2023: HFCs contribute 1.3% to climate warming influence of greenhouse gases
The US NOAA (National Oceanic and Atmospheric Administration) has released its 2023 update of the AGGI (Annual Greenhouse Gas Index) [1], 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 2023 is now 1.3% of the total (compared to about 1.25% in 2022).
Measured global atmospheric abundances of greenhouse gases are used to calculate changes in effective radiative forcing beginning in 1979 when NOAA's global air sampling network expanded significantly. The change in annual average total effective radiative forcing by all the long-lived greenhouse gases since the pre-industrial era is also used to define the NOAA Annual Greenhouse Gas Index (AGGI). For 2023, the AGGI was 1.51, which represents a 51% increase in effective radiative forcing from human-derived emissions of these gases since 1990.
The effective 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. While radiative forcing from HCFCs has recently peaked and started to decline, the increases in radiative forcing from 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. These trends reflect global controls placed on the production and trade of CFCs, HCFCs, and HFCs by the fully adjusted and amended Montreal Protocol on Substances that Deplete the Ozone Layer. While the radiative forcing from HFCs has been small relative to all other greenhouse gases (1.3% in 2023), 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 effective radiative forcing of the three main long-lived greenhouse (CO2, methane CH4, nitrous oxide N2O) gases continue to increase in the atmosphere. While the combined effective radiative forcing of these and all the other long-lived, well-mixed greenhouse gases included in the AGGI rose 51% from 1990 to 2023, CO2 has accounted for about 80% of this increase, which makes it by far the largest contributor to increases in effective radiative forcing from long-lived gases since 1990. The second largest contributor to the increase since 1990 was N2O, followed by methane. 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. The recent rapid increase follows a period from 1999 to 2006 when the atmospheric methane burden was nearly constant. The atmospheric burden of nitrous oxide continues to grow over time, furthermore, its annual increase is also increasing.
Chart 2, reproduced from NOAA [1], shows radiative forcing for CO2, CH4, N2O and groupings of gases that capture changes predominantly in the CFCs, HCFCs, and the HFCs through 2023. Carbon dioxide was by far the largest contributor to effective radiative forcing from these gases (66% of the total) and methane was the second largest contributor (16% of the total).
Chart 2: Radiative forcing
Chart 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 2023) 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, HFC-365mfc, HFC-227ea and HFC-152a) and SF6 for completeness, although SF6 only accounted for a small fraction of the radiative forcing from this group in 2023 (13%). Reproduced from NOAA [1].
Radiative Forcing Calculations (summary): The 2023 AGGI update has used updated equations recommended in the IPCC’s most recent assessment to calculate radiative forcing for all years from the greenhouse gases defining the AGGI. 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) [1]. Updated Summer 2024
References:
[1] Annual Greenhouse Gas Index (AGGI) - NOAA Global Monitoring Laboratory