GHG intensity, or Greenhouse Gas Intensity, refers to the amount of greenhouse gases (GHGs) emitted per unit of output or activity, commonly expressed in terms of CO₂-equivalents (CO₂e). It is a key metric for evaluating the climate impact of energy carriers, industrial processes, transport fuels, products, and organizations.
By measuring GHG emissions relative to a specific reference (e.g., per megajoule of energy, per tonne of product, or per kilometer traveled), GHG intensity enables comparative assessments, regulatory compliance, and informed decision-making in the transition to a low-carbon economy.
What does GHG intensity measure?
GHG intensity quantifies the carbon footprint of a given process, fuel, or activity in proportion to its output. It captures not just carbon dioxide (CO₂), but also other significant greenhouse gases like methane (CH₄) and nitrous oxide (N₂O), converted into CO₂-equivalent values using their Global Warming Potential (GWP) over a standard time horizon (typically 100 years).
Typical expressions include:
- gCO₂e/MJ (grams of CO₂ equivalent per megajoule of energy)
- kgCO₂e/km (kilograms of CO₂ equivalent per kilometer traveled)
- tCO₂e/tonne (tonnes of CO₂ equivalent per tonne of product)
This metric allows for the standardized comparison of different fuels, technologies, and supply chains, even when their emissions profiles vary in composition and timing.
Why is GHG intensity important?
GHG intensity is a foundational concept in climate policy, environmental reporting, and sustainable energy planning. It serves several critical functions:
- Lifecycle emissions assessment: GHG intensity is used in Life Cycle Assessment (LCA) to evaluate emissions from cradle to grave—covering production, use, and disposal.
- Fuel comparison and certification: Regulatory schemes such as the EU Renewable Energy Directive (RED II) and California Low Carbon Fuel Standard (LCFS) use GHG intensity to determine which fuels qualify as low-carbon alternatives.
- Target-setting: Companies and governments use GHG intensity benchmarks to set emissions reduction goals and monitor progress over time.
- Product labeling: Carbon intensity values are used in eco-labels to inform consumers about the climate impact of products.
- Investment screening: ESG (Environmental, Social, and Governance) frameworks often include GHG intensity as a key indicator for sustainable finance.
Applications in different sectors
- Energy and fuels
GHG intensity is used to evaluate the climate impact of electricity, hydrogen, biofuels, natural gas, and synthetic e-fuels. For example:- Green hydrogen has near-zero GHG intensity.
- Blue hydrogen has low GHG intensity if carbon capture is efficient.
- Grey hydrogen has high GHG intensity due to fossil-based production.
- Transport
Regulators compare fuels based on gCO₂e/MJ or gCO₂e/km, allowing policymakers to favor low-intensity options such as electricity or sustainable aviation fuel (SAF). - Industry
Sectors such as steel, cement, and chemicals monitor GHG intensity per unit of output to track decarbonization efforts. - Agriculture and food
GHG intensity is used to compare the environmental impact of food products, such as meat vs. plant-based alternatives, based on emissions per kilogram produced.
Benefits of using GHG intensity
- Comparability: Provides a fair basis for comparing diverse processes and fuels.
- Transparency: Enhances traceability and credibility in emissions reporting.
- Performance monitoring: Allows progress tracking toward emissions reduction targets.
- Policy alignment: Supports compliance with carbon regulations and low-carbon fuel mandates.
- Market incentives: Enables access to carbon credits, green certification, and sustainable investment schemes.
Challenges and limitations
While useful, GHG intensity metrics must be handled carefully:
- Data quality: Accurate measurement requires robust data on inputs, emissions, and system boundaries.
- System boundaries: Lifecycle stages included (e.g., well-to-wheel, cradle-to-gate) must be clearly defined to avoid misleading comparisons.
- Regional variability: Emissions factors can vary based on geography, technology, and energy mix.
Dynamic updates: GHG intensity values need regular revision as production methods, energy sources, and regulations evolve.