Greater minds than mine will dissect but my two - penneths - worth; it is quite a big drop but this year's trend (that «nice sinusoidal» I have been having my nose rubbed in since I first realised that AGW was political not scientific) was skewed in April already (for Mauna Loa) Globally this» The last year of data are still preliminary, pending recalibrations of reference gases and other quality control checks.» (wattsupwiththat.com)
The last year of data are still preliminary, pending recalibrations of reference gases and other quality control checks. (esrl.noaa.gov)
Then there are the reference gases, air + CO2 originally, the holes there are obvious, there have been two other reference mixtures used since, yet no steps in the released data? (wattsupwiththat.com)