Global and Regional Methane Emissions: An Overview

Global and Regional Methane Emissions

Introduction

  • Lecture presented by Associate Professor Jatin Kala (J.Kala@murdoch.edu.au) from Murdoch University.

  • Lecture Outline:

    • Global Methane Budget.

    • Data from the Global Carbon Project - Methane Budget.

    • Methane emissions in Australia.

    • Data from the Australian Government.

Key Concepts about Methane as a Greenhouse Gas

  • After carbon dioxide (CO2), methane (CH4) is the most significant greenhouse gas contributing to human-induced climate change.

  • Agriculture is a primary contributor to total methane emissions, alongside many other sources.

  • Over a 100-year period, methane possesses a Global Warming Potential (GWP) approximately 28 times that of carbon dioxide.

  • Methane concentrations in the atmosphere are currently increasing.

  • Methane remains in the atmosphere for a relatively short period, roughly 9-13 years.

  • Due to its high GWP and shorter atmospheric lifetime, methane represents a good target for climate change mitigation efforts.

Global Methane Concentrations

  • Visualizations of Methane Emission Sources are available from NASA (e.g., https://svs.gsfc.nasa.gov/4799).

  • Historical Trends:

    • Data from Antarctic (Law Dome) ice/firn cores, and Cape Grim (flasks/in situ) measurements (Etheridge et al., 1996, 1998; MacFarling Meure et al., 2006; Rubino et al., 2019; updated to 2020).

    • Methane (CH_4) mixing ratios (in ppb) show a clear increase from below 800 ppb before 1800 to over 1800 ppb by 2000, further increasing towards 1900 ppb by 2020.

  • Recent Trends (1983-2022):

    • Data from NOAA, AGAGE, CSIRO, and UCI sources (https://essd.copernicus.org/preprints/essd-2024-115/).

    • Atmospheric (CH_4) concentrations (in ppb) have risen from approximately 1650 ppb in 1983 to nearly 1900 ppb by 2022.

    • The rate of change of methane (d(CH_4)/dt) in ppb per year has fluctuated but generally indicates a continuous increase in atmospheric concentrations.

Global Methane Budget (Average over 2010-2019)

  • Data from the Global Carbon Project (latest update: https://essd.copernicus.org/preprints/essd-2024-115/).

  • Total Emissions (in teragrams of (CH4) per year (Tg (CH4) /yr)):

    • Bottom-up view (BU): 669 Tg (CH_4) /yr (range: 512-849).

    • Top-down view (TD): 575 Tg (CH_4) /yr (range: 553-586).

  • Total Sinks:

    • BU: 633 Tg (CH_4) /yr (range: 507-796).

    • TD: 554 Tg (CH_4) /yr (range: 550-567).

  • Change in Atmospheric Abundance:

    • BU: 36 Tg (CH_4) /yr.

    • TD: 21 Tg (CH_4) /yr.

    • The observed atmospheric growth rate is 20.9 Tg (CH_4) /yr (range: 20.1-21.7). The difference between budget imbalances and observed growth rate reflects uncertainties.

  • Emission Sources (TD view):

    • Anthropogenic Fluxes:

      • Fossil fuel production and use: 120 Tg (CH_4) /yr (range: 117-125).

      • Agriculture and waste: 211 Tg (CH_4) /yr (range: 195-231).

      • Biomass and biofuel burning: 28 Tg (CH_4) /yr (range: 21-39).

    • Natural Fluxes:

      • Combined wetland & inland freshwaters emissions: 165 Tg (CH_4) /yr (range: 145-214).

      • Other natural (geological, oceans, termites, wild animals, permafrost, vegetation): 43 Tg (CH_4) /yr (range: 24-93).

  • Methane Sinks (TD view):

    • Sink from chemical reactions in the atmosphere: 521 Tg (CH_4) /yr (range: 485-532).

    • Sink in soils: 35 Tg (CH_4) /yr (range: 35-36).

  • Visual Representation of Sources: Dominant sources include Wetlands, Fossil fuels, Agriculture & Waste, and Biomass & biofuel burning, with varying emission densities (mg(CH_4).m^{-2}.day^{-1}) across different regions.

Methane Emissions in Australia

  • Data from the Department of Climate Change, Energy, the Environment and Water (https://www.dcceew.gov.au/climate-change/publications/national-greenhouse-gas-inventory-quarterly-update-march-2022).

  • Overall Trend (2000-2022):

    • Methane emissions, represented in millions of tonnes of CO2-equivalent (Mt CO2-e), showed fluctuations but generally hovered between approximately 10 Mt CO2-e and 15 Mt CO2-e.

    • There was a notable increase in methane emissions towards 2020.

  • Emissions by Sector (as of 2022):

    • Agriculture is the dominant source of methane emissions, contributing over 20\% of Australia's methane equivalent greenhouse gas emissions.

    • Fugitive Emissions (e.g., from mining and fossil fuel extraction) are another significant contributor, accounting for close to 20\%.

    • Waste (e.g., landfills) contributes a moderate amount, around 10\%.

    • Other sectors such as Electricity, Stationary Energy (excluding electricity), Transport, Industrial Processes, and LULUCF (Land Use, Land-Use Change and Forestry) contribute comparatively smaller percentages to methane emissions.

Take-Home Messages

  • There is a clear and urgent need to reduce methane emissions both globally and within Australia.

  • Australia has signed up for international initiatives like the Global Methane Pledge Project, demonstrating a commitment to methane reduction.

  • There is a crucial bidirectional relationship between climate and agriculture:

    • Climate affects Agriculture: Through factors like heatwaves, droughts, fires, and other compound extreme weather events.

    • Agriculture affects Climate: Primarily through methane emissions (e.g., from livestock and rice cultivation) and deforestation (impacting carbon sinks).

  • New Technologies for Reduction:

    • Research is ongoing to develop new technologies aimed at reducing methane emissions, particularly from cattle.

    • A critical consideration for these new technologies is careful assessment of cattle welfare.

    • For instance, studies on using seaweed as a feed additive to reduce methane from cows suggest it