Graph of the week

Welcome to the first installment of an experiment: The TCOE Graph of the week.[1]

This week’s graph highlights something everyone concenred about climate chaos (including me) should keep in mind: The issue doesn’t begin and end with CO2. Yes, CO2 is the most important single greenhouse gas, but other gases, including methane, nitrides of oxygen, and CFCs also contribute quite a bit.

Which brings me to the graph below, which comes from The NOAA’s Earth Systems Research Lab’s Annual Greenhouse Gas Index page, which I encourage you to check out.

(Click the graph to open a larger version in a new window.)

The graph’s caption:

Figure 4. Radiative forcing, relative to 1750, of all the long-lived greenhouse gases. The NOAA Annual Greenhouse Gas Index (AGGI), which is indexed to 1 for the year 1990, is shown on the right axis.

And the description from that page:

Figure 4 shows the radiative forcing results for the major gases and a set of 10 minor long-lived halogen gases including CFC-113, CCl4, CH3CCl3, HCFCs 22, 141b and 142b, HFC134a, SF6, and halons 1211 and 1301. Except for HFC-134a and SF6, which do not contain chlorine or bromine, these gases are also ozone-depleting gases and are regulated by the Montreal Protocol. As expected, CO2 dominates the total forcing with methane and the CFCs becoming relatively smaller contributors to the total forcing over time. The five major greenhouse gases account for about 97% of the direct radiative forcing by long-lived greenhouse gas increases since 1750. The remaining 3% is contributed by the 10 minor halogen gases.

Of the five long-lived greenhouse gases that contribute 97% to radiative climate forcing, CO2 and N2O are the only ones that continue to increase at a regular rate. While the radiative forcing of the long-lived, well-mixed greenhouse gases increased about 22% from 1990 to 2006 (~0.50 watts m-2), CO2 has accounted for about 80% of this increase (~0.40 watts m-2). Had the ozone-depleting gases not been regulated by the Montreal Protocol and its amendments, it is estimated that climate forcing would have been as much as 0.2 watt m-2 higher [Velders et al., 2007], or about one-half of the increase in radiative forcing due to CO2 alone since 1990.

An Annual Greenhouse Gas Index (AGGI) has been defined as the ratio of the total radiative forcing due to long-lived greenhouse gases for any year for which adequate global measurements exist to that which was present in 1990. 1990 was chosen because it is the baseline year for the Kyoto Protocol. This index, shown with the radiative forcing values in Table 2 [see original page for this table] and on the right-hand axis of Figure 4, is a measure of the interannual changes in conditions that affect carbon dioxide emission and uptake, methane and nitrous oxide sources and sinks, and the decline in the atmospheric abundance of ozone-depleting chemicals related to the Montreal Protocol. Most of this increase is related to CO2. For the year 2007, the AGGI was 1.24 (an increase in total radiative forcing of 24% since 1990). The increase in CO2 forcing alone since 1990 was about 34% (see Fig. 3). Thus, the slowdown in the methane growth rate and the decline in the CFCs has tempered the increase in the net radiative forcing considerably. The AGGI will be updated each spring when the air samples from all over the globe for the previous year have been obtained and analyzed.

Note the text: “Of the five long-lived greenhouse gases that contribute 97% to radiative climate forcing, CO2 and N2O are the only ones that continue to increase at a regular rate” and the reference to the “slowdown in the methane growth rate”. Since you can’t get to 97% of the forcing without methane, they’re including it as one of the long-lived gases, and it’s definitely on the upswing, as I pointed out recently (see Methane checkpoint). Old text on the page, perhaps?

[1] This is my attempt to hoist some important data out of the torrent that rushes by us here in energy and enviro geekdom, so that we can all take a minute or three to consider something that we might otherwise overlook.

I plan to use both pre-made graphs, like the one above, as well as some I construct. In the latter case, I’ll be sure to tell you exactly where my data came from and what, if any, massaging I did to it to produce a presentable graphic.

I will put all these entries in the “By the numbers” category as well as whatever else makes sense.

Suggestions for future installments are welcome, of course, and can be left in the comments.