With respect to greenhouse gases, do you know what CO 2 -equivalence is?

Here at DOTE we know that the human capacity for self-deception is effectively unbounded. I'm going to demonstrate that again today.

Finally, on October 15, 197 countries agreed to phase out hydrofluorocarbons (HFCs) , an incredibly potent greenhouse gas used in refrigerators and air conditioners. While this sounds obscure, it was probably the most important climate policy taken to date; by one estimate, it will prevent between 0.2°C and 0.44°C of warming by the end of the century. If ratified, this treaty will be legally binding and enforceable through trade sanctions.

They went to Kigali to eliminate hydrofluorocarbons (HFCs) and take 0.5C out of future global warming, and the 170 countries that successfully negotiated an amendment to the Montreal protocol treaty agreed to get rid of 90% of them. Not bad for four days and three long nights of hard work.

A much-ballyhooed agreement was reached this week in Kigali to phase out hydrofluorocarbons (HFCs). Here's The Guardian's first paragraph .

Here's the boilerplate from NOAA which tells you what you need to know.

Increases in the abundance of atmospheric greenhouse gases since the industrial revolution are mainly the result of human activity and are largely responsible for the observed increases in global temperature [IPCC 2013]. However, climate projections have model uncertainties that overwhelm the uncertainties in greenhouse gas measurements. We present here an index that is directly proportional to the direct warming influence (also know as climate forcing) supplied from these gases. Because it is based on the observed amounts of long-lived greenhouse gases in the atmosphere, this index contains relatively little uncertainty. The Intergovernmental Panel on Climate Change (IPCC) defines climate forcing as “An externally imposed perturbation in the radiative energy budget of the Earth climate system, e.g. through changes in solar radiation, changes in the Earth albedo, or changes in atmospheric gases and aerosol particles.” Thus climate forcing is a “change” in the status quo. IPCC takes the pre-industrial era (chosen as the year 1750) as the baseline. The perturbation to direct climate forcing (also termed “radiative forcing”) that has the largest magnitude and the least scientific uncertainty is the forcing related to changes in long-lived, well mixed greenhouse gases, in particular carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O), and halogenated compounds (mainly CFCs). Atmospheric global greenhouse gas abundances are used to calculate changes in radiative forcing beginning in 1979 when NOAA's global air sampling network expanded significantly. The change in annual average total radiative forcing by all the long-lived greenhouse gases since the pre-industrial era (1750) is also used to define the NOAA Annual Greenhouse Gas Index (AGGI), which was introduced in 2004 [Hofmann et al., 2006a] and has been updated annually since.

The AGGI measures "the change in annual average total radiative forcing by all the long-lived greenhouse gases since the pre-industrial era." The total radiative forcing from all the greenhouse gases humans have emitted to the atmosphere can be framed in terms of CO 2 -equivalence, i.e., in terms of CO 2 parts-per-million in the atmosphere used as a base unit for calculating radiative forcing by all greenhouse gases.

Got it?

OK, that's the science lesson. Let's move on to reality. All this data is from the NOAA document, which is updated annually. Here's the first graph.

Radiative forcing is expressed in watts per square meter (Wm-2, left scale).

Do you see HFCs in that graph? No, you don't. But you do see something at the bottom of the scale called "15-minor". What does that refer to?

Figure 4 [directly above] shows radiative forcing for the major gases and a set of 15 minor long-lived halogenated gases (CFC-113, CCl 4 , CH 3 CCl 3 , HCFCs 22, 141b and 142b, HFCs 134a, 152a, 23, 143a, and 125, SF 6 , and halons 1211, 1301 and 2402). Except for the HFCs and SF 6 , which do not contain chlorine or bromine, these gases are also ozone-depleting gases and are regulated by the Montreal Protocol. As expected, CO 2 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 96% of the direct radiative forcing by long-lived greenhouse gas increases since 1750. The remaining 4% is contributed by the 15 minor halogenated gases.

In short, the HFCs phased out in Kigali are among the "15 minor" greenhouse gases, and altogether these gases have contributed 4% of the direct radiative forcing since 1750.

Got it? I don't have to explain that, right?

And yet, we were asked in the opening quotes to believe that limiting HFCs would reduce warming by 0.5°C (The Guardian) or between 0.2°C and 0.44°C (Vox) by the end of the century.

Jesus Wept.

Let's move on to the second graph. Where do we stand? This is the CO-equivalence graph.

If you consult Table 2 in the NOAA document, you will find out that in 2015 CO2-equivalence stood at 485 ppm in the atmosphere.

In other words, if carbon dioxide were the only greenhouse gas we were emitting, it's as if the actual amount of CO 2 in the atmosphere stands at 485 parts-per-million (black line above), not slightly over 400 ppm as things currently stand (pale blue line above).

And the contribution of the "minor-15" gases, which include the HFCs, was trivial (looking at Table 2). The CO 2 contribution was 1.939 Wm-2. The methane contribution was 0.504 Wm-2. The total "minor-15" contribution was 0.118 Wm-2. That's 23% of the methane forcing, and 6% of the CO 2 forcing.

Now you are in a position to evaluate the relative importance of this agreement on limiting hydrofluorocarbon emissions. And when we talk about greenhouse gases, we are effectively at 485 ppm, not 400, because that's what CO2-equivalence fucking means.

So banning HFCs basically helps us not at all.