During April 2018, Scripps University measured an average of 410.26 ppm CO2 concentration at the Mauna Loa, Hawai’i Observatory.
This value is important. Why? Because 410.26 ppm is the largest CO2 concentration value for any April in recorded history. The unending trend toward higher concentrations with time, no matter the month or specific year-over-year value, as seen in the graphs below, is more significant.
When I wrote about this topic a few years ago, there were no monthly or annual CO2 averages that exceeded 400 ppm. In the intervening time, concentrations passed that threshold. Actually, monthly CO2 concentrations have not fallen below 400 ppm since Jan 2016; the same thing can be said for annual concentrations since 2015.
How do concentration measurements change during calendar years? The following two graphs demonstrate this.
Figure 1 – Monthly CO2 concentration values (red) from 2014 through 2018 (NOAA). Monthly CO2 concentration values with seasonal cycle removed (black).
Figure 2 – 60 year time series of CO2 concentrations at Mauna Loa Observatory. The red curve represents the seasonal cycle based on monthly average values. The black curve represents the data with the seasonal cycle removed to show the long-term trend. This graph shows the recent and ongoing increase in CO2 concentrations. Remember that as a greenhouse gas, CO2 increases the radiative forcing of the Earth, which increases the amount of energy in our climate system.
CO2 concentrations are increasing at an increasing rate – not a good trend with respect to minimizing future warming. Natural systems are not equipped to remove CO2 emissions quickly from the atmosphere. Indeed, natural systems will take tens of thousands of years to remove the CO2 we emitted in the course of a couple short centuries. Human systems do not yet exist that remove CO2 from any medium (air or water) at a large enough scale to make a difference to planetary CO2 concentrations. CO2 removal systems are not likely to exist for some time. I’ve written a sentence like that for nearly a decade now. Unfortunately, NOAA will extend the right side of the above graphs for years and decades to come.
CO2 concentrations rise when there is more CO2 emitted into the Earth system than removed from it. Recently, humans have only increased the CO2 emission rate, which means that CO2 concentrations have to rise, absent carbon sinks becoming more efficient.
The rise in CO2 concentrations will slow down, stop, and reverse when we decide it will. It depends first and foremost on the rate at which we emit CO2 into the atmosphere. We can choose 400 ppm or 450 ppm or almost any other concentration target (350 ppm seems out of reach within the next couple hundred years). That choice is dependent on the type of policies we decide to implement. It is our current policy to burn fossil fuels because we think doing so is cheap, although current practices are massively inefficient and done without proper market signals. We will widely deploy clean sources of energy when they are cheap, the timing of which we have some control over. We will remove CO2 from the atmosphere if we have cheap and effective technologies and mechanisms to do so, which we also control to some degree. These future trends depend on today’s innovation and investment in research, development, and deployment.