On June 5th, NOAA/ESRL announced the preliminary March 2018 global mean CO2 concentration was 408.75 ppm. This was a concerning increase of 2.71 ppm over 2017.
This rate of increase is of concern, since it is the highest monthly increase over prior year, that seems unrelated to an El Nino, and the highest monthly rate of increase since December, 2016. This CO2 concentration is another marker in the slowly accelerating rise observable in the monthly means since 1980.
The acceleration is less apparent in the annual monthly mean change, than in the five or ten year change in CO2 concentration.
What is noticeable in the annual monthly mean change is that since 2009, there have been more and higher peaks in the trend than in years prior to 2009. The five year change of 12.68 ppm continues the almost unbroken trend of months above a 12 ppm increase since March, 2016.
Where the increasing acceleration of CO2 concentration is most apparent is the increase over ten years. March 2018 is 22.68 ppm higher than 2008. This is the highest change of any month over one ten years before.
Given reports of annual increases in global anthroprogenic CO2 emissions this year over 2017, we can anticipate these monthly concentrations will continue to rise in year to come.