesting is the fact that the map changes over time, Earth as we know is not static.
CO2 science reviews this new paper, which suggests that for sea level rise and ocean mass, the signal to noise ratio is high low and adjustments further complicate the issue. It also suggests some studies aren’t appropriately correcting for these issues. For example, GRACE measurements related to Greenland and West Antarctica (which we also criticized in WUWT here and here):
“…non-ocean signals, such as in the Indian Ocean due to the 2004 Sumatran-Andean earthquake, and near Greenland and West Antarctica due to land signal leakage, can also corrupt the ocean trend estimates.”
Ocean Mass Trends (and Sea Level Estimates) from GRACE Reference
Quinn, K.J. and Ponte, R.M. 2010. Uncertainty in ocean mass trends from GRACE. Geophysical Journal International 181: 762-768.
Background
The authors write that “ocean mass, together with steric sea level, are the key components of total observed sea level change,” and that “monthly observations from the Gravity Recovery and Climate Experiment (GRACE) can provide estimates of the ocean mass component of the sea level budget, but full use of the data requires a detailed understanding of its errors and biases.”
What was done
In an effort designed to provide some of that “detailed understanding” of GRACE’s “errors and biases,” Quinn and Ponte conducted what they describe as “a detailed analysis of processing and post-processing factors affecting GRACE estimates of ocean mass trends,” by “comparing results from different data centers and exploring a range of post-processing filtering and modeling parameters, including the effects of geocenter motion, PGR [postglacial rebound], and atmospheric pressure.”
What was learned
The two researchers report that the mean ocean mass trends they calculated “vary quite dramatically depending on which GRACE product is used, which adjustments are applied, and how the data are processed.” More specifically, they state that “the PGR adjustment ranges from 1 to 2 mm/year, the geocenter adjustment may have biases on the order of 0.2 mm/year, and the atmospheric mass correction may have errors of up to 0.1 mm/year,” while “differences between GRACE data centers are quite large, up to 1 mm/year, and differences due to variations in the processing may be up to 0.5 mm/year.”
What it means
In light of the fact that Quinn and Ponte indicate that “over the last century, the rate of sea level rise has been only 1.7 ± 0.5 mm/year, based on tide gauge reconstructions (Church and White, 2006),” it seems a bit strange that one would ever question that result on the basis of a GRACE-derived assessment, with its many and potentially very large “errors and biases.” In addition, as Ramillien et al. (2006) have noted, “the GRACE data time series is still very short,” and results obtained from it “must be considered as preliminary since we cannot exclude that apparent trends [derived from it] only reflect inter-annual fluctuations.” And as Quinn and Ponte also add, “non-ocean signals, such as in the Indian Ocean due to the 2004 Sumatran-Andean earthquake, and near Greenland and West Antarctica due to land signal leakage, can also corrupt the ocean trend estimates.”
Clearly, the GRACE approach to evaluating ocean mass and sea level trends still has a long way to go — and must develop a long history of data acquisition — before it can ever be considered a reliable means of providing assessments of ocean mass and sea level change that are accurate enough to detect an anthropogenic signal that could be confidently distinguished from natural variability.
References
Church, J.A. and White, N.J. 2006. A 20th-century acceleration in global sea-level rise. Geophysical Research Letters 33: 10.1029/2005GL024826.
Ramillien, G., Lombard, A., Cazenave, A., Ivins, E.R., Llubes, M., Remy, F. and Biancale, R. 2006. Interannual variations of the mass balance of the Antarctica and Greenland ice sheets from GRACE. Global and Planetary Change 53: 198-208.
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For information, GRACE consist of two satellites, which follow each other and their mutual distance is measured with extremely high precision. The idea of GRACE is, that when passing more mass beneath, stronger gravity delays the leading satellite and the distance shrinks a bit and vice versa.
Anthony,
“CO2 science reviews this new paper, which suggests that for sea level rise and ocean mass, the signal to noise ratio is high and adjustments further complicate the issue. ”
I don’t think “high” is the adjective you intended to use in that sentence. A high signal to noise ratio is a good thing – much more signal than noise.
REPLY: thanks for pointing out my error. You are correct, fixed, Anthony
Anthony- “…the signal to noise ratio is high and adjustments further complicate the issue.”
I think you meant to say the signal to noise ratio is low, or poor.
It is very difficult to measure changes in total ice volume when the changes are in the low ppm/year, and the uncertainties are in the ppm/year. On the other hand, it creates lots of opportunities for interpretive shenanigans to support a policy position.
The force of gravity itself does not vary
It does!, as the image itself shows it. It can be, say, 9.79, 9.81, (acceleration in m/sec.sq.)
REPLY: I agree, poor wording. I was talking about it in the broader sense, I’ll make it clearer. – Anthony
IOW, GRACE is GROSS.
“The force of gravity itself does not vary, but it is an indication that Earth’s mass distribution isn’t smooth and uniform.”
Sure it varies. That’s exactly what the map shows. That’s what the satellites are measuring.
