For each of these graphical monthly outputs, I do a scale-matched blink
comparison for any changes in the earlier data, no earlier revisionism
this time.

For Mauna Loa data output 05 Dec 2023 at
https://gml.noaa.gov/webdata/ccgg/trends/co2_trend_mlo.png

Using the off-line javascript curve-fitter at statpages.info
Of curve types , linear=no acceleration, exponential=increasing
acceleration, quadratic=fixed acceleration, indicial= falling
acceleration; indicial was best fit by R^2 factor again, but only
marginally over the quadratic and exponential forms.

then adding yearly sine component,
y= a + b*x^c + d*sin(e*x+f)*(1+g*x)

where x is year minus 2000 for start year of 2003 to
avoid the decade of post-Pinatubo geodata recovery, 6
figures retained for anyone else repeating/checking this exercise (bear
in mind the graphical most recent data )
For Dec 2023 output
a= 371.068202
b= 1.120261
c= 1.205616
d= 3.015302
e= 6.269753
f= 6.360262
g= -0.002064

For nov 2023 output
a= 371.069662
b= 1.119870
c= 1.205726
d= 3.016018
e= 6.269782
f= 6.359960
g= -0.002087

To 2050 , ignoring the sine component,for Dec 2023 output= 496.274 ppm
(-0.01 ppm, perhaps the data revision of 3 months back is dropping out?)
previous history for the sine form of indicial curve type

To 2050, for Nov 2023 output= 496.286ppm (-0.20 )
To 2050, for Oct 2023 output= 496.481ppm (-0.24 )
To 2050, for Sep 2023 output= 496.723ppm (-0.26 but partial data
revisionism )
To 2050, for Aug 2023 output= 496.981ppm (+0.35 )
To 2050, for Jul 2023 output= 496.638ppm (+0.46 )
To 2050, for Jun 2023 output= 496.18 ppm ( +0.27 )
To 2050, for May 2023 output =495.91 ppm (-0.10)
To 2050, for Apr 2023 output =496.01 ppm (-0.80)
To 2050, for Mar 2023 output =496.81 ppm (-0.79)
To 2050, for Feb 2023 output =497.60 ppm (-0.67)
To 2050, for Jan 2023 output =498.27 ppm (-0.28)
To 2050, for Dec 2022 output =498.55 ppm (-0.27)
To 2050, for Nov output =498.82 ppm ( -0.49)
To 2050 ,for Oct output=499.31 ppm (-0.32)
To 2050 ,for Sept output=499.63 ppm (-0.04)
To 2050 , for August output= 499.67 ppm (+0.20)
July 2022 output data , to 2050 , 499.47 ppm (+0.04)
June 2022 output data , to 2050 , 498.43 ppm (+0.15)
May 2022 output To 2050 , 498.28 ppm (-0.39)
April output to 2050, 498.67 ppm (-0.83)
March output to 2050, 499.5 ppm (-0.20)
Feb output was 499.7 (-15.55)
Jan 2022 output was 515.25

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