Conversion factors in emissions’ accounting

This week, we want to continue with the topic of Greenhouse Gas (GHG) inventories. Now that we’ve covered how to identify emissions sources, the next step is understanding how to convert this data into a standardized format you can use in your inventory.

Emission conversion factors are essential tools that help translate everyday activities like using electricity, burning fuel, or running industrial processes, into measurable greenhouse gas emissions. They act as multipliers that convert things like kilowatt-hours of electricity or liters of diesel into equivalent amounts of CO₂. This allows us to quantify their environmental impact in a standardized way, making it easier to track emissions, compare across activities or sectors, and set meaningful reduction goals. Without these conversion factors, understanding or managing our carbon footprint would be nearly impossible.

But not all greenhouse gases are equal in their impact. That’s where the concept of Global Warming Potential (GWP) comes in. GWP allows us to compare the warming effect of different gases relative to carbon dioxide (CO₂), which has a GWP of 1. For example, methane (CH₄) has a GWP of 28, meaning it traps 28 times more heat than CO₂ over a 100-year period. By using GWP values, we express all emissions in terms of CO₂ equivalents (CO₂e), making climate impact calculations consistent and comparable. That’s why emissions are often reported in tons of CO₂e (tCO₂e), providing a single, aggregated figure that reflects total climate impact and supports progress tracking and goal setting.

The table below shows the GWP of common greenhouse gases:

Source: Greenhouse Gas Protocol

To calculate CO₂e emissions using GWP, regardless of which emissions scope (1, 2 or 3) they belong to, you simply multiply the amount of each greenhouse gas by its GWP value. The formula looks like this:

CO₂e = amount of gas x GWP

For example, if you emit 2 tons of methane (CH₄) and its GWP is 28, the CO₂e would be:

2 × 28 = 56 tCO₂e

Repeat this for each gas, then sum the results to get total emissions in tCO₂e.

Emissions from energy use 

Energy-related emissions follow the same logic. You apply emission factors to energy consumption data to calculate CO₂e. Common formats include:

• tCO₂e per MWh (for electricity)
• kg CO₂e per GJ (for fuels) — which can be converted to tons.

These factors depend on the source of energy. For example, in 2024, SEMARNAT set the official emission factor for electricity in Mexico (Scope 2) at 0.444 tCO₂e/MWh. Emission factors are usually published by governmental bodies and can differ by year and region.

Other useful resources include:

Calculation Tools and Guidance | GHG Protocol

Greenhouse Gas Equivalencies Calculator | US EPA

Greenhouse gas reporting: conversion factors 2024 – GOV.UK

Greenhouse Gas Emissions Calculator | 2021 Emission Factors | UNFCCC

I hope you found this interesting. As usual, if there is anything we can help you with, or if there is an ESG topic you would like to know more about, please let us know.

Best,

Marimar

CEO, Miranda ESG