Global and regional sea level change during the 20th century

Sea level variations prior to the launch of satellite altimeters are estimated by analyzing historic tide gauge records. Recently, a number of groups have reconstructed sea level by applying EOF techniques to fill missing observations. We complement this study with alternative methods. In a first step gaps in 178 records of sea level change are filled using the pattern recognition capabilities of artificial neural networks. Afterward satellite altimetry is used to extrapolate local sea level change to global fields. Patterns of sea level change are compared to prior studies. Global mean sea level change since 1900 is found to be 1.770.38mmyr(-1) on average. Local trends are essentially positive with the highest values found in the western tropical Pacific and in the Indian Ocean east of Madagascar where it reaches about +6mmyr(-1). Regions with negative trends are spotty with a minimum value of about (-2)mmyr(-1) south of the Aleutian Islands. Although the acceleration found for the global mean, +0.00420.0092mmyr(-2), is not significant, local values range from -0.1mmyr(-2) in the central Indian Ocean to +0.1mmyr(-2) in the western tropical Pacific and east of Japan. These extrema are associated with patterns of sea level change that differ significantly from the first half of the analyzed period (i.e., 1900-1950) to the second half (1950-2000). We take this as an indication of long period oceanic processes that are superimposed to the general sea level rise.