Gaia Galassi

A heuristic evaluation of long-term global sea-level acceleration

In view of the scientific and social implications, the global mean sea level rise (GMSLR) and its possible causes and future trend have been a challenge for so long. For the twentieth century, reconstructions generally indicate a rate of GMSLR in the range of 1.5 to 2.0 mm yr−1. However, the existence of nonlinear trends is still debated, and current estimates of the secular acceleration are subject to ample uncertainties. Here we use various GMSLR estimates published on scholarly journals since the 1940s for a heuristic assessment of global sea level acceleration. The approach, alternative to sea level reconstructions, is based on simple statistical methods and exploits the principles of meta-analysis. Our results point to a global sea level acceleration of 0.54 ± 0.27 mm/yr/century (1σ) between 1898 and 1975. This supports independent estimates and suggests that a sea level acceleration since the early 1900s is more likely than currently believed.

Mazara del Vallo Tide Gauge Observations (1906–16): Land Subsidence or Sea-Level Rise?

ABSTRACT Olivieri, M.; Spada, G.; Antonioli, A., and Galassi, G., 2015. Mazara del Vallo tide gauge observations (1906–16): Land subsidence or sea-level rise? Tide gauge (TG) data constitute an invaluable tool for the interpretation of short- and long-term sea-level changes occurring in the Mediterranean Sea. The complex geophysical environment and the limited amount of sufficiently long records make the interpretation of local signals problematic because these are often affected by interlacing processes. Starting from newly disclosed TG records from the site of Mazara del Vallo (SW Sicily), we analyze simultaneously the time series available from other locations in Sicily across the beginning of the 20th century (Messina and Palermo). Despite the limited record length, we show that these observations provide new perspectives on the causes of the observed sea-level variations in the central Mediterranean region, and, in particular, they challenge previous tenets regarding the extent of land movements caused by the 1908 Messina Straits earthquake.

Empirical mode decomposition of long-term polar motion observations

We use the Empirical Mode Decomposition (EMD) method to study the decadal variations in polar motion and its long-term trend since year 1900. The existence of the so-called “Markowitz wobble”, a multidecadal fluctuation of the mean pole of rotation whose nature has long been debated since its discovery in 1960, is confirmed. In the EMD approach, the Markowitz wobble naturally arises as an empirical oscillatory term in polar motion, showing significant amplitude variations and a period of approximately 3 decades. The path of the time-averaged, non-cyclic component of polar motion matches the results of previous investigations based on classical spectral methods. However, our analysis also reveals previously unnoticed steep variations (change points) in the rate and the direction of secular polar motion.