2022: HFCs contribute 1.27% to climate warming influence of greenhouse gases
The US NOAA (National Oceanic and Atmospheric Administration) has released its 2022 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 2022 is now 1.27% of the total (compared to 1.19% in 2021).
Direct radiative forcing from the sum of observed CFC changes ceased increasing in about 2000 and has continued to decline ever since, despite a temporary increase in CFC-11 emissions from 2013 to 2018. Increases in HCFCs and HFCs have offset the decline from CFCs so that radiative forcing from the sum of these three chemical classes has changed very little over the past decade. Of the ozone-depleting gases and their substitutes, the largest contributors to direct radiative forcing in 2022 were CFC-12, followed by CFC-11, HCFC-22, HCFC-134a and CFC-113. While the radiative forcing from HFCs has been small relative to all other greenhouse gases, the potential for large future increases led to the adoption of controls on HFC production in the Kigali amendment to the Montreal Protocol.
The atmospheric abundance and radiative forcing of the three main long-lived greenhouse gases (CO2, methane, N2O) continue to increase in the atmosphere. While the combined radiative forcing of these and all the other long-lived, well-mixed greenhouse gases included in the AGGI rose 49% from 1990 to 2022, CO2 has accounted for about 78% of this increase, methane and N2O contributed approximately 7.5% each to the increase. In total these three gases contributed 94% to the increase since 1990. The increase in atmospheric abundance of CO2 is accelerating, the atmospheric burden of methane has increased more rapidly over the past few years than at any other point in the on-going measurement record, which began in 1983, and the annual increases measured for N2O during 2020, 2021 and 2022 are among the fastest recorded since measurements began.
Figure 1 shows the trend in atmospheric concentration for HFC-134a, the most widely used HFC, compared to other main greenhouse gases.
Figure 1
Global average abundances of the major, well-mixed, long-lived greenhouse gases - carbon dioxide, methane, nitrous oxide, CFC-12 and CFC-11; and HCFC-22 and HFC-134a from the NOAA global air sampling network since the beginning of 1979.
The Annual Greenhouse Gas Index (AGGI) is calculated as the ratio of total direct radiative forcing due to these gases in a given year to its total in 1990. 1990 was chosen because it is the baseline year for the Kyoto Protocol and the publication year of the first IPCC Scientific Assessment of Climate Change. Most of this increase is related to CO2. For 2022, the AGGI was 1.49, which represents a 49% increase in total direct radiative forcing from human-derived emissions of these gases since 1990. This is shown in Figure 2.
Figure 2
Radiative forcing, relative to 1750, of virtually all 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. The “CFC*” grouping includes some other long-lived gases that are not CFCs (e.g., CCl4, CH3CCl3, and Halons), but the CFCs account for the majority (95% in 2022) of this radiative forcing. The “HCFC” grouping includes the three most abundant of these chemicals (HCFC-22, HCFC-141b, and HCFC-142b). The “HFC*” grouping includes the most abundant HFCs (HFC-134a, HFC-23, HFC-125, HFC-143a, and HFC-152a) and SF6 for completeness, although SF6< only accounted for a small fraction of the radiative forcing from this group in 2022 (13%).
Radiative Forcing Calculations
The 2022 AGGI has used updated equations recommended in the IPCC’s most recent report to recalculate direct radiative forcing for all years from the greenhouse gases defining the AGGI. This revision reflects an improved understanding of the absorption of light by long-lived greenhouse gases in Earth’s atmosphere, with the largest changes being noted for methane. These empirical expressions are derived from atmospheric radiative transfer models. As such, they generally have an uncertainty of about 10%, which is substantially smaller than uncertainties associated with climate projections. Uncertainties in the measured global average abundances of the long-lived greenhouse gases are even smaller (<1%).
Information in this news item is from NOAA Global Monitoring Laboratory - THE NOAA ANNUAL GREENHOUSE GAS INDEX (AGGI)
Explanatory note: Radiative forcing is the change in the net, downward minus upward, radiative flux (expressed in Watts per square metre; W m-2) at the tropopause or top of the atmosphere due to a change in an external driver of climate change, such as, for example, a change in the concentration of carbon dioxide (CO2) or the output of the Sun. For the purposes of the WG1 AR5 report, radiative forcing is further defined as the change relative to the year 1750 and, unless otherwise noted, refers to a global and annual average value.