Methods used for calculating sea level anomalies

The annual mean sea level anomalies presented for a given year are calculated by subtracting the long term annual mean at each station from annual means.

The long term mean for a station used is the arithmetic mean of all annual means available over the chosen baseline period: 1960-1990.

If the 'remove trend' option is selected, the anomalies used are the difference from a linear least-squares trend line fitted to all available data over the baseline period. However, if less than 70% of annual means are present over the period, the station is ignored and will not appear in the maps. (See the derived trends page for more information.)

In all cases:

Should you wish to further investigate the anomalies at a particular site, we would invite you to download the RLR data and examine the relevant station documentation.