SEA-LEVEL CHANGES UNDER INCREASING ATMOSPHERIC CO2 IN A TRANSIENT COUPLED OCEAN-ATMOSPHERE GCM EXPERIMENT

Climate change resulting from the enhanced greenhouse effect of increa sing atmospheric CO2 concentrations is expected to bring about global and local changes in sea level. A global rise in sea level would resul t from thermal expansion of seawater and from melting of land ice, whi le changes in ocean dynamics and atmospheric pressure patterns could a lter relative sea surface topography. Global and local sea level chang es have been diagnosed from a 75-yr experiment with a version of the U .K. Meteorological Office coupled ocean-atmosphere general circulation model in which the CO2 concentration increases at 1% per year. Over t he final decade, the component of mean global average sea level rise c aused by thermal expansion is 90 mm; on this time scale, a significant contribution is expected from melting of mountain glaciers, but the m odel does not represent these. Sea level rises over practically the en tire ocean area, but there is considerable variation in the magnitude, showing that the global figure by itself gives only a rough idea of t he local effect; the largest rises are found in the northwest Atlantic . Here it is illustrated how this local variation makes it difficult t o estimate global sea level rise from a limited number of coastal stat ions, as must usually be done in practice.