CH4-GWP

The importance of the global warming potential (GWP) of methane (CH4)

[ from earlier post and discussion ]
The image on the right is from Figure 8.32 IPCC AR5 and it shows that methane's GWP differs with the time horizon, i.e. the time over which it is calculated.

When expressed in carbon dioxide-equivalent (CO₂e) and calculated over a 10-year period, the current (at the time AR5 was written) global release of methane from all anthropogenic sources exceeds all anthropogenic carbon dioxide emissions as agents of global warming; that is, methane emissions are more important than carbon dioxide emissions for driving the current rate of global warming.

And unlike carbon dioxide, methane's GWP does rise as more of it is released (due to hydroxyl depletion).

The same values for methane's GWP that are used in above bar chart are also used in the graph below, indicating that, over the first few years after release, methane has a GWP of more than 150 times that of carbon dioxide.
[ from Most Important Message Ever and discussion ]

The graph in above image is actually conservative, as the IPCC in AR5 also gives higher values for methane's GWP (e.g. for fossil methane and when including climate change feedbacks), while there also is additional warming due to the carbon dioxide that results from methane's oxidation.

Since AR5, further research was also published (in 2016 and 2018) concluding that methane is more potent than the IPCC had described in AR5. The 2016 study found methane's 100-year GWP to be 14% higher than the IPCC value. Therefore, the image below is similarly updated by 14% and shows a graph that is based on the same (conservative) IPCC AR5 data.

[ from an earlier post and discussion ]

The importance of selecting a one-year GWP for methane

The graph indicates that methane's one-year GWP is 200. Selecting a one-year time horizon is most appropriate in regard to abrupt release of methane, such as eruptions from lakes and craters in what used-to-be-permafrost and from the seafloor of the Arctic Ocean.

Such events and developments can occur abruptly, i.e. over a very short timespan. Examples are described in studies such as this one and this one published in 2020, and in the analysis below.


Above image, from an earlier post, was created with content from a 2019 analysis by Natalia Shakhova et al. It shows that the situation is much more grim than many people may realize.

The image below, from an earlier post and using a 1-year GWP of 200, illustrates the threat.

A 5 Gt seafloor methane burst would double methane in the atmosphere and could instantly raise the CO₂e level to 1200 ppm and trigger the clouds feedback (top right panel of above chart).

[ from earlier post ]
Even without such a huge eruption of methane from the seafloor, there are further pollutants than just carbon dioxide and methane, such as nitrous oxide, nitrogen oxides, CFCs, carbon monoxide, black carbon, brown carbon and water vapor, and they haven't yet been included in the above CO₂e total. The levels of all these pollutants could rise strongly in a matter of years and further events and developments could happen such as feedbacks starting to kick in with much greater ferocity, while the resulting extreme weather events would cause sulfate cooling to end, resulting in an 18.43°C temperature rise that could be reached as early as 2026 (left panel of above chart).

To further illustrate this, the image on the right shows a trend that is based on NOAA 2006-2020 marine surface annual global mean methane data (downloaded March 2021) and that points at a mean of 3893 ppb getting crossed by the end of 2026, more than twice the 1935 ppb mean methane level recorded at 293 mb by the MetOp-1 satellite on July 1 pm, 2021.

Such a high mean methane level by 2026 cannot be ruled out, given the rapid recent growth in mean annual methane levels (15.85 ppb in 2020, see inset on image).

As said, there are further pollutants, in addition to methane, and additional feedbacks, events and developments to take into account.

One thing leads to another

[ abrupt release of methane,
see earlier post and discussion ]
As said, there are further pollutants, in addition to methane, and additional feedbacks, events and developments to take into account.

Heat reaching the seafloor of the Arctic Ocean could lead to hydrate destabilization and abrupt release of methane from hydrates and from free gas located underneath hydrates, which would further accelerate Arctic warming and lead to subsequent releases of methane from the seafloor.

As discussed in an earlier post, humans will likely go extinct with a 3°C rise, while a 5°C rise will likely end most life on Earth.

Keep in mind that, as discussed in an earlier post, the temperature rise from pre-industrial to 2020 may well be as large as 2.28°C, as the bottom figure in the bar on the left of above chart shows. So that is already very close to a 3°C rise.


Links

• IPCC, Chapter 8, Anthropogenic and Natural Radiative Forcing - Figure 8.32
In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I, AR5
https://ar5-syr.ipcc.ch/resources/htmlpdf/WG1AR5_Chapter08_FINAL

• Most Important Message Ever
https://arctic-news.blogspot.com/2019/07/most-important-message-ever.html

• Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing - by Maryam Etminan et al. (2016)
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL071930

• Large regional shortwave forcing by anthropogenic methane informed by Jovian observations - by William Collins (2018)
https://advances.sciencemag.org/content/4/9/eaas9593

• Confirm Methane's Importance
https://arctic-news.blogspot.com/2021/03/confirm-methanes-importance.html

• A Gas-Emission Crater in the Erkuta River Valley, Yamal Peninsula: Characteristics and Potential Formation Model - by Evgeny Chuvilin et al. (2020)
https://www.mdpi.com/2076-3263/10/5/170

• Conceptual Models of Gas Accumulation in the Shallow Permafrost of Northern West Siberia and Conditions for Explosive Gas Emissions - by Evgeny Chuvilin et al. (2020)
https://www.mdpi.com/2076-3263/10/5/195

• Understanding the Permafrost–Hydrate System and Associated Methane Releases in the East Siberian Arctic Shelf - by Natalia Shakhova et al. (2019)
https://www.mdpi.com/2076-3263/9/6/251

• When Will We Die?
https://arctic-news.blogspot.com/2019/06/when-will-we-die.html

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