Data downloaded 17 Oct 2023 from
https://www.metoffice.gov.uk/hadobs/hadsst4/data/download.html
selecting
HadSST.4.0.1.0_monthly_GLOBE.csv

Just this year data as quite dramatic considering on a global scale,
anomaly nearly doubling over just 8 months and large projected increases
just from recent couple of months increments in global SST, and not even
exponential curve-fit.
2023.0833, 0.66273
2023.1667, 0.66657
2023.2500, 0.78990
2023.3333, 0.84818
2023.4167, 0.82701
2023.5000, 0.9188
2023.5833, 1.0661
2023.6667, 1.1071
2023.7500, 1.0857

SST anamoly wrt the 1961 to 1990 average.
Using 249 datapoints from 2003.0 to 2023.75 to avoid the 10 year
recovery period of geodata post Mt Pinatubo eruption.
Using offline javascript curvefitter at statpages.info
and curve types linear (no acceleration), exponential (increasing
acceleration), quadratic (constant acceleration), indicial (falling
acceleration)
Best fit indicial and 6 figures retained for anyone else
repeating/checking this processing

p1= 0.407587 +/- 0.034321; p= 0.0000
p2= -0.003567 +/- 0.005719; p= 0.5333
p3= 0.000874 +/- 0.000209; p= 0.0000

For data to Sep 2023
best fit now quadratic, presumably due to rising ENSO cycle,
hopefully stabilising to indicial or quadratic in a few months time.
y= 0.407587 -0.003567*x +0.000874*x^2
where y is Hadley SST anomaly in deg C and x is year minus 2000
Projected to 2050, +2.4142 deg C
to 2100, +8.7909 deg C
[ for the best indicial curve fit this time,more conservative for comparison
Projected to 2050, +2.217 deg C
to 2100, +7.5826 deg C
still rising in either case ]

For data to Aug 2023 , best curve fit indicial
y= 0.383174 + 0.001021*x^1.895796
where y is Hadley SST anomaly in deg C and x is year minus 2000
Projected to 2050, +2.081129 deg C
to 2100, +6.701729 deg C

previous month processing for up to July 2023 data
Projected to 2050, +1.940949 deg C
to 2100, +5.844458 deg C

previous month processing for up to June 2023 data
y= 0.377054 +0.001667*x ^1.729662
Projected to 2050, 1.824424 deg C
to 2100, 5.177257 deg C

--
Global sea level rise to 2100 from curve-fitted existing altimetry data
<http://diverse.4mg.com/slr.htm>