Historical sea level changes

Last two decades

High-quality measurements of (near)-global sea level have been made since late 1992 by satellite altimeters, in particular, TOPEX/Poseidon (launched August, 1992) and 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 3.3 ± 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 represent 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:

And this shows it with the seasonal signal left in:

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 2008. There is a clear pattern of sea-level change that is also reflected in patterns of ocean heat storage.

This pattern primarily reflects interannual climate variability associated with the El Niño/La Niña cycle. 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, as is shown (below) by the trends from two subsets of the same dataset.

Movie of sea-level changes (2.2-Mb animated gif) over the last 16 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 December 2008 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!

Another movie of sea-level changes (2.3 Mb animated gif) over the last 16 years

Click on the map below to see a movie of monthly-mean sea-surface height from January 1993 to December 2008. 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 31/07/09

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