MEV 024: Unit 12 – Greenhouse gas emission and carbon sequestration

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 UNIT 12: GREENHOUSE GAS EMISSION AND CARBON SEQUESTRATION

12.1 Introduction

Climate change is one of the most pressing global issues today, and it is largely driven by the emission of greenhouse gases (GHGs) from both natural and anthropogenic sources. Agriculture, industry, transportation, and land use changes all contribute to the increase in atmospheric GHG concentrations. Simultaneously, mitigating climate change requires effective strategies to capture and store atmospheric carbon, a process known as carbon sequestration. This unit explores the nature of GHGs, their sources and impacts, estimation techniques, global efforts to address emissions, and carbon sequestration strategies.

12.2 Objectives

After completing this unit, learners will be able to:

  • Identify major greenhouse gases and their sources.
  • Understand the importance and process of GHG emission inventories.
  • Recognize the effects of GHGs on climate and ecosystems.
  • Examine international negotiations and agreements on GHG mitigation.
  • Understand carbon reservoirs and the concept of carbon sequestration.
  • Explore abiotic and biotic methods for carbon sequestration.
  • Learn methods to estimate soil carbon content.

12.3 Greenhouse Gases

Greenhouse gases are atmospheric gases that trap heat, contributing to the greenhouse effect and global warming. The primary GHGs include:

  • Carbon dioxide (CO₂)
  • Methane (CH₄)
  • Nitrous oxide (N₂O)
  • Fluorinated gases (e.g., CFCs, HFCs)
  • Water vapour (natural, acts as a feedback mechanism)

12.3.1 Sources of GHGs

  • Carbon Dioxide: Fossil fuel combustion, deforestation, land use changes.
  • Methane: Livestock digestion, rice paddies, wetlands, landfills.
  • Nitrous Oxide: Agricultural soils (fertilizers), fossil fuel combustion, biomass burning.
  • Fluorinated Gases: Industrial processes, refrigeration.

12.4 Greenhouse Gas Emission Inventories

GHG inventories are systematic accounts of emissions and removals of greenhouse gases, helping countries and sectors plan mitigation strategies.

12.4.1 Sectors and Categories

GHG inventories categorize emissions into key sectors:

  • Energy: Power plants, transportation.
  • Industrial Processes: Cement, chemicals.
  • Agriculture: Enteric fermentation, manure, rice cultivation.
  • Land Use, Land Use Change and Forestry (LULUCF): Deforestation, reforestation.
  • Waste Management: Landfills, wastewater treatment.

12.4.2 Estimation Methods

Common methods include:

  • Tiered Approaches (IPCC Guidelines):
    • Tier 1: Default emission factors.
    • Tier 2: Country-specific emission factors.
    • Tier 3: Detailed process-based models.
  • Life Cycle Assessment (LCA): Evaluates emissions across a product's life cycle.

12.4.3 Effect of Greenhouse Gases

  • Global Warming Potential (GWP): CH₄ and N₂O have higher GWPs than CO₂.
  • Impacts include:
    • Rising temperatures
    • Sea level rise
    • Extreme weather
    • Disruption of ecosystems
    • Food and water insecurity

12.5 International Negotiations on GHG and Climate Change

Key agreements and frameworks include:

  • UNFCCC (1992): Framework to combat climate change.
  • Kyoto Protocol (1997): Legally binding targets for developed countries.
  • Paris Agreement (2015): Global commitment to limit temperature rise to well below 2°C.

Other initiatives:

  • IPCC Reports: Provide scientific basis for policy.
  • Carbon markets: e.g., Clean Development Mechanism (CDM), carbon credits.

12.6 Global Carbon Reservoirs

Carbon exists in multiple global reservoirs:

  • Atmosphere: CO₂, CH₄, etc.
  • Biosphere: Plants, animals, organic matter.
  • Lithosphere: Fossil fuels, sedimentary rocks.
  • Hydrosphere: Oceans as major carbon sinks.

