Pekka, you say:
“El Nino and other climate variablity influences both the average temperature and the state of vegetation.”
I don’t accept this distinction – ENSO is just another temperature index, no different than other temperature indices fundamentally. ENSO oscillates and other temperature indices oscillate as well.
ML CO2 would show the best correlation with the SST anomaly of the corresponding latitude band. The same applies to the CO2 measurements from other latitudes.