Historic Contribution to Global Warming

Increases in the abundance of atmospheric greenhouse gases since the industrial revolution are mainly the result of human activity and are largely responsible for the observed increases in global temperature.

Measured global atmospheric abundances of greenhouse gases and their individual properties are used to calculate changes in effective radiative forcing (global warming). According to NOAA, 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 (https://gml.noaa.gov/aggi/aggi.html).

Compliance with the 2016 Kigali Amendment to the Montreal Protocol, which requires phase down of production and consumption of some hydrofluorocarbons (HFCs), is estimated to avoid 0.3–0.5°C of warming by 2100. This estimate does not include contributions from HFC-23 emissions. Under the provisions of the Kigali Amendment, current trends in consumption and emissions, and national policies, the contribution of HFCs to global annual average surface warming is projected to be 0.04 °C in 2100. This is substantially lower than under the scenario without HFC control measures, for which a contribution of 0.3–0.5 °C was projected (Scientific Assessment of Ozone Depletion 2022). Atmospheric degradation products and indirect GWPs are discussed here.

According to NOAA, for the gases CO₂, CH4, N2O and groupings of gases (predominantly 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). Since 1990, for the combined effective radiative forcing of long-lived, well-mixed greenhouse gases, CO₂ has accounted for about 80% of the 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.

NOAA explains that 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 production and trade of CFCs, HCFCs, and HFCs by the fully adjusted and amended Montreal Protocol on Substances that Deplete the Ozone Layer.

Contribution of HFOs and HCFOs to global warming

According to the Scientific Assessment of Ozone Depletion: 2022, their atmospheric lifetimes are small, and, therefore, their emissions do not contribute perceptibly to climate change. This is shown in SAP 2022 by Figure 7-5 (reproduced below). Atmospheric degradation products and indirect GWPs are discussed here.

Figure: Historical and projected contributions to climate change from ODSs, high-GWP HFCs, low-GWP HFOs and non-halogenated alternatives.