When will CO2 ...Part III - NOAA's monthly updates to the big 3 greenhouse gases.

NOAA's Earth System Research Laboratories (ERSL) operates the Global Monitoring Laboratory (GML):

ESRL's Global Monitoring Laboratory (GML) of the National Oceanic and Atmospheric Administration (NOAA) conducts research that addresses three major challenges; greenhouse gas and carbon cycle feedbacks, changes in clouds, aerosols, and surface radiation, and recovery of stratospheric ozone.

You can see that this source is essential for addressing the big questions about the atmosphere.

The GML includes the Carbon Cycle Greenhouse Gases (CCGG) research area, whose data products include trends in carbon dioxide, methane, nitrous oxide, and other gases.

The Carbon Cycle Greenhouse Gases (CCGG) research area operates the Global Greenhouse Gas Reference Network, measuring the atmospheric distribution and trends of the three main long-term drivers of climate change, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), as well as carbon monoxide (CO) which is an important indicator of air pollution.

Here is the web page for recent trends.

Each tab under "Trends in CO₂, CH₄, N₂O, SF₆" contains somewhere within it a data section with links to the complete globally averaged records, including globally averaged marine surface monthly mean data (text) or (CSV) files.

These were used to examine monthly trends over the last few decades. In addition, we assumed that forcings due to ALL OTHER species, ozone, other oxides of nitrogen or sulfur, halogenated species, and the rest DID NOT DECREASE. 

The observed trend over the satellite ear in the amounts of forcings from all these species is shown in the next figure. The thick red line at the top is the AGGI corresponding to forcings as if they were due to only CO₂ with a mole fraction twice that of the pre-industrial era.   

Despite notable decreases in CFCs, there has been sufficient addition of species other than CO₂, CH₄, and N₂O so that the radiative forcing from these other species has been approximately constant over the lst decade. The full AGGI update in the next year or two will ceretainly contain precise data, but this assumption will allow us to estimate the full forcings in the atmosphere.

These data, in the years 2001 to 2022, are well approximated by a quadratic fit, as shown in the following figure.

The error in the quadratic fit to the observed data for all other contributions to AGGI ranges from -0.000423613 to 0.000691483 with an rms error 0.000340728.

We will use monthly AGGI data for amounts of warming from CO₂, CH₄, and N₂O plus this quadratic estimate for forcings from the other species in the atmosphere.

The next figure shows the results: monthly forcings from CO₂, CH₄, and N₂O plus the quadratic estimate for forcings from the other species in the atmosphere, and in a thick red line, the level of radiative forcings from twice the pre-industrial mole fraction of  CO₂, 3.74613 W-m^-2

Two features really stand out: first, there is a significant month-to-month variation in the forcings for CO₂ and CH₄, and less so for N₂O; second, the total radiative forcing is quickly approaching the level of radiative forcings from twice the pre-industrial mole fraction of  CO₂, but it is obscured by the month-to-month variations.

We can solve both problems: first reduce monthly variations by using a twelve month moving average, and second, use the moving average to extrapolate those forcings to the point where twice the pre-industrial era ceiling is crossed. 

Note: All calculations were performed within Mathematica Home Edition 13.2.1.0. on a MacBook Pro with macOS Sonoma 14.5. A PDF of the original Mathematica output is available upon request to Jim Diamond, jimd at Linfield dot edu.