When will CO2 ... Part V - When will the AGGI cross the 2x Pre-Industrial limit?

In our previous posts, we have examined NOAA's AGGI data for the major non-condensing greenhouse gases and their cumulative radiative forcings; we then reduced monthly variations by using a twelve month moving average. 

Now we use the moving average to extrapolate those forcings to the point where twice the pre-industrial era ceiling is crossed.

The following figure shows, over the time period 2001 to the present and extrapolated to 2030, the AGGI computed from NOAA's monthly data for mole fractions of CO₂, CH₄, and N₂O, with the quadratic fit to forcings from other species; also shown is the twelve-month moving average, and its quadratic fit. The thick red line at the top is the climate ceiling at twice the pre-industrial level of forcings. It appears that these curves cross somewhere near 2030.

The next figure shows the same data for the period since NOAA's last AGGI update, from 2020 to 2030. As above, it shows the same approximate AGGI, the twelve-month moving average, and its quadratic fit, barely distinguishable from the moving average. The thick red line at the top is the climate ceiling at twice the pre-industrial level of forcings. It is clear that these curves cross somewhere near 2030; numerical calculation shows they cross in late November 2029, give or take a month.

No, crossing the 2x pre-industrial level of forcing will not be immediate disaster, just a slow-moving mess, guaranteed to make millions if not hundreds of millions of lives miserable, getting worse as the world's climate moves from its  transient climate response to its eventual pseudo-equilibrium state.

Discussion

When looking for policy solutions, it is not unreasonable to ask what are the effects of other species on our global cumulative radiative forcings. 

We considered each major greenhouse gas aside from CO₂, removed its forcing, and looked back to see when the atmosphere contained gases with that reduced level of forcing. To estimate future conditions, we added that same time gap to the present; this is equivalent to linearizing the relation between elapsed time and the AGGI, so this is not a sophisticated approach, but it is used here for only qualitative comparisons.

The following table summarizes 

• the current total forcing from all greenhouse gases in W-m^-2, the current AGGI, the current CO₂ in equivalent in ppm, the year at which the atmosphere most recently hit that level of equivalent CO₂, and the year when the earth will cross the 2x pre-industrial threshold with that amount of CO₂, 
• the same, were only CO₂, CH₄, and N₂O present at current mole fractions, 
• the same without N₂O , 
• the same without CH₄

Had we to worry about only CO₂, CH₄, and N₂O, the atmosphere would warm like it did a decade ago, moving the date at which we would cross the 2x pre-industrial era level to 2039; by 2030, a decade's grace period will look pretty inviting, but in the long run, it is less significant.

Having to worry about only CO₂ and CH₄ would get us only less than another six years, placing us with an atmosphere like it was in Obama's first year in office and postponing the crossing to 2044.

Getting rid of methane makes a significant difference; that gets us back to 1986, when the Reagan administration was negotiating the initial The Montreal Protocol on Substances That Deplete the Ozone Layer, a time when the AGGI was less than 1, postponing the crossing to 2068. We should be so lucky. 

Policy makers should make note of this: CH₄ is a major problem, and we should be very concerned with future fugitive emissions of methane from warming tundra and the like.

Now, what about clouds?

The Earthshine data suggests that reductions in albedo are adding another 0.5-0.7 W-m^-2 to warming, a total of about 4.1 W-m^-2

(https://www.sciencedirect.com/science/article/pii/S0273117723004660)

Were this the case, then the future looks worse than grim, plunging us into a world warming by 4° C or more.

The recent launch of the EarthCARE satellite and NASA's February launch of PACE are quite timely in this regard.

A thorough understanding of the earth's clouds and aerosols is essential, if we are to make the most prudent and immediate changes in policies to deal with global warming.

Here is a press announcement of the launch: 

 Falcon 9 launches ESA’s EarthCARE mission

  https://spacenews.com/falcon-9-launches-esas-earthcare-mission/ 

 A Falcon 9 successfully launched an Earth science mission for Europe and Japan May 28 as part of the European Space Agency’s ongoing, if temporary, reliance on SpaceX for space access. The Falcon 9 lifted off from Vandenberg Space Force Base in California at 6:20 p.m. Eastern. The payload, the Earth Cloud Aerosol and Radiation Explorer (EarthCARE) spacecraft, separated from the upper stage about 10 minutes after liftoff... 

Spacecraft controllers will spend the weeks and months ahead checking out the spacecraft’s instruments and calibrating them, she said. That will allow the first release of science data from EarthCARE around the end of this year or early next year. EarthCARE is an 800-million-euro ($870 million) ESA-led mission to study clouds and aerosols in the atmosphere. The spacecraft carries four instruments, including a cloud profiling radar provided by the Japanese space agency JAXA at a cost of 8.3 billion yen ($53 million). JAXA dubbed the spacecraft Hakuryu or “White Dragon” because of the spacecraft’s appearance... 

“EarthCARE is there to study the effect of clouds and aerosols on the thermal balance of the Earth,” said Dirk Bernaerts, ESA’s EarthCARE project manager, at a pre-launch briefing May 21. “It’s very important to observe them all together at the same location at the same time. That is what is unique about this spacecraft...”

These satellite missions could not be more vital nor more timely.

Concluding thoughts

Even without the reduction in albedo, our current climate policies are not working. We are adding about 3.5 W-m^-2 to the 240 W-m^-2 we get at the surface from the sun through our atmosphere, an increase of about 1.46% in the earth's energy budget; this increase goes on day after day, and gets worse as greenhouse gas mole fractions in the atmosphere increase.

Suppose an adult - let's call him Gordo - on a 2000 kcal/day diet increases his calorie consumption by 1.46% every day, just 30 kcal a day more, a little less than that in a teaspoon of butter. What would be the consequences? 

That's an extra 29.2 kcal each and every day. At that rate,  poor Gordo will gain more than 3 pounds a year, 2 stone 3 every decade. How many decades of weight gain will it take for Gordo to realize that he has become obese? Three decades of over eating will have made Gordo gain over 90 pounds.

Just like Gordo, we need to implement drastic measures.

Postscript - the relation between the AGGI and CO₂ equivalent

We digitized the CO₂ eq and AGGI data in Figure 4, NOAA, AGGI using the online tool using Plot Digitizer. These historic data were combined with the satellite era data to create this last figure.

This figure shows, in green, the relation beween CO₂ eq in ppm (on the ordinate) and the AGGI (abscissa). Historic data are labeled with the year at which the estimate was made. Satellite era data points are also labeled. The solid blue curve is CO₂ eq = 350 ppm, which was crossed in the early Kennedy administration, in1961 - remember those days? The solid red curve is the CO₂ equivalent at twice the pre-industrial level of radiative forcings, 554.3 ppm. The black spot [OG:Remember Treasure Island?] represents current conditions.

 

One final note: The radiative forcing for CO₂ is a function of the mole fraction of both CO₂ and N₂O. To calculate CO₂ eq for a given amount of forcing, we also use the pre-industrial mole fraction of N₂O, 273.87 ppb.

For more information 

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.