The US NOAA (National Oceanic and Atmospheric Administration) has released its 2015 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.
The HFC impact in 2016, slightly higher than in 2015, is now 0.89 % of the total, but its share remains unlikely to be significantly higher in the future following the adoption of the Kigali Amendment to the Montreal Protocol, requesting an international HFC phase-down.
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, represents 65.6 %, N2O 6.4 %, CH4 17%, CFC 11 and 12 7.5 % of all emissions.
The remaining 4% is contributed by the 15 minor halogenated gases, which are ODS (Ozone Depleting Substances) CFC-113, CCl4, CH3CCl3, HCFCs 22, 141b and 142b, and Halons 1211, 1301 and 2402; HFCs 134a, 152a, 23, 143a and 125, and SF6.
Figure 1 : 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).
The total radiative forcing increased by 39.9 % from 1990 to 2016 (by ~0.86 watts m-2), and CO2 has accounted for nearly 80% of this increase (~0.69 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 is equivalent to more than half of the increase in radiative forcing due to CO2 alone since 1990.
Figure 2: 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.