REPLY: I wasn’t clear with the original sentence, a bob-boo on my part due to starting the post, getting interrupted by a phone call, and coming back to it. I’ve clarified it now. – Anthony
There is strong correlation between North Atlantic Temperature anomaly and the gravity/magnetic anomaly in the Hudson Bay region.
http://www.vukcevic.talktalk.net/NATA.htm
They don’t even know the neutral density of the atmosphere at that altitude, so the drag could vary considerably.
Environmentalists have attempted to use the GRACE satellites to claim water levels in Indian aquafers could no longer sustain rice crops.
With GRACE like that, who needs ill favor?
“”” Enneagram says:
July 20, 2010 at 2:27 pm
The force of gravity itself does not vary
It does!, as the image itself shows it. It can be, say, 9.79, 9.81, (acceleration in m/sec.sq.) “””
Not according to my Physical Chemistry Book.
It says that ( g ) is 9.80665 and THAT IS AN EXACT VALUE ! ( ms^-2 )
But what of the surface of the ocean; is it in hydrostatic equilibrium.
Gravity is supposed to be stronger at the poles since one is closer to the earth center; so does water run “downhill” from the equator; does the rotation create a equatorial hill that water runs off or dows all that shape the surface to a gravitationally level surface so water doesn’t tend to run anywhere ?
When attempting to quantify the gravitational effects of the Earth as a function of position (i.e., model the Earth’s gravitational effects), measurements are made of entities that are affected by the Earth’s gravitation. A model is then constructed that couples quantitative values of the model parameters to those measurements. Values for the model parameters are then estimated that in some sense “best fit” the measurements. Three commonly used “best fit” criteria are: (1) weighted-least-squares (WLS), (2) maximum likelihood (ML), and (3) minimum variance (MV). As I understand it, provided the errors associated with the measurements are zero mean and Gaussianly distributed with known standard deviations, all three “best fit” criteria will produce the same estimates of the model parameters. However, if the measurement errors aren’t Gaussian with known standard deviations, the three “best fit” criteria will give different estimates of the model parameters.
No matter which “best fit” criterion is used, when estimating the values of model parameters from a set of measurements, all models contain three kinds of parameters: (1) model parameters that are exactly known (called constants), (2) model parameters that are treated as known but are in fact estimates (often called “Q-parameters” or “consider parameters”), and (3) model parameters (sometimes called “P-parameters”) whose values are to be estimated from the measurements. Examples of constants are the speed of light in a vacuum, pi, e, etc. Examples of Q-parameters are the total mass of the Earth, the force on an orbiting object from the solar wind, the force on an object from friction, the mass and position of the moon, etc. In theory, the state of knowledge of the Q-parameters can be expressed as a correlation matrix. In practice, it is sometimes the case that the diagonal elements of the Q-parameter correlation matrix are known fairly well, but many off-diagonal terms are unknown. The model Q-parameters will have various effects on the measurements–ranging from negligible to significant. For example, an error in the position of Pluto may have a negligible effect on the measurements while an error is the solar wind may have a significant effect.
When using measurements to estimate P-parameters values, the Q-parameters are often treated as constants–i.e., uncertainties in their values are ignored. This is a common practice and works in many applications. However, when characterizing the accuracy of the P-parameter estimates (i.e., quantifying the P-parameter uncertainties), it is often critical to include the Q-parameter uncertainties. Ignoring these uncertainties often leads to P-parameter estimated errors that are significantly smaller (better) than their actual errors.
For the GRACE system to generate estimates of the change in ice volume over areas of the Earth’s surface, a model must exist that couples ice-change to the measurements made by the GRACE system. Because in practice it is often impossible to treat every component of a model as a P-parameter, expect the GRACE system model that relates model parameter values to GRACE system measurements will undoubtedly contain both constants and Q-parameters. Any discussion of the accuracy of the GRACE system in estimating the change in ice volume must include a discussion of all model Q-parameters. Maybe they have, but I doubt it. Experience has taught me (a) a full treatment of Q-parameter effects on P-parameter estimates is seldom performed, and (b) that without such a treatment, reported P-parameter accuracies are often meaningless.
Bottom line, given the preponderance of funding to find any evidence that supports global warming, at this point in time I’m skeptical that the GRACE system can determine, for example, Greenland ice loss/gain to any meaningful accuracy.
The universal force of gravity itself does not vary, but the pits and bumps are a local indication that Earth’s mass distribution isn’t smooth and uniform. . . . Even more interesting is the fact that the map changes over time, Earth as we know is not static.
Gravity is a curvature of space-time that just looks like a force. The GRACE satellites use a 1-dimensional distance to map a 4-dimensional entity, and that takes a lot of assumptions plugged into computers to get answers. Gravity field changes measurable at the resolution you get with GRACE take geological time scales, and the satellites have been up only a brief time. The only map changes you will see are increased resolution as more passes build up the database.
If you want to measure the force aspect of gravity directly, you can use gravimeters, which have much higher accuracy, one millionth of a ‘g’ for a coffee can sized portable one. I recall that they can tell the difference between the top and the bottom of a step ladder.
GRACE has the advantage of quick worldwide coverage, but it’s measuring the field several hundred miles above the earth, hundreds of miles away from the Greenland ice cap. Only a surface based gravimeter survey could provide the accuracy needed to measure ice cap mass changes.
