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 $(CO<em>2)$, methane $(CH</em>4)$ 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 $(CH<em>4)$ per year (Tg $(CH</em>4)$ /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 $CO<em>2$-equivalent (Mt $CO</em>2$-e), showed fluctuations but generally hovered between approximately $10$ Mt $CO<em>2$-e and $15$ Mt $CO</em>2$-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