The US NOAA (National Oceanic and Atmospheric Administration) has released its 2017 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 2017 is now 0.98 % of the total. The Kigali Amendment to the Montreal Protocol, requiring an international phase-down of HFCs, which are substitutes for CFCs and other ozone-depleting gases, will ensure that radiative forcing for HFCs does not increase substantially in the future.
Radiative forcing from the sum of observed CFC changes ceased increasing in about 2000 and continued to decline through 2017. This is a response to decreased emissions related to the Montreal Protocol on Substances that Deplete the Ozone Layer.
While the radiative forcing of the long-lived, well-mixed greenhouse gases increased 41% from 1990 to 2017 (by ~0.90 watts m-2), CO2 has accounted for about 80% of this increase (~0.72 watts m-2). The CO2 increase is accelerating, higher than the average of the previous decade, and much higher than the two decades before that.
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).
Figure: 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 2017 were about 24% of this category.
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.