-
Global Warming Potential vs Radiative Forcing
Global warming potential is "...the ratio of the cumulative radiative forcing (the energy being added to the planet, based on radiative efficiency and lifetime) over a time horizon from the instantaneous release of 1 kg of a given gas, such as desflurane, relative to that of 1 kg of carbon dioxide." A 100 year time horizon is commonly used as GWP100, reflecting the long lifetime of CO2, representing the warming potential of a single emission of a gas compared to the same mass of CO2. GWP is then used to derive CO2-equivalents.
Although GWP allows a simplistic comparison of greenhouse gases (eg. desflurane GWP 2530), it is misleading to use it to assess the climate impact of volatile anaesthetic agents primarily because of their short lifetimes, but also because "GWP does not consider the actual atmospheric abundance of a greenhouse gas, nor does it represent any of the physical complexity of the overall climate system..."
"Based on climate science, we assert that this is a physically unsound approach for determining the potential climate impact of volatile anaesthetic gases, and that it is the atmospheric concentration and radiative forcing of individual greenhouse gases that matter..." – Slingo & Slingo.
Instead climate scientists today prefer to use radiative forcing, "... the difference between the energy entering the planet and the energy leaving it..."
The percentage contribution of all volatile anaesthetic gases to radiative forcing is <0.01% compared to that from carbon dioxide. In comparison, the global emission reductions due to the COVID-19 lockdown were almost 1000x greater than the cumulative impact from anaesthetic volatile gases, and yet this reduction was undetectable above normal climate variability.
Atmospheric concentration (ppt) Atmospheric lifetime (y) (Effective) radiative forcing (Wm-2) Carbon dioxide 420,000,000 100+ 2.16 Methane 1,920,000 12.4 0.54 Nitrous oxide 336,000 123 0.21 Desflurane 0.37 14.1 0.00017 Sevoflurane 0.16 1.4 0.00003 Isoflurane 0.11 3.5 0.00006 "On the basis of GWP, anaesthetic gases appear to be very 'damaging'. However, this conclusion is scientifically unsound: their lifetimes are short; their emissions, accumulation and resulting atmospheric concentrations are minute; and their actual radiative forcing is vanishingly small."
More complexity...
Beyond the over-simplification of GWP and CO2e, Slingo & Slingo also explore the challenge in linking the minute radiative forcing of volatile anaesthetic gases to actual climate change and impact.
summary"...future warming will be determined by how successful we are in controlling our direct carbon dioxide emissions. ... While changing a vaporiser feels achievable and tangible, the scientific reality is inconsequential when we consider all the steps from GWP to climate impact. ... It is carbon dioxide emissions that will define our future, not the use of volatile anaesthetic agents."
- J M Slingo and M E Slingo.
- Meteorological Office, Exeter, UK.
- Anaesthesia. 2024 Mar 1; 79 (3): 252260252-260.
AbstractThe dedication of the international anaesthetic community to reducing the environmental impact of healthcare is important and to be celebrated. When this is underpinned by robust science, it has the potential to make a real difference. However, volatile anaesthetic agents have been widely promoted in the medical literature as damaging to the climate, leading to a drive to remove them from clinical practice. This is based on notional 'CO2 -equivalent' values created using the simple emission metric known as the global warming potential. Here, we assert that when proper consideration is given to the science of climate change, volatile anaesthetic gas emissions cannot be simply equated to real carbon dioxide emissions, and that their climate impact is vanishingly small. This paper gives anaesthetists a framework to make informed choices founded on climate science and calls for attention to be refocused on the urgent need to reduce the real carbon dioxide emissions associated with healthcare.© 2024 Association of Anaesthetists.
This article appears in the collection: What contribution does anesthesia make to climate change?.
Notes
Global Warming Potential vs Radiative Forcing
Global warming potential is "...the ratio of the cumulative radiative forcing (the energy being added to the planet, based on radiative efficiency and lifetime) over a time horizon from the instantaneous release of 1 kg of a given gas, such as desflurane, relative to that of 1 kg of carbon dioxide." A 100 year time horizon is commonly used as GWP100, reflecting the long lifetime of CO2, representing the warming potential of a single emission of a gas compared to the same mass of CO2. GWP is then used to derive CO2-equivalents.
Although GWP allows a simplistic comparison of greenhouse gases (eg. desflurane GWP 2530), it is misleading to use it to assess the climate impact of volatile anaesthetic agents primarily because of their short lifetimes, but also because "GWP does not consider the actual atmospheric abundance of a greenhouse gas, nor does it represent any of the physical complexity of the overall climate system..."
"Based on climate science, we assert that this is a physically unsound approach for determining the potential climate impact of volatile anaesthetic gases, and that it is the atmospheric concentration and radiative forcing of individual greenhouse gases that matter..." – Slingo & Slingo.
Instead climate scientists today prefer to use radiative forcing, "... the difference between the energy entering the planet and the energy leaving it..."
The percentage contribution of all volatile anaesthetic gases to radiative forcing is <0.01% compared to that from carbon dioxide. In comparison, the global emission reductions due to the COVID-19 lockdown were almost 1000x greater than the cumulative impact from anaesthetic volatile gases, and yet this reduction was undetectable above normal climate variability.
Atmospheric concentration (ppt) Atmospheric lifetime (y) (Effective) radiative forcing (Wm-2) Carbon dioxide 420,000,000 100+ 2.16 Methane 1,920,000 12.4 0.54 Nitrous oxide 336,000 123 0.21 Desflurane 0.37 14.1 0.00017 Sevoflurane 0.16 1.4 0.00003 Isoflurane 0.11 3.5 0.00006 "On the basis of GWP, anaesthetic gases appear to be very 'damaging'. However, this conclusion is scientifically unsound: their lifetimes are short; their emissions, accumulation and resulting atmospheric concentrations are minute; and their actual radiative forcing is vanishingly small."
More complexity...
Beyond the over-simplification of GWP and CO2e, Slingo & Slingo also explore the challenge in linking the minute radiative forcing of volatile anaesthetic gases to actual climate change and impact.
"...future warming will be determined by how successful we are in controlling our direct carbon dioxide emissions. ... While changing a vaporiser feels achievable and tangible, the scientific reality is inconsequential when we consider all the steps from GWP to climate impact. ... It is carbon dioxide emissions that will define our future, not the use of volatile anaesthetic agents."
Daniel Jolley