[updated Oct 2020]
This is a graph of climate data provided by the Bureau of Meteorology for the Sydney Observatory hill weather station from 1859 – the present. The monthly average maximum and minimum temperatures are unmodified monthly means from the BOMs data. The other averages are moving averages are calculated by me, rounded to 2 decimal places.
I can’t vouch for exactly what this says but there’s some interesting trends here. The mean maximums and minimums show a clear warming trend, but there’s also a lot of fluctuations, sometimes over periods as long as 10 years.
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 Aug 2020, I’ll update this as more data becomes available