Select a start year and end year from the date slider below to see a chart of annual Mean Sea Level (MSL) for the selected period. If a end year in the future is selected, i.e. beyond which there is available observed data, then a linear (black line) and polynomial (purple line) trendline based on the selected observed data, will each show an estimate of MSL from the year which observed data ends up to the end year selected by the user. All values in the chart are Relative Sea Level (RSL), i.e. are not corrected for Vertical Land Movement (VLM).

The mean annual rate of Relative Sea Level (RSL) change for Wellington between
and is approximately ** mm** per year with a Standard Error of
+/- mm per year.

Corrected for subsidence and Vertical Land Movement (VLM) of +/-
mm per year (GPS Solution: JPL14), the mean annual rate of
Absolute Sea Level (ASL) change for Wellington between
and is approximately ** mm** per year
() with a Standard Error of +/- mm per year.

The mean Relative Sea Level acceleration for Wellington between and is approximately ** mm/year ^{2}**.

The blue line in the above chart is the annual observed Relative MSL for the selected period at Wellington. This is given as a height above the pre-1945 Chart Datum (mm). The intersecting black line is the linear trendline for the selected period. It's gradient is the average annual rate of MSL change who's equation is shown in the legend at the top of the chart. The intersecting purple line is the corresponding quadratic or second degree polynomial trendline for the selected period who's equation is also shown in the legend at the top of the chart. Hover over each trendline's equation to see it's coefficient of determination R2 value in the tooltip.

The light blue line is the 1995-2014 IPCC Baseline which is the average mean sea level at Wellington for the period 1995-2014 inclusive and is 790 mm above the pre-1945 Chart Datum. This baseline is used by the IPCC as a zero for projections and is also used by the NZ Government and Councils for planning and decision making.

The turquoise, sapphire, gold, red and dark red lines which begin at zero in 2005 and end in 2150 are the five Shared Socioeconomic Pathways (SSP) scenarios with medium confidence for projected sea level rise at Wellington inclusive of VLM and are sourced from NZ SeaRise (site ID: 2502). These have been converted to heights above the pre-1945 Chart Datum by adding 789 mm. Hover over any of the SSP scenarios to see the mean 50th percentile value (p50) in the tooltip with the 17th (p17) and 83rd (p83) percentile values given alongside in brackets.

Hover above the blue line showing annual observed Relative MSL to see individual annual MSL values in the tooltip with values corresponding to +/- one standard deviation given alongside in brackets.

You can show or hide any of the lines in the above chart by clicking on it's line segment representation in the chart legend. Please note that the blue line showing annual observed Relative MSL is actually made up of two lines with the exact same values. This is because the Google Charts API used on this site can only generate one trendline per series. Therefore to show both a linear and second degree polynomial trendline, two separate series/lines with the same data were needed. This is why there are two representations of the annual observed Relative MSL in the legend. Each with it's own associated trendline. So to show/hide the line showing annual observed Relative MSL you will need to click on both it's representations in the legend.

Please note that Mean Sea Level predicted from the facility to project the above trendlines into the future are estimates only.

###### Station Documentation

Data for 1891-2013 comes from the work of Paul H. Denys, R. John Beavan, John Hannah, Chris F. Pearson, Neville Palmer, Mike Denham, Sigrun Hreinsdottir and retrieved January 2020 from URL https://doi.org/10.1029/2019JB018055 "Sea Level Rise in New Zealand: The Effect of Vertical Land Motion on Century-Long Tide Gauge Records in a Tectonically Active Region".

Data for 2014-2022 is from The Permanent Service for Mean Sea Level (PSMSL) and retrieved March 2024. This has been converted to the pre-1945 Chart Datum by subtracting 6318 mm.

Data for 2023 is downloaded from Greater Wellington Regional Council Environmental Data Dashboard and processed by Sea Level NZ using the University of Hawaii Sea Level Center SLP64 software. The SLP64 software uses a 119-point convolution filter to obtain daily MSL values. A simple average of all daily values is calculated if 7 or fewer days are missing to give monthly values and a simple average of monthly values is calculated to give annual values. This data has been converted from the current Chart Datum to the pre-1945 Chart Datum by subtracting 334 mm, which is made up of subtracting 14 mm to convert it to the 1945-2016 Chart Datum and then a further 320 mm has then been subtracted to convert it to the pre-1945 Chart Datum

From February 2023, all annual MSL values for Wellington prior to and including 1944 have had 40 mm added to eliminate the unknown datum shift that occurred with the movement and installation of new tide gauge in late 1944.

See here for current and historic Benchmark to Datum relationships at Wellington Harbour.