415 ppm CO2 threshold crossed May 2019

Some things in climate science are worryingly unpredictable – like when will the next ice shelf collapse off Antarctica? Or whether tropical storms will increase in frequency and strength in a warm world? Etc etc. However some things, like the ever increasing levels of CO2 in our atmosphere are getting all too predictable – Yesterday CO2 reached its annual maximum in the Mauna Loa Observatory, Hawaii crossing 415 ppm (13th May 2019).  Not that 415 ppm is an important figure, rather just a symbolic one.  Nonetheless, to honour this event I have updated our plot of CO2 over the last 3.5 million years.  And just to confirm, as has been the case for every May/June since the 1950s, atmospheric CO2 is higher NOW than it has been for around 2.5 million years. 

Plio-Pleistocene CO2 from ice core (red) and boron isotopes (blue). Sources indicated on text and listed  here . Data downloadable  here  and Rscript  here  to make your own version of this figure.

Plio-Pleistocene CO2 from ice core (red) and boron isotopes (blue). Sources indicated on text and listed here. Data downloadable here and Rscript here to make your own version of this figure.

To put this in context, this is a long time ago, e.g. this is what our human ancestors looked like back then (here).

New this year to the Pliocene to Pleistocene CO2 compilation: (i) new data from Dyez et al. (2018) for the interval around 1.5 million years ago; (ii) recalculation of Pliocene CO2 by Sosdian et al. (2018) and this.  This recalculation makes the data more accurate but also a little more uncertain. It also lowers the mean by 22 ppm – this doesn’t sound like a huge deal but makes the current CO2 higher than nearly all of the Pliocene.  Despite lots of talk it is still growing at 2-3 ppm per year - so I reckon by the time my kids leave school (ten years time) we will be outside of the Pliocene envelope and will have to go back 15 million years to the Miocene to see similar levels of CO2. It’s obviously not too late to act but we need to act fast!