Steve Nerem's blog
Regarding the glacial isostatic adjustment (GIA) correction, Professor Dick Peltier, Director of the Centre for Global Change Science at the University of Toronto and one of the leading experts on GIA and its effects on sea level, sent us the initial reference for the GIA correction that we apply to the global mean sea level estimate. The GIA FAQ and 2011_1 release notes have been updated with this reference. Here is Prof. Peltier's view on our applying the GIA correction and the recent attention it has received (hyperlinks added by us):
"...the upward correction of 0.3 mm/yr to the rate of sea level rise being measured by the altimetric satellites Topex/Poseidon and Jason-1 is a correction that was first pointed out as necessary by myself. The initial reference in which this was noted is the following:
Peltier, W.R., 2001, Global glacial isostatic adjustment and modern instrumental records of relative sea level history, on page 80 in chapter 4 of the book Sea level Rise:History and Consequences, Bruce C. Douglas, Michael S. Keaney and Stephen R. Leatherman eds, Academic Press, volume 75 in the International Geophysics Series.
The result was most recently reconfirmed in the following two papers:
Peltier, W.R. and Luthcke, S.B., 2009, On the origins of earth rotation anomalies: new insights on the basis of both "paleogeodetic" data and Gravity Recovery and Climate Experiment (GRACE) data. J. Geophys. Res. 114, B11405, doi:10.1029/2009JB006352.
Peltier, W.R., 2009. Closure of the budget of global sea level rise over the GRACE era. Quat. Sci. Rev., doi:10.1176/2009JCL12481.1
The physical reason for the necessity of this adjustment to the atimetric satellite measurements of global sea level rise is due to the fact that, due to the large mass of water that was added to the ocean basins during the last deglaciation event of the Late Quaternary ice-age, the ocean basins are continuing to subside of average by this amount.I'm assuming that the adjustment that Nerem has been making to his analysis of the satellite altimetry observations is this adjustment that I have previously shown to be required. Presumably he has referenced my original papers in deciding to inlcude. It has always been inlcuded in the analyses being perfomed by the group of Anny Cazenave who is the leading European scientist working in this area.There should be nothing controversial about the necessity of making this correction. Since the need of it was established 10 years ago I'm surprised that it should be attracting attention!"-- Dick Peltier, June 19, 2011
Welcome to the new webpages from the University of Colorado sea level group! We apologize for the delay in updating our sea level releases, but the transition to these new web pages took longer than we thought. In addition, we have made many improvements to our data (new orbits, new tide model, new corrections) which ultimately had little effect on global mean sea level, but brought us up to date with the latest advances in the field.
One important change in these releases is that we are now adding a correction of 0.3 mm/year due to Glacial Isostatic Adjustment (GIA), so you may notice that the rate of sea level rise is now 0.3 mm/year higher than earlier releases. This is a correction to account for the fact that the global ocean basins are getting slightly larger over time as mantle material moves from under the oceans into previously glaciated regions on land. Simply subtract 0.3 mm/year if you prefer to not include the GIA correction.
You may also note that rate of sea level rise over recent years has been less than the long-term average. This is believed to be due to the recent La Nina's we have been experiencing, though research on this is continuing. We will soon add a plot to the web site illustrating this effect.
Let us know if you spot any bugs in the new web pages. Thanks for your interest!