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Causes: Methane CH4

Dairy cows are our single largest source – image Monika Kubala

Methane (CH4)

Summary

“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)

Summary

“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

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 takes about 12 years to break down into carbon dioxide (CO2) and enters the carbon cycle.

    The most 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.

    MethaneSAT is a joint US-New Zealand space mission scheduled for launch in 2022, to monitor global methane emissions. The aim is to accurately measure real-time methane emissions over large areas and also focus on specific targets, allowing actual methane outputs to be more accurately measured.

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

  • Ruminant animals, primarily sheep and cows, are the largest producer of anthropogenic methane gas in Aotearoa (see the round graph in the tab above).

    Methanogenic microorganisms live in the gut of these animals to breakdown the food using a process called enteric fermentation (Fig. 3).

    Here in New Zealand, the number of dairy cows in Canterbury increased from 490 in 1994 to 1,253,993 in 2015.

    This has and continues to result in huge quantities of methane escaping into the atmosphere directly from the animals, through effluent ponds, and also by adding fertiliser to land.

    While enteric fermentation is natural in grazing animals, around the world, particularly in places like Brazil, humans have burned down millions of hectares of forest and wetlands that once recycled methane efficiently, with millions of domesticated ruminants that graze on grass or are fed grains from grasses.

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

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