El Niño is behind rise in sea level

Image of the Month - December 1998

Global Mean Sea Level (MSL, blue line) and Sea Surface Temperature (SST, red dotted line) from early 1993 to mid-1998. In 1997 there was a rise of 15 mm. (Credits CNRS/Legos)

Is the mean sea level rising? This question is focusing the attention of climatologists, as it could be a sign of global warming of the atmosphere, which would in turn lead to a warming of the oceans. Thermal expansion of water and melting of the polar ice caps and glaciers would then cause sea level to rise. It certainly did rise in 1997, but this was a direct consequence of El Niño rather than the indication of a clear trend towards global warming.

The meteorological effects of El Niño 1997-1998 were felt worldwide, but it also contributed to variations in mean sea level. Indeed, sea level anomalies measured by Topex/Poseidon were over 20 centimeters in the equatorial Pacific when the phenomenon was at its height (and as much as 30 centimeters off the coast of Peru). These anomalies obviously had an effect on the global mean of sea levels.

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