The US NOAA (National Oceanic and Atmospheric Administration) has released its 2018 update of the AGGI (Annual Greenhouse Gas Index), which follows the evolution of the radiative forcing (ability of all greenhouse gases to trap heat) since the onset of the industrial revolution. The HFC impact in 2018 is now 1.03% of the total (compared to 0.98% in 2017). The five major greenhouse gases (CO2, CH4, N2O, CFC-12 and CFC-11) account for about 96% of the direct radiative forcing by long-lived greenhouse gas increases since 1750. The 15 minor halogenated gases (including HFCs) contribute the remaining 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. HFCs are included in the 15 minor gases category (red band) and in 2018 were about 25% of this category.
Of the five long-lived greenhouse gases, CO2 and N2O are the only ones that continue to increase at regular rates over decades. Radiative forcing from CH4 increased since 2007 after remaining nearly constant from 1999 to 2006. From 1990 to 2018, CO2 has accounted for about 81% of the increase in radiative forcing. Had ozone-depleting gases not been regulated by the Montreal Protocol and its amendments, it is estimated that they would have contributed an additional radiative forcing more than half of the increase in due to CO2 alone since 1990. The recent Kigali Amendment to the Montreal Protocol controls future production of HFCs, which are substitutes for CFCs and other ozone-depleting gases, to ensure that radiative forcing for these substitutes does not increase substantially in the future.
Global average abundances of the major greenhouse gases – CO2 (in ppm, parts per million), methane and N2O (in ppb, parts per billion), CFC-12, CFC-11, HCFC-22 and HFC-134a (in ppt, parts per trillion).
Footnote: The AGGI is a measure of the climate-warming influence of long-lived trace gases and how that influence has changed since the onset of the industrial revolution. The warming influence of long-lived greenhouse gases is well understood by scientists and has been reported by NOAA through a range of national and international assessments. The results reported 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.