The US NOAA (National Oceanic and Atmospheric Administration) has released its 2014 update of the AGGI (Annual Greenhouse Gas Index), intended to follow the evolution of the radiative forcing (ability of all greenhouse gases to trap heat) of greenhouse gases. See footnote.
As in 2013, the HFC impact remains just below 0.8% of the total, a share that is unlikely to be higher in the future if the proposals for an international HFC phase-down are adopted.
By contrast, the contribution of the five more important greenhouse gases account for around 96 % of the total impact. CO2 , by far the largest contributor to the AGGI in terms of both amount and rate of increase, represent 65%, N2O 6.4 %, CH4 17%, CFC 11 and 12 7.7 % of all emissions.
The remaining 4% is contributed by the 15 minor halogenated gases, which, besides HFCs 134a, 152a, 23, 143a, and 125, and SF6 , are ODS (Ozone Depleting Substances) CFC-113, CCl4, CH3CCl3, HCFCs 22, 141b and 142b, and Halons 1211, 1301 and 2402.
Figure : Global average abundances of the major greenhouse gases CO2 (in ppm), methane and N2O (in ppb), CFC-12, CFC-11, HCFC-22 and HFC-134a (in ppt).
In terms of CO2 equivalents, the atmosphere in 2014 contained 481 ppm, of which 397 was CO2 alone.
The total radiative forcing increased 36 % from 1990 to 2014 (by ~0.77 watts m-2), and CO2 has accounted for nearly 80% of this increase (~0.62 watts m-2). The CFC PHASE OUT, and the substitution of CFCs and HCFCs, notably by HFCs, avoided an additional 0.3 W m-2 of global radiative forcing. This has offset more than half of the increase in radiative forcing due to CO2 alone since 1990.
Figure : Share of the long-lived, well-mixed greenhouse gases. The impacts from PFCs and SF6 are too low to appear on this scale of graph.
Source : AGGI and Private Communication (for the 15 minor gases)
Note : The results reported here are based mainly on atmospheric measurements of long-lived, well mixed gases and have small uncertainties. They encompass all emissions of greenhouse gases, including those from countries that do not report under the Rio Convention.