engleski

A fresh look at sea levels and sea-level trends

When considering sea level, one usually starts with the comparison of past sea levels obtained by a method to the observed values and then proceeds by applying the method to determine future sea levels. The method utilized may be either process-based or semi-empirical. Here we use three variants of the semi-empirical method in the analysis and projection of not only sea levels but also sea-level trends. The variants differ in assuming that the response of sea level to temperature forcing is equilibrium, inertial or a combination of the two. All variants enable the temperatures, sea levels and/or sea-level trends to be successfully regressed, albeit with controlling parameters that differ among the cases. The related response times vary considerably, with a realistic value (ca. 50 years) obtained only if both the equilibrium and inertial dynamics are taken into account. Comparison of computed sea levels to those measured over the last century or so shows that the best agreement is provided by the purely inertial variant of the semi-empirical method. Comparison of computed sea-level trends to the corresponding values determined from available measurements points to the equilibrium-cum-inertial variant of the semi-empirical method as the most successful one. Sea levels projected by using the three variants are similar through the middle of the 21st century, but they radically diverge by the end of the 23rd century. Sea-level trends considerably differ throughout the projection interval. The present study reveals how careful one has to be while calibrating a method on the data having a specific spectral content and then using the method to prepare projections under the forcing having different spectral characteristics.

sea-level; temperature; trends

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