What was done
The authors analyzed several hydrographic data sets having pertinence to the climate of the Baltic Sea region.  The parameters studied included salinity (1886-1996), sea level (1891-1993), and river runoff (1920-1990).

What was learned
Freshwater supply to the Baltic Sea exhibited large variations on time scales as long as several decades.  As a result, the salinity of the Baltic Sea also showed large-scale variations on a time scale of several decades; but there was no long-term trend in salinity over the century.  On the other hand, water exchange through the Danish Straits (calculated from sea level and river runoff data) showed relatively small variations; yet it too exhibited no trend during the century.

What it means
The authors note the importance of establishing a baseline of natural variability against which to compare climate data in the search for potential anthropogenic-induced signals.  In this regard, they conclude from their work that "climate control simulations must cover several decades, probably up to 100 years in order to capture the natural variability of present day climate."  We also note that the observation of "no trend" in either freshwater supply to the Baltic Sea or seawater salinity over the past century argues strongly for little net change in local climate over that period.