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Historical sea level changes

Last two decades

 


Please note that we have upgraded our processing of the earlier missions (TOPEX/Poseidon and Jason-1) to what is known as 'GDR-D' standard.

The most important difference is that orbits for all missions are now in ITRF2008 (Altamimi et al, 2008). Orbits for TOPEX/Poseidon and Jason-1 are the GSFC std1204 orbits (Lemoine et al, 2010). The ITRF2008 orbits that are supplied with the data are used for OSTM/Jason-2.

Other significant differences are that all missions now use the GOT4.8 tide model. The Chambers et al (2003) SSB correction is used for TOPEX/Poseidon. The Tran et al (2010) SSB correction is used for Jason-1.

These changes make a noticeable difference to the shape (but not the overall trend) of the GMSL curves. They make little difference to regional patterns.


References

Altamimi, Z., X. Collilieux and L. Métivier (2011), ITRF2008: An improved solution of the international terrestrial reference frame. J. Geodesy, 85(8), 457-473, doi:10.1007/s00190-011-0444-4.

Chambers, D. P., S. A. Hayes, J. C. Ries and T. J. Urban (2003), New TOPEX sea state bias models and their effect on global mean sea level. J. Geophys. Res., 108(10), doi:10.1029/2003JC001839.

Lemoine, F.G., N.P. Zelinsky, D.S. Chinn et al (2010), Towards development of consistent orbit series for TOPEX, Jason-1 and Jason-2. Advances in Space Research, 46(12), 1513-1540, doi: 10.1016/j.asr.2010.05.007.

Tran, N., D. Vandemark, S. Labroue, H. Feng, B. Chapron, H. L. Tolman, J. Lambin and N. Picot (2010), Sea state bias in altimeter sea level estimates determined by combining wave model and satellite data. J. Geophys. Res., 115(3), doi:10.1029/2009JC005534.


Also note that updates to this site and the data sets displayed on and available from it will be, at best, erratic for the foreseeable future due to staffing issues.


 

High quality measurements of (near)-global sea level have been made since late 1992 by satellite altimeters, in particular, TOPEX/Poseidon (launched August, 1992), Jason-1 (launched December, 2001) and Jason-2 (launched June, 2008). This data has shown a more-or-less steady increase in Global Mean Sea Level (GMSL) of around 3.2 ± 0.4 mm/year over that period. This is more than 50% larger than the average value over the 20th century. Whether or not this represents a further increase in the rate of sea level rise is not yet certain.

The two plots below show the GMSL measured from TOPEX/Poseidon, Jason-1 and Jason-2.

This one shows it with the seasonal signal removed: (get the data)

Plot of global sea level from 1993 to 2012


And this shows it with the seasonal signal left in:


Sea level and El Niño

Plot of global sea level vs the SOI index from 1993 to 2012

There are a number of changes of slope over short periods in the GMSL record. This variability is at least partly related to El Niño and La Niña (sea level rises during El Niño and falls during La Niña) and associated changes in the hydrological cycle.

The above graph shows detrended GMSL (from the top graph) versus the Southern Oscillation (SOI) index, which is one of the common indexes of the El Niño/La Niña cycle.

Clearly (see, e.g. 1997/1998) sea level is higher during an El Niño event (SOI -ve) and lower (see, e.g. 1999/2000 and 2010/2011) during La Niña (SOI +ve).

SOI data is from the Australian Bureau of Meteorology and data and graphs can be downloaded and seen at the Bureau of Meterology's web site.


Regional trends

Sea level does not rise (or fall) uniformly over the oceans. This is illustrated by the map (below) showing sea-level trends from 1993 to 2014. There is a clear pattern of sea-level change that is also reflected in patterns of ocean heat storage.

Plot of sea level trends from 1993 to 2014



This pattern reflects interannual climate variability associated with the El Niño/La Niña cycle and the Indian Ocean Dipole, but also longer term changes such as the increase in sea levels in the Western Tropical Pacific due to changes in the Trade Winds. During El Niño years sea level rises in the eastern Pacific and falls in the western Pacific, whereas in La Niña years the opposite is true.

Plot of sea level trends from 1993 to 2003 and 2003 to 2013


Movie of sea-level changes (3MB animated gif) over the last 20 years - this version has had the seasonal (annual+semi-annual) signal removed at each point. This is comparable to the top figure (above).

Click on the map below to see a movie of monthly-mean sea-surface height from January 1993 to September 2013 with the seasonal signal removed. The plot at the top of the page shows the time series of the means of these fields.

The data that is displayed here can be downloaded from the "Sea level data>Data downloads" page on this site.

Note the 1997/98 El Niño event!

Sea surface height 1993-2010


Another movie of sea-level changes (3MB animated gif) over the last 20 years

Click on the map below to see a movie of monthly-mean sea-surface height from January 1993 to September 2013. The seasonal signal has not been removed from this, so you should see the pumping as the water in each hemisphere warms and expands in Spring and Summer and cools and shrinks in Autumn and Winter. The second plot (above) shows the time series of the means of these fields.

The data that is displayed here can be downloaded from the "Sea level data>Data downloads" page on this site.

Note especially the 1997/98 El Niño event!

Website owner: Neil White | Last modified 18/09/14


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