A correlation between El Niño and global CO2

It was only when I read the Met Office news release “La Niña cools 2018 CO₂ forecast” that it occurred to me that there might be a link between ENSO events in the central Pacific Ocean and global CO2 measured at nearby Mauna Loa. So today I cobbled together a hybrid application made up of code from my ENSO and CO2 programs to plot charts of both of them to see what I can find, never really expecting to see very much in the way of a link, I was wrong.

Figure 1

In the above image (fig 1) the top chart is of the 12 monthly change in global CO2 measured at Mauna Loa, the bottom Chart is the SST anomaly in Niño region 3.4 of the central Pacific. These two charts span the period from when CO2 readings first started at Mauna Loa in March 1958.

The top chart needs a bit of explaining because it’s a bit complicated. The readings are monthly anomalies of the rate of change of CO2, but because the CO2 levels have been rising rather quickly as we all know, I though I would make my long-term average variable, and base it on a linear trend for the sixty year period between 1958 and 2018. As far as I can see the rate of change has increased from around 0.73 ppm per year in 1958 to 2.37 ppm  a year in 2018.  So I wrote a little function to calculate the LTA for any particular month to calculate a variable LTA and with it a monthly anomaly if that makes sense, and because the rate of change is over 12 months, I thought it better if the series was centred to better correspond with the ONI, which itself is a three-month average. If this doesn’t seem particular scientific to you, that’s OK, I don’t mind, but I’m betting there’s some fancy statistical name for what I’ve done.

Anyway the interesting thing is that the results do show a good deal of correlation between global CO2 and ENSO, I can’t quantify it exactly, but there’s no doubt that it exists. Here’s a close up of the last 20 years to give you a better look (fig 2).

Figure 2

I have no idea why there is any correlation at all. Do the global levels of CO2 have an influence on the SST in the central Pacific, or does the SST in the central Pacific somehow affect the levels of global CO2? It’s sheer speculation but does more CO2 percolates out of the central Pacific when an El Niño event is in progress and SST are well above average than when a La Niña is ongoing – who knows it could even be the CO2 that’s being released by the bleaching of the coral reefs across the world. As usual letters to the editor are welcome on this subject.