Carbon cycles among these reservoirs through processes such as photosynthesis, respiration, decomposition, and combustion.

12.7 Carbon Sequestration

Carbon sequestration refers to the long-term storage of atmospheric carbon in terrestrial, oceanic, or geological reservoirs.

12.7.1 Abiotic Strategies

  • Geological Sequestration: Injecting CO₂ into underground rock formations.
  • Mineral Carbonation: Reacting CO₂ with minerals to form stable carbonates.
  • Ocean Sequestration: Deep-ocean injection (controversial due to ecological risks).

12.7.2 Biotic Strategies

  • Afforestation/Reforestation
  • Agroforestry
  • Soil Organic Carbon Enhancement
  • Biochar application

Biotic methods are sustainable and enhance ecosystem services.

12.7.3 Carbon Sequestration Potential of Biomes

  • Forests: High potential due to dense biomass.
  • Grasslands: Effective in sequestering carbon in soil.
  • Wetlands: Store carbon in anaerobic soils.
  • Agricultural Lands: Enhanced through conservation practices.

12.8 Estimation of Soil Carbon

Soil carbon estimation methods include:

  • Direct Sampling and Analysis: Measuring organic carbon content via laboratory tests.
  • Remote Sensing and GIS: Large-scale mapping and monitoring.
  • Models: e.g., Century model, RothC, DNDC.
  • Bulk Density and Depth Estimation: To calculate carbon stock (Mg C/ha).

Monitoring soil carbon is critical for evaluating sequestration success and soil health.

12.9 Let Us Sum Up

  • Greenhouse gases contribute to climate change and originate from various human and natural sources.
  • GHG inventories are crucial for tracking emissions and formulating mitigation strategies.
  • Carbon sequestration, both abiotic and biotic, helps reduce atmospheric CO₂ concentrations.
  • International efforts aim to limit emissions and foster climate resilience.
  • Accurate estimation of soil carbon helps assess sequestration efficiency and soil productivity.

12.10 Key Words

·         Greenhouse Gases (GHGs): Gases in the Earth’s atmosphere that trap heat by absorbing infrared radiation, thereby contributing to the greenhouse effect. Major GHGs include carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O).

·         Carbon Dioxide (CO₂): A colorless, odorless gas produced by burning carbon-based fuels and organic matter and by respiration. It is the primary greenhouse gas emitted through human activities.

·         Methane (CH₄): A potent greenhouse gas with a global warming potential many times greater than CO₂. It is released from livestock, wetlands, rice paddies, and fossil fuel extraction.

·         Global Warming Potential (GWP): A relative measure of how much heat a greenhouse gas traps in the atmosphere over a specific time period (usually 100 years) compared to carbon dioxide. For example, methane has a GWP approximately 25–28 times higher than CO₂.

·         Carbon Sequestration: The process of capturing and storing atmospheric carbon dioxide in order to mitigate climate change. This can occur naturally or through human-engineered processes.

·         Abiotic Sequestration: Non-biological methods of storing carbon, such as geological sequestration (injecting CO₂ into underground rock formations) and mineral carbonation (binding CO₂ with minerals to form stable compounds).

·         Biotic Sequestration: The process of capturing carbon through biological activities such as tree planting, forest preservation, soil organic matter accumulation, and biochar application.

·         GHG Inventories: Comprehensive accounts of greenhouse gas emissions and removals within a specified region and time period. They help track sources and guide mitigation strategies.

·         Kyoto Protocol: An international treaty adopted in 1997 under the UNFCCC that sets legally binding emission reduction targets for developed countries.

·         Paris Agreement: A landmark international agreement adopted in 2015 under the UNFCCC, aiming to limit global temperature rise to well below 2°C and pursue efforts to limit it to 1.5°C above pre-industrial levels.

·         Soil Carbon Estimation: The process of measuring the amount of carbon stored in soil organic matter. It is essential for assessing the potential and effectiveness of carbon sequestration practices in agriculture and land use.

 

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