Refrigerant 101 Toolkit

Global Warming Potential Explained

Global Warming Potential (GWP) is a metric used to compare the ability of different greenhouse gases (GHGs) to trap heat in the atmosphere over a specific time period, typically 20, 100, or 500 years. It provides a common scale to evaluate the impact of various gases relative to carbon dioxide (CO₂), the baseline with a GWP of 1. GWP is crucial for understanding and managing climate change, as it allows for assessment and comparison of the impacts of different gases emitted from various sources.

Key Greenhouse Gases and Their GWP

Carbon Dioxide (CO₂): GWP of 1 (reference gas)

Methane (CH₄): GWP of 28-36 over 100 years

Nitrous Oxide (N₂O): GWP of 298 over 100 years

Hydrofluorocarbons (HFCs): GWP ranging from 12 to 14,800 over 100 years

Perfluorocarbons (PFCs): GWP ranging from 7,390 to 12,200 over 100 years

Sulfur Hexafluoride (SF₆): GWP of 23,500 over 100 years

How is GWP Calculated?

GWP is calculated by integrating the radiative forcing (a measure of the influence a factor has in altering the balance of incoming and outgoing energy in the Earth’s atmosphere) of a gas over a specific time horizon, compared to the radiative forcing of CO₂. The calculation considers the absorption of infrared radiation, the spectral location of its absorbing wavelengths, and the atmospheric lifetime of the gas.

Measuring Greenhouse Gas Emissions

To effectively manage and reduce GHG emissions, it is essential to measure and report them accurately. The most common methods and protocols used today include:

1. Direct Measurement: This involves using sensors and instruments to measure the concentration of GHGs emitted from a specific source, such as industrial smokestacks or exhausts. While accurate, direct measurement is complex.
2. Emission Factors: This method estimates emissions based on the activity level and emission factors, which represent the average emission rate of a given source relative to the quantity of activity. For instance, fuel consumption data can be multiplied by the emission factor for CO₂ to estimate total emissions.
3. Mass Balance: This approach calculates emissions based on the input and output of a substance in a process. For example, in a chemical manufacturing plant, the amount of raw material entering and the final product leaving.
4. Modeling: Computer models simulate the production and dispersal of GHGs based on various inputs, including economic activity, fuel usage, and population data. Models can provide comprehensive estimates but require significant data and expertise to implement accurately.
5. Carbon Footprinting: This process involves calculating the total emissions caused by an individual, organization, product, or service. It considers direct emissions from owned or controlled sources and indirect emissions from the production of purchased electricity, heat, and cooling.

Reporting and Standards

Several frameworks and protocols guide the measurement and reporting of GHG emissions:

• The Greenhouse Gas Protocol: Developed by the World Resources Institute (WRI) and the World Business Council for Sustainable Development (WBCSD), this is the most widely used international accounting tool for government and business leaders to understand, quantify, and manage GHG emissions.
• ISO 14064: Part of the ISO 14000 series of international standards for environmental management, ISO 14064 provides specifications and guidance for the organization and verification of GHG inventories.
• The United Nations Framework Convention on Climate Change (UNFCCC): This international environmental treaty aims to stabilize GHG concentrations in the atmosphere. It requires member countries to submit national inventories of GHG emissions and removals.