Thermosteric sea level (ThSL) is a major component of the global mean sea level rise observed during the late 20th century, and is projected to continue through the 21st century and beyond. At global scale, thermosteric sea-level rise is explained by the expansion in volume of the global ocean due to a net increase in ocean heat content over the past 50 years. At regional level, geographical patterns are produced in response to dynamical processes, with some areas experiencing variations above and others below the observed global mean. In this talk, we first provide an overview of the challenges in estimating ThSL for the upper 700 m of the ocean, from sparse and unevenly distributed subsurface ocean temperature data, measured by a large and changing mix of instruments. We then discuss the impact of different instrumental bias corrections and mapping approaches on the global evolution and spatio-temporal variability of ThSL estimates.