Open Thread

Sea level will rise due to thermal expansion, ice sheet melt and river sedimentation. All river sediment ends up eventually on the sea floor displacing water.

Say, does the U. of Colo. deduct this sedimentation increase from its GIA? If not, why not?

Monckton of Brenchley says:
July 23, 2012 at 4:49 pm
Fourthly, when it became apparent to the Colorado team that, as a result of the stasis in “global warming”, their post-1993 rate of sea level rise was about to fall below the psychological threshold of 3 mm/year (or 30 cm/century), it was decided to add a so-called “global isostatic adjustment” to the sea-level rise as a way of demonstrating that, were it not for “global warming”, the natural recovery of land altitudes by isostatic rebound following the melting of the great glaciers that once covered much of the northern hemisphere would show a fall in sea level.

Two years ago there was a controversy about this readjustment. Here is a link to an article about it:
http://www.foxnews.com/scitech/2011/06/17/research-center-under-fire-for-adjusted-sea-level-data/
A quote from the article said:

“’We have to account for the fact that the ocean basins are actually getting slightly bigger… water volume is expanding,’ he [Steve Nerem, the director ] said, a phenomenon they call glacial isostatic adjustment (GIA).”

To which I responded:

Let’s say the ocean basins were shrinking. Would he have reduced the rate of sea level rise to compensate? To ask the question is to know the answer.

A WUWT thread a month earlier, with some good comments, can be found here:
http://wattsupwiththat.com/2011/05/05/new-sea-level-page-from-university-of-colorado-now-up/
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One objection I have to this readjustment is that it unjustifiably and misleadingly redefined “sea level” for propagandistic purposes (as my jibe above implied). Here are the standard definitions of “sea level”:
Mean sea level (MSL) is a measure of the average height of the ocean’s surface (such as the halfway point between the mean high tide and the mean low tide); used as a standard in reckoning land elevation.[1]
http://en.wikipedia.org/wiki/Sea_level
“Sea level, average height of the ocean” [NB, “height,” not “volume.”]
http://en.wikipedia.org/wiki/Sea_level_(disambiguation)
(My dictionaries define sea level similarly.)
From:

Glacial isostatic adjustment [GIA] and sea-level change
State of the art report – Technical Report TR-09-11
Pippa Whitehouse, Durham University, April 2009
http://www.skb.se/upload/publications/pdf/TR-09-11webb.pdf
“1.2.1:
“Relative sea-level is a height which is defined by the position of the interface between the ocean and the land (Figure 1-1). A rise in relative sea-level can occur due to an increase in the height of the ocean surface (for example, due to a change in the shape of the geoid, an increase in the volume of water in the oceans, or a decrease in the storage capacity of the oceans) and/or a drop in the height of the land (for example due to ice sheet loading, or tectonic activity).”
………………………….
“4.9.4 Sea-level change
“GIA is a major contributor to sea-level change. The geometry of ice-loading and the timing and source of melting produce a unique pattern of sea-level change following perturbations to the geoid and solid surfaces.”

The boldfaced portion above implies that the sea level changes as the ocean floors sink or rise. Steve Nerem’s interpretation is that the sea level should remain constant as the ocean floors sink or rise, by applying a correction factor to ensure that it does so on paper, regardless of what’s happening in the real world, and in defiance of what the conventions in his field prescribe.
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A few months ago I visited the U. Colo. site. I read some of their material, which I’ve posted below. I was amazed at this sentence in their last paragraph. “this [GIA] correction is now scientifically well-understood and is applied to GMSL estimates by nearly all research groups around the world.” Is it really true, or are they being disingenuous? I.e., do the other research groups “apply” it, but not call the result “sea level”? (Or have they all recently acted in concert to support the warmist narrative?) This question deserves critical attention from WUWTers, and a thread devoted to the topic titled “On the Level?” First, here are some links:
Home page:
http://sealevel.colorado.edu/
raw data (with GIA correction):
http://sealevel.colorado.edu/files/2011_rel4/sl_ns_global.txt
chart with GIA correction
http://sealevel.colorado.edu/files/2011_rel4/sl_ns_global.eps
Under “Similar plots” there is only a chart and data set for “Seasonal signals Retained.” There’s nothing showing one with GIA correction removed.
Chart through July without GIA (from WUWT, not available from UC itself via home page)
http://climate4you.com/images/UnivColorado%20MeanSeaLevelSince1992%20With1yrRunningAverage.gif

