In addition, the calculation of saturation q is a nonlinear function of T, so if you want to compare monthly means of other reanalyses, you have to calculate q (sfc) for each time step in a monthly average and then average (or compute Td from each time step of q and T in the other reanalyses).
global average sfc T anomalies [as] indicative of anomalies in outgoing energy... is not well supported over the historical temperature record in the model ensemble or more recent satellite observations
We know there is a build up of ocean heat prior to El Nino, and a discharge (and sfc T warming) during late stages of El Nino, but is the observing system sufficient to track it?