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Causes: Methane CH4

Dairy cows are our single largest source – image Monika Kubala | Drilliing for gas – image J. Penrose

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Methane (CH4)

Summary

The atmospheric methane growth rates of the 2020s far exceed the latest baseline projections. –  Shindell et al, 30 July 2024

  • Methane is created though biological process.
  • Natural gas is mostly methane; it is not a climate-friendly alternative or low-emissions transition energy. This map shows the incredible volume being leaked. Note, the satellite was only launched in mid 2024 so not all areas have been mapped.
  • During the first 20 years after methane is emitted into the atmosphere, it was assumed to have  84 x the global warming potential of CO2; ~50% of warming happens within 12.4 years, after which some breaks down into CO2, adding to existing warming potential. However:

Current models uniformly underestimate the atmospheric lifetime of methane because they uniformly overestimate how much hydroxyl radical (OH), the chemical species responsible for most of the destruction of methane, the atmosphere contains. The cause of this discrepancy… is due in part to a previously unrecognized pathway of water vapor absorption in the ultraviolet that causes models to calculate OH concentrations that are too high and thus methane lifetimes that are too short. Science 2024

The global monetized benefits for all market and non-market impacts are approximately US$4,300 per tonne of methane reduced. When accounting for these benefits nearly 85% of the targeted measures have benefits that outweigh the net costs. The benefits of the annually avoided premature deaths alone from a 1.5°C-consistent-methane mitigation strategy is approximately US$450 billion per year. – UN Global Methane Assessment 2021

Without strengthening mitigation efforts, greenhouse gas emissions are projected to lead to warming of 3.2C degrees. To limit warming to 1.5 degrees requires global greenhouse gas emissions to peak before 2025 at the latest and be reduced by 43% by 2030. Emissions from methane…need to be reduced by about a third by 2030. Even if we do this it is almost inevitable that we will at least temporarily exceed 1.5C. – Jim Shea, IPCC 2022: Mitigation (Video 2)

  • Growing grass does not offset agricultural emissions:

Grassland carbon stocks would need to increase by approximately 25% − 2,000%, indicating that solely relying on carbon sequestration in grasslands to offset warming effect of emissions from current ruminant systems is not feasible.”- Wang et al, 22 November, 2023

  • MethaneSat to monitor methane emissions including those across Aotearoa is now in orbit.

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Summary

The atmospheric methane growth rates of the 2020s far exceed the latest baseline projections. –  Shindell et al, 30 July 2024

  • Methane is created though biological process.
  • Natural gas is mostly methane; it is not a climate-friendly alternative or low-emissions transition energy. This map shows the incredible volume being leaked. Note, the satellite was only launched in mid 2024 so not all areas have been mapped.
  • During the first 20 years after methane is emitted into the atmosphere, it was assumed to have  84 x the global warming potential of CO2; ~50% of warming happens within 12.4 years, after which some breaks down into CO2, adding to existing warming potential. However:

Current models uniformly underestimate the atmospheric lifetime of methane because they uniformly overestimate how much hydroxyl radical (OH), the chemical species responsible for most of the destruction of methane, the atmosphere contains. The cause of this discrepancy… is due in part to a previously unrecognized pathway of water vapor absorption in the ultraviolet that causes models to calculate OH concentrations that are too high and thus methane lifetimes that are too short. Science 2024

The global monetized benefits for all market and non-market impacts are approximately US$4,300 per tonne of methane reduced. When accounting for these benefits nearly 85% of the targeted measures have benefits that outweigh the net costs. The benefits of the annually avoided premature deaths alone from a 1.5°C-consistent-methane mitigation strategy is approximately US$450 billion per year. – UN Global Methane Assessment 2021

Without strengthening mitigation efforts, greenhouse gas emissions are projected to lead to warming of 3.2C degrees. To limit warming to 1.5 degrees requires global greenhouse gas emissions to peak before 2025 at the latest and be reduced by 43% by 2030. Emissions from methane…need to be reduced by about a third by 2030. Even if we do this it is almost inevitable that we will at least temporarily exceed 1.5C. – Jim Shea, IPCC 2022: Mitigation (Video 2)

  • Growing grass does not offset agricultural emissions:

Grassland carbon stocks would need to increase by approximately 25% − 2,000%, indicating that solely relying on carbon sequestration in grasslands to offset warming effect of emissions from current ruminant systems is not feasible.”- Wang et al, 22 November, 2023

  • MethaneSat to monitor methane emissions including those across Aotearoa is now in orbit.

Instructions for interactive graphs (Credit: The 2°Institute.)

  • Mouse over anywhere on the graphs to see the changes over the last thousand years.
  • To see time periods of your choice, hold your mouse button down on one section then drag the mouse across a few years, then release it.
  • To see how this compares to the past 800,000 years, click on the ‘time’ icon on the top left.
  • To return the graphs to their original position, double-click the time icon.

Instructions for interactive graphs (Credit: The 2°Institute.)

  • Mouse over anywhere on the graphs to see the changes over the last thousand years.
  • To see time periods of your choice, hold your mouse button down on one section then drag the mouse across a few years, then release it.
  • To see how this compares to the past 800,000 years, click on the ‘time’ icon on the top left.
  • To return the graphs to their original position, double-click the time icon.
  • Methane is produced by single-celled ‘methanogenic’ microorganisms that feed on plants in anaerobic (oxygen-free) conditions. They are vital microorganisms because the help decay dead plants and animals. This helps to recycle the nutrients back into the food chain. In the same way that we and other animals breath out carbon dioxide as a waste product, these organisms release methane is a waste product. Methanogenic microorganisms are some of the oldest forms of life on Earth (Archaea) and they’re found everywhere, including in some trees.

    Most of the methane they produce is absorbed back into the ground. Much was locked away for many millions of years along with coal (which is why it’s so often found in coal mines) and during the most recent Glacial epoch as frozen clathrates. However, clathrates are now defrosting (see the tab below) the microbes have sprung back into life, and methane is escaping into the atmosphere at a rapidly accelerating rate.

    Methane that escapes into the atmosphere was assumed to take 12 years to break down into carbon dioxide (CO2) and enters the carbon cycle. However this assumption was based how quickly hydroxyl radicals (OH) in the troposphere broke down the methane. There appears to be fewer hydroxyl radicals than previously estimated, meaning that the warming effect of methane is lasting longer than anticipated.

    The New Zealand Greenhouse Gas Inventory report summarised in the graph below uses a range of parameters to assess how much methane is produced by different activities. Some of this is based on estimates, others on actual measurements. Agriculture produces 36.5%. (Image credit: New Zealand Greenhouse Gas Inventory 1990-2018 [April 2020]).

    Research published February 2020 revealed a way to distinguish emission from biogenic sources—agriculture, livestock etc—and fossil fuel sources.

    Click on the following tabs to find out more about the sources of methane.

Methane escaping from lake – image: Katie Orlinksy, National Geographic

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