Propane has a 20-year GWP of only 0.072, much lower than previously assumed, according to the Intergovernmental Panel on Climate Change.
The Intergovernmental Panel on Climate Change (IPCC) released its Climate Change 2021 – The Physical Science Basis report on Monday (August 9), which includes official global warming potential (GWP) figures for hydrocarbons for the first time.
The report states that popular natural refrigerant propane (R290) has a 20-year GWP of 0.072 and a 100-year GWP of 0.02. Butane (R600) has a GWP20 of 0.022 and a GWP100 of 0.006.
These figures are much lower than traditionally assumed. Historically, R290 has been assumed to have a GWP of 3 due to its chemical formula, which includes three carbon atoms. Three is very low, compared to most HFCs, but still many times higher than the actual value.
"Historically, people assumed the GWP of R290 was 3, because the chemical formula for propane is C3H8 — meaning it has 3 carbon atoms,” explained Dr Daniel Colbourne of Re-phridge in the UK. “So, when it degrades in the atmosphere it will combine with oxygen (O2) to produce three CO2 molecules, hence a GWP of 3, and this proliferated throughout reports and papers.”
The addition of hydrocarbons to the list of GWP values is not the only change. R32, one of the commonly used HFC competitors to hydrocarbons in single-split air conditioning, has had its GWP100 updated by the IPCC. It is tradtionally given as around 675, meaning it is below the 750 GWP limit for new single-split units coming into force in the EU from January 1, 2025. However, the updated figures from the new IPCC report, give R32's 100-year GWP as 771, meaning that it most likely no longer will be possible to use in new equipment from that date.
The 20-year GWP for R32 is much higher at 2690, according to the IPCC report. Read more about the 20-year vs 100-year GWP debate here.
The Big Picture
The overall conclusions of the new IPCC report do not make for very optimistic reading.
“The report shows that emissions of greenhouse gases from human activities are responsible for approximately 1.1°C (1.98°F) of warming since 1850-1900, and finds that averaged over the next 20 years, global temperature is expected to reach or exceed 1.5°C (2.7°F) of warming,” the panel stated in a press release.
“Unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5°C (2.7°F) or even 2°C (3.6°F) will be beyond reach.”
The full IPCC report is available here.
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