[Updated Oct 2020]
Sea level is another hot (haw haw) topic with regards the changing climate, the BOM maintains historical tidal measurements for Sydney going back to 1914. The data was tougher to find than for temperature but it’s just as interesting. Graphing tidal averages over time highlights long and short term trends in sea level. Like temperature it gets more interesting when looking at the longer term averages, there are trends of rising and falling sea level lasting 10 years or more, but the clear long term trend is up.
NOAA has a good page on sea level and factors that can cause it to change. They say long term trends are primarily due to melting glaciers and thermal expansion of the ocean due to warmer water temperatures. On shorter term trends they name “Seasonal weather patterns, variations in the Earth’s declination, changes in coastal and ocean circulation, anthropogenic influences (such as dredging), vertical land motion, and the El Niño Southern Oscillation” as just a few of the many factors influencing changes in sea level over time.
The monthly averages are straight from the BOM. The other averages over greater time periods are moving averages that I’ve calculated based on this data. The chart is interactive, so have a play by selecting the data sets you want to see. You have to be a bit patient, it can take a few seconds after each click to send the new data up and re-graph it.
The BOM data goes up to August 2020, I’ll update this as more data becomes available