410 ppm CO2 for April 2018 - first time in millions of years....

So with spring having sprung we reach the highest monthly CO2 at the Mauna Loa for 2018 - April 2018 was 410.26 ppm, thats 1.26 ppm above last years peak (Mauna Loa data here). 

@thefosterlab we determine the levels of CO2 over the last 50-60 million years using the boron isotope proxy.  It is often said that at 410 ppm CO2 is now higher than any level the Earth has seen for at least 3 million years.  As this revised plot shows (see here for Rscript and here for data), this is likely true, but we are now beginning to creep over even the highest values in the Pliocene 3 million years ago.

Atmospheric CO2 from AD 1000 to AD 2018 (right) from a mix of ice core records and measuresments of the astmosphere from Mauna Lao.  On the left is a compilation of ice core CO2 (red) and boron isotope based estimates (blue).  Note the age scales are different but y-axis is the same. See this document for references.

Beyond the Pliocene we have to go to the Middle Miocene Climatic Optimum around 16 million years ago to see CO2 >450 ppm. There have been several papers recently on this topic (e.g. this one by James Super of Yale) and I desparately need to find time to update the compilation on p-CO2.org...at current rates of CO2 rise though I probably have a couple of years before Earth crosses 450 ppm....