Just for the sake of correctness:
The used Keeling data are to be understood as results of measurements done in the middle of the respective month - so, for working with the precise data one has to replace the second line of my code by:
dataKeeling = TimeSeries[{DateObject[{#1, #2, 15}], #3} & @@@ dataRaw[[62 ;; -9, {1, 2, 9}]]];
This means a shift in the data of 15 days. Sorry for this flaw!
