Geodetic Observations and Global Reference Frame Contributions to Understanding Sea Level Rise and Variability

Climate models that are used to study the effects of atmospheric greenhouse gases predict an overall increase in the global temperature over the next century of from 1.4- to 5.8 °C degrees centigrade [Houghton et al., 1996, 2001]. An increase of this magnitude could have numerous catastrophic effects, not the least of which might be a global rise in sea level due to a combination of melting polar ice caps and glaciers and the thermal expansion of sea water. The global rate of sea level rise during the last century has apparently been somewhat in excess of 1 mm/yr [Douglas et al., 2001] with a recent acceleration being reported [Church and White, 2005]. One of the important goals of all national and international global change programs is to improve our understanding of the mechanisms and implications of observed sea level changes. Geodetic observations can characterize highly precise spatial and temporal changes of the Earth system that relate to sea level changes. The challenge for quantifying long-term change in sea level imposes most stringent observation requirements, and can only be addressed within the context of a stable, global reference system, such that a sea level measurement today can be meaningfully compared with a measurement 10 years later, with sub-millimeter accuracy. Only geodetic observations can provide the basis for a global reference frame with sufficient accuracy. Significantly, this reference frame is extensible to all regional and local studies in order to link multi-disciplinary observations and ensure long-term consistency, precision and accuracy. The reference frame becomes the foundation to connect observations in space and time and defines the framework in which global and regional observations of sea level changes can be understood and properly interpreted. For this workshop, we will address topics that will help to identify geodetic requirements to meet the rigorous scientific demands for understanding sea-level rise and variability. In particular, we stress the need for the continuity of the geodetic observational series that serves basic research, applications and operational needs.