Addressing Questions Regarding the Recent GIA Correction
Edited: 2011-07-18
[Update, 2011/06/20: Media Matters has published a story on the attention our GIA correction has received.]
Regarding the Fox News article by Maxim Lott (derived from previous blogs, e.g., Heartland Institute/Forbes) that questions our application of the glacial isostatic adjustment (GIA) correction to the altimeter-based global mean sea level (GMSL) time series and rate estimates, we would like to direct interest to our Frequently Asked Questions (FAQ) page that discusses the GIA effect and also the differences between our global mean sea level estimates from altimetry and regional/local relative sea level measured by tide gauges. These FAQs were updated in May with content partially derived from the discussion with Mr. Maxim, but much of this important content unfortunately did not get published in the Fox News article or in recent blogs.
We would also suggest consulting the other unaffiliated sea level research groups around the world that independently estimate global mean sea level from altimetry and also apply the scientifically well-understood GIA correction. Their current GMSL rate estimates are listed on the left sidebar of our site for reference. Note that our current rate estimate is actually the lowest of the groups, which does not support the claim that we “doctor the sea level data” to artificially support pro-climate change opinions. Instead, we strive to produce estimates of the global mean sea level time series and rate using the best available information to address the following questions:
How is the volume of the ocean changing?
How much of this is due to thermal expansion?
How much of this is due to addition of water that was previously stored as ice on land?
As the science of sea level change becomes better understood through peer-reviewed research, we include these advances in our global mean sea level estimates. This includes continuously improving some our applied altimetry corrections, such as better satellite orbits, ocean tides, and sea state bias models (all of which, along with the GIA correction, were updated and documented in our last 2011_1 release). For further study, we encourage interested parties to consult the references supplied in the FAQs and cataloged in our library and to also contact other research groups and scientists specifically studying global and regional sea level change.
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What is glacial isostatic adjustment (GIA), and why do you correct for it?
The correction for glacial isostatic adjustment (GIA) accounts for the fact that the ocean basins are getting slightly larger since the end of the last glacial cycle. GIA is not caused by current glacier melt, but by the rebound of the Earth from the several kilometer thick ice sheets that covered much of North America and Europe around 20,000 years ago. Mantle material is still moving from under the oceans into previously glaciated regions on land. The effect is that currently some land surfaces are rising and some ocean bottoms are falling relative to the center of the Earth (the center of the reference frame of the satellite altimeter). Averaged over the global ocean surface, the mean rate of sea level change due to GIA is independently estimated from models at -0.3 mm/yr (Peltier, 2001, 2002, 2009; Peltier & Luthcke, 2009). The magnitude of this correction is small (smaller than the ±0.4 mm/yr uncertainty of the estimated GMSL rate), but the GIA uncertainty is at least 50 percent. However, since the ocean basins are getting larger due to GIA, this will reduce by a very small amount the relative sea level rise that is seen along the coasts. To understand the relative sea level effects of global oceanic volume changes (as estimated by the GMSL) at a specific location, issues such as GIA, tectonic uplift, and self attraction and loading (SAL, e.g., Tamisiea et al., 2010), must also be considered. For more discussion on the GMSL and how it relates to tide gauges, see the GMSL and tide gauge FAQs.
There are many different scientific questions that are being asked where GMSL measurements can contribute. We are focused on just a few of these:
How is the volume of the ocean changing?
How much of this is due to thermal expansion?
How much of this is due to addition of water that was previously stored as ice on land?
In order to answer these questions, we have to account for the fact that the ocean is actually getting bigger due to GIA at the same time as the water volume is expanding. This means that if we measure a change in GMSL of 3 mm/yr, the volume change is actually closer to 3.3 mm/yr because of GIA. Removing known components of sea level change, such as GIA or the solid earth and ocean tides, reveals the remaining signals contained in the altimetry measurement. These can include water volume changes, steric effects, and the interannual variability caused by events such as the ENSO. We apply a correction for GIA because we want our sea level time series to reflect purely oceanographic phenomena. In essence, we would like our GMSL time series to be a proxy for ocean water volume changes. This is what is needed for comparisons to global climate models, for example, and other oceanographic datasets.
There are other science questions that researchers are investigating, such as the effect of ocean volume change on local sea level rates, but this is not the focus of our research. When studying local sea level rates, which is important for policy planning, one definitely needs to account for the fact that in areas where GIA is causing an uplift, this somewhat mitigates the ocean volume change. This is being taken into account in these investigations. Also note that GIA can cause subsidence far away from the source of the old ice sheet, and that there are even larger cases of uplift and subsidence unconnected to GIA that are 10-20 times larger. For example, large parts of New Orleans are subsiding more than 10 mm/year—three times the current rate of GMSL—and so they see a much higher rate of sea level rise that has nothing to do with climate change.
Prior to release 2011_rel1, we did not account for GIA in estimates of the global mean sea level rate, but this correction is now scientifically well-understood and is applied to GMSL estimates by nearly all research groups around the world. Including the GIA correction has the effect of increasing previous estimates of the global mean sea level rate by 0.3 mm/yr.
See also:
Addressing Questions Regarding the Recent GIA Correction
GIA FAQ Updated with Peltier Reference

By Joe Romm and Climate Guest Blogger on May 7, 2013 at 12:37 pm
For instance, if somebody raises the standard talking point (#1 on the list) that the “climate’s changed before,” you can say, “Climate reacts to whatever forces it to change at the time; humans are now the dominant forcing.” That is actually quite similar to what was my standard response, “The climate changes when it is forced to change, and now humans are forcing it to change far more rapidly than it did in the past” … Working in the “humans are now the dominant forcing” part is a good idea.

That assumes the climate system can’t generate its own internal forcings, which it can as a result of the peaks or valleys of its internal oscillations coinciding. Analogously, a double pendulum (a pendulum with a second pendulum attached to its end) will swing erratically if released from a ten o’clock position, and even unexpectedly loop over the 12 o’clock position if the lower pendulum kicks in at the top of an upswing, even though no external forcing has been applied. (A youTube video of such a pendulum was posted here on WUWT within the past ten days.) The climate system probably has lots of internal oscillations, some unknown.