The spatial distribution of sea level change and its global average (global mean sea level or GMSL) are routinely measured by altimetric satellites. There are over 20 years of altimetric measurements of GMSL, showing variability due to the seasonal cycle, ENSO events as well as a long term upward trend of about 3 mm/yr (about 1 and 3/16 inches every 10 years). The data are usually filtered so that seasonal cycles are removed. They are cross-calibrated amongst the various satellites, to remove instrument biases. However each center does treat the satellite data slightly differently, to account for errors introduced from the atmosphere, tide, change in the shape of the Earth over time, etc. Details on how they process the satellite data into sea level trends is given in detail at each of their websites. The following provide GMSL data:
- Global Mean Sea Level Trend from Integrated Multi-Mission Ocean Altimeters TOPEX/Poseidon Jason-1 and OSTM/Jason-2 Version 2: http://podaac.jpl.nasa.gov/dataset/MERGED_TP_J1_OSTM_OST_GMSL_ASCII_V2
- NOAA - global and regional mean time series and trend maps: http://www.star.nesdis.noaa.gov/sod/lsa/SeaLevelRise/
- University of Colorado - global and regional mean time series and trend maps: http://sealevel.colorado.edu/
- CSIRO - Global mean time series: http://www.cmar.csiro.au/sealevel/index.html
- AVISO -global mean time series: http://www.aviso.altimetry.fr/en/data/products/ocean-indicators-products...