Anthony,
Gravity is a curvature of space-time in the presence of mass, not a “force”, as I am sure you are aware. The curvature varies with the mass since there is no elemental force of gravity as was believed by Newton. If we think of it properly, there is no mistake. Of course mass is also itself relativistic, rest mass visa vi mass in motion and the energy/mass imparted to such a system. So, the entire analysis per GRACE is somewhat more complicated and less enlightening, to me at least, particularly given the signal to noise situation involved per the above. Not sure any of this GRACE stuff is of much practical use or can really be shown to have any effect on climate.
Thanks for the gravity lesson, but I was thinking in Newtonian terms, not Einsteinian.
I may be being terribly dim here but aren’t these coupled satellites measuring, (allegedly) changes in gravity?
What effect does the recent “unprecedented” collapse of the
Ionosphere /Thermosphere have on the measurements?Even, leaving aside the paper’s criticisms, it appears the data is of no use to measure ice anywhere.
I bet I f’d up the strike thing again. Sigh.
“Gravity is a curvature of space-time that just looks like a force.”
Actually “gravity is due to radially oriented electrostatic dipoles inside the Earth’s protons, neutrons and electrons.” Therefore, “If the electric field within the Earth changes, the amount of this dipolar distortion will change and the force of its gravity will change.”
Hope that helps.
“Electric Gravity” and “Newton’s Electric Clockwork Solar System,” by Wal Thornhill
“GRACE-derived assessment, with its many and potentially very large “errors and biases.”
So NASA spends $100 million putting two tinker toys in orbit
and the data they send back really means nothing
Maybe social services wasn’t such a bad idea after all.
@ur momisugly Zeke the Sneak July 20, 2010 at 3:04 pm
Why would they need to know the neutral density of the atmosphere? How would that affect one satellite and not the other?
From the paper you cite by Quinn and Ponte –
“Perhaps the most significant development of recent years is the realization that mass contributions from land ice have contributed to contemporary SLR much more than assumed just five years ago. Related to this finding is the fact that large polar ice sheets appear to be much more sensitive to surface warming than previously realized, such that surprisingly large dynamical changes are now being observed on the Greenland and West Antarctic ice sheets.”
There is nothing in this paper that appears very encouraging from a denier’s point of view. I am surprised you chose it as an example of “doubt and error” in the climate community.
REPLY: “GeoFlynx” if you call me a “denier” again, I will ban you.
Trollbox for you until you apologize
– Anthony
This is from the “flintstones universe”, directly from “The Twilight zone”:
Gravity is a curvature of space-time that just looks like a force
In 50 – 100 years or so, maybe this will have produced enough data to tell us something. Or not. I won’t be hear except in component form. So I won’t care and will never know.
Zeke the Sneak says:
July 20, 2010 at 4:01 pm
“Gravity is a curvature of space-time that just looks like a force.”
You are right. Excuse them, they are a production “Hanna-Barbera”, Characters of the Flintstones Universe, they believe in a universe made out from round stones and where phantoms like anti-matter, black holes exist. However their time is over.
So, as these satellites are travelling around the Earth, how do they account for the gravity effects of the moon, planets, sun, etc?
Even if the more distant objects have no or little effect, surely the moon must have to be accounted for if they are measuring gravity to such fine tolerances.
Great article and i love how the readers dont let you get away with anything!!!!
REPLY: thanks, our readers, with the exception of a few trolls, are generally pretty sharp- Anthony
Thanks for the discussion. Reed Coray and Mike McMillan give a clear description, that for that too. My experience with gravity is confined to mineral and petroleum exploration. Useful tool but not in any way, shape or form definitive. I have often wished it was so but it is not. No geophysical remote sensing tool to data has replaced direct measurements. Given the gravity texture of the underlying structures and the scales at which they exist, combined with the texture of the surface and attempting to map on near continent wide basis; I think it will be a long, long time before any results like ice thickness from GRACE can be trusted.
“”” Zeke the Sneak says:
July 20, 2010 at 4:01 pm
“Gravity is a curvature of space-time that just looks like a force.”
Actually “gravity is due to radially oriented electrostatic dipoles inside the Earth’s protons, neutrons and electrons.” Therefore, “If the electric field within the Earth changes, the amount of this dipolar distortion will change and the force of its gravity will change.” “””
That’s wonderful; we know that electrostatic forces can both attract and repel; so if your theory is correct; then one must be able to get gravity to push, as well as pull.
If that were the case; then we really wouldn’t need any energy at all.
We know how to completely shield from the EM forces; but so far we haven’t found any gravity shields. Gravity does have infinite range like EM does.
Does the GRACE team also have contemporaneous high accuracy surface atmospheric pressure measurements to compensate for the inverse barometer effect on the sea surface level? Come to think of it they would also require contemporaneous surface wind measurements in order to work out how the wind has piled the water up against coasts etc.
I’m willing to bet they model this if they bother correcting at all. Another source of some (relatively) big errors ( 1 millibar = 1 cm change in sea level).