Assuming an atmospheric half-life of 120 years for CO2 (there is no solid estimate, but most put it over 100 years) and 110 months for CH4 (as stated in IPCC AR5, 2013), it is natural to ask how much CO2 and CH4 must be emitted into the atmosphere each year to account for both this exponential decay and the current global amount measured. To smooth things out, keeping a running 12-month tally takes into effect all of the seasonal variations that naturally occur. I used the data available at NOAA to create the plots of the running global 12-month change in these atmospheric gasses. You can see an explanation of my methodology in more detail in this recent post.
Here is the CO2 graph:
Of course, CO2 is also removed from the atmosphere through natural forces, including sequestration by plants and absorption by the oceans. These rates change as the oceans get saturated and carbons sinks like the Brazilian rain forest tip and become carbon sources. For that reason, I have not taken any of these natural forces into consideration in my CO2 graph. There is probably a great deal more natural noise in the CO2 graph than the CH4 graph given below. However, the general information the CO2 graph provides tells the story of the tough road ahead. The goal is to get CO2 to zero by 2050 so that the natural decay will eventually mitigate the atmospheric abundance. Maybe that will happen, but successfully navigating that road is surely an unlikely one.
I want to point out one feature of this CO2 graph that I haven’t seen discussed anywhere. You will notice that there is a cyclical nature to the CO2 growth rate. The peaks seem to be about 2 to 6 years apart. I don’t know why this is taking place or the source of this noise. Maybe it corresponds to ENSO cycles, maybe something else. But it is certainly a curious artifact.
Here is the CH4 graph:
What we see in this graph is a stunning growth rate beginning roughly in 2014 after a long stable period. Where is this extra methane coming from? Maybe from the methane clathrates or the melting Siberian permafrost or the more recent release from the Siberian carbonate rock formations. Maybe it’s a combination of these sources and more. The reality is that the growth of CH4 in the atmosphere is out of control. The signal we see today may be tomorrow’s noise if we also face a blue ocean event or some other catastrophic tipping point that signals the release of a true methane bomb into our atmosphere.
Keeping in mind that methane is 84 times as powerful a greenhouse gas as CO2, methane deserves at least as much of our attention as CO2. Then again, we can’t control methane release the way we can control CO2 release. Transitioning to clean wind, solar, EVs does little to mitigate naturally occurring methane. As our CO2 situation gradually improves, methane will be released from the East Siberian Arctic Sea possibly in gigatons. The Arctic, Siberia and other sequestered sources will become the new ground zero for climate change on steroids.
Okay, maybe the title is a bit strong. No doubt, CO2 is the elephant in the room that is ransacking everything in real time. We can watch the disasters unfold and point to CO2 directly, as the IPCC unequivocally did in their most recent report. But, if all goes to plan and we somehow manage to follow RCP 4.5 and CO2 really does get to net-zero by 2050 with only 2.0c in global warming at that point, we will still be left with no Arctic ice and permafrost collapse possibly producing massive methane expulsions. Although CO2 is rightfully the “gas of the day” and we should cheer all efforts to control it, it’s the methane that lies ahead of us that will truly make us all feel stupid.