Since 1993, measurements from the TOPEX and Jason series of satellite radar altimeters have allowed estimates of global mean sea level. These measurements are continuously calibrated against a network of tide gauges. When seasonal and other variations are subtracted, they allow estimation of the global mean sea level rate. As new data, models and corrections become available, we continuously revise these estimates (about every two months) to improve their quality.

2011_rel2: Global Mean Sea Level Time Series (seasonal signals removed)

Edited: 2011-07-19


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Global Mean Sea Level Time Series (seasonal signals retained)

Release Notes

2011 Release 2 (2011-07-19):

  • Added Jason-2/OSTM GDR cycles 95-102
  • Updated Sea State Bias Model on TOPEX (Jason-1/2 updated in 2011_rel1) to CLS Collinear v. 2009 (Tran et al., 2010)
  • Replaced classical GDR Inverted Barometer correction on all missions with improved AVISO Dynamic Atmopshere Correction (DAC) that combines MOG2D high frequency and inverted barometer low frequency signals (Pascual et al., 2008)
  • Fixed bug which resulted in rejection of two TOPEX cycles with insufficient number of retrievals from the GMSL time series.  These were incorrectly included in previous releases at times 1992.9323 and 2000.6424.
  • Although the latest Jason-2 GMSL estimates (cycles 95-102) are well below the trend line, most likely due to the recent La Nina (we plan to add a sea level/ENSO comparison page shortly), the rate increased slightly from 3.1 to 3.2 mm/yr due to the improvements to the TOPEX SSB model and replacement of the classical IB correction with the improved DAC correction, as noted above.  


GIA FAQ Updated with Peltier Reference

Edited: 2011-07-19

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

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:

  1. How is the volume of the ocean changing?
  2. How much of this is due to thermal expansion?
  3. 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.

Bug Fixed in Trend Map Grid File

Edited: 2011-05-27

A bug introduced in release 2011_rel1 that caused incorrect line wrapping and subsequent spurious values in the sea level trend map data file has been fixed. Please download the new data file.

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